Re: [RFC 0/3] Convert XFS inode hashes to radix trees

Re: [RFC 0/3] Convert XFS inode hashes to radix trees

[Chris Wedgwood]

On Tue, Oct 03, 2006 at 04:06:10PM +1000, David Chinner wrote:

> Overall, the patchset removes more than 200 lines of code from the
> xfs inode caching and lookup code and provides more consistent
> scalability for large numbers of cached inodes. The only down side
> is that it limits us to 32 bit inode numbers of 32 bit platforms due
> to the way the radix tree uses unsigned longs for it's indexes

    commit afefdbb28a0a2af689926c30b94a14aea6036719
    tree 6ee500575cac928cd90045bcf5b691cf2b8daa09
    parent 1d32849b14bc8792e6f35ab27dd990d74b16126c
    author David Howells <dhowells@redhat.com> 1159863226 -0700
    committer Linus Torvalds <torvalds@g5.osdl.org> 1159887820 -0700

    [PATCH] VFS: Make filldir_t and struct kstat deal in 64-bit inode numbers

    These patches make the kernel pass 64-bit inode numbers internally when
    communicating to userspace, even on a 32-bit system.  They are required
    because some filesystems have intrinsic 64-bit inode numbers: NFS3+ and XFS
    for example.  The 64-bit inode numbers are then propagated to userspace
    automatically where the arch supports it.
    [...]

Doing this will mean XFS won't be able to support 32-bit inodes on
32-bit platforms the above (merged) patch --- though given that cheap
64-bit systems are now abundant does anyone really care?

Re: [RFC 0/3] Convert XFS inode hashes to radix trees

[David Chinner]

On Tue, Oct 03, 2006 at 02:23:35PM -0700, Chris Wedgwood wrote:
> On Tue, Oct 03, 2006 at 04:06:10PM +1000, David Chinner wrote:
> > Overall, the patchset removes more than 200 lines of code from the
> > xfs inode caching and lookup code and provides more consistent
> > scalability for large numbers of cached inodes. The only down side
> > is that it limits us to 32 bit inode numbers of 32 bit platforms due
> > to the way the radix tree uses unsigned longs for it's indexes
> 
>     commit afefdbb28a0a2af689926c30b94a14aea6036719
>     tree 6ee500575cac928cd90045bcf5b691cf2b8daa09
>     parent 1d32849b14bc8792e6f35ab27dd990d74b16126c
>     author David Howells <dhowells@redhat.com> 1159863226 -0700
>     committer Linus Torvalds <torvalds@g5.osdl.org> 1159887820 -0700
> 
>     [PATCH] VFS: Make filldir_t and struct kstat deal in 64-bit inode numbers
> 
>     These patches make the kernel pass 64-bit inode numbers internally when
>     communicating to userspace, even on a 32-bit system.  They are required
>     because some filesystems have intrinsic 64-bit inode numbers: NFS3+ and XFS
>     for example.  The 64-bit inode numbers are then propagated to userspace
>     automatically where the arch supports it.
>     [...]
> 
> Doing this will mean XFS won't be able to support 32-bit inodes on
> 32-bit platforms the above (merged) patch --- though given that cheap
> 64-bit systems are now abundant does anyone really care?

That's a good question. In a recent thread on linux-fsdevel about
these patches Christoph Hellwig pointed out that 32bit user space is
not ready for 64 bit inodes, so it's probably going to be a while
before the second half of this mod is ready (which exports 64 bit
inodes ito userspace on 32bit platforms).

http://marc.theaimsgroup.com/?l=linux-fsdevel&m=115946211808497&w=2
http://marc.theaimsgroup.com/?l=linux-fsdevel&m=115948836023569&w=2

ISTR someone else also menitoning that 64bit inodes on 32-bit machines
also breaks the dynamic linker, but I can't find a reference to that
atm.

As it stands, there's still a few barriers to getting 64 bit inodes
on 32 bit platforms and I can't see them going away quickly. Right
now I see little reason in moving to 64 bit inodes for 32 bit
platforms for XFS because of the 16TB filesystem size limit (that
only needs 33-36 bit inodes depending on the inode size) and no
32bit platform is currently able to repair a filesystem of that
size.

And yes, 64 bit systems are cheap, cheap, cheap so IMO this
functionality is really irrelevant moving forward. If it had come
along a couple of years ago then it would be different, but I think
mainstream technology is finally catching up with XFS so it's not a
critical issue anymore... ;)

Cheers,

Dave.
-- 
Dave Chinner
Principal Engineer
SGI Australian Software Group

Re: [RFC 0/3] Convert XFS inode hashes to radix trees

[Chris Wedgwood]

On Wed, Oct 04, 2006 at 08:22:56AM +1000, David Chinner wrote:

> That's a good question. In a recent thread on linux-fsdevel about
> these patches Christoph Hellwig pointed out that 32bit user space is
> not ready for 64 bit inodes, so it's probably going to be a while
> before the second half of this mod is ready (which exports 64 bit
> inodes ito userspace on 32bit platforms).

yes a patch changing struct kstat and filldir* was merged...

> http://marc.theaimsgroup.com/?l=linux-fsdevel&m=115946211808497&w=2
> http://marc.theaimsgroup.com/?l=linux-fsdevel&m=115948836023569&w=2

> As it stands, there's still a few barriers to getting 64 bit inodes
> on 32 bit platforms and I can't see them going away quickly. Right
> now I see little reason in moving to 64 bit inodes for 32 bit
> platforms for XFS because of the 16TB filesystem size limit (that
> only needs 33-36 bit inodes depending on the inode size) and no
> 32bit platform is currently able to repair a filesystem of that
> size.

so that leaves NFS3+

is it really worth the pain then?

Re: [RFC 0/3] Convert XFS inode hashes to radix trees

[David Chinner]

On Wed, Oct 04, 2006 at 08:22:56AM +1000, David Chinner wrote:
> On Tue, Oct 03, 2006 at 02:23:35PM -0700, Chris Wedgwood wrote:
> > On Tue, Oct 03, 2006 at 04:06:10PM +1000, David Chinner wrote:
> > > Overall, the patchset removes more than 200 lines of code from the
> > > xfs inode caching and lookup code and provides more consistent
> > > scalability for large numbers of cached inodes. The only down side
> > > is that it limits us to 32 bit inode numbers of 32 bit platforms due
> > > to the way the radix tree uses unsigned longs for it's indexes
> > 
> >     commit afefdbb28a0a2af689926c30b94a14aea6036719
> >     tree 6ee500575cac928cd90045bcf5b691cf2b8daa09
> >     parent 1d32849b14bc8792e6f35ab27dd990d74b16126c
> >     author David Howells <dhowells@redhat.com> 1159863226 -0700
> >     committer Linus Torvalds <torvalds@g5.osdl.org> 1159887820 -0700
> > 
> >     [PATCH] VFS: Make filldir_t and struct kstat deal in 64-bit inode numbers
> > 
> >     These patches make the kernel pass 64-bit inode numbers internally when
> >     communicating to userspace, even on a 32-bit system.  They are required
> >     because some filesystems have intrinsic 64-bit inode numbers: NFS3+ and XFS
> >     for example.  The 64-bit inode numbers are then propagated to userspace
> >     automatically where the arch supports it.
> >     [...]
> > 
> > Doing this will mean XFS won't be able to support 32-bit inodes on
> > 32-bit platforms the above (merged) patch --- though given that cheap
> > 64-bit systems are now abundant does anyone really care?
> 
> That's a good question. In a recent thread on linux-fsdevel about
> these patches Christoph Hellwig pointed out that 32bit user space is
> not ready for 64 bit inodes, so it's probably going to be a while
> before the second half of this mod is ready (which exports 64 bit
> inodes ito userspace on 32bit platforms).

Ahhh.... I think I misread what Chris wrote here - _32_ bit inodes on
32 bit platforms not working? I can't see how this would be the
case with the mods I posted given that they are entirely internal to
XFS and don't change any external inode number interfaces. And the
above commit shouldn't break XFS either.

Cheers,

Dave.
-- 
Dave Chinner
Principal Engineer
SGI Australian Software Group

Re: [RFC 0/3] Convert XFS inode hashes to radix trees

[Andi Kleen]

David Chinner <dgc@sgi.com> writes:
> 
> And yes, 64 bit systems are cheap, cheap, cheap so IMO this
> functionality is really irrelevant moving forward. If it had come
> along a couple of years ago then it would be different, but I think
> mainstream technology is finally catching up with XFS so it's not a
> critical issue anymore... ;)

One issue is that people often still run a lot of 32bit userland
even with 64bit kernels. The compat layer will just truncate
the inodes I think. But so far I haven't heard of anybody
complaining on x86-64.

-Andi

Re: [RFC 0/3] Convert XFS inode hashes to radix trees

[Trond Myklebust]

On Wed, 2006-10-04 at 08:22 +1000, David Chinner wrote:
> On Tue, Oct 03, 2006 at 02:23:35PM -0700, Chris Wedgwood wrote:
> > On Tue, Oct 03, 2006 at 04:06:10PM +1000, David Chinner wrote:
> > > Overall, the patchset removes more than 200 lines of code from the
> > > xfs inode caching and lookup code and provides more consistent
> > > scalability for large numbers of cached inodes. The only down side
> > > is that it limits us to 32 bit inode numbers of 32 bit platforms due
> > > to the way the radix tree uses unsigned longs for it's indexes
> > 
> >     commit afefdbb28a0a2af689926c30b94a14aea6036719
> >     tree 6ee500575cac928cd90045bcf5b691cf2b8daa09
> >     parent 1d32849b14bc8792e6f35ab27dd990d74b16126c
> >     author David Howells <dhowells@redhat.com> 1159863226 -0700
> >     committer Linus Torvalds <torvalds@g5.osdl.org> 1159887820 -0700
> > 
> >     [PATCH] VFS: Make filldir_t and struct kstat deal in 64-bit inode numbers
> > 
> >     These patches make the kernel pass 64-bit inode numbers internally when
> >     communicating to userspace, even on a 32-bit system.  They are required
> >     because some filesystems have intrinsic 64-bit inode numbers: NFS3+ and XFS
> >     for example.  The 64-bit inode numbers are then propagated to userspace
> >     automatically where the arch supports it.
> >     [...]
> > 
> > Doing this will mean XFS won't be able to support 32-bit inodes on
> > 32-bit platforms the above (merged) patch --- though given that cheap
> > 64-bit systems are now abundant does anyone really care?

Which completely ignored the fact that NFS systems are already having to
truncate 64-bit inode numbers to 32-bits and pass these truncated values
up to userspace. Collisions have been observed in the wild, and I've
already had to change the 64-bit->32-bit hashing algorithm on at least
one occasion.

By moving that truncation into userspace, we will at least give 64-bit
standards-compliant programs a chance to work correctly.

Trond

Re: [RFC 0/3] Convert XFS inode hashes to radix trees

[David Chinner]

On Wed, Oct 04, 2006 at 07:59:15PM +0200, Andi Kleen wrote:
> David Chinner <dgc@sgi.com> writes:
> > 
> > And yes, 64 bit systems are cheap, cheap, cheap so IMO this
> > functionality is really irrelevant moving forward. If it had come
> > along a couple of years ago then it would be different, but I think
> > mainstream technology is finally catching up with XFS so it's not a
> > critical issue anymore... ;)
> 
> One issue is that people often still run a lot of 32bit userland
> even with 64bit kernels.

Which is one of the reasons why XFS uses 32 bit inodes by default
even on 64 bit kernels. XFS does not use 64 bit inodes unless you
tell it to via the inode64 mount option....

Cheers,

Dave.
-- 
Dave Chinner
Principal Engineer
SGI Australian Software Group