Ext4 developers get together planning

Ext4 developers get together planning

[Theodore Ts'o]

Looking at the Vault schedule, it looks like the best time to schedule
the ext4 developer's workshop will be Wednesday from noon to 3pm (we'll
meet for lunch and then continue until Jan Kara's ext4 file system
scalaing talk.

And then we can pick up Thursday morning starting at 10am and go on
until Lunch.  (Or we could start at 9am and skip the Sasha Levin's file
system fuzzing talk, but I suspect some people wouldn't want to miss
Sasha's talk.)

Does that work for everyone?

Things which I expect will be on the schedule include:

* ext4 encryption progress report (Michael Halcrow, Ted)
* making ext4 smr friendly (Abutalib, Peter, Ted, Tim, Adrian)
* improving the ext4 block allocator (Jun He)

Since Jaeguk probably would only be interested in the encryption
discussions, I'm going to suggest that we schedule the encryption
discussions for Thursday morning, and the SMR discussions for Wednesday
afternoon, since our minds will be fresh immediately after the SMR
discussions on Thursday morning.

What other topics would people like to include?  Please suggest them on
this e-mail thread.

Finally, if you are planning on attending, please send me a private
e-mail so I know who to expect.  For those of you coming from academia,
if you haven't already registered for Vault yet, I've recently received
from Angela on a few compliementary academic registrations, so please
contact me if you could use one or two.

Cheers,

                                                - Ted

Re: Ext4 developers get together planning

[Jan Kara]

On Mon 02-03-15 10:53:36, Ted Tso wrote:
> 
> Looking at the Vault schedule, it looks like the best time to schedule
> the ext4 developer's workshop will be Wednesday from noon to 3pm (we'll
> meet for lunch and then continue until Jan Kara's ext4 file system
> scalaing talk.
> 
> And then we can pick up Thursday morning starting at 10am and go on
> until Lunch.  (Or we could start at 9am and skip the Sasha Levin's file
> system fuzzing talk, but I suspect some people wouldn't want to miss
> Sasha's talk.)
> 
> Does that work for everyone?
> 
> Things which I expect will be on the schedule include:
> 
> * ext4 encryption progress report (Michael Halcrow, Ted)
> * making ext4 smr friendly (Abutalib, Peter, Ted, Tim, Adrian)
> * improving the ext4 block allocator (Jun He)
> 
> Since Jaeguk probably would only be interested in the encryption
> discussions, I'm going to suggest that we schedule the encryption
> discussions for Thursday morning, and the SMR discussions for Wednesday
> afternoon, since our minds will be fresh immediately after the SMR
> discussions on Thursday morning.
> 
> What other topics would people like to include?  Please suggest them on
> this e-mail thread.
  I have about 4 bugs we have in ext4 that I didn't get to fixing because
the fix isn't immediately obvious. Maybe some discussion on these would be
useful. The issues I'm aware of are:
1) filling of hole from ext4_page_mkwrite() in nodelalloc mode (or when we
   are running out of space) can race with DIO read of the same location
   resulting in DIO read returning uninitialized block data (possible
   security issue).

   I think using uninitialized extents is the right solution here if we can
   but what about indirect mapped files (think of ext2 / ext3 compatibility
   modes)?

2) When doing AIO DIO write we store pointer to ioend structure in the
   inode. However in dioread_nolock mode, we can run two AIO DIO overwrites
   in parallel and thus one ioend just overwrites the other resulting in
   nasty issues. No idea how to best fix this (but I didn't think much
   about it).

3) inode->i_writecount >= 1 doesn't actually guarantee that ->release()
   method will be called (as there are places that increase / decrease
   i_writecount without actually opening the file). Thus we can leave
   preallocated blocks in an inode.

   Truncating blocks in ext4_clear_inode() isn't completely reliable since
   filesystem may be remounted R/O by then. We can create our own writer
   count but that seems like a bit of an overkill...

4) There's the longstanding issue with punch hole racing with page fault
   that can lead to stale data exposure or fs corruption. Proper fix in mm
   is tricky and won't happen soon so should we go the way XFS recently
   went and just create special locking for that withing ext4?

								Honza
-- 
Jan Kara <jack@suse.cz>
SUSE Labs, CR

Re: Ext4 developers get together planning

[Darrick J. Wong]

Are you all set for the ext4 summit?  What is the dial in number for those of
us who cannot make it?

--D

On Mon, Mar 02, 2015 at 10:53:36AM -0500, Theodore Ts'o wrote:
> 
> Looking at the Vault schedule, it looks like the best time to schedule
> the ext4 developer's workshop will be Wednesday from noon to 3pm (we'll
> meet for lunch and then continue until Jan Kara's ext4 file system
> scalaing talk.
> 
> And then we can pick up Thursday morning starting at 10am and go on
> until Lunch.  (Or we could start at 9am and skip the Sasha Levin's file
> system fuzzing talk, but I suspect some people wouldn't want to miss
> Sasha's talk.)
> 
> Does that work for everyone?
> 
> Things which I expect will be on the schedule include:
> 
> * ext4 encryption progress report (Michael Halcrow, Ted)
> * making ext4 smr friendly (Abutalib, Peter, Ted, Tim, Adrian)
> * improving the ext4 block allocator (Jun He)
> 
> Since Jaeguk probably would only be interested in the encryption
> discussions, I'm going to suggest that we schedule the encryption
> discussions for Thursday morning, and the SMR discussions for Wednesday
> afternoon, since our minds will be fresh immediately after the SMR
> discussions on Thursday morning.
> 
> What other topics would people like to include?  Please suggest them on
> this e-mail thread.
> 
> Finally, if you are planning on attending, please send me a private
> e-mail so I know who to expect.  For those of you coming from academia,
> if you haven't already registered for Vault yet, I've recently received
> from Angela on a few compliementary academic registrations, so please
> contact me if you could use one or two.
> 
> Cheers,
> 
>                                                 - Ted
> 
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Re: Ext4 developers get together planning

[Theodore Ts'o]

On Tue, Mar 10, 2015 at 06:37:20PM -0700, Darrick J. Wong wrote:
> Are you all set for the ext4 summit?  What is the dial in number for those of
> us who cannot make it?

I'm really sorry; I wasn't able to get a proper Polycom-type unit set
up.  I could try to set up something using a cell phone in
speakerphone, but I suspect the sound quality would make it be largely
useless for someone trying to follow the discussion.

						- Ted