* Re: [LSF/MM TOPIC] Badblocks checking/representation in filesystems
@ 2017-01-17 22:15 ` Andiry Xu
0 siblings, 0 replies; 42+ messages in thread
From: Andiry Xu @ 2017-01-17 22:15 UTC (permalink / raw)
To: Vishal Verma
Cc: Slava Dubeyko, Darrick J. Wong, linux-nvdimm@lists.01.org,
linux-block@vger.kernel.org, Viacheslav Dubeyko, Linux FS Devel,
lsf-pc@lists.linux-foundation.org
Hi,
On Tue, Jan 17, 2017 at 1:35 PM, Vishal Verma <vishal.l.verma@intel.com> wrote:
> On 01/16, Darrick J. Wong wrote:
>> On Fri, Jan 13, 2017 at 05:49:10PM -0700, Vishal Verma wrote:
>> > On 01/14, Slava Dubeyko wrote:
>> > >
>> > > ---- Original Message ----
>> > > Subject: [LSF/MM TOPIC] Badblocks checking/representation in filesystems
>> > > Sent: Jan 13, 2017 1:40 PM
>> > > From: "Verma, Vishal L" <vishal.l.verma@intel.com>
>> > > To: lsf-pc@lists.linux-foundation.org
>> > > Cc: linux-nvdimm@lists.01.org, linux-block@vger.kernel.org, linux-fsdevel@vger.kernel.org
>> > >
>> > > > The current implementation of badblocks, where we consult the badblocks
>> > > > list for every IO in the block driver works, and is a last option
>> > > > failsafe, but from a user perspective, it isn't the easiest interface to
>> > > > work with.
>> > >
>> > > As I remember, FAT and HFS+ specifications contain description of bad blocks
>> > > (physical sectors) table. I believe that this table was used for the case of
>> > > floppy media. But, finally, this table becomes to be the completely obsolete
>> > > artefact because mostly storage devices are reliably enough. Why do you need
>>
>> ext4 has a badblocks inode to own all the bad spots on disk, but ISTR it
>> doesn't support(??) extents or 64-bit filesystems, and might just be a
>> vestigial organ at this point. XFS doesn't have anything to track bad
>> blocks currently....
>>
>> > > in exposing the bad blocks on the file system level? Do you expect that next
>> > > generation of NVM memory will be so unreliable that file system needs to manage
>> > > bad blocks? What's about erasure coding schemes? Do file system really need to suffer
>> > > from the bad block issue?
>> > >
>> > > Usually, we are using LBAs and it is the responsibility of storage device to map
>> > > a bad physical block/page/sector into valid one. Do you mean that we have
>> > > access to physical NVM memory address directly? But it looks like that we can
>> > > have a "bad block" issue even we will access data into page cache's memory
>> > > page (if we will use NVM memory for page cache, of course). So, what do you
>> > > imply by "bad block" issue?
>> >
>> > We don't have direct physical access to the device's address space, in
>> > the sense the device is still free to perform remapping of chunks of NVM
>> > underneath us. The problem is that when a block or address range (as
>> > small as a cache line) goes bad, the device maintains a poison bit for
>> > every affected cache line. Behind the scenes, it may have already
>> > remapped the range, but the cache line poison has to be kept so that
>> > there is a notification to the user/owner of the data that something has
>> > been lost. Since NVM is byte addressable memory sitting on the memory
>> > bus, such a poisoned cache line results in memory errors and SIGBUSes.
>> > Compared to tradational storage where an app will get nice and friendly
>> > (relatively speaking..) -EIOs. The whole badblocks implementation was
>> > done so that the driver can intercept IO (i.e. reads) to _known_ bad
>> > locations, and short-circuit them with an EIO. If the driver doesn't
>> > catch these, the reads will turn into a memory bus access, and the
>> > poison will cause a SIGBUS.
>>
>> "driver" ... you mean XFS? Or do you mean the thing that makes pmem
>> look kind of like a traditional block device? :)
>
> Yes, the thing that makes pmem look like a block device :) --
> drivers/nvdimm/pmem.c
>
>>
>> > This effort is to try and make this badblock checking smarter - and try
>> > and reduce the penalty on every IO to a smaller range, which only the
>> > filesystem can do.
>>
>> Though... now that XFS merged the reverse mapping support, I've been
>> wondering if there'll be a resubmission of the device errors callback?
>> It still would be useful to be able to inform the user that part of
>> their fs has gone bad, or, better yet, if the buffer is still in memory
>> someplace else, just write it back out.
>>
>> Or I suppose if we had some kind of raid1 set up between memories we
>> could read one of the other copies and rewrite it into the failing
>> region immediately.
>
> Yes, that is kind of what I was hoping to accomplish via this
> discussion. How much would filesystems want to be involved in this sort
> of badblocks handling, if at all. I can refresh my patches that provide
> the fs notification, but that's the easy bit, and a starting point.
>
I have some questions. Why moving badblock handling to file system
level avoid the checking phase? In file system level for each I/O I
still have to check the badblock list, right? Do you mean during mount
it can go through the pmem device and locates all the data structures
mangled by badblocks and handle them accordingly, so that during
normal running the badblocks will never be accessed? Or, if there is
replicataion/snapshot support, use a copy to recover the badblocks?
How about operations bypass the file system, i.e. mmap?
>>
>> > > > A while back, Dave Chinner had suggested a move towards smarter
>> > > > handling, and I posted initial RFC patches [1], but since then the topic
>> > > > hasn't really moved forward.
>> > > >
>> > > > I'd like to propose and have a discussion about the following new
>> > > > functionality:
>> > > >
>> > > > 1. Filesystems develop a native representation of badblocks. For
>> > > > example, in xfs, this would (presumably) be linked to the reverse
>> > > > mapping btree. The filesystem representation has the potential to be
>> > > > more efficient than the block driver doing the check, as the fs can
>> > > > check the IO happening on a file against just that file's range.
>>
>> OTOH that means we'd have to check /every/ file IO request against the
>> rmapbt, which will make things reaaaaaally slow. I suspect it might be
>> preferable just to let the underlying pmem driver throw an error at us.
>>
>> (Or possibly just cache the bad extents in memory.)
>
> Interesting - this would be a good discussion to have. My motivation for
> this was the reasoning that the pmem driver has to check every single IO
> against badblocks, and maybe the fs can do a better job. But if you
> think the fs will actually be slower, we should try to somehow benchmark
> that!
>
>>
>> > > What do you mean by "file system can check the IO happening on a file"?
>> > > Do you mean read or write operation? What's about metadata?
>> >
>> > For the purpose described above, i.e. returning early EIOs when
>> > possible, this will be limited to reads and metadata reads. If we're
>> > about to do a metadata read, and realize the block(s) about to be read
>> > are on the badblocks list, then we do the same thing as when we discover
>> > other kinds of metadata corruption.
>>
>> ...fail and shut down? :)
>>
>> Actually, for metadata either we look at the xfs_bufs to see if it's in
>> memory (XFS doesn't directly access metadata) and write it back out; or
>> we could fire up the online repair tool to rebuild the metadata.
>
> Agreed, I was just stressing that this scenario does not change from
> status quo, and really recovering from corruption isn't the problem
> we're trying to solve here :)
>
>>
>> > > If we are talking about the discovering a bad block on read operation then
>> > > rare modern file system is able to survive as for the case of metadata as
>> > > for the case of user data. Let's imagine that we have really mature file
>> > > system driver then what does it mean to encounter a bad block? The failure
>> > > to read a logical block of some metadata (bad block) means that we are
>> > > unable to extract some part of a metadata structure. From file system
>> > > driver point of view, it looks like that our file system is corrupted, we need
>> > > to stop the file system operations and, finally, to check and recover file
>> > > system volume by means of fsck tool. If we find a bad block for some
>> > > user file then, again, it looks like an issue. Some file systems simply
>> > > return "unrecovered read error". Another one, theoretically, is able
>> > > to survive because of snapshots, for example. But, anyway, it will look
>> > > like as Read-Only mount state and the user will need to resolve such
>> > > trouble by hands.
>> >
>> > As far as I can tell, all of these things remain the same. The goal here
>> > isn't to survive more NVM badblocks than we would've before, and lost
>> > data or lost metadata will continue to have the same consequences as
>> > before, and will need the same recovery actions/intervention as before.
>> > The goal is to make the failure model similar to what users expect
>> > today, and as much as possible make recovery actions too similarly
>> > intuitive.
>> >
>> > >
>> > > If we are talking about discovering a bad block during write operation then,
>> > > again, we are in trouble. Usually, we are using asynchronous model
>> > > of write/flush operation. We are preparing the consistent state of all our
>> > > metadata structures in the memory, at first. The flush operations for metadata
>> > > and user data can be done in different times. And what should be done if we
>> > > discover bad block for any piece of metadata or user data? Simple tracking of
>> > > bad blocks is not enough at all. Let's consider user data, at first. If we cannot
>> > > write some file's block successfully then we have two ways: (1) forget about
>> > > this piece of data; (2) try to change the associated LBA for this piece of data.
>> > > The operation of re-allocation LBA number for discovered bad block
>> > > (user data case) sounds as real pain. Because you need to rebuild the metadata
>> > > that track the location of this part of file. And it sounds as practically
>> > > impossible operation, for the case of LFS file system, for example.
>> > > If we have trouble with flushing any part of metadata then it sounds as
>> > > complete disaster for any file system.
>> >
>> > Writes can get more complicated in certain cases. If it is a regular
>> > page cache writeback, or any aligned write that goes through the block
>> > driver, that is completely fine. The block driver will check that the
>> > block was previously marked as bad, do a "clear poison" operation
>> > (defined in the ACPI spec), which tells the firmware that the poison bit
>> > is not OK to be cleared, and writes the new data. This also removes the
>> > block from the badblocks list, and in this scheme, triggers a
>> > notification to the filesystem that it too can remove the block from its
>> > accounting. mmap writes and DAX can get more complicated, and at times
>> > they will just trigger a SIGBUS, and there's no way around that.
>> >
>> > >
>> > > Are you really sure that file system should process bad block issue?
>> > >
>> > > >In contrast, today, the block driver checks against the whole block device
>> > > > range for every IO. On encountering badblocks, the filesystem can
>> > > > generate a better notification/error message that points the user to
>> > > > (file, offset) as opposed to the block driver, which can only provide
>> > > > (block-device, sector).
>>
>> <shrug> We can do the translation with the backref info...
>
> Yes we should at least do that. I'm guessing this would happen in XFS
> when it gets an EIO from an IO submission? The bio submission path in
> the fs is probably not synchronous (correct?), but whenever it gets the
> EIO, I'm guessing we just print a loud error message after doing the
> backref lookup..
>
>>
>> > > > 2. The block layer adds a notifier to badblock addition/removal
>> > > > operations, which the filesystem subscribes to, and uses to maintain its
>> > > > badblocks accounting. (This part is implemented as a proof of concept in
>> > > > the RFC mentioned above [1]).
>> > >
>> > > I am not sure that any bad block notification during/after IO operation
>> > > is valuable for file system. Maybe, it could help if file system simply will
>> > > know about bad block beforehand the operation of logical block allocation.
>> > > But what subsystem will discover bad blocks before any IO operations?
>> > > How file system will receive information or some bad block table?
>> >
>> > The driver populates its badblocks lists whenever an Address Range Scrub
>> > is started (also via ACPI methods). This is always done at
>> > initialization time, so that it can build an in-memory representation of
>> > the badblocks. Additionally, this can also be triggered manually. And
>> > finally badblocks can also get populated for new latent errors when a
>> > machine check exception occurs. All of these can trigger notification to
>> > the file system without actual user reads happening.
>> >
>> > > I am not convinced that suggested badblocks approach is really feasible.
>> > > Also I am not sure that file system should see the bad blocks at all.
>> > > Why hardware cannot manage this issue for us?
>> >
>> > Hardware does manage the actual badblocks issue for us in the sense that
>> > when it discovers a badblock it will do the remapping. But since this is
>> > on the memory bus, and has different error signatures than applications
>> > are used to, we want to make the error handling similar to the existing
>> > storage model.
>>
>> Yes please and thank you, to the "error handling similar to the existing
>> storage model". Even better if this just gets added to a layer
>> underneath the fs so that IO to bad regions returns EIO. 8-)
>
> This (if this just gets added to a layer underneath the fs so that IO to bad
> regions returns EIO) already happens :) See pmem_do_bvec() in
> drivers/nvdimm/pmem.c, where we return EIO for a known badblock on a
> read. I'm wondering if this can be improved..
>
The pmem_do_bvec() read logic is like this:
pmem_do_bvec()
if (is_bad_pmem())
return -EIO;
else
memcpy_from_pmem();
Note memcpy_from_pmem() is calling memcpy_mcsafe(). Does this imply
that even if a block is not in the badblock list, it still can be bad
and causes MCE? Does the badblock list get changed during file system
running? If that is the case, should the file system get a
notification when it gets changed? If a block is good when I first
read it, can I still trust it to be good for the second access?
Thanks,
Andiry
>>
>> (Sleeeeep...)
>>
>> --D
>>
>> >
>> > --
>> > To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in
>> > the body of a message to majordomo@vger.kernel.org
>> > More majordomo info at http://vger.kernel.org/majordomo-info.html
> --
> To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at http://vger.kernel.org/majordomo-info.html
_______________________________________________
Linux-nvdimm mailing list
Linux-nvdimm@lists.01.org
https://lists.01.org/mailman/listinfo/linux-nvdimm
^ permalink raw reply [flat|nested] 42+ messages in thread* Re: [LSF/MM TOPIC] Badblocks checking/representation in filesystems
2017-01-17 22:15 ` Andiry Xu
@ 2017-01-17 22:37 ` Vishal Verma
-1 siblings, 0 replies; 42+ messages in thread
From: Vishal Verma @ 2017-01-17 22:37 UTC (permalink / raw)
To: Andiry Xu
Cc: Darrick J. Wong, Slava Dubeyko, lsf-pc@lists.linux-foundation.org,
linux-nvdimm@lists.01.org, linux-block@vger.kernel.org,
Linux FS Devel, Viacheslav Dubeyko
On 01/17, Andiry Xu wrote:
> Hi,
>
> On Tue, Jan 17, 2017 at 1:35 PM, Vishal Verma <vishal.l.verma@intel.com> wrote:
> > On 01/16, Darrick J. Wong wrote:
> >> On Fri, Jan 13, 2017 at 05:49:10PM -0700, Vishal Verma wrote:
> >> > On 01/14, Slava Dubeyko wrote:
> >> > >
> >> > > ---- Original Message ----
> >> > > Subject: [LSF/MM TOPIC] Badblocks checking/representation in filesystems
> >> > > Sent: Jan 13, 2017 1:40 PM
> >> > > From: "Verma, Vishal L" <vishal.l.verma@intel.com>
> >> > > To: lsf-pc@lists.linux-foundation.org
> >> > > Cc: linux-nvdimm@lists.01.org, linux-block@vger.kernel.org, linux-fsdevel@vger.kernel.org
> >> > >
> >> > > > The current implementation of badblocks, where we consult the badblocks
> >> > > > list for every IO in the block driver works, and is a last option
> >> > > > failsafe, but from a user perspective, it isn't the easiest interface to
> >> > > > work with.
> >> > >
> >> > > As I remember, FAT and HFS+ specifications contain description of bad blocks
> >> > > (physical sectors) table. I believe that this table was used for the case of
> >> > > floppy media. But, finally, this table becomes to be the completely obsolete
> >> > > artefact because mostly storage devices are reliably enough. Why do you need
> >>
> >> ext4 has a badblocks inode to own all the bad spots on disk, but ISTR it
> >> doesn't support(??) extents or 64-bit filesystems, and might just be a
> >> vestigial organ at this point. XFS doesn't have anything to track bad
> >> blocks currently....
> >>
> >> > > in exposing the bad blocks on the file system level? Do you expect that next
> >> > > generation of NVM memory will be so unreliable that file system needs to manage
> >> > > bad blocks? What's about erasure coding schemes? Do file system really need to suffer
> >> > > from the bad block issue?
> >> > >
> >> > > Usually, we are using LBAs and it is the responsibility of storage device to map
> >> > > a bad physical block/page/sector into valid one. Do you mean that we have
> >> > > access to physical NVM memory address directly? But it looks like that we can
> >> > > have a "bad block" issue even we will access data into page cache's memory
> >> > > page (if we will use NVM memory for page cache, of course). So, what do you
> >> > > imply by "bad block" issue?
> >> >
> >> > We don't have direct physical access to the device's address space, in
> >> > the sense the device is still free to perform remapping of chunks of NVM
> >> > underneath us. The problem is that when a block or address range (as
> >> > small as a cache line) goes bad, the device maintains a poison bit for
> >> > every affected cache line. Behind the scenes, it may have already
> >> > remapped the range, but the cache line poison has to be kept so that
> >> > there is a notification to the user/owner of the data that something has
> >> > been lost. Since NVM is byte addressable memory sitting on the memory
> >> > bus, such a poisoned cache line results in memory errors and SIGBUSes.
> >> > Compared to tradational storage where an app will get nice and friendly
> >> > (relatively speaking..) -EIOs. The whole badblocks implementation was
> >> > done so that the driver can intercept IO (i.e. reads) to _known_ bad
> >> > locations, and short-circuit them with an EIO. If the driver doesn't
> >> > catch these, the reads will turn into a memory bus access, and the
> >> > poison will cause a SIGBUS.
> >>
> >> "driver" ... you mean XFS? Or do you mean the thing that makes pmem
> >> look kind of like a traditional block device? :)
> >
> > Yes, the thing that makes pmem look like a block device :) --
> > drivers/nvdimm/pmem.c
> >
> >>
> >> > This effort is to try and make this badblock checking smarter - and try
> >> > and reduce the penalty on every IO to a smaller range, which only the
> >> > filesystem can do.
> >>
> >> Though... now that XFS merged the reverse mapping support, I've been
> >> wondering if there'll be a resubmission of the device errors callback?
> >> It still would be useful to be able to inform the user that part of
> >> their fs has gone bad, or, better yet, if the buffer is still in memory
> >> someplace else, just write it back out.
> >>
> >> Or I suppose if we had some kind of raid1 set up between memories we
> >> could read one of the other copies and rewrite it into the failing
> >> region immediately.
> >
> > Yes, that is kind of what I was hoping to accomplish via this
> > discussion. How much would filesystems want to be involved in this sort
> > of badblocks handling, if at all. I can refresh my patches that provide
> > the fs notification, but that's the easy bit, and a starting point.
> >
>
> I have some questions. Why moving badblock handling to file system
> level avoid the checking phase? In file system level for each I/O I
> still have to check the badblock list, right? Do you mean during mount
> it can go through the pmem device and locates all the data structures
> mangled by badblocks and handle them accordingly, so that during
> normal running the badblocks will never be accessed? Or, if there is
> replicataion/snapshot support, use a copy to recover the badblocks?
>
> How about operations bypass the file system, i.e. mmap?
Hi Andiry,
I do mean that in the filesystem, for every IO, the badblocks will be
checked. Currently, the pmem driver does this, and the hope is that the
filesystem can do a better job at it. The driver unconditionally checks
every IO for badblocks on the whole device. Depending on how the
badblocks are represented in the filesystem, we might be able to quickly
tell if a file/range has existing badblocks, and error out the IO
accordingly.
At mount the the fs would read the existing badblocks on the block
device, and build its own representation of them. Then during normal
use, if the underlying badblocks change, the fs would get a notification
that would allow it to also update its own representation.
Yes, if there is replication etc support in the filesystem, we could try
to recover using that, but I haven't put much thought in that direction.
Like I said in a previous reply, mmap can be a tricky case, and other
than handling the machine check exception, there may not be anything
else we can do..
If the range we're faulting on has known errors in badblocks, the fault
will fail with SIGBUS (see where pmem_direct_access() fails due to
badblocks). For latent errors that are not known in badblocks, if the
platform has MCE recovery, there is an MCE handler for pmem currently,
that will add that address to badblocks. If MCE recovery is absent, then
the system will crash/reboot, and the next time the driver populates
badblocks, that address will appear in it.
>
> >>
> >> > > > A while back, Dave Chinner had suggested a move towards smarter
> >> > > > handling, and I posted initial RFC patches [1], but since then the topic
> >> > > > hasn't really moved forward.
> >> > > >
> >> > > > I'd like to propose and have a discussion about the following new
> >> > > > functionality:
> >> > > >
> >> > > > 1. Filesystems develop a native representation of badblocks. For
> >> > > > example, in xfs, this would (presumably) be linked to the reverse
> >> > > > mapping btree. The filesystem representation has the potential to be
> >> > > > more efficient than the block driver doing the check, as the fs can
> >> > > > check the IO happening on a file against just that file's range.
> >>
> >> OTOH that means we'd have to check /every/ file IO request against the
> >> rmapbt, which will make things reaaaaaally slow. I suspect it might be
> >> preferable just to let the underlying pmem driver throw an error at us.
> >>
> >> (Or possibly just cache the bad extents in memory.)
> >
> > Interesting - this would be a good discussion to have. My motivation for
> > this was the reasoning that the pmem driver has to check every single IO
> > against badblocks, and maybe the fs can do a better job. But if you
> > think the fs will actually be slower, we should try to somehow benchmark
> > that!
> >
> >>
> >> > > What do you mean by "file system can check the IO happening on a file"?
> >> > > Do you mean read or write operation? What's about metadata?
> >> >
> >> > For the purpose described above, i.e. returning early EIOs when
> >> > possible, this will be limited to reads and metadata reads. If we're
> >> > about to do a metadata read, and realize the block(s) about to be read
> >> > are on the badblocks list, then we do the same thing as when we discover
> >> > other kinds of metadata corruption.
> >>
> >> ...fail and shut down? :)
> >>
> >> Actually, for metadata either we look at the xfs_bufs to see if it's in
> >> memory (XFS doesn't directly access metadata) and write it back out; or
> >> we could fire up the online repair tool to rebuild the metadata.
> >
> > Agreed, I was just stressing that this scenario does not change from
> > status quo, and really recovering from corruption isn't the problem
> > we're trying to solve here :)
> >
> >>
> >> > > If we are talking about the discovering a bad block on read operation then
> >> > > rare modern file system is able to survive as for the case of metadata as
> >> > > for the case of user data. Let's imagine that we have really mature file
> >> > > system driver then what does it mean to encounter a bad block? The failure
> >> > > to read a logical block of some metadata (bad block) means that we are
> >> > > unable to extract some part of a metadata structure. From file system
> >> > > driver point of view, it looks like that our file system is corrupted, we need
> >> > > to stop the file system operations and, finally, to check and recover file
> >> > > system volume by means of fsck tool. If we find a bad block for some
> >> > > user file then, again, it looks like an issue. Some file systems simply
> >> > > return "unrecovered read error". Another one, theoretically, is able
> >> > > to survive because of snapshots, for example. But, anyway, it will look
> >> > > like as Read-Only mount state and the user will need to resolve such
> >> > > trouble by hands.
> >> >
> >> > As far as I can tell, all of these things remain the same. The goal here
> >> > isn't to survive more NVM badblocks than we would've before, and lost
> >> > data or lost metadata will continue to have the same consequences as
> >> > before, and will need the same recovery actions/intervention as before.
> >> > The goal is to make the failure model similar to what users expect
> >> > today, and as much as possible make recovery actions too similarly
> >> > intuitive.
> >> >
> >> > >
> >> > > If we are talking about discovering a bad block during write operation then,
> >> > > again, we are in trouble. Usually, we are using asynchronous model
> >> > > of write/flush operation. We are preparing the consistent state of all our
> >> > > metadata structures in the memory, at first. The flush operations for metadata
> >> > > and user data can be done in different times. And what should be done if we
> >> > > discover bad block for any piece of metadata or user data? Simple tracking of
> >> > > bad blocks is not enough at all. Let's consider user data, at first. If we cannot
> >> > > write some file's block successfully then we have two ways: (1) forget about
> >> > > this piece of data; (2) try to change the associated LBA for this piece of data.
> >> > > The operation of re-allocation LBA number for discovered bad block
> >> > > (user data case) sounds as real pain. Because you need to rebuild the metadata
> >> > > that track the location of this part of file. And it sounds as practically
> >> > > impossible operation, for the case of LFS file system, for example.
> >> > > If we have trouble with flushing any part of metadata then it sounds as
> >> > > complete disaster for any file system.
> >> >
> >> > Writes can get more complicated in certain cases. If it is a regular
> >> > page cache writeback, or any aligned write that goes through the block
> >> > driver, that is completely fine. The block driver will check that the
> >> > block was previously marked as bad, do a "clear poison" operation
> >> > (defined in the ACPI spec), which tells the firmware that the poison bit
> >> > is not OK to be cleared, and writes the new data. This also removes the
> >> > block from the badblocks list, and in this scheme, triggers a
> >> > notification to the filesystem that it too can remove the block from its
> >> > accounting. mmap writes and DAX can get more complicated, and at times
> >> > they will just trigger a SIGBUS, and there's no way around that.
> >> >
> >> > >
> >> > > Are you really sure that file system should process bad block issue?
> >> > >
> >> > > >In contrast, today, the block driver checks against the whole block device
> >> > > > range for every IO. On encountering badblocks, the filesystem can
> >> > > > generate a better notification/error message that points the user to
> >> > > > (file, offset) as opposed to the block driver, which can only provide
> >> > > > (block-device, sector).
> >>
> >> <shrug> We can do the translation with the backref info...
> >
> > Yes we should at least do that. I'm guessing this would happen in XFS
> > when it gets an EIO from an IO submission? The bio submission path in
> > the fs is probably not synchronous (correct?), but whenever it gets the
> > EIO, I'm guessing we just print a loud error message after doing the
> > backref lookup..
> >
> >>
> >> > > > 2. The block layer adds a notifier to badblock addition/removal
> >> > > > operations, which the filesystem subscribes to, and uses to maintain its
> >> > > > badblocks accounting. (This part is implemented as a proof of concept in
> >> > > > the RFC mentioned above [1]).
> >> > >
> >> > > I am not sure that any bad block notification during/after IO operation
> >> > > is valuable for file system. Maybe, it could help if file system simply will
> >> > > know about bad block beforehand the operation of logical block allocation.
> >> > > But what subsystem will discover bad blocks before any IO operations?
> >> > > How file system will receive information or some bad block table?
> >> >
> >> > The driver populates its badblocks lists whenever an Address Range Scrub
> >> > is started (also via ACPI methods). This is always done at
> >> > initialization time, so that it can build an in-memory representation of
> >> > the badblocks. Additionally, this can also be triggered manually. And
> >> > finally badblocks can also get populated for new latent errors when a
> >> > machine check exception occurs. All of these can trigger notification to
> >> > the file system without actual user reads happening.
> >> >
> >> > > I am not convinced that suggested badblocks approach is really feasible.
> >> > > Also I am not sure that file system should see the bad blocks at all.
> >> > > Why hardware cannot manage this issue for us?
> >> >
> >> > Hardware does manage the actual badblocks issue for us in the sense that
> >> > when it discovers a badblock it will do the remapping. But since this is
> >> > on the memory bus, and has different error signatures than applications
> >> > are used to, we want to make the error handling similar to the existing
> >> > storage model.
> >>
> >> Yes please and thank you, to the "error handling similar to the existing
> >> storage model". Even better if this just gets added to a layer
> >> underneath the fs so that IO to bad regions returns EIO. 8-)
> >
> > This (if this just gets added to a layer underneath the fs so that IO to bad
> > regions returns EIO) already happens :) See pmem_do_bvec() in
> > drivers/nvdimm/pmem.c, where we return EIO for a known badblock on a
> > read. I'm wondering if this can be improved..
> >
>
> The pmem_do_bvec() read logic is like this:
>
> pmem_do_bvec()
> if (is_bad_pmem())
> return -EIO;
> else
> memcpy_from_pmem();
>
> Note memcpy_from_pmem() is calling memcpy_mcsafe(). Does this imply
> that even if a block is not in the badblock list, it still can be bad
> and causes MCE? Does the badblock list get changed during file system
> running? If that is the case, should the file system get a
> notification when it gets changed? If a block is good when I first
> read it, can I still trust it to be good for the second access?
Yes, if a block is not in the badblocks list, it can still cause an
MCE. This is the latent error case I described above. For a simple read()
via the pmem driver, this will get handled by memcpy_mcsafe. For mmap,
an MCE is inevitable.
Yes the badblocks list may change while a filesystem is running. The RFC
patches[1] I linked to add a notification for the filesystem when this
happens.
No, if the media, for some reason, 'dvelops' a bad cell, a second
consecutive read does have a chance of being bad. Once a location has
been marked as bad, it will stay bad till the ACPI clear error 'DSM' has
been called to mark it as clean.
[1]: http://www.linux.sgi.com/archives/xfs/2016-06/msg00299.html
>
> Thanks,
> Andiry
>
> >>
> >> (Sleeeeep...)
> >>
> >> --D
> >>
> >> >
> >> > --
> >> > To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in
> >> > the body of a message to majordomo@vger.kernel.org
> >> > More majordomo info at http://vger.kernel.org/majordomo-info.html
> > --
> > To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in
> > the body of a message to majordomo@vger.kernel.org
> > More majordomo info at http://vger.kernel.org/majordomo-info.html
^ permalink raw reply [flat|nested] 42+ messages in thread
* Re: [LSF/MM TOPIC] Badblocks checking/representation in filesystems
@ 2017-01-17 22:37 ` Vishal Verma
0 siblings, 0 replies; 42+ messages in thread
From: Vishal Verma @ 2017-01-17 22:37 UTC (permalink / raw)
To: Andiry Xu
Cc: Slava Dubeyko, Darrick J. Wong, linux-nvdimm@lists.01.org,
linux-block@vger.kernel.org, Viacheslav Dubeyko, Linux FS Devel,
lsf-pc@lists.linux-foundation.org
On 01/17, Andiry Xu wrote:
> Hi,
>
> On Tue, Jan 17, 2017 at 1:35 PM, Vishal Verma <vishal.l.verma@intel.com> wrote:
> > On 01/16, Darrick J. Wong wrote:
> >> On Fri, Jan 13, 2017 at 05:49:10PM -0700, Vishal Verma wrote:
> >> > On 01/14, Slava Dubeyko wrote:
> >> > >
> >> > > ---- Original Message ----
> >> > > Subject: [LSF/MM TOPIC] Badblocks checking/representation in filesystems
> >> > > Sent: Jan 13, 2017 1:40 PM
> >> > > From: "Verma, Vishal L" <vishal.l.verma@intel.com>
> >> > > To: lsf-pc@lists.linux-foundation.org
> >> > > Cc: linux-nvdimm@lists.01.org, linux-block@vger.kernel.org, linux-fsdevel@vger.kernel.org
> >> > >
> >> > > > The current implementation of badblocks, where we consult the badblocks
> >> > > > list for every IO in the block driver works, and is a last option
> >> > > > failsafe, but from a user perspective, it isn't the easiest interface to
> >> > > > work with.
> >> > >
> >> > > As I remember, FAT and HFS+ specifications contain description of bad blocks
> >> > > (physical sectors) table. I believe that this table was used for the case of
> >> > > floppy media. But, finally, this table becomes to be the completely obsolete
> >> > > artefact because mostly storage devices are reliably enough. Why do you need
> >>
> >> ext4 has a badblocks inode to own all the bad spots on disk, but ISTR it
> >> doesn't support(??) extents or 64-bit filesystems, and might just be a
> >> vestigial organ at this point. XFS doesn't have anything to track bad
> >> blocks currently....
> >>
> >> > > in exposing the bad blocks on the file system level? Do you expect that next
> >> > > generation of NVM memory will be so unreliable that file system needs to manage
> >> > > bad blocks? What's about erasure coding schemes? Do file system really need to suffer
> >> > > from the bad block issue?
> >> > >
> >> > > Usually, we are using LBAs and it is the responsibility of storage device to map
> >> > > a bad physical block/page/sector into valid one. Do you mean that we have
> >> > > access to physical NVM memory address directly? But it looks like that we can
> >> > > have a "bad block" issue even we will access data into page cache's memory
> >> > > page (if we will use NVM memory for page cache, of course). So, what do you
> >> > > imply by "bad block" issue?
> >> >
> >> > We don't have direct physical access to the device's address space, in
> >> > the sense the device is still free to perform remapping of chunks of NVM
> >> > underneath us. The problem is that when a block or address range (as
> >> > small as a cache line) goes bad, the device maintains a poison bit for
> >> > every affected cache line. Behind the scenes, it may have already
> >> > remapped the range, but the cache line poison has to be kept so that
> >> > there is a notification to the user/owner of the data that something has
> >> > been lost. Since NVM is byte addressable memory sitting on the memory
> >> > bus, such a poisoned cache line results in memory errors and SIGBUSes.
> >> > Compared to tradational storage where an app will get nice and friendly
> >> > (relatively speaking..) -EIOs. The whole badblocks implementation was
> >> > done so that the driver can intercept IO (i.e. reads) to _known_ bad
> >> > locations, and short-circuit them with an EIO. If the driver doesn't
> >> > catch these, the reads will turn into a memory bus access, and the
> >> > poison will cause a SIGBUS.
> >>
> >> "driver" ... you mean XFS? Or do you mean the thing that makes pmem
> >> look kind of like a traditional block device? :)
> >
> > Yes, the thing that makes pmem look like a block device :) --
> > drivers/nvdimm/pmem.c
> >
> >>
> >> > This effort is to try and make this badblock checking smarter - and try
> >> > and reduce the penalty on every IO to a smaller range, which only the
> >> > filesystem can do.
> >>
> >> Though... now that XFS merged the reverse mapping support, I've been
> >> wondering if there'll be a resubmission of the device errors callback?
> >> It still would be useful to be able to inform the user that part of
> >> their fs has gone bad, or, better yet, if the buffer is still in memory
> >> someplace else, just write it back out.
> >>
> >> Or I suppose if we had some kind of raid1 set up between memories we
> >> could read one of the other copies and rewrite it into the failing
> >> region immediately.
> >
> > Yes, that is kind of what I was hoping to accomplish via this
> > discussion. How much would filesystems want to be involved in this sort
> > of badblocks handling, if at all. I can refresh my patches that provide
> > the fs notification, but that's the easy bit, and a starting point.
> >
>
> I have some questions. Why moving badblock handling to file system
> level avoid the checking phase? In file system level for each I/O I
> still have to check the badblock list, right? Do you mean during mount
> it can go through the pmem device and locates all the data structures
> mangled by badblocks and handle them accordingly, so that during
> normal running the badblocks will never be accessed? Or, if there is
> replicataion/snapshot support, use a copy to recover the badblocks?
>
> How about operations bypass the file system, i.e. mmap?
Hi Andiry,
I do mean that in the filesystem, for every IO, the badblocks will be
checked. Currently, the pmem driver does this, and the hope is that the
filesystem can do a better job at it. The driver unconditionally checks
every IO for badblocks on the whole device. Depending on how the
badblocks are represented in the filesystem, we might be able to quickly
tell if a file/range has existing badblocks, and error out the IO
accordingly.
At mount the the fs would read the existing badblocks on the block
device, and build its own representation of them. Then during normal
use, if the underlying badblocks change, the fs would get a notification
that would allow it to also update its own representation.
Yes, if there is replication etc support in the filesystem, we could try
to recover using that, but I haven't put much thought in that direction.
Like I said in a previous reply, mmap can be a tricky case, and other
than handling the machine check exception, there may not be anything
else we can do..
If the range we're faulting on has known errors in badblocks, the fault
will fail with SIGBUS (see where pmem_direct_access() fails due to
badblocks). For latent errors that are not known in badblocks, if the
platform has MCE recovery, there is an MCE handler for pmem currently,
that will add that address to badblocks. If MCE recovery is absent, then
the system will crash/reboot, and the next time the driver populates
badblocks, that address will appear in it.
>
> >>
> >> > > > A while back, Dave Chinner had suggested a move towards smarter
> >> > > > handling, and I posted initial RFC patches [1], but since then the topic
> >> > > > hasn't really moved forward.
> >> > > >
> >> > > > I'd like to propose and have a discussion about the following new
> >> > > > functionality:
> >> > > >
> >> > > > 1. Filesystems develop a native representation of badblocks. For
> >> > > > example, in xfs, this would (presumably) be linked to the reverse
> >> > > > mapping btree. The filesystem representation has the potential to be
> >> > > > more efficient than the block driver doing the check, as the fs can
> >> > > > check the IO happening on a file against just that file's range.
> >>
> >> OTOH that means we'd have to check /every/ file IO request against the
> >> rmapbt, which will make things reaaaaaally slow. I suspect it might be
> >> preferable just to let the underlying pmem driver throw an error at us.
> >>
> >> (Or possibly just cache the bad extents in memory.)
> >
> > Interesting - this would be a good discussion to have. My motivation for
> > this was the reasoning that the pmem driver has to check every single IO
> > against badblocks, and maybe the fs can do a better job. But if you
> > think the fs will actually be slower, we should try to somehow benchmark
> > that!
> >
> >>
> >> > > What do you mean by "file system can check the IO happening on a file"?
> >> > > Do you mean read or write operation? What's about metadata?
> >> >
> >> > For the purpose described above, i.e. returning early EIOs when
> >> > possible, this will be limited to reads and metadata reads. If we're
> >> > about to do a metadata read, and realize the block(s) about to be read
> >> > are on the badblocks list, then we do the same thing as when we discover
> >> > other kinds of metadata corruption.
> >>
> >> ...fail and shut down? :)
> >>
> >> Actually, for metadata either we look at the xfs_bufs to see if it's in
> >> memory (XFS doesn't directly access metadata) and write it back out; or
> >> we could fire up the online repair tool to rebuild the metadata.
> >
> > Agreed, I was just stressing that this scenario does not change from
> > status quo, and really recovering from corruption isn't the problem
> > we're trying to solve here :)
> >
> >>
> >> > > If we are talking about the discovering a bad block on read operation then
> >> > > rare modern file system is able to survive as for the case of metadata as
> >> > > for the case of user data. Let's imagine that we have really mature file
> >> > > system driver then what does it mean to encounter a bad block? The failure
> >> > > to read a logical block of some metadata (bad block) means that we are
> >> > > unable to extract some part of a metadata structure. From file system
> >> > > driver point of view, it looks like that our file system is corrupted, we need
> >> > > to stop the file system operations and, finally, to check and recover file
> >> > > system volume by means of fsck tool. If we find a bad block for some
> >> > > user file then, again, it looks like an issue. Some file systems simply
> >> > > return "unrecovered read error". Another one, theoretically, is able
> >> > > to survive because of snapshots, for example. But, anyway, it will look
> >> > > like as Read-Only mount state and the user will need to resolve such
> >> > > trouble by hands.
> >> >
> >> > As far as I can tell, all of these things remain the same. The goal here
> >> > isn't to survive more NVM badblocks than we would've before, and lost
> >> > data or lost metadata will continue to have the same consequences as
> >> > before, and will need the same recovery actions/intervention as before.
> >> > The goal is to make the failure model similar to what users expect
> >> > today, and as much as possible make recovery actions too similarly
> >> > intuitive.
> >> >
> >> > >
> >> > > If we are talking about discovering a bad block during write operation then,
> >> > > again, we are in trouble. Usually, we are using asynchronous model
> >> > > of write/flush operation. We are preparing the consistent state of all our
> >> > > metadata structures in the memory, at first. The flush operations for metadata
> >> > > and user data can be done in different times. And what should be done if we
> >> > > discover bad block for any piece of metadata or user data? Simple tracking of
> >> > > bad blocks is not enough at all. Let's consider user data, at first. If we cannot
> >> > > write some file's block successfully then we have two ways: (1) forget about
> >> > > this piece of data; (2) try to change the associated LBA for this piece of data.
> >> > > The operation of re-allocation LBA number for discovered bad block
> >> > > (user data case) sounds as real pain. Because you need to rebuild the metadata
> >> > > that track the location of this part of file. And it sounds as practically
> >> > > impossible operation, for the case of LFS file system, for example.
> >> > > If we have trouble with flushing any part of metadata then it sounds as
> >> > > complete disaster for any file system.
> >> >
> >> > Writes can get more complicated in certain cases. If it is a regular
> >> > page cache writeback, or any aligned write that goes through the block
> >> > driver, that is completely fine. The block driver will check that the
> >> > block was previously marked as bad, do a "clear poison" operation
> >> > (defined in the ACPI spec), which tells the firmware that the poison bit
> >> > is not OK to be cleared, and writes the new data. This also removes the
> >> > block from the badblocks list, and in this scheme, triggers a
> >> > notification to the filesystem that it too can remove the block from its
> >> > accounting. mmap writes and DAX can get more complicated, and at times
> >> > they will just trigger a SIGBUS, and there's no way around that.
> >> >
> >> > >
> >> > > Are you really sure that file system should process bad block issue?
> >> > >
> >> > > >In contrast, today, the block driver checks against the whole block device
> >> > > > range for every IO. On encountering badblocks, the filesystem can
> >> > > > generate a better notification/error message that points the user to
> >> > > > (file, offset) as opposed to the block driver, which can only provide
> >> > > > (block-device, sector).
> >>
> >> <shrug> We can do the translation with the backref info...
> >
> > Yes we should at least do that. I'm guessing this would happen in XFS
> > when it gets an EIO from an IO submission? The bio submission path in
> > the fs is probably not synchronous (correct?), but whenever it gets the
> > EIO, I'm guessing we just print a loud error message after doing the
> > backref lookup..
> >
> >>
> >> > > > 2. The block layer adds a notifier to badblock addition/removal
> >> > > > operations, which the filesystem subscribes to, and uses to maintain its
> >> > > > badblocks accounting. (This part is implemented as a proof of concept in
> >> > > > the RFC mentioned above [1]).
> >> > >
> >> > > I am not sure that any bad block notification during/after IO operation
> >> > > is valuable for file system. Maybe, it could help if file system simply will
> >> > > know about bad block beforehand the operation of logical block allocation.
> >> > > But what subsystem will discover bad blocks before any IO operations?
> >> > > How file system will receive information or some bad block table?
> >> >
> >> > The driver populates its badblocks lists whenever an Address Range Scrub
> >> > is started (also via ACPI methods). This is always done at
> >> > initialization time, so that it can build an in-memory representation of
> >> > the badblocks. Additionally, this can also be triggered manually. And
> >> > finally badblocks can also get populated for new latent errors when a
> >> > machine check exception occurs. All of these can trigger notification to
> >> > the file system without actual user reads happening.
> >> >
> >> > > I am not convinced that suggested badblocks approach is really feasible.
> >> > > Also I am not sure that file system should see the bad blocks at all.
> >> > > Why hardware cannot manage this issue for us?
> >> >
> >> > Hardware does manage the actual badblocks issue for us in the sense that
> >> > when it discovers a badblock it will do the remapping. But since this is
> >> > on the memory bus, and has different error signatures than applications
> >> > are used to, we want to make the error handling similar to the existing
> >> > storage model.
> >>
> >> Yes please and thank you, to the "error handling similar to the existing
> >> storage model". Even better if this just gets added to a layer
> >> underneath the fs so that IO to bad regions returns EIO. 8-)
> >
> > This (if this just gets added to a layer underneath the fs so that IO to bad
> > regions returns EIO) already happens :) See pmem_do_bvec() in
> > drivers/nvdimm/pmem.c, where we return EIO for a known badblock on a
> > read. I'm wondering if this can be improved..
> >
>
> The pmem_do_bvec() read logic is like this:
>
> pmem_do_bvec()
> if (is_bad_pmem())
> return -EIO;
> else
> memcpy_from_pmem();
>
> Note memcpy_from_pmem() is calling memcpy_mcsafe(). Does this imply
> that even if a block is not in the badblock list, it still can be bad
> and causes MCE? Does the badblock list get changed during file system
> running? If that is the case, should the file system get a
> notification when it gets changed? If a block is good when I first
> read it, can I still trust it to be good for the second access?
Yes, if a block is not in the badblocks list, it can still cause an
MCE. This is the latent error case I described above. For a simple read()
via the pmem driver, this will get handled by memcpy_mcsafe. For mmap,
an MCE is inevitable.
Yes the badblocks list may change while a filesystem is running. The RFC
patches[1] I linked to add a notification for the filesystem when this
happens.
No, if the media, for some reason, 'dvelops' a bad cell, a second
consecutive read does have a chance of being bad. Once a location has
been marked as bad, it will stay bad till the ACPI clear error 'DSM' has
been called to mark it as clean.
[1]: http://www.linux.sgi.com/archives/xfs/2016-06/msg00299.html
>
> Thanks,
> Andiry
>
> >>
> >> (Sleeeeep...)
> >>
> >> --D
> >>
> >> >
> >> > --
> >> > To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in
> >> > the body of a message to majordomo@vger.kernel.org
> >> > More majordomo info at http://vger.kernel.org/majordomo-info.html
> > --
> > To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in
> > the body of a message to majordomo@vger.kernel.org
> > More majordomo info at http://vger.kernel.org/majordomo-info.html
_______________________________________________
Linux-nvdimm mailing list
Linux-nvdimm@lists.01.org
https://lists.01.org/mailman/listinfo/linux-nvdimm
^ permalink raw reply [flat|nested] 42+ messages in thread
* Re: [LSF/MM TOPIC] Badblocks checking/representation in filesystems
2017-01-17 22:37 ` Vishal Verma
@ 2017-01-17 23:20 ` Andiry Xu
-1 siblings, 0 replies; 42+ messages in thread
From: Andiry Xu @ 2017-01-17 23:20 UTC (permalink / raw)
To: Vishal Verma
Cc: Darrick J. Wong, Slava Dubeyko, lsf-pc@lists.linux-foundation.org,
linux-nvdimm@lists.01.org, linux-block@vger.kernel.org,
Linux FS Devel, Viacheslav Dubeyko
On Tue, Jan 17, 2017 at 2:37 PM, Vishal Verma <vishal.l.verma@intel.com> wrote:
> On 01/17, Andiry Xu wrote:
>> Hi,
>>
>> On Tue, Jan 17, 2017 at 1:35 PM, Vishal Verma <vishal.l.verma@intel.com> wrote:
>> > On 01/16, Darrick J. Wong wrote:
>> >> On Fri, Jan 13, 2017 at 05:49:10PM -0700, Vishal Verma wrote:
>> >> > On 01/14, Slava Dubeyko wrote:
>> >> > >
>> >> > > ---- Original Message ----
>> >> > > Subject: [LSF/MM TOPIC] Badblocks checking/representation in filesystems
>> >> > > Sent: Jan 13, 2017 1:40 PM
>> >> > > From: "Verma, Vishal L" <vishal.l.verma@intel.com>
>> >> > > To: lsf-pc@lists.linux-foundation.org
>> >> > > Cc: linux-nvdimm@lists.01.org, linux-block@vger.kernel.org, linux-fsdevel@vger.kernel.org
>> >> > >
>> >> > > > The current implementation of badblocks, where we consult the badblocks
>> >> > > > list for every IO in the block driver works, and is a last option
>> >> > > > failsafe, but from a user perspective, it isn't the easiest interface to
>> >> > > > work with.
>> >> > >
>> >> > > As I remember, FAT and HFS+ specifications contain description of bad blocks
>> >> > > (physical sectors) table. I believe that this table was used for the case of
>> >> > > floppy media. But, finally, this table becomes to be the completely obsolete
>> >> > > artefact because mostly storage devices are reliably enough. Why do you need
>> >>
>> >> ext4 has a badblocks inode to own all the bad spots on disk, but ISTR it
>> >> doesn't support(??) extents or 64-bit filesystems, and might just be a
>> >> vestigial organ at this point. XFS doesn't have anything to track bad
>> >> blocks currently....
>> >>
>> >> > > in exposing the bad blocks on the file system level? Do you expect that next
>> >> > > generation of NVM memory will be so unreliable that file system needs to manage
>> >> > > bad blocks? What's about erasure coding schemes? Do file system really need to suffer
>> >> > > from the bad block issue?
>> >> > >
>> >> > > Usually, we are using LBAs and it is the responsibility of storage device to map
>> >> > > a bad physical block/page/sector into valid one. Do you mean that we have
>> >> > > access to physical NVM memory address directly? But it looks like that we can
>> >> > > have a "bad block" issue even we will access data into page cache's memory
>> >> > > page (if we will use NVM memory for page cache, of course). So, what do you
>> >> > > imply by "bad block" issue?
>> >> >
>> >> > We don't have direct physical access to the device's address space, in
>> >> > the sense the device is still free to perform remapping of chunks of NVM
>> >> > underneath us. The problem is that when a block or address range (as
>> >> > small as a cache line) goes bad, the device maintains a poison bit for
>> >> > every affected cache line. Behind the scenes, it may have already
>> >> > remapped the range, but the cache line poison has to be kept so that
>> >> > there is a notification to the user/owner of the data that something has
>> >> > been lost. Since NVM is byte addressable memory sitting on the memory
>> >> > bus, such a poisoned cache line results in memory errors and SIGBUSes.
>> >> > Compared to tradational storage where an app will get nice and friendly
>> >> > (relatively speaking..) -EIOs. The whole badblocks implementation was
>> >> > done so that the driver can intercept IO (i.e. reads) to _known_ bad
>> >> > locations, and short-circuit them with an EIO. If the driver doesn't
>> >> > catch these, the reads will turn into a memory bus access, and the
>> >> > poison will cause a SIGBUS.
>> >>
>> >> "driver" ... you mean XFS? Or do you mean the thing that makes pmem
>> >> look kind of like a traditional block device? :)
>> >
>> > Yes, the thing that makes pmem look like a block device :) --
>> > drivers/nvdimm/pmem.c
>> >
>> >>
>> >> > This effort is to try and make this badblock checking smarter - and try
>> >> > and reduce the penalty on every IO to a smaller range, which only the
>> >> > filesystem can do.
>> >>
>> >> Though... now that XFS merged the reverse mapping support, I've been
>> >> wondering if there'll be a resubmission of the device errors callback?
>> >> It still would be useful to be able to inform the user that part of
>> >> their fs has gone bad, or, better yet, if the buffer is still in memory
>> >> someplace else, just write it back out.
>> >>
>> >> Or I suppose if we had some kind of raid1 set up between memories we
>> >> could read one of the other copies and rewrite it into the failing
>> >> region immediately.
>> >
>> > Yes, that is kind of what I was hoping to accomplish via this
>> > discussion. How much would filesystems want to be involved in this sort
>> > of badblocks handling, if at all. I can refresh my patches that provide
>> > the fs notification, but that's the easy bit, and a starting point.
>> >
>>
>> I have some questions. Why moving badblock handling to file system
>> level avoid the checking phase? In file system level for each I/O I
>> still have to check the badblock list, right? Do you mean during mount
>> it can go through the pmem device and locates all the data structures
>> mangled by badblocks and handle them accordingly, so that during
>> normal running the badblocks will never be accessed? Or, if there is
>> replicataion/snapshot support, use a copy to recover the badblocks?
>>
>> How about operations bypass the file system, i.e. mmap?
>
> Hi Andiry,
>
> I do mean that in the filesystem, for every IO, the badblocks will be
> checked. Currently, the pmem driver does this, and the hope is that the
> filesystem can do a better job at it. The driver unconditionally checks
> every IO for badblocks on the whole device. Depending on how the
> badblocks are represented in the filesystem, we might be able to quickly
> tell if a file/range has existing badblocks, and error out the IO
> accordingly.
>
> At mount the the fs would read the existing badblocks on the block
> device, and build its own representation of them. Then during normal
> use, if the underlying badblocks change, the fs would get a notification
> that would allow it to also update its own representation.
>
> Yes, if there is replication etc support in the filesystem, we could try
> to recover using that, but I haven't put much thought in that direction.
>
> Like I said in a previous reply, mmap can be a tricky case, and other
> than handling the machine check exception, there may not be anything
> else we can do..
> If the range we're faulting on has known errors in badblocks, the fault
> will fail with SIGBUS (see where pmem_direct_access() fails due to
> badblocks). For latent errors that are not known in badblocks, if the
> platform has MCE recovery, there is an MCE handler for pmem currently,
> that will add that address to badblocks. If MCE recovery is absent, then
> the system will crash/reboot, and the next time the driver populates
> badblocks, that address will appear in it.
Thank you for reply. That is very clear.
>>
>> >>
>> >> > > > A while back, Dave Chinner had suggested a move towards smarter
>> >> > > > handling, and I posted initial RFC patches [1], but since then the topic
>> >> > > > hasn't really moved forward.
>> >> > > >
>> >> > > > I'd like to propose and have a discussion about the following new
>> >> > > > functionality:
>> >> > > >
>> >> > > > 1. Filesystems develop a native representation of badblocks. For
>> >> > > > example, in xfs, this would (presumably) be linked to the reverse
>> >> > > > mapping btree. The filesystem representation has the potential to be
>> >> > > > more efficient than the block driver doing the check, as the fs can
>> >> > > > check the IO happening on a file against just that file's range.
>> >>
>> >> OTOH that means we'd have to check /every/ file IO request against the
>> >> rmapbt, which will make things reaaaaaally slow. I suspect it might be
>> >> preferable just to let the underlying pmem driver throw an error at us.
>> >>
>> >> (Or possibly just cache the bad extents in memory.)
>> >
>> > Interesting - this would be a good discussion to have. My motivation for
>> > this was the reasoning that the pmem driver has to check every single IO
>> > against badblocks, and maybe the fs can do a better job. But if you
>> > think the fs will actually be slower, we should try to somehow benchmark
>> > that!
>> >
>> >>
>> >> > > What do you mean by "file system can check the IO happening on a file"?
>> >> > > Do you mean read or write operation? What's about metadata?
>> >> >
>> >> > For the purpose described above, i.e. returning early EIOs when
>> >> > possible, this will be limited to reads and metadata reads. If we're
>> >> > about to do a metadata read, and realize the block(s) about to be read
>> >> > are on the badblocks list, then we do the same thing as when we discover
>> >> > other kinds of metadata corruption.
>> >>
>> >> ...fail and shut down? :)
>> >>
>> >> Actually, for metadata either we look at the xfs_bufs to see if it's in
>> >> memory (XFS doesn't directly access metadata) and write it back out; or
>> >> we could fire up the online repair tool to rebuild the metadata.
>> >
>> > Agreed, I was just stressing that this scenario does not change from
>> > status quo, and really recovering from corruption isn't the problem
>> > we're trying to solve here :)
>> >
>> >>
>> >> > > If we are talking about the discovering a bad block on read operation then
>> >> > > rare modern file system is able to survive as for the case of metadata as
>> >> > > for the case of user data. Let's imagine that we have really mature file
>> >> > > system driver then what does it mean to encounter a bad block? The failure
>> >> > > to read a logical block of some metadata (bad block) means that we are
>> >> > > unable to extract some part of a metadata structure. From file system
>> >> > > driver point of view, it looks like that our file system is corrupted, we need
>> >> > > to stop the file system operations and, finally, to check and recover file
>> >> > > system volume by means of fsck tool. If we find a bad block for some
>> >> > > user file then, again, it looks like an issue. Some file systems simply
>> >> > > return "unrecovered read error". Another one, theoretically, is able
>> >> > > to survive because of snapshots, for example. But, anyway, it will look
>> >> > > like as Read-Only mount state and the user will need to resolve such
>> >> > > trouble by hands.
>> >> >
>> >> > As far as I can tell, all of these things remain the same. The goal here
>> >> > isn't to survive more NVM badblocks than we would've before, and lost
>> >> > data or lost metadata will continue to have the same consequences as
>> >> > before, and will need the same recovery actions/intervention as before.
>> >> > The goal is to make the failure model similar to what users expect
>> >> > today, and as much as possible make recovery actions too similarly
>> >> > intuitive.
>> >> >
>> >> > >
>> >> > > If we are talking about discovering a bad block during write operation then,
>> >> > > again, we are in trouble. Usually, we are using asynchronous model
>> >> > > of write/flush operation. We are preparing the consistent state of all our
>> >> > > metadata structures in the memory, at first. The flush operations for metadata
>> >> > > and user data can be done in different times. And what should be done if we
>> >> > > discover bad block for any piece of metadata or user data? Simple tracking of
>> >> > > bad blocks is not enough at all. Let's consider user data, at first. If we cannot
>> >> > > write some file's block successfully then we have two ways: (1) forget about
>> >> > > this piece of data; (2) try to change the associated LBA for this piece of data.
>> >> > > The operation of re-allocation LBA number for discovered bad block
>> >> > > (user data case) sounds as real pain. Because you need to rebuild the metadata
>> >> > > that track the location of this part of file. And it sounds as practically
>> >> > > impossible operation, for the case of LFS file system, for example.
>> >> > > If we have trouble with flushing any part of metadata then it sounds as
>> >> > > complete disaster for any file system.
>> >> >
>> >> > Writes can get more complicated in certain cases. If it is a regular
>> >> > page cache writeback, or any aligned write that goes through the block
>> >> > driver, that is completely fine. The block driver will check that the
>> >> > block was previously marked as bad, do a "clear poison" operation
>> >> > (defined in the ACPI spec), which tells the firmware that the poison bit
>> >> > is not OK to be cleared, and writes the new data. This also removes the
>> >> > block from the badblocks list, and in this scheme, triggers a
>> >> > notification to the filesystem that it too can remove the block from its
>> >> > accounting. mmap writes and DAX can get more complicated, and at times
>> >> > they will just trigger a SIGBUS, and there's no way around that.
>> >> >
>> >> > >
>> >> > > Are you really sure that file system should process bad block issue?
>> >> > >
>> >> > > >In contrast, today, the block driver checks against the whole block device
>> >> > > > range for every IO. On encountering badblocks, the filesystem can
>> >> > > > generate a better notification/error message that points the user to
>> >> > > > (file, offset) as opposed to the block driver, which can only provide
>> >> > > > (block-device, sector).
>> >>
>> >> <shrug> We can do the translation with the backref info...
>> >
>> > Yes we should at least do that. I'm guessing this would happen in XFS
>> > when it gets an EIO from an IO submission? The bio submission path in
>> > the fs is probably not synchronous (correct?), but whenever it gets the
>> > EIO, I'm guessing we just print a loud error message after doing the
>> > backref lookup..
>> >
>> >>
>> >> > > > 2. The block layer adds a notifier to badblock addition/removal
>> >> > > > operations, which the filesystem subscribes to, and uses to maintain its
>> >> > > > badblocks accounting. (This part is implemented as a proof of concept in
>> >> > > > the RFC mentioned above [1]).
>> >> > >
>> >> > > I am not sure that any bad block notification during/after IO operation
>> >> > > is valuable for file system. Maybe, it could help if file system simply will
>> >> > > know about bad block beforehand the operation of logical block allocation.
>> >> > > But what subsystem will discover bad blocks before any IO operations?
>> >> > > How file system will receive information or some bad block table?
>> >> >
>> >> > The driver populates its badblocks lists whenever an Address Range Scrub
>> >> > is started (also via ACPI methods). This is always done at
>> >> > initialization time, so that it can build an in-memory representation of
>> >> > the badblocks. Additionally, this can also be triggered manually. And
>> >> > finally badblocks can also get populated for new latent errors when a
>> >> > machine check exception occurs. All of these can trigger notification to
>> >> > the file system without actual user reads happening.
>> >> >
>> >> > > I am not convinced that suggested badblocks approach is really feasible.
>> >> > > Also I am not sure that file system should see the bad blocks at all.
>> >> > > Why hardware cannot manage this issue for us?
>> >> >
>> >> > Hardware does manage the actual badblocks issue for us in the sense that
>> >> > when it discovers a badblock it will do the remapping. But since this is
>> >> > on the memory bus, and has different error signatures than applications
>> >> > are used to, we want to make the error handling similar to the existing
>> >> > storage model.
>> >>
>> >> Yes please and thank you, to the "error handling similar to the existing
>> >> storage model". Even better if this just gets added to a layer
>> >> underneath the fs so that IO to bad regions returns EIO. 8-)
>> >
>> > This (if this just gets added to a layer underneath the fs so that IO to bad
>> > regions returns EIO) already happens :) See pmem_do_bvec() in
>> > drivers/nvdimm/pmem.c, where we return EIO for a known badblock on a
>> > read. I'm wondering if this can be improved..
>> >
>>
>> The pmem_do_bvec() read logic is like this:
>>
>> pmem_do_bvec()
>> if (is_bad_pmem())
>> return -EIO;
>> else
>> memcpy_from_pmem();
>>
>> Note memcpy_from_pmem() is calling memcpy_mcsafe(). Does this imply
>> that even if a block is not in the badblock list, it still can be bad
>> and causes MCE? Does the badblock list get changed during file system
>> running? If that is the case, should the file system get a
>> notification when it gets changed? If a block is good when I first
>> read it, can I still trust it to be good for the second access?
>
> Yes, if a block is not in the badblocks list, it can still cause an
> MCE. This is the latent error case I described above. For a simple read()
> via the pmem driver, this will get handled by memcpy_mcsafe. For mmap,
> an MCE is inevitable.
>
> Yes the badblocks list may change while a filesystem is running. The RFC
> patches[1] I linked to add a notification for the filesystem when this
> happens.
>
This is really bad and it makes file system implementation much more
complicated. And badblock notification does not help very much,
because any block can be bad potentially, no matter it is in badblock
list or not. And file system has to perform checking for every read,
using memcpy_mcsafe. This is disaster for file system like NOVA, which
uses pointer de-reference to access data structures on pmem. Now if I
want to read a field in an inode on pmem, I have to copy it to DRAM
first and make sure memcpy_mcsafe() does not report anything wrong.
> No, if the media, for some reason, 'dvelops' a bad cell, a second
> consecutive read does have a chance of being bad. Once a location has
> been marked as bad, it will stay bad till the ACPI clear error 'DSM' has
> been called to mark it as clean.
>
I wonder what happens to write in this case? If a block is bad but not
reported in badblock list. Now I write to it without reading first. Do
I clear the poison with the write? Or still require a ACPI DSM?
> [1]: http://www.linux.sgi.com/archives/xfs/2016-06/msg00299.html
>
Thank you for the patchset. I will look into it.
Thanks,
Andiry
>
>>
>> Thanks,
>> Andiry
>>
>> >>
>> >> (Sleeeeep...)
>> >>
>> >> --D
>> >>
>> >> >
>> >> > --
>> >> > To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in
>> >> > the body of a message to majordomo@vger.kernel.org
>> >> > More majordomo info at http://vger.kernel.org/majordomo-info.html
>> > --
>> > To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in
>> > the body of a message to majordomo@vger.kernel.org
>> > More majordomo info at http://vger.kernel.org/majordomo-info.html
^ permalink raw reply [flat|nested] 42+ messages in thread
* Re: [LSF/MM TOPIC] Badblocks checking/representation in filesystems
@ 2017-01-17 23:20 ` Andiry Xu
0 siblings, 0 replies; 42+ messages in thread
From: Andiry Xu @ 2017-01-17 23:20 UTC (permalink / raw)
To: Vishal Verma
Cc: Slava Dubeyko, Darrick J. Wong, linux-nvdimm@lists.01.org,
linux-block@vger.kernel.org, Viacheslav Dubeyko, Linux FS Devel,
lsf-pc@lists.linux-foundation.org
On Tue, Jan 17, 2017 at 2:37 PM, Vishal Verma <vishal.l.verma@intel.com> wrote:
> On 01/17, Andiry Xu wrote:
>> Hi,
>>
>> On Tue, Jan 17, 2017 at 1:35 PM, Vishal Verma <vishal.l.verma@intel.com> wrote:
>> > On 01/16, Darrick J. Wong wrote:
>> >> On Fri, Jan 13, 2017 at 05:49:10PM -0700, Vishal Verma wrote:
>> >> > On 01/14, Slava Dubeyko wrote:
>> >> > >
>> >> > > ---- Original Message ----
>> >> > > Subject: [LSF/MM TOPIC] Badblocks checking/representation in filesystems
>> >> > > Sent: Jan 13, 2017 1:40 PM
>> >> > > From: "Verma, Vishal L" <vishal.l.verma@intel.com>
>> >> > > To: lsf-pc@lists.linux-foundation.org
>> >> > > Cc: linux-nvdimm@lists.01.org, linux-block@vger.kernel.org, linux-fsdevel@vger.kernel.org
>> >> > >
>> >> > > > The current implementation of badblocks, where we consult the badblocks
>> >> > > > list for every IO in the block driver works, and is a last option
>> >> > > > failsafe, but from a user perspective, it isn't the easiest interface to
>> >> > > > work with.
>> >> > >
>> >> > > As I remember, FAT and HFS+ specifications contain description of bad blocks
>> >> > > (physical sectors) table. I believe that this table was used for the case of
>> >> > > floppy media. But, finally, this table becomes to be the completely obsolete
>> >> > > artefact because mostly storage devices are reliably enough. Why do you need
>> >>
>> >> ext4 has a badblocks inode to own all the bad spots on disk, but ISTR it
>> >> doesn't support(??) extents or 64-bit filesystems, and might just be a
>> >> vestigial organ at this point. XFS doesn't have anything to track bad
>> >> blocks currently....
>> >>
>> >> > > in exposing the bad blocks on the file system level? Do you expect that next
>> >> > > generation of NVM memory will be so unreliable that file system needs to manage
>> >> > > bad blocks? What's about erasure coding schemes? Do file system really need to suffer
>> >> > > from the bad block issue?
>> >> > >
>> >> > > Usually, we are using LBAs and it is the responsibility of storage device to map
>> >> > > a bad physical block/page/sector into valid one. Do you mean that we have
>> >> > > access to physical NVM memory address directly? But it looks like that we can
>> >> > > have a "bad block" issue even we will access data into page cache's memory
>> >> > > page (if we will use NVM memory for page cache, of course). So, what do you
>> >> > > imply by "bad block" issue?
>> >> >
>> >> > We don't have direct physical access to the device's address space, in
>> >> > the sense the device is still free to perform remapping of chunks of NVM
>> >> > underneath us. The problem is that when a block or address range (as
>> >> > small as a cache line) goes bad, the device maintains a poison bit for
>> >> > every affected cache line. Behind the scenes, it may have already
>> >> > remapped the range, but the cache line poison has to be kept so that
>> >> > there is a notification to the user/owner of the data that something has
>> >> > been lost. Since NVM is byte addressable memory sitting on the memory
>> >> > bus, such a poisoned cache line results in memory errors and SIGBUSes.
>> >> > Compared to tradational storage where an app will get nice and friendly
>> >> > (relatively speaking..) -EIOs. The whole badblocks implementation was
>> >> > done so that the driver can intercept IO (i.e. reads) to _known_ bad
>> >> > locations, and short-circuit them with an EIO. If the driver doesn't
>> >> > catch these, the reads will turn into a memory bus access, and the
>> >> > poison will cause a SIGBUS.
>> >>
>> >> "driver" ... you mean XFS? Or do you mean the thing that makes pmem
>> >> look kind of like a traditional block device? :)
>> >
>> > Yes, the thing that makes pmem look like a block device :) --
>> > drivers/nvdimm/pmem.c
>> >
>> >>
>> >> > This effort is to try and make this badblock checking smarter - and try
>> >> > and reduce the penalty on every IO to a smaller range, which only the
>> >> > filesystem can do.
>> >>
>> >> Though... now that XFS merged the reverse mapping support, I've been
>> >> wondering if there'll be a resubmission of the device errors callback?
>> >> It still would be useful to be able to inform the user that part of
>> >> their fs has gone bad, or, better yet, if the buffer is still in memory
>> >> someplace else, just write it back out.
>> >>
>> >> Or I suppose if we had some kind of raid1 set up between memories we
>> >> could read one of the other copies and rewrite it into the failing
>> >> region immediately.
>> >
>> > Yes, that is kind of what I was hoping to accomplish via this
>> > discussion. How much would filesystems want to be involved in this sort
>> > of badblocks handling, if at all. I can refresh my patches that provide
>> > the fs notification, but that's the easy bit, and a starting point.
>> >
>>
>> I have some questions. Why moving badblock handling to file system
>> level avoid the checking phase? In file system level for each I/O I
>> still have to check the badblock list, right? Do you mean during mount
>> it can go through the pmem device and locates all the data structures
>> mangled by badblocks and handle them accordingly, so that during
>> normal running the badblocks will never be accessed? Or, if there is
>> replicataion/snapshot support, use a copy to recover the badblocks?
>>
>> How about operations bypass the file system, i.e. mmap?
>
> Hi Andiry,
>
> I do mean that in the filesystem, for every IO, the badblocks will be
> checked. Currently, the pmem driver does this, and the hope is that the
> filesystem can do a better job at it. The driver unconditionally checks
> every IO for badblocks on the whole device. Depending on how the
> badblocks are represented in the filesystem, we might be able to quickly
> tell if a file/range has existing badblocks, and error out the IO
> accordingly.
>
> At mount the the fs would read the existing badblocks on the block
> device, and build its own representation of them. Then during normal
> use, if the underlying badblocks change, the fs would get a notification
> that would allow it to also update its own representation.
>
> Yes, if there is replication etc support in the filesystem, we could try
> to recover using that, but I haven't put much thought in that direction.
>
> Like I said in a previous reply, mmap can be a tricky case, and other
> than handling the machine check exception, there may not be anything
> else we can do..
> If the range we're faulting on has known errors in badblocks, the fault
> will fail with SIGBUS (see where pmem_direct_access() fails due to
> badblocks). For latent errors that are not known in badblocks, if the
> platform has MCE recovery, there is an MCE handler for pmem currently,
> that will add that address to badblocks. If MCE recovery is absent, then
> the system will crash/reboot, and the next time the driver populates
> badblocks, that address will appear in it.
Thank you for reply. That is very clear.
>>
>> >>
>> >> > > > A while back, Dave Chinner had suggested a move towards smarter
>> >> > > > handling, and I posted initial RFC patches [1], but since then the topic
>> >> > > > hasn't really moved forward.
>> >> > > >
>> >> > > > I'd like to propose and have a discussion about the following new
>> >> > > > functionality:
>> >> > > >
>> >> > > > 1. Filesystems develop a native representation of badblocks. For
>> >> > > > example, in xfs, this would (presumably) be linked to the reverse
>> >> > > > mapping btree. The filesystem representation has the potential to be
>> >> > > > more efficient than the block driver doing the check, as the fs can
>> >> > > > check the IO happening on a file against just that file's range.
>> >>
>> >> OTOH that means we'd have to check /every/ file IO request against the
>> >> rmapbt, which will make things reaaaaaally slow. I suspect it might be
>> >> preferable just to let the underlying pmem driver throw an error at us.
>> >>
>> >> (Or possibly just cache the bad extents in memory.)
>> >
>> > Interesting - this would be a good discussion to have. My motivation for
>> > this was the reasoning that the pmem driver has to check every single IO
>> > against badblocks, and maybe the fs can do a better job. But if you
>> > think the fs will actually be slower, we should try to somehow benchmark
>> > that!
>> >
>> >>
>> >> > > What do you mean by "file system can check the IO happening on a file"?
>> >> > > Do you mean read or write operation? What's about metadata?
>> >> >
>> >> > For the purpose described above, i.e. returning early EIOs when
>> >> > possible, this will be limited to reads and metadata reads. If we're
>> >> > about to do a metadata read, and realize the block(s) about to be read
>> >> > are on the badblocks list, then we do the same thing as when we discover
>> >> > other kinds of metadata corruption.
>> >>
>> >> ...fail and shut down? :)
>> >>
>> >> Actually, for metadata either we look at the xfs_bufs to see if it's in
>> >> memory (XFS doesn't directly access metadata) and write it back out; or
>> >> we could fire up the online repair tool to rebuild the metadata.
>> >
>> > Agreed, I was just stressing that this scenario does not change from
>> > status quo, and really recovering from corruption isn't the problem
>> > we're trying to solve here :)
>> >
>> >>
>> >> > > If we are talking about the discovering a bad block on read operation then
>> >> > > rare modern file system is able to survive as for the case of metadata as
>> >> > > for the case of user data. Let's imagine that we have really mature file
>> >> > > system driver then what does it mean to encounter a bad block? The failure
>> >> > > to read a logical block of some metadata (bad block) means that we are
>> >> > > unable to extract some part of a metadata structure. From file system
>> >> > > driver point of view, it looks like that our file system is corrupted, we need
>> >> > > to stop the file system operations and, finally, to check and recover file
>> >> > > system volume by means of fsck tool. If we find a bad block for some
>> >> > > user file then, again, it looks like an issue. Some file systems simply
>> >> > > return "unrecovered read error". Another one, theoretically, is able
>> >> > > to survive because of snapshots, for example. But, anyway, it will look
>> >> > > like as Read-Only mount state and the user will need to resolve such
>> >> > > trouble by hands.
>> >> >
>> >> > As far as I can tell, all of these things remain the same. The goal here
>> >> > isn't to survive more NVM badblocks than we would've before, and lost
>> >> > data or lost metadata will continue to have the same consequences as
>> >> > before, and will need the same recovery actions/intervention as before.
>> >> > The goal is to make the failure model similar to what users expect
>> >> > today, and as much as possible make recovery actions too similarly
>> >> > intuitive.
>> >> >
>> >> > >
>> >> > > If we are talking about discovering a bad block during write operation then,
>> >> > > again, we are in trouble. Usually, we are using asynchronous model
>> >> > > of write/flush operation. We are preparing the consistent state of all our
>> >> > > metadata structures in the memory, at first. The flush operations for metadata
>> >> > > and user data can be done in different times. And what should be done if we
>> >> > > discover bad block for any piece of metadata or user data? Simple tracking of
>> >> > > bad blocks is not enough at all. Let's consider user data, at first. If we cannot
>> >> > > write some file's block successfully then we have two ways: (1) forget about
>> >> > > this piece of data; (2) try to change the associated LBA for this piece of data.
>> >> > > The operation of re-allocation LBA number for discovered bad block
>> >> > > (user data case) sounds as real pain. Because you need to rebuild the metadata
>> >> > > that track the location of this part of file. And it sounds as practically
>> >> > > impossible operation, for the case of LFS file system, for example.
>> >> > > If we have trouble with flushing any part of metadata then it sounds as
>> >> > > complete disaster for any file system.
>> >> >
>> >> > Writes can get more complicated in certain cases. If it is a regular
>> >> > page cache writeback, or any aligned write that goes through the block
>> >> > driver, that is completely fine. The block driver will check that the
>> >> > block was previously marked as bad, do a "clear poison" operation
>> >> > (defined in the ACPI spec), which tells the firmware that the poison bit
>> >> > is not OK to be cleared, and writes the new data. This also removes the
>> >> > block from the badblocks list, and in this scheme, triggers a
>> >> > notification to the filesystem that it too can remove the block from its
>> >> > accounting. mmap writes and DAX can get more complicated, and at times
>> >> > they will just trigger a SIGBUS, and there's no way around that.
>> >> >
>> >> > >
>> >> > > Are you really sure that file system should process bad block issue?
>> >> > >
>> >> > > >In contrast, today, the block driver checks against the whole block device
>> >> > > > range for every IO. On encountering badblocks, the filesystem can
>> >> > > > generate a better notification/error message that points the user to
>> >> > > > (file, offset) as opposed to the block driver, which can only provide
>> >> > > > (block-device, sector).
>> >>
>> >> <shrug> We can do the translation with the backref info...
>> >
>> > Yes we should at least do that. I'm guessing this would happen in XFS
>> > when it gets an EIO from an IO submission? The bio submission path in
>> > the fs is probably not synchronous (correct?), but whenever it gets the
>> > EIO, I'm guessing we just print a loud error message after doing the
>> > backref lookup..
>> >
>> >>
>> >> > > > 2. The block layer adds a notifier to badblock addition/removal
>> >> > > > operations, which the filesystem subscribes to, and uses to maintain its
>> >> > > > badblocks accounting. (This part is implemented as a proof of concept in
>> >> > > > the RFC mentioned above [1]).
>> >> > >
>> >> > > I am not sure that any bad block notification during/after IO operation
>> >> > > is valuable for file system. Maybe, it could help if file system simply will
>> >> > > know about bad block beforehand the operation of logical block allocation.
>> >> > > But what subsystem will discover bad blocks before any IO operations?
>> >> > > How file system will receive information or some bad block table?
>> >> >
>> >> > The driver populates its badblocks lists whenever an Address Range Scrub
>> >> > is started (also via ACPI methods). This is always done at
>> >> > initialization time, so that it can build an in-memory representation of
>> >> > the badblocks. Additionally, this can also be triggered manually. And
>> >> > finally badblocks can also get populated for new latent errors when a
>> >> > machine check exception occurs. All of these can trigger notification to
>> >> > the file system without actual user reads happening.
>> >> >
>> >> > > I am not convinced that suggested badblocks approach is really feasible.
>> >> > > Also I am not sure that file system should see the bad blocks at all.
>> >> > > Why hardware cannot manage this issue for us?
>> >> >
>> >> > Hardware does manage the actual badblocks issue for us in the sense that
>> >> > when it discovers a badblock it will do the remapping. But since this is
>> >> > on the memory bus, and has different error signatures than applications
>> >> > are used to, we want to make the error handling similar to the existing
>> >> > storage model.
>> >>
>> >> Yes please and thank you, to the "error handling similar to the existing
>> >> storage model". Even better if this just gets added to a layer
>> >> underneath the fs so that IO to bad regions returns EIO. 8-)
>> >
>> > This (if this just gets added to a layer underneath the fs so that IO to bad
>> > regions returns EIO) already happens :) See pmem_do_bvec() in
>> > drivers/nvdimm/pmem.c, where we return EIO for a known badblock on a
>> > read. I'm wondering if this can be improved..
>> >
>>
>> The pmem_do_bvec() read logic is like this:
>>
>> pmem_do_bvec()
>> if (is_bad_pmem())
>> return -EIO;
>> else
>> memcpy_from_pmem();
>>
>> Note memcpy_from_pmem() is calling memcpy_mcsafe(). Does this imply
>> that even if a block is not in the badblock list, it still can be bad
>> and causes MCE? Does the badblock list get changed during file system
>> running? If that is the case, should the file system get a
>> notification when it gets changed? If a block is good when I first
>> read it, can I still trust it to be good for the second access?
>
> Yes, if a block is not in the badblocks list, it can still cause an
> MCE. This is the latent error case I described above. For a simple read()
> via the pmem driver, this will get handled by memcpy_mcsafe. For mmap,
> an MCE is inevitable.
>
> Yes the badblocks list may change while a filesystem is running. The RFC
> patches[1] I linked to add a notification for the filesystem when this
> happens.
>
This is really bad and it makes file system implementation much more
complicated. And badblock notification does not help very much,
because any block can be bad potentially, no matter it is in badblock
list or not. And file system has to perform checking for every read,
using memcpy_mcsafe. This is disaster for file system like NOVA, which
uses pointer de-reference to access data structures on pmem. Now if I
want to read a field in an inode on pmem, I have to copy it to DRAM
first and make sure memcpy_mcsafe() does not report anything wrong.
> No, if the media, for some reason, 'dvelops' a bad cell, a second
> consecutive read does have a chance of being bad. Once a location has
> been marked as bad, it will stay bad till the ACPI clear error 'DSM' has
> been called to mark it as clean.
>
I wonder what happens to write in this case? If a block is bad but not
reported in badblock list. Now I write to it without reading first. Do
I clear the poison with the write? Or still require a ACPI DSM?
> [1]: http://www.linux.sgi.com/archives/xfs/2016-06/msg00299.html
>
Thank you for the patchset. I will look into it.
Thanks,
Andiry
>
>>
>> Thanks,
>> Andiry
>>
>> >>
>> >> (Sleeeeep...)
>> >>
>> >> --D
>> >>
>> >> >
>> >> > --
>> >> > To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in
>> >> > the body of a message to majordomo@vger.kernel.org
>> >> > More majordomo info at http://vger.kernel.org/majordomo-info.html
>> > --
>> > To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in
>> > the body of a message to majordomo@vger.kernel.org
>> > More majordomo info at http://vger.kernel.org/majordomo-info.html
_______________________________________________
Linux-nvdimm mailing list
Linux-nvdimm@lists.01.org
https://lists.01.org/mailman/listinfo/linux-nvdimm
^ permalink raw reply [flat|nested] 42+ messages in thread
* Re: [LSF/MM TOPIC] Badblocks checking/representation in filesystems
2017-01-17 23:20 ` Andiry Xu
@ 2017-01-17 23:51 ` Vishal Verma
-1 siblings, 0 replies; 42+ messages in thread
From: Vishal Verma @ 2017-01-17 23:51 UTC (permalink / raw)
To: Andiry Xu
Cc: Darrick J. Wong, Slava Dubeyko, lsf-pc@lists.linux-foundation.org,
linux-nvdimm@lists.01.org, linux-block@vger.kernel.org,
Linux FS Devel, Viacheslav Dubeyko
On 01/17, Andiry Xu wrote:
<snip>
> >>
> >> The pmem_do_bvec() read logic is like this:
> >>
> >> pmem_do_bvec()
> >> if (is_bad_pmem())
> >> return -EIO;
> >> else
> >> memcpy_from_pmem();
> >>
> >> Note memcpy_from_pmem() is calling memcpy_mcsafe(). Does this imply
> >> that even if a block is not in the badblock list, it still can be bad
> >> and causes MCE? Does the badblock list get changed during file system
> >> running? If that is the case, should the file system get a
> >> notification when it gets changed? If a block is good when I first
> >> read it, can I still trust it to be good for the second access?
> >
> > Yes, if a block is not in the badblocks list, it can still cause an
> > MCE. This is the latent error case I described above. For a simple read()
> > via the pmem driver, this will get handled by memcpy_mcsafe. For mmap,
> > an MCE is inevitable.
> >
> > Yes the badblocks list may change while a filesystem is running. The RFC
> > patches[1] I linked to add a notification for the filesystem when this
> > happens.
> >
>
> This is really bad and it makes file system implementation much more
> complicated. And badblock notification does not help very much,
> because any block can be bad potentially, no matter it is in badblock
> list or not. And file system has to perform checking for every read,
> using memcpy_mcsafe. This is disaster for file system like NOVA, which
> uses pointer de-reference to access data structures on pmem. Now if I
> want to read a field in an inode on pmem, I have to copy it to DRAM
> first and make sure memcpy_mcsafe() does not report anything wrong.
You have a good point, and I don't know if I have an answer for this..
Assuming a system with MCE recovery, maybe NOVA can add a mce handler
similar to nfit_handle_mce(), and handle errors as they happen, but I'm
being very hand-wavey here and don't know how much/how well that might
work..
>
> > No, if the media, for some reason, 'dvelops' a bad cell, a second
> > consecutive read does have a chance of being bad. Once a location has
> > been marked as bad, it will stay bad till the ACPI clear error 'DSM' has
> > been called to mark it as clean.
> >
>
> I wonder what happens to write in this case? If a block is bad but not
> reported in badblock list. Now I write to it without reading first. Do
> I clear the poison with the write? Or still require a ACPI DSM?
With writes, my understanding is there is still a possibility that an
internal read-modify-write can happen, and cause a MCE (this is the same
as writing to a bad DRAM cell, which can also cause an MCE). You can't
really use the ACPI DSM preemptively because you don't know whether the
location was bad. The error flow will be something like write causes the
MCE, a badblock gets added (either through the mce handler or after the
next reboot), and the recovery path is now the same as a regular badblock.
>
> > [1]: http://www.linux.sgi.com/archives/xfs/2016-06/msg00299.html
> >
>
> Thank you for the patchset. I will look into it.
>
^ permalink raw reply [flat|nested] 42+ messages in thread
* Re: [LSF/MM TOPIC] Badblocks checking/representation in filesystems
@ 2017-01-17 23:51 ` Vishal Verma
0 siblings, 0 replies; 42+ messages in thread
From: Vishal Verma @ 2017-01-17 23:51 UTC (permalink / raw)
To: Andiry Xu
Cc: Slava Dubeyko, Darrick J. Wong, linux-nvdimm@lists.01.org,
linux-block@vger.kernel.org, Viacheslav Dubeyko, Linux FS Devel,
lsf-pc@lists.linux-foundation.org
On 01/17, Andiry Xu wrote:
<snip>
> >>
> >> The pmem_do_bvec() read logic is like this:
> >>
> >> pmem_do_bvec()
> >> if (is_bad_pmem())
> >> return -EIO;
> >> else
> >> memcpy_from_pmem();
> >>
> >> Note memcpy_from_pmem() is calling memcpy_mcsafe(). Does this imply
> >> that even if a block is not in the badblock list, it still can be bad
> >> and causes MCE? Does the badblock list get changed during file system
> >> running? If that is the case, should the file system get a
> >> notification when it gets changed? If a block is good when I first
> >> read it, can I still trust it to be good for the second access?
> >
> > Yes, if a block is not in the badblocks list, it can still cause an
> > MCE. This is the latent error case I described above. For a simple read()
> > via the pmem driver, this will get handled by memcpy_mcsafe. For mmap,
> > an MCE is inevitable.
> >
> > Yes the badblocks list may change while a filesystem is running. The RFC
> > patches[1] I linked to add a notification for the filesystem when this
> > happens.
> >
>
> This is really bad and it makes file system implementation much more
> complicated. And badblock notification does not help very much,
> because any block can be bad potentially, no matter it is in badblock
> list or not. And file system has to perform checking for every read,
> using memcpy_mcsafe. This is disaster for file system like NOVA, which
> uses pointer de-reference to access data structures on pmem. Now if I
> want to read a field in an inode on pmem, I have to copy it to DRAM
> first and make sure memcpy_mcsafe() does not report anything wrong.
You have a good point, and I don't know if I have an answer for this..
Assuming a system with MCE recovery, maybe NOVA can add a mce handler
similar to nfit_handle_mce(), and handle errors as they happen, but I'm
being very hand-wavey here and don't know how much/how well that might
work..
>
> > No, if the media, for some reason, 'dvelops' a bad cell, a second
> > consecutive read does have a chance of being bad. Once a location has
> > been marked as bad, it will stay bad till the ACPI clear error 'DSM' has
> > been called to mark it as clean.
> >
>
> I wonder what happens to write in this case? If a block is bad but not
> reported in badblock list. Now I write to it without reading first. Do
> I clear the poison with the write? Or still require a ACPI DSM?
With writes, my understanding is there is still a possibility that an
internal read-modify-write can happen, and cause a MCE (this is the same
as writing to a bad DRAM cell, which can also cause an MCE). You can't
really use the ACPI DSM preemptively because you don't know whether the
location was bad. The error flow will be something like write causes the
MCE, a badblock gets added (either through the mce handler or after the
next reboot), and the recovery path is now the same as a regular badblock.
>
> > [1]: http://www.linux.sgi.com/archives/xfs/2016-06/msg00299.html
> >
>
> Thank you for the patchset. I will look into it.
>
_______________________________________________
Linux-nvdimm mailing list
Linux-nvdimm@lists.01.org
https://lists.01.org/mailman/listinfo/linux-nvdimm
^ permalink raw reply [flat|nested] 42+ messages in thread
* Re: [LSF/MM TOPIC] Badblocks checking/representation in filesystems
2017-01-17 23:51 ` Vishal Verma
@ 2017-01-18 1:58 ` Andiry Xu
-1 siblings, 0 replies; 42+ messages in thread
From: Andiry Xu @ 2017-01-18 1:58 UTC (permalink / raw)
To: Vishal Verma
Cc: Darrick J. Wong, Slava Dubeyko, lsf-pc@lists.linux-foundation.org,
linux-nvdimm@lists.01.org, linux-block@vger.kernel.org,
Linux FS Devel, Viacheslav Dubeyko
On Tue, Jan 17, 2017 at 3:51 PM, Vishal Verma <vishal.l.verma@intel.com> wrote:
> On 01/17, Andiry Xu wrote:
>
> <snip>
>
>> >>
>> >> The pmem_do_bvec() read logic is like this:
>> >>
>> >> pmem_do_bvec()
>> >> if (is_bad_pmem())
>> >> return -EIO;
>> >> else
>> >> memcpy_from_pmem();
>> >>
>> >> Note memcpy_from_pmem() is calling memcpy_mcsafe(). Does this imply
>> >> that even if a block is not in the badblock list, it still can be bad
>> >> and causes MCE? Does the badblock list get changed during file system
>> >> running? If that is the case, should the file system get a
>> >> notification when it gets changed? If a block is good when I first
>> >> read it, can I still trust it to be good for the second access?
>> >
>> > Yes, if a block is not in the badblocks list, it can still cause an
>> > MCE. This is the latent error case I described above. For a simple read()
>> > via the pmem driver, this will get handled by memcpy_mcsafe. For mmap,
>> > an MCE is inevitable.
>> >
>> > Yes the badblocks list may change while a filesystem is running. The RFC
>> > patches[1] I linked to add a notification for the filesystem when this
>> > happens.
>> >
>>
>> This is really bad and it makes file system implementation much more
>> complicated. And badblock notification does not help very much,
>> because any block can be bad potentially, no matter it is in badblock
>> list or not. And file system has to perform checking for every read,
>> using memcpy_mcsafe. This is disaster for file system like NOVA, which
>> uses pointer de-reference to access data structures on pmem. Now if I
>> want to read a field in an inode on pmem, I have to copy it to DRAM
>> first and make sure memcpy_mcsafe() does not report anything wrong.
>
> You have a good point, and I don't know if I have an answer for this..
> Assuming a system with MCE recovery, maybe NOVA can add a mce handler
> similar to nfit_handle_mce(), and handle errors as they happen, but I'm
> being very hand-wavey here and don't know how much/how well that might
> work..
>
>>
>> > No, if the media, for some reason, 'dvelops' a bad cell, a second
>> > consecutive read does have a chance of being bad. Once a location has
>> > been marked as bad, it will stay bad till the ACPI clear error 'DSM' has
>> > been called to mark it as clean.
>> >
>>
>> I wonder what happens to write in this case? If a block is bad but not
>> reported in badblock list. Now I write to it without reading first. Do
>> I clear the poison with the write? Or still require a ACPI DSM?
>
> With writes, my understanding is there is still a possibility that an
> internal read-modify-write can happen, and cause a MCE (this is the same
> as writing to a bad DRAM cell, which can also cause an MCE). You can't
> really use the ACPI DSM preemptively because you don't know whether the
> location was bad. The error flow will be something like write causes the
> MCE, a badblock gets added (either through the mce handler or after the
> next reboot), and the recovery path is now the same as a regular badblock.
>
This is different from my understanding. Right now write_pmem() in
pmem_do_bvec() does not use memcpy_mcsafe(). If the block is bad it
clears poison and writes to pmem again. Seems to me writing to bad
blocks does not cause MCE. Do we need memcpy_mcsafe for pmem stores?
Thanks,
Andiry
>>
>> > [1]: http://www.linux.sgi.com/archives/xfs/2016-06/msg00299.html
>> >
>>
>> Thank you for the patchset. I will look into it.
>>
^ permalink raw reply [flat|nested] 42+ messages in thread
* Re: [LSF/MM TOPIC] Badblocks checking/representation in filesystems
@ 2017-01-18 1:58 ` Andiry Xu
0 siblings, 0 replies; 42+ messages in thread
From: Andiry Xu @ 2017-01-18 1:58 UTC (permalink / raw)
To: Vishal Verma
Cc: Slava Dubeyko, Darrick J. Wong, linux-nvdimm@lists.01.org,
linux-block@vger.kernel.org, Viacheslav Dubeyko, Linux FS Devel,
lsf-pc@lists.linux-foundation.org
On Tue, Jan 17, 2017 at 3:51 PM, Vishal Verma <vishal.l.verma@intel.com> wrote:
> On 01/17, Andiry Xu wrote:
>
> <snip>
>
>> >>
>> >> The pmem_do_bvec() read logic is like this:
>> >>
>> >> pmem_do_bvec()
>> >> if (is_bad_pmem())
>> >> return -EIO;
>> >> else
>> >> memcpy_from_pmem();
>> >>
>> >> Note memcpy_from_pmem() is calling memcpy_mcsafe(). Does this imply
>> >> that even if a block is not in the badblock list, it still can be bad
>> >> and causes MCE? Does the badblock list get changed during file system
>> >> running? If that is the case, should the file system get a
>> >> notification when it gets changed? If a block is good when I first
>> >> read it, can I still trust it to be good for the second access?
>> >
>> > Yes, if a block is not in the badblocks list, it can still cause an
>> > MCE. This is the latent error case I described above. For a simple read()
>> > via the pmem driver, this will get handled by memcpy_mcsafe. For mmap,
>> > an MCE is inevitable.
>> >
>> > Yes the badblocks list may change while a filesystem is running. The RFC
>> > patches[1] I linked to add a notification for the filesystem when this
>> > happens.
>> >
>>
>> This is really bad and it makes file system implementation much more
>> complicated. And badblock notification does not help very much,
>> because any block can be bad potentially, no matter it is in badblock
>> list or not. And file system has to perform checking for every read,
>> using memcpy_mcsafe. This is disaster for file system like NOVA, which
>> uses pointer de-reference to access data structures on pmem. Now if I
>> want to read a field in an inode on pmem, I have to copy it to DRAM
>> first and make sure memcpy_mcsafe() does not report anything wrong.
>
> You have a good point, and I don't know if I have an answer for this..
> Assuming a system with MCE recovery, maybe NOVA can add a mce handler
> similar to nfit_handle_mce(), and handle errors as they happen, but I'm
> being very hand-wavey here and don't know how much/how well that might
> work..
>
>>
>> > No, if the media, for some reason, 'dvelops' a bad cell, a second
>> > consecutive read does have a chance of being bad. Once a location has
>> > been marked as bad, it will stay bad till the ACPI clear error 'DSM' has
>> > been called to mark it as clean.
>> >
>>
>> I wonder what happens to write in this case? If a block is bad but not
>> reported in badblock list. Now I write to it without reading first. Do
>> I clear the poison with the write? Or still require a ACPI DSM?
>
> With writes, my understanding is there is still a possibility that an
> internal read-modify-write can happen, and cause a MCE (this is the same
> as writing to a bad DRAM cell, which can also cause an MCE). You can't
> really use the ACPI DSM preemptively because you don't know whether the
> location was bad. The error flow will be something like write causes the
> MCE, a badblock gets added (either through the mce handler or after the
> next reboot), and the recovery path is now the same as a regular badblock.
>
This is different from my understanding. Right now write_pmem() in
pmem_do_bvec() does not use memcpy_mcsafe(). If the block is bad it
clears poison and writes to pmem again. Seems to me writing to bad
blocks does not cause MCE. Do we need memcpy_mcsafe for pmem stores?
Thanks,
Andiry
>>
>> > [1]: http://www.linux.sgi.com/archives/xfs/2016-06/msg00299.html
>> >
>>
>> Thank you for the patchset. I will look into it.
>>
_______________________________________________
Linux-nvdimm mailing list
Linux-nvdimm@lists.01.org
https://lists.01.org/mailman/listinfo/linux-nvdimm
^ permalink raw reply [flat|nested] 42+ messages in thread
* Re: [LSF/MM TOPIC] Badblocks checking/representation in filesystems
@ 2017-01-20 0:32 ` Verma, Vishal L
0 siblings, 0 replies; 42+ messages in thread
From: Verma, Vishal L @ 2017-01-20 0:32 UTC (permalink / raw)
To: andiry@gmail.com
Cc: darrick.wong@oracle.com, Vyacheslav.Dubeyko@wdc.com,
linux-block@vger.kernel.org, slava@dubeyko.com,
lsf-pc@lists.linux-foundation.org, linux-nvdimm@ml01.01.org,
linux-fsdevel@vger.kernel.org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^ permalink raw reply [flat|nested] 42+ messages in thread
* Re: [LSF/MM TOPIC] Badblocks checking/representation in filesystems
@ 2017-01-20 0:32 ` Verma, Vishal L
0 siblings, 0 replies; 42+ messages in thread
From: Verma, Vishal L @ 2017-01-20 0:32 UTC (permalink / raw)
To: andiry@gmail.com
Cc: darrick.wong@oracle.com, Vyacheslav.Dubeyko@wdc.com,
linux-block@vger.kernel.org, slava@dubeyko.com,
lsf-pc@lists.linux-foundation.org, linux-nvdimm@ml01.01.org,
linux-fsdevel@vger.kernel.org
On Tue, 2017-01-17 at 17:58 -0800, Andiry Xu wrote:
> On Tue, Jan 17, 2017 at 3:51 PM, Vishal Verma <vishal.l.verma@intel.co
> m> wrote:
> > On 01/17, Andiry Xu wrote:
> >
> > <snip>
> >
> > > > >
> > > > > The pmem_do_bvec() read logic is like this:
> > > > >
> > > > > pmem_do_bvec()
> > > > > if (is_bad_pmem())
> > > > > return -EIO;
> > > > > else
> > > > > memcpy_from_pmem();
> > > > >
> > > > > Note memcpy_from_pmem() is calling memcpy_mcsafe(). Does this
> > > > > imply
> > > > > that even if a block is not in the badblock list, it still can
> > > > > be bad
> > > > > and causes MCE? Does the badblock list get changed during file
> > > > > system
> > > > > running? If that is the case, should the file system get a
> > > > > notification when it gets changed? If a block is good when I
> > > > > first
> > > > > read it, can I still trust it to be good for the second
> > > > > access?
> > > >
> > > > Yes, if a block is not in the badblocks list, it can still cause
> > > > an
> > > > MCE. This is the latent error case I described above. For a
> > > > simple read()
> > > > via the pmem driver, this will get handled by memcpy_mcsafe. For
> > > > mmap,
> > > > an MCE is inevitable.
> > > >
> > > > Yes the badblocks list may change while a filesystem is running.
> > > > The RFC
> > > > patches[1] I linked to add a notification for the filesystem
> > > > when this
> > > > happens.
> > > >
> > >
> > > This is really bad and it makes file system implementation much
> > > more
> > > complicated. And badblock notification does not help very much,
> > > because any block can be bad potentially, no matter it is in
> > > badblock
> > > list or not. And file system has to perform checking for every
> > > read,
> > > using memcpy_mcsafe. This is disaster for file system like NOVA,
> > > which
> > > uses pointer de-reference to access data structures on pmem. Now
> > > if I
> > > want to read a field in an inode on pmem, I have to copy it to
> > > DRAM
> > > first and make sure memcpy_mcsafe() does not report anything
> > > wrong.
> >
> > You have a good point, and I don't know if I have an answer for
> > this..
> > Assuming a system with MCE recovery, maybe NOVA can add a mce
> > handler
> > similar to nfit_handle_mce(), and handle errors as they happen, but
> > I'm
> > being very hand-wavey here and don't know how much/how well that
> > might
> > work..
> >
> > >
> > > > No, if the media, for some reason, 'dvelops' a bad cell, a
> > > > second
> > > > consecutive read does have a chance of being bad. Once a
> > > > location has
> > > > been marked as bad, it will stay bad till the ACPI clear error
> > > > 'DSM' has
> > > > been called to mark it as clean.
> > > >
> > >
> > > I wonder what happens to write in this case? If a block is bad but
> > > not
> > > reported in badblock list. Now I write to it without reading
> > > first. Do
> > > I clear the poison with the write? Or still require a ACPI DSM?
> >
> > With writes, my understanding is there is still a possibility that
> > an
> > internal read-modify-write can happen, and cause a MCE (this is the
> > same
> > as writing to a bad DRAM cell, which can also cause an MCE). You
> > can't
> > really use the ACPI DSM preemptively because you don't know whether
> > the
> > location was bad. The error flow will be something like write causes
> > the
> > MCE, a badblock gets added (either through the mce handler or after
> > the
> > next reboot), and the recovery path is now the same as a regular
> > badblock.
> >
>
> This is different from my understanding. Right now write_pmem() in
> pmem_do_bvec() does not use memcpy_mcsafe(). If the block is bad it
> clears poison and writes to pmem again. Seems to me writing to bad
> blocks does not cause MCE. Do we need memcpy_mcsafe for pmem stores?
You are right, writes don't use memcpy_mcsafe, and will not directly
cause an MCE. However a write can cause an asynchronous 'CMCI' -
corrected machine check interrupt, but this is not critical, and wont be
a memory error as the core didn't consume poison. memcpy_mcsafe cannot
protect against this because the write is 'posted' and the CMCI is not
synchronous. Note that this is only in the latent error or memmap-store
case.
>
> Thanks,
> Andiry
>
> > >
> > > > [1]: http://www.linux.sgi.com/archives/xfs/2016-06/msg00299.html
> > > >
> > >
> > > Thank you for the patchset. I will look into it.
> > >
^ permalink raw reply [flat|nested] 42+ messages in thread
* Re: [LSF/MM TOPIC] Badblocks checking/representation in filesystems
@ 2017-01-20 0:32 ` Verma, Vishal L
0 siblings, 0 replies; 42+ messages in thread
From: Verma, Vishal L @ 2017-01-20 0:32 UTC (permalink / raw)
To: andiry-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org
Cc: Vyacheslav.Dubeyko-Sjgp3cTcYWE@public.gmane.org,
darrick.wong-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org,
linux-nvdimm-y27Ovi1pjclAfugRpC6u6w@public.gmane.org,
linux-block-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
slava-yeENwD64cLxBDgjK7y7TUQ@public.gmane.org,
linux-fsdevel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
lsf-pc-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org
On Tue, 2017-01-17 at 17:58 -0800, Andiry Xu wrote:
> On Tue, Jan 17, 2017 at 3:51 PM, Vishal Verma <vishal.l.verma@intel.co
> m> wrote:
> > On 01/17, Andiry Xu wrote:
> >
> > <snip>
> >
> > > > >
> > > > > The pmem_do_bvec() read logic is like this:
> > > > >
> > > > > pmem_do_bvec()
> > > > > if (is_bad_pmem())
> > > > > return -EIO;
> > > > > else
> > > > > memcpy_from_pmem();
> > > > >
> > > > > Note memcpy_from_pmem() is calling memcpy_mcsafe(). Does this
> > > > > imply
> > > > > that even if a block is not in the badblock list, it still can
> > > > > be bad
> > > > > and causes MCE? Does the badblock list get changed during file
> > > > > system
> > > > > running? If that is the case, should the file system get a
> > > > > notification when it gets changed? If a block is good when I
> > > > > first
> > > > > read it, can I still trust it to be good for the second
> > > > > access?
> > > >
> > > > Yes, if a block is not in the badblocks list, it can still cause
> > > > an
> > > > MCE. This is the latent error case I described above. For a
> > > > simple read()
> > > > via the pmem driver, this will get handled by memcpy_mcsafe. For
> > > > mmap,
> > > > an MCE is inevitable.
> > > >
> > > > Yes the badblocks list may change while a filesystem is running.
> > > > The RFC
> > > > patches[1] I linked to add a notification for the filesystem
> > > > when this
> > > > happens.
> > > >
> > >
> > > This is really bad and it makes file system implementation much
> > > more
> > > complicated. And badblock notification does not help very much,
> > > because any block can be bad potentially, no matter it is in
> > > badblock
> > > list or not. And file system has to perform checking for every
> > > read,
> > > using memcpy_mcsafe. This is disaster for file system like NOVA,
> > > which
> > > uses pointer de-reference to access data structures on pmem. Now
> > > if I
> > > want to read a field in an inode on pmem, I have to copy it to
> > > DRAM
> > > first and make sure memcpy_mcsafe() does not report anything
> > > wrong.
> >
> > You have a good point, and I don't know if I have an answer for
> > this..
> > Assuming a system with MCE recovery, maybe NOVA can add a mce
> > handler
> > similar to nfit_handle_mce(), and handle errors as they happen, but
> > I'm
> > being very hand-wavey here and don't know how much/how well that
> > might
> > work..
> >
> > >
> > > > No, if the media, for some reason, 'dvelops' a bad cell, a
> > > > second
> > > > consecutive read does have a chance of being bad. Once a
> > > > location has
> > > > been marked as bad, it will stay bad till the ACPI clear error
> > > > 'DSM' has
> > > > been called to mark it as clean.
> > > >
> > >
> > > I wonder what happens to write in this case? If a block is bad but
> > > not
> > > reported in badblock list. Now I write to it without reading
> > > first. Do
> > > I clear the poison with the write? Or still require a ACPI DSM?
> >
> > With writes, my understanding is there is still a possibility that
> > an
> > internal read-modify-write can happen, and cause a MCE (this is the
> > same
> > as writing to a bad DRAM cell, which can also cause an MCE). You
> > can't
> > really use the ACPI DSM preemptively because you don't know whether
> > the
> > location was bad. The error flow will be something like write causes
> > the
> > MCE, a badblock gets added (either through the mce handler or after
> > the
> > next reboot), and the recovery path is now the same as a regular
> > badblock.
> >
>
> This is different from my understanding. Right now write_pmem() in
> pmem_do_bvec() does not use memcpy_mcsafe(). If the block is bad it
> clears poison and writes to pmem again. Seems to me writing to bad
> blocks does not cause MCE. Do we need memcpy_mcsafe for pmem stores?
You are right, writes don't use memcpy_mcsafe, and will not directly
cause an MCE. However a write can cause an asynchronous 'CMCI' -
corrected machine check interrupt, but this is not critical, and wont be
a memory error as the core didn't consume poison. memcpy_mcsafe cannot
protect against this because the write is 'posted' and the CMCI is not
synchronous. Note that this is only in the latent error or memmap-store
case.
>
> Thanks,
> Andiry
>
> > >
> > > > [1]: http://www.linux.sgi.com/archives/xfs/2016-06/msg00299.html
> > > >
> > >
> > > Thank you for the patchset. I will look into it.
> > >
_______________________________________________
Linux-nvdimm mailing list
Linux-nvdimm@lists.01.org
https://lists.01.org/mailman/listinfo/linux-nvdimm
^ permalink raw reply [flat|nested] 42+ messages in thread
* Re: [LSF/MM TOPIC] Badblocks checking/representation in filesystems
2017-01-17 22:15 ` Andiry Xu
(?)
(?)
@ 2017-01-18 0:16 ` Andreas Dilger
2017-01-18 2:01 ` Andiry Xu
-1 siblings, 1 reply; 42+ messages in thread
From: Andreas Dilger @ 2017-01-18 0:16 UTC (permalink / raw)
To: Andiry Xu
Cc: Vishal Verma, Darrick J. Wong, Slava Dubeyko,
lsf-pc@lists.linux-foundation.org, linux-nvdimm@lists.01.org,
linux-block@vger.kernel.org, Linux FS Devel, Viacheslav Dubeyko
[-- Attachment #1: Type: text/plain, Size: 5863 bytes --]
On Jan 17, 2017, at 3:15 PM, Andiry Xu <andiry@gmail.com> wrote:
> On Tue, Jan 17, 2017 at 1:35 PM, Vishal Verma <vishal.l.verma@intel.com> wrote:
>> On 01/16, Darrick J. Wong wrote:
>>> On Fri, Jan 13, 2017 at 05:49:10PM -0700, Vishal Verma wrote:
>>>> On 01/14, Slava Dubeyko wrote:
>>>>>
>>>>> ---- Original Message ----
>>>>> Subject: [LSF/MM TOPIC] Badblocks checking/representation in filesystems
>>>>> Sent: Jan 13, 2017 1:40 PM
>>>>> From: "Verma, Vishal L" <vishal.l.verma@intel.com>
>>>>> To: lsf-pc@lists.linux-foundation.org
>>>>> Cc: linux-nvdimm@lists.01.org, linux-block@vger.kernel.org, linux-fsdevel@vger.kernel.org
>>>>>
>>>>>> The current implementation of badblocks, where we consult the
>>>>>> badblocks list for every IO in the block driver works, and is a
>>>>>> last option failsafe, but from a user perspective, it isn't the
>>>>>> easiest interface to work with.
>>>>>
>>>>> As I remember, FAT and HFS+ specifications contain description of bad blocks
>>>>> (physical sectors) table. I believe that this table was used for the case of
>>>>> floppy media. But, finally, this table becomes to be the completely obsolete
>>>>> artefact because mostly storage devices are reliably enough. Why do you need
>>>
>>> ext4 has a badblocks inode to own all the bad spots on disk, but ISTR it
>>> doesn't support(??) extents or 64-bit filesystems, and might just be a
>>> vestigial organ at this point. XFS doesn't have anything to track bad
>>> blocks currently....
>>>
>>>>> in exposing the bad blocks on the file system level? Do you expect that next
>>>>> generation of NVM memory will be so unreliable that file system needs to manage
>>>>> bad blocks? What's about erasure coding schemes? Do file system really need to suffer
>>>>> from the bad block issue?
>>>>>
>>>>> Usually, we are using LBAs and it is the responsibility of storage device to map
>>>>> a bad physical block/page/sector into valid one. Do you mean that we have
>>>>> access to physical NVM memory address directly? But it looks like that we can
>>>>> have a "bad block" issue even we will access data into page cache's memory
>>>>> page (if we will use NVM memory for page cache, of course). So, what do you
>>>>> imply by "bad block" issue?
>>>>
>>>> We don't have direct physical access to the device's address space, in
>>>> the sense the device is still free to perform remapping of chunks of NVM
>>>> underneath us. The problem is that when a block or address range (as
>>>> small as a cache line) goes bad, the device maintains a poison bit for
>>>> every affected cache line. Behind the scenes, it may have already
>>>> remapped the range, but the cache line poison has to be kept so that
>>>> there is a notification to the user/owner of the data that something has
>>>> been lost. Since NVM is byte addressable memory sitting on the memory
>>>> bus, such a poisoned cache line results in memory errors and SIGBUSes.
>>>> Compared to tradational storage where an app will get nice and friendly
>>>> (relatively speaking..) -EIOs. The whole badblocks implementation was
>>>> done so that the driver can intercept IO (i.e. reads) to _known_ bad
>>>> locations, and short-circuit them with an EIO. If the driver doesn't
>>>> catch these, the reads will turn into a memory bus access, and the
>>>> poison will cause a SIGBUS.
>>>
>>> "driver" ... you mean XFS? Or do you mean the thing that makes pmem
>>> look kind of like a traditional block device? :)
>>
>> Yes, the thing that makes pmem look like a block device :) --
>> drivers/nvdimm/pmem.c
>>
>>>
>>>> This effort is to try and make this badblock checking smarter - and try
>>>> and reduce the penalty on every IO to a smaller range, which only the
>>>> filesystem can do.
>>>
>>> Though... now that XFS merged the reverse mapping support, I've been
>>> wondering if there'll be a resubmission of the device errors callback?
>>> It still would be useful to be able to inform the user that part of
>>> their fs has gone bad, or, better yet, if the buffer is still in memory
>>> someplace else, just write it back out.
>>>
>>> Or I suppose if we had some kind of raid1 set up between memories we
>>> could read one of the other copies and rewrite it into the failing
>>> region immediately.
>>
>> Yes, that is kind of what I was hoping to accomplish via this
>> discussion. How much would filesystems want to be involved in this sort
>> of badblocks handling, if at all. I can refresh my patches that provide
>> the fs notification, but that's the easy bit, and a starting point.
>>
>
> I have some questions. Why moving badblock handling to file system
> level avoid the checking phase? In file system level for each I/O I
> still have to check the badblock list, right? Do you mean during mount
> it can go through the pmem device and locates all the data structures
> mangled by badblocks and handle them accordingly, so that during
> normal running the badblocks will never be accessed? Or, if there is
> replicataion/snapshot support, use a copy to recover the badblocks?
With ext4 badblocks, the main outcome is that the bad blocks would be
pemanently marked in the allocation bitmap as being used, and they would
never be allocated to a file, so they should never be accessed unless
doing a full device scan (which ext4 and e2fsck never do). That would
avoid the need to check every I/O against the bad blocks list, if the
driver knows that the filesystem will handle this.
The one caveat is that ext4 only allows 32-bit block numbers in the
badblocks list, since this feature hasn't been used in a long time.
This is good for up to 16TB filesystems, but if there was a demand to
use this feature again it would be possible allow 64-bit block numbers.
Cheers, Andreas
[-- Attachment #2: Message signed with OpenPGP using GPGMail --]
[-- Type: application/pgp-signature, Size: 833 bytes --]
^ permalink raw reply [flat|nested] 42+ messages in thread
* Re: [LSF/MM TOPIC] Badblocks checking/representation in filesystems
2017-01-18 0:16 ` Andreas Dilger
@ 2017-01-18 2:01 ` Andiry Xu
0 siblings, 0 replies; 42+ messages in thread
From: Andiry Xu @ 2017-01-18 2:01 UTC (permalink / raw)
To: Andreas Dilger
Cc: Vishal Verma, Darrick J. Wong, Slava Dubeyko,
lsf-pc@lists.linux-foundation.org, linux-nvdimm@lists.01.org,
linux-block@vger.kernel.org, Linux FS Devel, Viacheslav Dubeyko
On Tue, Jan 17, 2017 at 4:16 PM, Andreas Dilger <adilger@dilger.ca> wrote:
> On Jan 17, 2017, at 3:15 PM, Andiry Xu <andiry@gmail.com> wrote:
>> On Tue, Jan 17, 2017 at 1:35 PM, Vishal Verma <vishal.l.verma@intel.com> wrote:
>>> On 01/16, Darrick J. Wong wrote:
>>>> On Fri, Jan 13, 2017 at 05:49:10PM -0700, Vishal Verma wrote:
>>>>> On 01/14, Slava Dubeyko wrote:
>>>>>>
>>>>>> ---- Original Message ----
>>>>>> Subject: [LSF/MM TOPIC] Badblocks checking/representation in filesystems
>>>>>> Sent: Jan 13, 2017 1:40 PM
>>>>>> From: "Verma, Vishal L" <vishal.l.verma@intel.com>
>>>>>> To: lsf-pc@lists.linux-foundation.org
>>>>>> Cc: linux-nvdimm@lists.01.org, linux-block@vger.kernel.org, linux-fsdevel@vger.kernel.org
>>>>>>
>>>>>>> The current implementation of badblocks, where we consult the
>>>>>>> badblocks list for every IO in the block driver works, and is a
>>>>>>> last option failsafe, but from a user perspective, it isn't the
>>>>>>> easiest interface to work with.
>>>>>>
>>>>>> As I remember, FAT and HFS+ specifications contain description of bad blocks
>>>>>> (physical sectors) table. I believe that this table was used for the case of
>>>>>> floppy media. But, finally, this table becomes to be the completely obsolete
>>>>>> artefact because mostly storage devices are reliably enough. Why do you need
>>>>
>>>> ext4 has a badblocks inode to own all the bad spots on disk, but ISTR it
>>>> doesn't support(??) extents or 64-bit filesystems, and might just be a
>>>> vestigial organ at this point. XFS doesn't have anything to track bad
>>>> blocks currently....
>>>>
>>>>>> in exposing the bad blocks on the file system level? Do you expect that next
>>>>>> generation of NVM memory will be so unreliable that file system needs to manage
>>>>>> bad blocks? What's about erasure coding schemes? Do file system really need to suffer
>>>>>> from the bad block issue?
>>>>>>
>>>>>> Usually, we are using LBAs and it is the responsibility of storage device to map
>>>>>> a bad physical block/page/sector into valid one. Do you mean that we have
>>>>>> access to physical NVM memory address directly? But it looks like that we can
>>>>>> have a "bad block" issue even we will access data into page cache's memory
>>>>>> page (if we will use NVM memory for page cache, of course). So, what do you
>>>>>> imply by "bad block" issue?
>>>>>
>>>>> We don't have direct physical access to the device's address space, in
>>>>> the sense the device is still free to perform remapping of chunks of NVM
>>>>> underneath us. The problem is that when a block or address range (as
>>>>> small as a cache line) goes bad, the device maintains a poison bit for
>>>>> every affected cache line. Behind the scenes, it may have already
>>>>> remapped the range, but the cache line poison has to be kept so that
>>>>> there is a notification to the user/owner of the data that something has
>>>>> been lost. Since NVM is byte addressable memory sitting on the memory
>>>>> bus, such a poisoned cache line results in memory errors and SIGBUSes.
>>>>> Compared to tradational storage where an app will get nice and friendly
>>>>> (relatively speaking..) -EIOs. The whole badblocks implementation was
>>>>> done so that the driver can intercept IO (i.e. reads) to _known_ bad
>>>>> locations, and short-circuit them with an EIO. If the driver doesn't
>>>>> catch these, the reads will turn into a memory bus access, and the
>>>>> poison will cause a SIGBUS.
>>>>
>>>> "driver" ... you mean XFS? Or do you mean the thing that makes pmem
>>>> look kind of like a traditional block device? :)
>>>
>>> Yes, the thing that makes pmem look like a block device :) --
>>> drivers/nvdimm/pmem.c
>>>
>>>>
>>>>> This effort is to try and make this badblock checking smarter - and try
>>>>> and reduce the penalty on every IO to a smaller range, which only the
>>>>> filesystem can do.
>>>>
>>>> Though... now that XFS merged the reverse mapping support, I've been
>>>> wondering if there'll be a resubmission of the device errors callback?
>>>> It still would be useful to be able to inform the user that part of
>>>> their fs has gone bad, or, better yet, if the buffer is still in memory
>>>> someplace else, just write it back out.
>>>>
>>>> Or I suppose if we had some kind of raid1 set up between memories we
>>>> could read one of the other copies and rewrite it into the failing
>>>> region immediately.
>>>
>>> Yes, that is kind of what I was hoping to accomplish via this
>>> discussion. How much would filesystems want to be involved in this sort
>>> of badblocks handling, if at all. I can refresh my patches that provide
>>> the fs notification, but that's the easy bit, and a starting point.
>>>
>>
>> I have some questions. Why moving badblock handling to file system
>> level avoid the checking phase? In file system level for each I/O I
>> still have to check the badblock list, right? Do you mean during mount
>> it can go through the pmem device and locates all the data structures
>> mangled by badblocks and handle them accordingly, so that during
>> normal running the badblocks will never be accessed? Or, if there is
>> replicataion/snapshot support, use a copy to recover the badblocks?
>
> With ext4 badblocks, the main outcome is that the bad blocks would be
> pemanently marked in the allocation bitmap as being used, and they would
> never be allocated to a file, so they should never be accessed unless
> doing a full device scan (which ext4 and e2fsck never do). That would
> avoid the need to check every I/O against the bad blocks list, if the
> driver knows that the filesystem will handle this.
>
Thank you for explanation. However this only works for free blocks,
right? What about allocated blocks, like file data and metadata?
Thanks,
Andiry
> The one caveat is that ext4 only allows 32-bit block numbers in the
> badblocks list, since this feature hasn't been used in a long time.
> This is good for up to 16TB filesystems, but if there was a demand to
> use this feature again it would be possible allow 64-bit block numbers.
>
> Cheers, Andreas
>
>
>
>
>
^ permalink raw reply [flat|nested] 42+ messages in thread
* Re: [LSF/MM TOPIC] Badblocks checking/representation in filesystems
@ 2017-01-18 2:01 ` Andiry Xu
0 siblings, 0 replies; 42+ messages in thread
From: Andiry Xu @ 2017-01-18 2:01 UTC (permalink / raw)
To: Andreas Dilger
Cc: Slava Dubeyko, Darrick J. Wong, linux-nvdimm@lists.01.org,
linux-block@vger.kernel.org, Viacheslav Dubeyko, Linux FS Devel,
lsf-pc@lists.linux-foundation.org
On Tue, Jan 17, 2017 at 4:16 PM, Andreas Dilger <adilger@dilger.ca> wrote:
> On Jan 17, 2017, at 3:15 PM, Andiry Xu <andiry@gmail.com> wrote:
>> On Tue, Jan 17, 2017 at 1:35 PM, Vishal Verma <vishal.l.verma@intel.com> wrote:
>>> On 01/16, Darrick J. Wong wrote:
>>>> On Fri, Jan 13, 2017 at 05:49:10PM -0700, Vishal Verma wrote:
>>>>> On 01/14, Slava Dubeyko wrote:
>>>>>>
>>>>>> ---- Original Message ----
>>>>>> Subject: [LSF/MM TOPIC] Badblocks checking/representation in filesystems
>>>>>> Sent: Jan 13, 2017 1:40 PM
>>>>>> From: "Verma, Vishal L" <vishal.l.verma@intel.com>
>>>>>> To: lsf-pc@lists.linux-foundation.org
>>>>>> Cc: linux-nvdimm@lists.01.org, linux-block@vger.kernel.org, linux-fsdevel@vger.kernel.org
>>>>>>
>>>>>>> The current implementation of badblocks, where we consult the
>>>>>>> badblocks list for every IO in the block driver works, and is a
>>>>>>> last option failsafe, but from a user perspective, it isn't the
>>>>>>> easiest interface to work with.
>>>>>>
>>>>>> As I remember, FAT and HFS+ specifications contain description of bad blocks
>>>>>> (physical sectors) table. I believe that this table was used for the case of
>>>>>> floppy media. But, finally, this table becomes to be the completely obsolete
>>>>>> artefact because mostly storage devices are reliably enough. Why do you need
>>>>
>>>> ext4 has a badblocks inode to own all the bad spots on disk, but ISTR it
>>>> doesn't support(??) extents or 64-bit filesystems, and might just be a
>>>> vestigial organ at this point. XFS doesn't have anything to track bad
>>>> blocks currently....
>>>>
>>>>>> in exposing the bad blocks on the file system level? Do you expect that next
>>>>>> generation of NVM memory will be so unreliable that file system needs to manage
>>>>>> bad blocks? What's about erasure coding schemes? Do file system really need to suffer
>>>>>> from the bad block issue?
>>>>>>
>>>>>> Usually, we are using LBAs and it is the responsibility of storage device to map
>>>>>> a bad physical block/page/sector into valid one. Do you mean that we have
>>>>>> access to physical NVM memory address directly? But it looks like that we can
>>>>>> have a "bad block" issue even we will access data into page cache's memory
>>>>>> page (if we will use NVM memory for page cache, of course). So, what do you
>>>>>> imply by "bad block" issue?
>>>>>
>>>>> We don't have direct physical access to the device's address space, in
>>>>> the sense the device is still free to perform remapping of chunks of NVM
>>>>> underneath us. The problem is that when a block or address range (as
>>>>> small as a cache line) goes bad, the device maintains a poison bit for
>>>>> every affected cache line. Behind the scenes, it may have already
>>>>> remapped the range, but the cache line poison has to be kept so that
>>>>> there is a notification to the user/owner of the data that something has
>>>>> been lost. Since NVM is byte addressable memory sitting on the memory
>>>>> bus, such a poisoned cache line results in memory errors and SIGBUSes.
>>>>> Compared to tradational storage where an app will get nice and friendly
>>>>> (relatively speaking..) -EIOs. The whole badblocks implementation was
>>>>> done so that the driver can intercept IO (i.e. reads) to _known_ bad
>>>>> locations, and short-circuit them with an EIO. If the driver doesn't
>>>>> catch these, the reads will turn into a memory bus access, and the
>>>>> poison will cause a SIGBUS.
>>>>
>>>> "driver" ... you mean XFS? Or do you mean the thing that makes pmem
>>>> look kind of like a traditional block device? :)
>>>
>>> Yes, the thing that makes pmem look like a block device :) --
>>> drivers/nvdimm/pmem.c
>>>
>>>>
>>>>> This effort is to try and make this badblock checking smarter - and try
>>>>> and reduce the penalty on every IO to a smaller range, which only the
>>>>> filesystem can do.
>>>>
>>>> Though... now that XFS merged the reverse mapping support, I've been
>>>> wondering if there'll be a resubmission of the device errors callback?
>>>> It still would be useful to be able to inform the user that part of
>>>> their fs has gone bad, or, better yet, if the buffer is still in memory
>>>> someplace else, just write it back out.
>>>>
>>>> Or I suppose if we had some kind of raid1 set up between memories we
>>>> could read one of the other copies and rewrite it into the failing
>>>> region immediately.
>>>
>>> Yes, that is kind of what I was hoping to accomplish via this
>>> discussion. How much would filesystems want to be involved in this sort
>>> of badblocks handling, if at all. I can refresh my patches that provide
>>> the fs notification, but that's the easy bit, and a starting point.
>>>
>>
>> I have some questions. Why moving badblock handling to file system
>> level avoid the checking phase? In file system level for each I/O I
>> still have to check the badblock list, right? Do you mean during mount
>> it can go through the pmem device and locates all the data structures
>> mangled by badblocks and handle them accordingly, so that during
>> normal running the badblocks will never be accessed? Or, if there is
>> replicataion/snapshot support, use a copy to recover the badblocks?
>
> With ext4 badblocks, the main outcome is that the bad blocks would be
> pemanently marked in the allocation bitmap as being used, and they would
> never be allocated to a file, so they should never be accessed unless
> doing a full device scan (which ext4 and e2fsck never do). That would
> avoid the need to check every I/O against the bad blocks list, if the
> driver knows that the filesystem will handle this.
>
Thank you for explanation. However this only works for free blocks,
right? What about allocated blocks, like file data and metadata?
Thanks,
Andiry
> The one caveat is that ext4 only allows 32-bit block numbers in the
> badblocks list, since this feature hasn't been used in a long time.
> This is good for up to 16TB filesystems, but if there was a demand to
> use this feature again it would be possible allow 64-bit block numbers.
>
> Cheers, Andreas
>
>
>
>
>
_______________________________________________
Linux-nvdimm mailing list
Linux-nvdimm@lists.01.org
https://lists.01.org/mailman/listinfo/linux-nvdimm
^ permalink raw reply [flat|nested] 42+ messages in thread
* Re: [LSF/MM TOPIC] Badblocks checking/representation in filesystems
@ 2017-01-18 3:08 ` Lu Zhang
0 siblings, 0 replies; 42+ messages in thread
From: Lu Zhang @ 2017-01-18 3:08 UTC (permalink / raw)
To: Andiry Xu
Cc: Andreas Dilger, Slava Dubeyko, Darrick J. Wong,
linux-nvdimm@lists.01.org, linux-block@vger.kernel.org,
Viacheslav Dubeyko, Linux FS Devel,
lsf-pc@lists.linux-foundation.org
I'm curious about the fault model and corresponding hardware ECC mechanisms
for NVDIMMs. In my understanding for memory accesses to trigger MCE, it
means the memory controller finds a detectable but uncorrectable error
(DUE). So if there is no hardware ECC support the media errors won't even
be noticed, not to mention badblocks or machine checks.
Current hardware ECC support for DRAM usually employs (72, 64) single-bit
error correction mechanism, and for advanced ECCs there are techniques like
Chipkill or SDDC which can tolerate a single DRAM chip failure. What is the
expected ECC mode for NVDIMMs, assuming that PCM or 3dXpoint based
technology might have higher error rates?
If DUE does happen and is flagged to the file system via MCE (somehow...),
and the fs finds that the error corrupts its allocated data page, or
metadata, now if the fs wants to recover its data the intuition is that
there needs to be a stronger error correction mechanism to correct the
hardware-uncorrectable errors. So knowing the hardware ECC baseline is
helpful for the file system to understand how severe are the faults in
badblocks, and develop its recovery methods.
Regards,
Lu
On Tue, Jan 17, 2017 at 6:01 PM, Andiry Xu <andiry@gmail.com> wrote:
> On Tue, Jan 17, 2017 at 4:16 PM, Andreas Dilger <adilger@dilger.ca> wrote:
> > On Jan 17, 2017, at 3:15 PM, Andiry Xu <andiry@gmail.com> wrote:
> >> On Tue, Jan 17, 2017 at 1:35 PM, Vishal Verma <vishal.l.verma@intel.com>
> wrote:
> >>> On 01/16, Darrick J. Wong wrote:
> >>>> On Fri, Jan 13, 2017 at 05:49:10PM -0700, Vishal Verma wrote:
> >>>>> On 01/14, Slava Dubeyko wrote:
> >>>>>>
> >>>>>> ---- Original Message ----
> >>>>>> Subject: [LSF/MM TOPIC] Badblocks checking/representation in
> filesystems
> >>>>>> Sent: Jan 13, 2017 1:40 PM
> >>>>>> From: "Verma, Vishal L" <vishal.l.verma@intel.com>
> >>>>>> To: lsf-pc@lists.linux-foundation.org
> >>>>>> Cc: linux-nvdimm@lists.01.org, linux-block@vger.kernel.org,
> linux-fsdevel@vger.kernel.org
> >>>>>>
> >>>>>>> The current implementation of badblocks, where we consult the
> >>>>>>> badblocks list for every IO in the block driver works, and is a
> >>>>>>> last option failsafe, but from a user perspective, it isn't the
> >>>>>>> easiest interface to work with.
> >>>>>>
> >>>>>> As I remember, FAT and HFS+ specifications contain description of
> bad blocks
> >>>>>> (physical sectors) table. I believe that this table was used for
> the case of
> >>>>>> floppy media. But, finally, this table becomes to be the completely
> obsolete
> >>>>>> artefact because mostly storage devices are reliably enough. Why do
> you need
> >>>>
> >>>> ext4 has a badblocks inode to own all the bad spots on disk, but ISTR
> it
> >>>> doesn't support(??) extents or 64-bit filesystems, and might just be a
> >>>> vestigial organ at this point. XFS doesn't have anything to track bad
> >>>> blocks currently....
> >>>>
> >>>>>> in exposing the bad blocks on the file system level? Do you expect
> that next
> >>>>>> generation of NVM memory will be so unreliable that file system
> needs to manage
> >>>>>> bad blocks? What's about erasure coding schemes? Do file system
> really need to suffer
> >>>>>> from the bad block issue?
> >>>>>>
> >>>>>> Usually, we are using LBAs and it is the responsibility of storage
> device to map
> >>>>>> a bad physical block/page/sector into valid one. Do you mean that
> we have
> >>>>>> access to physical NVM memory address directly? But it looks like
> that we can
> >>>>>> have a "bad block" issue even we will access data into page cache's
> memory
> >>>>>> page (if we will use NVM memory for page cache, of course). So,
> what do you
> >>>>>> imply by "bad block" issue?
> >>>>>
> >>>>> We don't have direct physical access to the device's address space,
> in
> >>>>> the sense the device is still free to perform remapping of chunks of
> NVM
> >>>>> underneath us. The problem is that when a block or address range (as
> >>>>> small as a cache line) goes bad, the device maintains a poison bit
> for
> >>>>> every affected cache line. Behind the scenes, it may have already
> >>>>> remapped the range, but the cache line poison has to be kept so that
> >>>>> there is a notification to the user/owner of the data that something
> has
> >>>>> been lost. Since NVM is byte addressable memory sitting on the memory
> >>>>> bus, such a poisoned cache line results in memory errors and
> SIGBUSes.
> >>>>> Compared to tradational storage where an app will get nice and
> friendly
> >>>>> (relatively speaking..) -EIOs. The whole badblocks implementation was
> >>>>> done so that the driver can intercept IO (i.e. reads) to _known_ bad
> >>>>> locations, and short-circuit them with an EIO. If the driver doesn't
> >>>>> catch these, the reads will turn into a memory bus access, and the
> >>>>> poison will cause a SIGBUS.
> >>>>
> >>>> "driver" ... you mean XFS? Or do you mean the thing that makes pmem
> >>>> look kind of like a traditional block device? :)
> >>>
> >>> Yes, the thing that makes pmem look like a block device :) --
> >>> drivers/nvdimm/pmem.c
> >>>
> >>>>
> >>>>> This effort is to try and make this badblock checking smarter - and
> try
> >>>>> and reduce the penalty on every IO to a smaller range, which only the
> >>>>> filesystem can do.
> >>>>
> >>>> Though... now that XFS merged the reverse mapping support, I've been
> >>>> wondering if there'll be a resubmission of the device errors callback?
> >>>> It still would be useful to be able to inform the user that part of
> >>>> their fs has gone bad, or, better yet, if the buffer is still in
> memory
> >>>> someplace else, just write it back out.
> >>>>
> >>>> Or I suppose if we had some kind of raid1 set up between memories we
> >>>> could read one of the other copies and rewrite it into the failing
> >>>> region immediately.
> >>>
> >>> Yes, that is kind of what I was hoping to accomplish via this
> >>> discussion. How much would filesystems want to be involved in this sort
> >>> of badblocks handling, if at all. I can refresh my patches that provide
> >>> the fs notification, but that's the easy bit, and a starting point.
> >>>
> >>
> >> I have some questions. Why moving badblock handling to file system
> >> level avoid the checking phase? In file system level for each I/O I
> >> still have to check the badblock list, right? Do you mean during mount
> >> it can go through the pmem device and locates all the data structures
> >> mangled by badblocks and handle them accordingly, so that during
> >> normal running the badblocks will never be accessed? Or, if there is
> >> replicataion/snapshot support, use a copy to recover the badblocks?
> >
> > With ext4 badblocks, the main outcome is that the bad blocks would be
> > pemanently marked in the allocation bitmap as being used, and they would
> > never be allocated to a file, so they should never be accessed unless
> > doing a full device scan (which ext4 and e2fsck never do). That would
> > avoid the need to check every I/O against the bad blocks list, if the
> > driver knows that the filesystem will handle this.
> >
>
> Thank you for explanation. However this only works for free blocks,
> right? What about allocated blocks, like file data and metadata?
>
> Thanks,
> Andiry
>
> > The one caveat is that ext4 only allows 32-bit block numbers in the
> > badblocks list, since this feature hasn't been used in a long time.
> > This is good for up to 16TB filesystems, but if there was a demand to
> > use this feature again it would be possible allow 64-bit block numbers.
> >
> > Cheers, Andreas
> >
> >
> >
> >
> >
> _______________________________________________
> Linux-nvdimm mailing list
> Linux-nvdimm@lists.01.org
> https://lists.01.org/mailman/listinfo/linux-nvdimm
>
_______________________________________________
Linux-nvdimm mailing list
Linux-nvdimm@lists.01.org
https://lists.01.org/mailman/listinfo/linux-nvdimm
^ permalink raw reply [flat|nested] 42+ messages in thread
* Re: [LSF/MM TOPIC] Badblocks checking/representation in filesystems
@ 2017-01-18 3:08 ` Lu Zhang
0 siblings, 0 replies; 42+ messages in thread
From: Lu Zhang @ 2017-01-18 3:08 UTC (permalink / raw)
To: Andiry Xu
Cc: Andreas Dilger, Slava Dubeyko, Darrick J. Wong,
linux-nvdimm-hn68Rpc1hR1g9hUCZPvPmw@public.gmane.org,
linux-block-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
Viacheslav Dubeyko, Linux FS Devel,
lsf-pc-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org
I'm curious about the fault model and corresponding hardware ECC mechanisms
for NVDIMMs. In my understanding for memory accesses to trigger MCE, it
means the memory controller finds a detectable but uncorrectable error
(DUE). So if there is no hardware ECC support the media errors won't even
be noticed, not to mention badblocks or machine checks.
Current hardware ECC support for DRAM usually employs (72, 64) single-bit
error correction mechanism, and for advanced ECCs there are techniques like
Chipkill or SDDC which can tolerate a single DRAM chip failure. What is the
expected ECC mode for NVDIMMs, assuming that PCM or 3dXpoint based
technology might have higher error rates?
If DUE does happen and is flagged to the file system via MCE (somehow...),
and the fs finds that the error corrupts its allocated data page, or
metadata, now if the fs wants to recover its data the intuition is that
there needs to be a stronger error correction mechanism to correct the
hardware-uncorrectable errors. So knowing the hardware ECC baseline is
helpful for the file system to understand how severe are the faults in
badblocks, and develop its recovery methods.
Regards,
Lu
On Tue, Jan 17, 2017 at 6:01 PM, Andiry Xu <andiry-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
> On Tue, Jan 17, 2017 at 4:16 PM, Andreas Dilger <adilger-m1MBpc4rdrD3fQ9qLvQP4Q@public.gmane.org> wrote:
> > On Jan 17, 2017, at 3:15 PM, Andiry Xu <andiry-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
> >> On Tue, Jan 17, 2017 at 1:35 PM, Vishal Verma <vishal.l.verma-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
> wrote:
> >>> On 01/16, Darrick J. Wong wrote:
> >>>> On Fri, Jan 13, 2017 at 05:49:10PM -0700, Vishal Verma wrote:
> >>>>> On 01/14, Slava Dubeyko wrote:
> >>>>>>
> >>>>>> ---- Original Message ----
> >>>>>> Subject: [LSF/MM TOPIC] Badblocks checking/representation in
> filesystems
> >>>>>> Sent: Jan 13, 2017 1:40 PM
> >>>>>> From: "Verma, Vishal L" <vishal.l.verma-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
> >>>>>> To: lsf-pc-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org
> >>>>>> Cc: linux-nvdimm-hn68Rpc1hR1g9hUCZPvPmw@public.gmane.org, linux-block-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
> linux-fsdevel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
> >>>>>>
> >>>>>>> The current implementation of badblocks, where we consult the
> >>>>>>> badblocks list for every IO in the block driver works, and is a
> >>>>>>> last option failsafe, but from a user perspective, it isn't the
> >>>>>>> easiest interface to work with.
> >>>>>>
> >>>>>> As I remember, FAT and HFS+ specifications contain description of
> bad blocks
> >>>>>> (physical sectors) table. I believe that this table was used for
> the case of
> >>>>>> floppy media. But, finally, this table becomes to be the completely
> obsolete
> >>>>>> artefact because mostly storage devices are reliably enough. Why do
> you need
> >>>>
> >>>> ext4 has a badblocks inode to own all the bad spots on disk, but ISTR
> it
> >>>> doesn't support(??) extents or 64-bit filesystems, and might just be a
> >>>> vestigial organ at this point. XFS doesn't have anything to track bad
> >>>> blocks currently....
> >>>>
> >>>>>> in exposing the bad blocks on the file system level? Do you expect
> that next
> >>>>>> generation of NVM memory will be so unreliable that file system
> needs to manage
> >>>>>> bad blocks? What's about erasure coding schemes? Do file system
> really need to suffer
> >>>>>> from the bad block issue?
> >>>>>>
> >>>>>> Usually, we are using LBAs and it is the responsibility of storage
> device to map
> >>>>>> a bad physical block/page/sector into valid one. Do you mean that
> we have
> >>>>>> access to physical NVM memory address directly? But it looks like
> that we can
> >>>>>> have a "bad block" issue even we will access data into page cache's
> memory
> >>>>>> page (if we will use NVM memory for page cache, of course). So,
> what do you
> >>>>>> imply by "bad block" issue?
> >>>>>
> >>>>> We don't have direct physical access to the device's address space,
> in
> >>>>> the sense the device is still free to perform remapping of chunks of
> NVM
> >>>>> underneath us. The problem is that when a block or address range (as
> >>>>> small as a cache line) goes bad, the device maintains a poison bit
> for
> >>>>> every affected cache line. Behind the scenes, it may have already
> >>>>> remapped the range, but the cache line poison has to be kept so that
> >>>>> there is a notification to the user/owner of the data that something
> has
> >>>>> been lost. Since NVM is byte addressable memory sitting on the memory
> >>>>> bus, such a poisoned cache line results in memory errors and
> SIGBUSes.
> >>>>> Compared to tradational storage where an app will get nice and
> friendly
> >>>>> (relatively speaking..) -EIOs. The whole badblocks implementation was
> >>>>> done so that the driver can intercept IO (i.e. reads) to _known_ bad
> >>>>> locations, and short-circuit them with an EIO. If the driver doesn't
> >>>>> catch these, the reads will turn into a memory bus access, and the
> >>>>> poison will cause a SIGBUS.
> >>>>
> >>>> "driver" ... you mean XFS? Or do you mean the thing that makes pmem
> >>>> look kind of like a traditional block device? :)
> >>>
> >>> Yes, the thing that makes pmem look like a block device :) --
> >>> drivers/nvdimm/pmem.c
> >>>
> >>>>
> >>>>> This effort is to try and make this badblock checking smarter - and
> try
> >>>>> and reduce the penalty on every IO to a smaller range, which only the
> >>>>> filesystem can do.
> >>>>
> >>>> Though... now that XFS merged the reverse mapping support, I've been
> >>>> wondering if there'll be a resubmission of the device errors callback?
> >>>> It still would be useful to be able to inform the user that part of
> >>>> their fs has gone bad, or, better yet, if the buffer is still in
> memory
> >>>> someplace else, just write it back out.
> >>>>
> >>>> Or I suppose if we had some kind of raid1 set up between memories we
> >>>> could read one of the other copies and rewrite it into the failing
> >>>> region immediately.
> >>>
> >>> Yes, that is kind of what I was hoping to accomplish via this
> >>> discussion. How much would filesystems want to be involved in this sort
> >>> of badblocks handling, if at all. I can refresh my patches that provide
> >>> the fs notification, but that's the easy bit, and a starting point.
> >>>
> >>
> >> I have some questions. Why moving badblock handling to file system
> >> level avoid the checking phase? In file system level for each I/O I
> >> still have to check the badblock list, right? Do you mean during mount
> >> it can go through the pmem device and locates all the data structures
> >> mangled by badblocks and handle them accordingly, so that during
> >> normal running the badblocks will never be accessed? Or, if there is
> >> replicataion/snapshot support, use a copy to recover the badblocks?
> >
> > With ext4 badblocks, the main outcome is that the bad blocks would be
> > pemanently marked in the allocation bitmap as being used, and they would
> > never be allocated to a file, so they should never be accessed unless
> > doing a full device scan (which ext4 and e2fsck never do). That would
> > avoid the need to check every I/O against the bad blocks list, if the
> > driver knows that the filesystem will handle this.
> >
>
> Thank you for explanation. However this only works for free blocks,
> right? What about allocated blocks, like file data and metadata?
>
> Thanks,
> Andiry
>
> > The one caveat is that ext4 only allows 32-bit block numbers in the
> > badblocks list, since this feature hasn't been used in a long time.
> > This is good for up to 16TB filesystems, but if there was a demand to
> > use this feature again it would be possible allow 64-bit block numbers.
> >
> > Cheers, Andreas
> >
> >
> >
> >
> >
> _______________________________________________
> Linux-nvdimm mailing list
> Linux-nvdimm-hn68Rpc1hR1g9hUCZPvPmw@public.gmane.org
> https://lists.01.org/mailman/listinfo/linux-nvdimm
>
^ permalink raw reply [flat|nested] 42+ messages in thread
* Re: [LSF/MM TOPIC] Badblocks checking/representation in filesystems
2017-01-18 3:08 ` Lu Zhang
@ 2017-01-20 0:46 ` Vishal Verma
-1 siblings, 0 replies; 42+ messages in thread
From: Vishal Verma @ 2017-01-20 0:46 UTC (permalink / raw)
To: Lu Zhang
Cc: Andiry Xu, Andreas Dilger, Slava Dubeyko, Darrick J. Wong,
linux-nvdimm@lists.01.org, linux-block@vger.kernel.org,
Viacheslav Dubeyko, Linux FS Devel,
lsf-pc@lists.linux-foundation.org
On 01/17, Lu Zhang wrote:
> I'm curious about the fault model and corresponding hardware ECC mechanisms
> for NVDIMMs. In my understanding for memory accesses to trigger MCE, it
> means the memory controller finds a detectable but uncorrectable error
> (DUE). So if there is no hardware ECC support the media errors won't even
> be noticed, not to mention badblocks or machine checks.
>
> Current hardware ECC support for DRAM usually employs (72, 64) single-bit
> error correction mechanism, and for advanced ECCs there are techniques like
> Chipkill or SDDC which can tolerate a single DRAM chip failure. What is the
> expected ECC mode for NVDIMMs, assuming that PCM or 3dXpoint based
> technology might have higher error rates?
I'm sure once NVDIMMs start becoming widely available, there will be
more information on how they do ECC..
>
> If DUE does happen and is flagged to the file system via MCE (somehow...),
> and the fs finds that the error corrupts its allocated data page, or
> metadata, now if the fs wants to recover its data the intuition is that
> there needs to be a stronger error correction mechanism to correct the
> hardware-uncorrectable errors. So knowing the hardware ECC baseline is
> helpful for the file system to understand how severe are the faults in
> badblocks, and develop its recovery methods.
Like mentioned before, this discussion is more about presentation of
errors in a known consumable format, rather than recovering from errors.
While recovering from errors is interesting, we already have layers
like RAID for that, and they are as applicable to NVDIMM backed storage
as they have been for disk/SSD based storage.
>
> Regards,
> Lu
>
> On Tue, Jan 17, 2017 at 6:01 PM, Andiry Xu <andiry@gmail.com> wrote:
>
> > On Tue, Jan 17, 2017 at 4:16 PM, Andreas Dilger <adilger@dilger.ca> wrote:
> > > On Jan 17, 2017, at 3:15 PM, Andiry Xu <andiry@gmail.com> wrote:
> > >> On Tue, Jan 17, 2017 at 1:35 PM, Vishal Verma <vishal.l.verma@intel.com>
> > wrote:
> > >>> On 01/16, Darrick J. Wong wrote:
> > >>>> On Fri, Jan 13, 2017 at 05:49:10PM -0700, Vishal Verma wrote:
> > >>>>> On 01/14, Slava Dubeyko wrote:
> > >>>>>>
> > >>>>>> ---- Original Message ----
> > >>>>>> Subject: [LSF/MM TOPIC] Badblocks checking/representation in
> > filesystems
> > >>>>>> Sent: Jan 13, 2017 1:40 PM
> > >>>>>> From: "Verma, Vishal L" <vishal.l.verma@intel.com>
> > >>>>>> To: lsf-pc@lists.linux-foundation.org
> > >>>>>> Cc: linux-nvdimm@lists.01.org, linux-block@vger.kernel.org,
> > linux-fsdevel@vger.kernel.org
> > >>>>>>
> > >>>>>>> The current implementation of badblocks, where we consult the
> > >>>>>>> badblocks list for every IO in the block driver works, and is a
> > >>>>>>> last option failsafe, but from a user perspective, it isn't the
> > >>>>>>> easiest interface to work with.
> > >>>>>>
> > >>>>>> As I remember, FAT and HFS+ specifications contain description of
> > bad blocks
> > >>>>>> (physical sectors) table. I believe that this table was used for
> > the case of
> > >>>>>> floppy media. But, finally, this table becomes to be the completely
> > obsolete
> > >>>>>> artefact because mostly storage devices are reliably enough. Why do
> > you need
> > >>>>
> > >>>> ext4 has a badblocks inode to own all the bad spots on disk, but ISTR
> > it
> > >>>> doesn't support(??) extents or 64-bit filesystems, and might just be a
> > >>>> vestigial organ at this point. XFS doesn't have anything to track bad
> > >>>> blocks currently....
> > >>>>
> > >>>>>> in exposing the bad blocks on the file system level? Do you expect
> > that next
> > >>>>>> generation of NVM memory will be so unreliable that file system
> > needs to manage
> > >>>>>> bad blocks? What's about erasure coding schemes? Do file system
> > really need to suffer
> > >>>>>> from the bad block issue?
> > >>>>>>
> > >>>>>> Usually, we are using LBAs and it is the responsibility of storage
> > device to map
> > >>>>>> a bad physical block/page/sector into valid one. Do you mean that
> > we have
> > >>>>>> access to physical NVM memory address directly? But it looks like
> > that we can
> > >>>>>> have a "bad block" issue even we will access data into page cache's
> > memory
> > >>>>>> page (if we will use NVM memory for page cache, of course). So,
> > what do you
> > >>>>>> imply by "bad block" issue?
> > >>>>>
> > >>>>> We don't have direct physical access to the device's address space,
> > in
> > >>>>> the sense the device is still free to perform remapping of chunks of
> > NVM
> > >>>>> underneath us. The problem is that when a block or address range (as
> > >>>>> small as a cache line) goes bad, the device maintains a poison bit
> > for
> > >>>>> every affected cache line. Behind the scenes, it may have already
> > >>>>> remapped the range, but the cache line poison has to be kept so that
> > >>>>> there is a notification to the user/owner of the data that something
> > has
> > >>>>> been lost. Since NVM is byte addressable memory sitting on the memory
> > >>>>> bus, such a poisoned cache line results in memory errors and
> > SIGBUSes.
> > >>>>> Compared to tradational storage where an app will get nice and
> > friendly
> > >>>>> (relatively speaking..) -EIOs. The whole badblocks implementation was
> > >>>>> done so that the driver can intercept IO (i.e. reads) to _known_ bad
> > >>>>> locations, and short-circuit them with an EIO. If the driver doesn't
> > >>>>> catch these, the reads will turn into a memory bus access, and the
> > >>>>> poison will cause a SIGBUS.
> > >>>>
> > >>>> "driver" ... you mean XFS? Or do you mean the thing that makes pmem
> > >>>> look kind of like a traditional block device? :)
> > >>>
> > >>> Yes, the thing that makes pmem look like a block device :) --
> > >>> drivers/nvdimm/pmem.c
> > >>>
> > >>>>
> > >>>>> This effort is to try and make this badblock checking smarter - and
> > try
> > >>>>> and reduce the penalty on every IO to a smaller range, which only the
> > >>>>> filesystem can do.
> > >>>>
> > >>>> Though... now that XFS merged the reverse mapping support, I've been
> > >>>> wondering if there'll be a resubmission of the device errors callback?
> > >>>> It still would be useful to be able to inform the user that part of
> > >>>> their fs has gone bad, or, better yet, if the buffer is still in
> > memory
> > >>>> someplace else, just write it back out.
> > >>>>
> > >>>> Or I suppose if we had some kind of raid1 set up between memories we
> > >>>> could read one of the other copies and rewrite it into the failing
> > >>>> region immediately.
> > >>>
> > >>> Yes, that is kind of what I was hoping to accomplish via this
> > >>> discussion. How much would filesystems want to be involved in this sort
> > >>> of badblocks handling, if at all. I can refresh my patches that provide
> > >>> the fs notification, but that's the easy bit, and a starting point.
> > >>>
> > >>
> > >> I have some questions. Why moving badblock handling to file system
> > >> level avoid the checking phase? In file system level for each I/O I
> > >> still have to check the badblock list, right? Do you mean during mount
> > >> it can go through the pmem device and locates all the data structures
> > >> mangled by badblocks and handle them accordingly, so that during
> > >> normal running the badblocks will never be accessed? Or, if there is
> > >> replicataion/snapshot support, use a copy to recover the badblocks?
> > >
> > > With ext4 badblocks, the main outcome is that the bad blocks would be
> > > pemanently marked in the allocation bitmap as being used, and they would
> > > never be allocated to a file, so they should never be accessed unless
> > > doing a full device scan (which ext4 and e2fsck never do). That would
> > > avoid the need to check every I/O against the bad blocks list, if the
> > > driver knows that the filesystem will handle this.
> > >
> >
> > Thank you for explanation. However this only works for free blocks,
> > right? What about allocated blocks, like file data and metadata?
> >
> > Thanks,
> > Andiry
> >
> > > The one caveat is that ext4 only allows 32-bit block numbers in the
> > > badblocks list, since this feature hasn't been used in a long time.
> > > This is good for up to 16TB filesystems, but if there was a demand to
> > > use this feature again it would be possible allow 64-bit block numbers.
> > >
> > > Cheers, Andreas
> > >
> > >
> > >
> > >
> > >
> > _______________________________________________
> > Linux-nvdimm mailing list
> > Linux-nvdimm@lists.01.org
> > https://lists.01.org/mailman/listinfo/linux-nvdimm
> >
> _______________________________________________
> Linux-nvdimm mailing list
> Linux-nvdimm@lists.01.org
> https://lists.01.org/mailman/listinfo/linux-nvdimm
^ permalink raw reply [flat|nested] 42+ messages in thread
* Re: [LSF/MM TOPIC] Badblocks checking/representation in filesystems
@ 2017-01-20 0:46 ` Vishal Verma
0 siblings, 0 replies; 42+ messages in thread
From: Vishal Verma @ 2017-01-20 0:46 UTC (permalink / raw)
To: Lu Zhang
Cc: Andreas Dilger, Slava Dubeyko, Darrick J. Wong,
linux-nvdimm@lists.01.org, linux-block@vger.kernel.org,
Linux FS Devel, Viacheslav Dubeyko, Andiry Xu,
lsf-pc@lists.linux-foundation.org
On 01/17, Lu Zhang wrote:
> I'm curious about the fault model and corresponding hardware ECC mechanisms
> for NVDIMMs. In my understanding for memory accesses to trigger MCE, it
> means the memory controller finds a detectable but uncorrectable error
> (DUE). So if there is no hardware ECC support the media errors won't even
> be noticed, not to mention badblocks or machine checks.
>
> Current hardware ECC support for DRAM usually employs (72, 64) single-bit
> error correction mechanism, and for advanced ECCs there are techniques like
> Chipkill or SDDC which can tolerate a single DRAM chip failure. What is the
> expected ECC mode for NVDIMMs, assuming that PCM or 3dXpoint based
> technology might have higher error rates?
I'm sure once NVDIMMs start becoming widely available, there will be
more information on how they do ECC..
>
> If DUE does happen and is flagged to the file system via MCE (somehow...),
> and the fs finds that the error corrupts its allocated data page, or
> metadata, now if the fs wants to recover its data the intuition is that
> there needs to be a stronger error correction mechanism to correct the
> hardware-uncorrectable errors. So knowing the hardware ECC baseline is
> helpful for the file system to understand how severe are the faults in
> badblocks, and develop its recovery methods.
Like mentioned before, this discussion is more about presentation of
errors in a known consumable format, rather than recovering from errors.
While recovering from errors is interesting, we already have layers
like RAID for that, and they are as applicable to NVDIMM backed storage
as they have been for disk/SSD based storage.
>
> Regards,
> Lu
>
> On Tue, Jan 17, 2017 at 6:01 PM, Andiry Xu <andiry@gmail.com> wrote:
>
> > On Tue, Jan 17, 2017 at 4:16 PM, Andreas Dilger <adilger@dilger.ca> wrote:
> > > On Jan 17, 2017, at 3:15 PM, Andiry Xu <andiry@gmail.com> wrote:
> > >> On Tue, Jan 17, 2017 at 1:35 PM, Vishal Verma <vishal.l.verma@intel.com>
> > wrote:
> > >>> On 01/16, Darrick J. Wong wrote:
> > >>>> On Fri, Jan 13, 2017 at 05:49:10PM -0700, Vishal Verma wrote:
> > >>>>> On 01/14, Slava Dubeyko wrote:
> > >>>>>>
> > >>>>>> ---- Original Message ----
> > >>>>>> Subject: [LSF/MM TOPIC] Badblocks checking/representation in
> > filesystems
> > >>>>>> Sent: Jan 13, 2017 1:40 PM
> > >>>>>> From: "Verma, Vishal L" <vishal.l.verma@intel.com>
> > >>>>>> To: lsf-pc@lists.linux-foundation.org
> > >>>>>> Cc: linux-nvdimm@lists.01.org, linux-block@vger.kernel.org,
> > linux-fsdevel@vger.kernel.org
> > >>>>>>
> > >>>>>>> The current implementation of badblocks, where we consult the
> > >>>>>>> badblocks list for every IO in the block driver works, and is a
> > >>>>>>> last option failsafe, but from a user perspective, it isn't the
> > >>>>>>> easiest interface to work with.
> > >>>>>>
> > >>>>>> As I remember, FAT and HFS+ specifications contain description of
> > bad blocks
> > >>>>>> (physical sectors) table. I believe that this table was used for
> > the case of
> > >>>>>> floppy media. But, finally, this table becomes to be the completely
> > obsolete
> > >>>>>> artefact because mostly storage devices are reliably enough. Why do
> > you need
> > >>>>
> > >>>> ext4 has a badblocks inode to own all the bad spots on disk, but ISTR
> > it
> > >>>> doesn't support(??) extents or 64-bit filesystems, and might just be a
> > >>>> vestigial organ at this point. XFS doesn't have anything to track bad
> > >>>> blocks currently....
> > >>>>
> > >>>>>> in exposing the bad blocks on the file system level? Do you expect
> > that next
> > >>>>>> generation of NVM memory will be so unreliable that file system
> > needs to manage
> > >>>>>> bad blocks? What's about erasure coding schemes? Do file system
> > really need to suffer
> > >>>>>> from the bad block issue?
> > >>>>>>
> > >>>>>> Usually, we are using LBAs and it is the responsibility of storage
> > device to map
> > >>>>>> a bad physical block/page/sector into valid one. Do you mean that
> > we have
> > >>>>>> access to physical NVM memory address directly? But it looks like
> > that we can
> > >>>>>> have a "bad block" issue even we will access data into page cache's
> > memory
> > >>>>>> page (if we will use NVM memory for page cache, of course). So,
> > what do you
> > >>>>>> imply by "bad block" issue?
> > >>>>>
> > >>>>> We don't have direct physical access to the device's address space,
> > in
> > >>>>> the sense the device is still free to perform remapping of chunks of
> > NVM
> > >>>>> underneath us. The problem is that when a block or address range (as
> > >>>>> small as a cache line) goes bad, the device maintains a poison bit
> > for
> > >>>>> every affected cache line. Behind the scenes, it may have already
> > >>>>> remapped the range, but the cache line poison has to be kept so that
> > >>>>> there is a notification to the user/owner of the data that something
> > has
> > >>>>> been lost. Since NVM is byte addressable memory sitting on the memory
> > >>>>> bus, such a poisoned cache line results in memory errors and
> > SIGBUSes.
> > >>>>> Compared to tradational storage where an app will get nice and
> > friendly
> > >>>>> (relatively speaking..) -EIOs. The whole badblocks implementation was
> > >>>>> done so that the driver can intercept IO (i.e. reads) to _known_ bad
> > >>>>> locations, and short-circuit them with an EIO. If the driver doesn't
> > >>>>> catch these, the reads will turn into a memory bus access, and the
> > >>>>> poison will cause a SIGBUS.
> > >>>>
> > >>>> "driver" ... you mean XFS? Or do you mean the thing that makes pmem
> > >>>> look kind of like a traditional block device? :)
> > >>>
> > >>> Yes, the thing that makes pmem look like a block device :) --
> > >>> drivers/nvdimm/pmem.c
> > >>>
> > >>>>
> > >>>>> This effort is to try and make this badblock checking smarter - and
> > try
> > >>>>> and reduce the penalty on every IO to a smaller range, which only the
> > >>>>> filesystem can do.
> > >>>>
> > >>>> Though... now that XFS merged the reverse mapping support, I've been
> > >>>> wondering if there'll be a resubmission of the device errors callback?
> > >>>> It still would be useful to be able to inform the user that part of
> > >>>> their fs has gone bad, or, better yet, if the buffer is still in
> > memory
> > >>>> someplace else, just write it back out.
> > >>>>
> > >>>> Or I suppose if we had some kind of raid1 set up between memories we
> > >>>> could read one of the other copies and rewrite it into the failing
> > >>>> region immediately.
> > >>>
> > >>> Yes, that is kind of what I was hoping to accomplish via this
> > >>> discussion. How much would filesystems want to be involved in this sort
> > >>> of badblocks handling, if at all. I can refresh my patches that provide
> > >>> the fs notification, but that's the easy bit, and a starting point.
> > >>>
> > >>
> > >> I have some questions. Why moving badblock handling to file system
> > >> level avoid the checking phase? In file system level for each I/O I
> > >> still have to check the badblock list, right? Do you mean during mount
> > >> it can go through the pmem device and locates all the data structures
> > >> mangled by badblocks and handle them accordingly, so that during
> > >> normal running the badblocks will never be accessed? Or, if there is
> > >> replicataion/snapshot support, use a copy to recover the badblocks?
> > >
> > > With ext4 badblocks, the main outcome is that the bad blocks would be
> > > pemanently marked in the allocation bitmap as being used, and they would
> > > never be allocated to a file, so they should never be accessed unless
> > > doing a full device scan (which ext4 and e2fsck never do). That would
> > > avoid the need to check every I/O against the bad blocks list, if the
> > > driver knows that the filesystem will handle this.
> > >
> >
> > Thank you for explanation. However this only works for free blocks,
> > right? What about allocated blocks, like file data and metadata?
> >
> > Thanks,
> > Andiry
> >
> > > The one caveat is that ext4 only allows 32-bit block numbers in the
> > > badblocks list, since this feature hasn't been used in a long time.
> > > This is good for up to 16TB filesystems, but if there was a demand to
> > > use this feature again it would be possible allow 64-bit block numbers.
> > >
> > > Cheers, Andreas
> > >
> > >
> > >
> > >
> > >
> > _______________________________________________
> > Linux-nvdimm mailing list
> > Linux-nvdimm@lists.01.org
> > https://lists.01.org/mailman/listinfo/linux-nvdimm
> >
> _______________________________________________
> Linux-nvdimm mailing list
> Linux-nvdimm@lists.01.org
> https://lists.01.org/mailman/listinfo/linux-nvdimm
_______________________________________________
Linux-nvdimm mailing list
Linux-nvdimm@lists.01.org
https://lists.01.org/mailman/listinfo/linux-nvdimm
^ permalink raw reply [flat|nested] 42+ messages in thread
* Re: [LSF/MM TOPIC] Badblocks checking/representation in filesystems
2017-01-20 0:46 ` Vishal Verma
@ 2017-01-20 9:24 ` Yasunori Goto
-1 siblings, 0 replies; 42+ messages in thread
From: Yasunori Goto @ 2017-01-20 9:24 UTC (permalink / raw)
To: Vishal Verma
Cc: Lu Zhang, Andreas Dilger, Slava Dubeyko, Darrick J. Wong,
linux-nvdimm@lists.01.org, linux-block@vger.kernel.org,
Linux FS Devel, Viacheslav Dubeyko, Andiry Xu,
lsf-pc@lists.linux-foundation.org
Hello,
Virshal-san.
First of all, your discussion is quite interesting for me. Thanks.
> >
> > If DUE does happen and is flagged to the file system via MCE (somehow...),
> > and the fs finds that the error corrupts its allocated data page, or
> > metadata, now if the fs wants to recover its data the intuition is that
> > there needs to be a stronger error correction mechanism to correct the
> > hardware-uncorrectable errors. So knowing the hardware ECC baseline is
> > helpful for the file system to understand how severe are the faults in
> > badblocks, and develop its recovery methods.
>
> Like mentioned before, this discussion is more about presentation of
> errors in a known consumable format, rather than recovering from errors.
> While recovering from errors is interesting, we already have layers
> like RAID for that, and they are as applicable to NVDIMM backed storage
> as they have been for disk/SSD based storage.
I have one question here.
Certainly, user can use LVM mirroring for storage mode of NVDIMM.
However, NVDIMM has DAX mode.
Can user use LVM mirroring for NVDIMM DAX mode?
I could not find any information that LVM support DAX....
In addition, current specs of NVDIMM (*) only define interleave feature of NVDIMMs.
They does not mention about mirroring feature.
So, I don't understand how to use mirroring for DAX.
(*) "NVDIMM Namespace Specification" , "NVDIMM Block Window Driver Writer’s Guide",
and "ACPI 6.1"
Regards,
---
Yasunori Goto
^ permalink raw reply [flat|nested] 42+ messages in thread* Re: [LSF/MM TOPIC] Badblocks checking/representation in filesystems
@ 2017-01-20 9:24 ` Yasunori Goto
0 siblings, 0 replies; 42+ messages in thread
From: Yasunori Goto @ 2017-01-20 9:24 UTC (permalink / raw)
To: Vishal Verma
Cc: Andreas Dilger, Slava Dubeyko, Darrick J. Wong,
linux-nvdimm@lists.01.org, linux-block@vger.kernel.org, Andiry Xu,
Viacheslav Dubeyko, Linux FS Devel,
lsf-pc@lists.linux-foundation.org
Hello,
Virshal-san.
First of all, your discussion is quite interesting for me. Thanks.
> >
> > If DUE does happen and is flagged to the file system via MCE (somehow...),
> > and the fs finds that the error corrupts its allocated data page, or
> > metadata, now if the fs wants to recover its data the intuition is that
> > there needs to be a stronger error correction mechanism to correct the
> > hardware-uncorrectable errors. So knowing the hardware ECC baseline is
> > helpful for the file system to understand how severe are the faults in
> > badblocks, and develop its recovery methods.
>
> Like mentioned before, this discussion is more about presentation of
> errors in a known consumable format, rather than recovering from errors.
> While recovering from errors is interesting, we already have layers
> like RAID for that, and they are as applicable to NVDIMM backed storage
> as they have been for disk/SSD based storage.
I have one question here.
Certainly, user can use LVM mirroring for storage mode of NVDIMM.
However, NVDIMM has DAX mode.
Can user use LVM mirroring for NVDIMM DAX mode?
I could not find any information that LVM support DAX....
In addition, current specs of NVDIMM (*) only define interleave feature of NVDIMMs.
They does not mention about mirroring feature.
So, I don't understand how to use mirroring for DAX.
(*) "NVDIMM Namespace Specification" , "NVDIMM Block Window Driver Writer’s Guide",
and "ACPI 6.1"
Regards,
---
Yasunori Goto
_______________________________________________
Linux-nvdimm mailing list
Linux-nvdimm@lists.01.org
https://lists.01.org/mailman/listinfo/linux-nvdimm
^ permalink raw reply [flat|nested] 42+ messages in thread* Re: [LSF/MM TOPIC] Badblocks checking/representation in filesystems
@ 2017-01-21 0:23 ` Kani, Toshimitsu
0 siblings, 0 replies; 42+ messages in thread
From: Kani, Toshimitsu @ 2017-01-21 0:23 UTC (permalink / raw)
To: y-goto@jp.fujitsu.com, vishal.l.verma@intel.com
Cc: Vyacheslav.Dubeyko@wdc.com, linux-block@vger.kernel.org,
lsf-pc@lists.linux-foundation.org, linux-nvdimm@ml01.01.org,
slava@dubeyko.com, adilger@dilger.ca, darrick.wong@oracle.com,
linux-fsdevel@vger.kernel.org, andiry@gmail.com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^ permalink raw reply [flat|nested] 42+ messages in thread
* Re: [LSF/MM TOPIC] Badblocks checking/representation in filesystems
@ 2017-01-21 0:23 ` Kani, Toshimitsu
0 siblings, 0 replies; 42+ messages in thread
From: Kani, Toshimitsu @ 2017-01-21 0:23 UTC (permalink / raw)
To: y-goto@jp.fujitsu.com, vishal.l.verma@intel.com
Cc: Vyacheslav.Dubeyko@wdc.com, linux-block@vger.kernel.org,
lsf-pc@lists.linux-foundation.org, linux-nvdimm@ml01.01.org,
slava@dubeyko.com, adilger@dilger.ca, darrick.wong@oracle.com,
linux-fsdevel@vger.kernel.org, andiry@gmail.com
On Fri, 2017-01-20 at 18:24 +0900, Yasunori Goto wrote:
:
> >
> > Like mentioned before, this discussion is more about presentation
> > of errors in a known consumable format, rather than recovering from
> > errors. While recovering from errors is interesting, we already
> > have layers like RAID for that, and they are as applicable to
> > NVDIMM backed storage as they have been for disk/SSD based storage.
>
> I have one question here.
>
> Certainly, user can use LVM mirroring for storage mode of NVDIMM.
> However, NVDIMM has DAX mode.
> Can user use LVM mirroring for NVDIMM DAX mode?
> I could not find any information that LVM support DAX....
dm-linear and dm-stripe support DAX. This is done by mapping block
allocations to LVM physical devices. Once blocks are allocated, all
DAX I/Os are direct and do not go through the device-mapper layer. We
may be able to change it for read/write paths, but it remains true for
mmap. So, I do not think DAX can be supported with LVM mirroring.
This does not preclude hardware mirroring, though.
-Toshi
^ permalink raw reply [flat|nested] 42+ messages in thread
* Re: [LSF/MM TOPIC] Badblocks checking/representation in filesystems
@ 2017-01-21 0:23 ` Kani, Toshimitsu
0 siblings, 0 replies; 42+ messages in thread
From: Kani, Toshimitsu @ 2017-01-21 0:23 UTC (permalink / raw)
To: y-goto-+CUm20s59erQFUHtdCDX3A@public.gmane.org,
vishal.l.verma-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org
Cc: adilger-m1MBpc4rdrD3fQ9qLvQP4Q@public.gmane.org,
Vyacheslav.Dubeyko-Sjgp3cTcYWE@public.gmane.org,
darrick.wong-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org,
linux-nvdimm-y27Ovi1pjclAfugRpC6u6w@public.gmane.org,
linux-block-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
andiry-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org,
slava-yeENwD64cLxBDgjK7y7TUQ@public.gmane.org,
linux-fsdevel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
lsf-pc-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org
On Fri, 2017-01-20 at 18:24 +0900, Yasunori Goto wrote:
:
> >
> > Like mentioned before, this discussion is more about presentation
> > of errors in a known consumable format, rather than recovering from
> > errors. While recovering from errors is interesting, we already
> > have layers like RAID for that, and they are as applicable to
> > NVDIMM backed storage as they have been for disk/SSD based storage.
>
> I have one question here.
>
> Certainly, user can use LVM mirroring for storage mode of NVDIMM.
> However, NVDIMM has DAX mode.
> Can user use LVM mirroring for NVDIMM DAX mode?
> I could not find any information that LVM support DAX....
dm-linear and dm-stripe support DAX. This is done by mapping block
allocations to LVM physical devices. Once blocks are allocated, all
DAX I/Os are direct and do not go through the device-mapper layer. We
may be able to change it for read/write paths, but it remains true for
mmap. So, I do not think DAX can be supported with LVM mirroring.
This does not preclude hardware mirroring, though.
-Toshi
_______________________________________________
Linux-nvdimm mailing list
Linux-nvdimm@lists.01.org
https://lists.01.org/mailman/listinfo/linux-nvdimm
^ permalink raw reply [flat|nested] 42+ messages in thread
* Re: [LSF/MM TOPIC] Badblocks checking/representation in filesystems
2017-01-18 2:01 ` Andiry Xu
@ 2017-01-20 0:55 ` Verma, Vishal L
-1 siblings, 0 replies; 42+ messages in thread
From: Verma, Vishal L @ 2017-01-20 0:55 UTC (permalink / raw)
To: andiry@gmail.com, adilger@dilger.ca
Cc: darrick.wong@oracle.com, Vyacheslav.Dubeyko@wdc.com,
linux-block@vger.kernel.org, slava@dubeyko.com,
lsf-pc@lists.linux-foundation.org, linux-nvdimm@ml01.01.org,
linux-fsdevel@vger.kernel.org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^ permalink raw reply [flat|nested] 42+ messages in thread
* Re: [LSF/MM TOPIC] Badblocks checking/representation in filesystems
@ 2017-01-20 0:55 ` Verma, Vishal L
0 siblings, 0 replies; 42+ messages in thread
From: Verma, Vishal L @ 2017-01-20 0:55 UTC (permalink / raw)
To: andiry@gmail.com, adilger@dilger.ca
Cc: darrick.wong@oracle.com, Vyacheslav.Dubeyko@wdc.com,
linux-block@vger.kernel.org, slava@dubeyko.com,
lsf-pc@lists.linux-foundation.org, linux-nvdimm@ml01.01.org,
linux-fsdevel@vger.kernel.org
On Tue, 2017-01-17 at 18:01 -0800, Andiry Xu wrote:
> On Tue, Jan 17, 2017 at 4:16 PM, Andreas Dilger <adilger@dilger.ca>
> wrote:
> > On Jan 17, 2017, at 3:15 PM, Andiry Xu <andiry@gmail.com> wrote:
> > > On Tue, Jan 17, 2017 at 1:35 PM, Vishal Verma <vishal.l.verma@inte
> > > l.com> wrote:
> > > > On 01/16, Darrick J. Wong wrote:
> > > > > On Fri, Jan 13, 2017 at 05:49:10PM -0700, Vishal Verma wrote:
> > > > > > On 01/14, Slava Dubeyko wrote:
> > > > > > >
> > > > > > > ---- Original Message ----
> > > > > > > Subject: [LSF/MM TOPIC] Badblocks checking/representation
> > > > > > > in filesystems
> > > > > > > Sent: Jan 13, 2017 1:40 PM
> > > > > > > From: "Verma, Vishal L" <vishal.l.verma@intel.com>
> > > > > > > To: lsf-pc@lists.linux-foundation.org
> > > > > > > Cc: linux-nvdimm@lists.01.org, linux-block@vger.kernel.org
> > > > > > > , linux-fsdevel@vger.kernel.org
> > > > > > >
> > > > > > > > The current implementation of badblocks, where we
> > > > > > > > consult the
> > > > > > > > badblocks list for every IO in the block driver works,
> > > > > > > > and is a
> > > > > > > > last option failsafe, but from a user perspective, it
> > > > > > > > isn't the
> > > > > > > > easiest interface to work with.
> > > > > > >
> > > > > > > As I remember, FAT and HFS+ specifications contain
> > > > > > > description of bad blocks
> > > > > > > (physical sectors) table. I believe that this table was
> > > > > > > used for the case of
> > > > > > > floppy media. But, finally, this table becomes to be the
> > > > > > > completely obsolete
> > > > > > > artefact because mostly storage devices are reliably
> > > > > > > enough. Why do you need
> > > > >
> > > > > ext4 has a badblocks inode to own all the bad spots on disk,
> > > > > but ISTR it
> > > > > doesn't support(??) extents or 64-bit filesystems, and might
> > > > > just be a
> > > > > vestigial organ at this point. XFS doesn't have anything to
> > > > > track bad
> > > > > blocks currently....
> > > > >
> > > > > > > in exposing the bad blocks on the file system level? Do
> > > > > > > you expect that next
> > > > > > > generation of NVM memory will be so unreliable that file
> > > > > > > system needs to manage
> > > > > > > bad blocks? What's about erasure coding schemes? Do file
> > > > > > > system really need to suffer
> > > > > > > from the bad block issue?
> > > > > > >
> > > > > > > Usually, we are using LBAs and it is the responsibility of
> > > > > > > storage device to map
> > > > > > > a bad physical block/page/sector into valid one. Do you
> > > > > > > mean that we have
> > > > > > > access to physical NVM memory address directly? But it
> > > > > > > looks like that we can
> > > > > > > have a "bad block" issue even we will access data into
> > > > > > > page cache's memory
> > > > > > > page (if we will use NVM memory for page cache, of
> > > > > > > course). So, what do you
> > > > > > > imply by "bad block" issue?
> > > > > >
> > > > > > We don't have direct physical access to the device's address
> > > > > > space, in
> > > > > > the sense the device is still free to perform remapping of
> > > > > > chunks of NVM
> > > > > > underneath us. The problem is that when a block or address
> > > > > > range (as
> > > > > > small as a cache line) goes bad, the device maintains a
> > > > > > poison bit for
> > > > > > every affected cache line. Behind the scenes, it may have
> > > > > > already
> > > > > > remapped the range, but the cache line poison has to be kept
> > > > > > so that
> > > > > > there is a notification to the user/owner of the data that
> > > > > > something has
> > > > > > been lost. Since NVM is byte addressable memory sitting on
> > > > > > the memory
> > > > > > bus, such a poisoned cache line results in memory errors and
> > > > > > SIGBUSes.
> > > > > > Compared to tradational storage where an app will get nice
> > > > > > and friendly
> > > > > > (relatively speaking..) -EIOs. The whole badblocks
> > > > > > implementation was
> > > > > > done so that the driver can intercept IO (i.e. reads) to
> > > > > > _known_ bad
> > > > > > locations, and short-circuit them with an EIO. If the driver
> > > > > > doesn't
> > > > > > catch these, the reads will turn into a memory bus access,
> > > > > > and the
> > > > > > poison will cause a SIGBUS.
> > > > >
> > > > > "driver" ... you mean XFS? Or do you mean the thing that
> > > > > makes pmem
> > > > > look kind of like a traditional block device? :)
> > > >
> > > > Yes, the thing that makes pmem look like a block device :) --
> > > > drivers/nvdimm/pmem.c
> > > >
> > > > >
> > > > > > This effort is to try and make this badblock checking
> > > > > > smarter - and try
> > > > > > and reduce the penalty on every IO to a smaller range, which
> > > > > > only the
> > > > > > filesystem can do.
> > > > >
> > > > > Though... now that XFS merged the reverse mapping support,
> > > > > I've been
> > > > > wondering if there'll be a resubmission of the device errors
> > > > > callback?
> > > > > It still would be useful to be able to inform the user that
> > > > > part of
> > > > > their fs has gone bad, or, better yet, if the buffer is still
> > > > > in memory
> > > > > someplace else, just write it back out.
> > > > >
> > > > > Or I suppose if we had some kind of raid1 set up between
> > > > > memories we
> > > > > could read one of the other copies and rewrite it into the
> > > > > failing
> > > > > region immediately.
> > > >
> > > > Yes, that is kind of what I was hoping to accomplish via this
> > > > discussion. How much would filesystems want to be involved in
> > > > this sort
> > > > of badblocks handling, if at all. I can refresh my patches that
> > > > provide
> > > > the fs notification, but that's the easy bit, and a starting
> > > > point.
> > > >
> > >
> > > I have some questions. Why moving badblock handling to file system
> > > level avoid the checking phase? In file system level for each I/O
> > > I
> > > still have to check the badblock list, right? Do you mean during
> > > mount
> > > it can go through the pmem device and locates all the data
> > > structures
> > > mangled by badblocks and handle them accordingly, so that during
> > > normal running the badblocks will never be accessed? Or, if there
> > > is
> > > replicataion/snapshot support, use a copy to recover the
> > > badblocks?
> >
> > With ext4 badblocks, the main outcome is that the bad blocks would
> > be
> > pemanently marked in the allocation bitmap as being used, and they
> > would
> > never be allocated to a file, so they should never be accessed
> > unless
> > doing a full device scan (which ext4 and e2fsck never do). That
> > would
> > avoid the need to check every I/O against the bad blocks list, if
> > the
> > driver knows that the filesystem will handle this.
> >
>
> Thank you for explanation. However this only works for free blocks,
> right? What about allocated blocks, like file data and metadata?
>
Like Andreas said, the ext4 badblocks feature has not been in use, and
the current block layer badblocks are distinct and unrelated to these.
Can the ext4 badblocks infrastructure be revived and extended if we
decide to add badblocks to filesystems? Maybe - that was one of the
topics I was hoping to discuss/find out more about.
^ permalink raw reply [flat|nested] 42+ messages in thread