Re: [PATCH 2/2] xfs: Extend xattr extent counter to 32-bits

[Chandan Rajendra <chandan@linux.ibm.com>]

On Tuesday, April 7, 2020 5:00 AM Dave Chinner wrote: 
> On Mon, Apr 06, 2020 at 10:06:03AM -0700, Darrick J. Wong wrote:
> > On Sat, Apr 04, 2020 at 02:22:03PM +0530, Chandan Rajendra wrote:
> > > XFS has a per-inode xattr extent counter which is 16 bits wide. A workload
> > > which
> > > 1. Creates 1,000,000 255-byte sized xattrs,
> > > 2. Deletes 50% of these xattrs in an alternating manner,
> > > 3. Tries to create 400,000 new 255-byte sized xattrs
> > > causes the following message to be printed on the console,
> > > 
> > > XFS (loop0): xfs_iflush_int: detected corrupt incore inode 131, total extents = -19916, nblocks = 102937, ptr ffff9ce33b098c00
> > > XFS (loop0): xfs_do_force_shutdown(0x8) called from line 3739 of file fs/xfs/xfs_inode.c. Return address = ffffffffa4a94173
> > > 
> > > This indicates that we overflowed the 16-bits wide xattr extent counter.
> > > 
> > > I have been informed that there are instances where a single file has
> > >  > 100 million hardlinks. With parent pointers being stored in xattr,
> > > we will overflow the 16-bits wide xattr extent counter when large
> > > number of hardlinks are created.
> > > 
> > > Hence this commit extends xattr extent counter to 32-bits. It also introduces
> > > an incompat flag to prevent older kernels from mounting newer filesystems with
> > > 32-bit wide xattr extent counter.
> > > 
> > > Signed-off-by: Chandan Rajendra <chandanrlinux@gmail.com>
> > > ---
> > >  fs/xfs/libxfs/xfs_format.h     | 28 +++++++++++++++++++++-------
> > >  fs/xfs/libxfs/xfs_inode_buf.c  | 27 +++++++++++++++++++--------
> > >  fs/xfs/libxfs/xfs_inode_fork.c |  3 ++-
> > >  fs/xfs/libxfs/xfs_log_format.h |  5 +++--
> > >  fs/xfs/libxfs/xfs_types.h      |  4 ++--
> > >  fs/xfs/scrub/inode.c           |  7 ++++---
> > >  fs/xfs/xfs_inode_item.c        |  3 ++-
> > >  fs/xfs/xfs_log_recover.c       | 13 ++++++++++---
> > >  8 files changed, 63 insertions(+), 27 deletions(-)
> > > 
> > > diff --git a/fs/xfs/libxfs/xfs_format.h b/fs/xfs/libxfs/xfs_format.h
> > > index 045556e78ee2c..0a4266b0d46e1 100644
> > > --- a/fs/xfs/libxfs/xfs_format.h
> > > +++ b/fs/xfs/libxfs/xfs_format.h
> > > @@ -465,10 +465,12 @@ xfs_sb_has_ro_compat_feature(
> > >  #define XFS_SB_FEAT_INCOMPAT_FTYPE	(1 << 0)	/* filetype in dirent */
> > >  #define XFS_SB_FEAT_INCOMPAT_SPINODES	(1 << 1)	/* sparse inode chunks */
> > >  #define XFS_SB_FEAT_INCOMPAT_META_UUID	(1 << 2)	/* metadata UUID */
> > > +#define XFS_SB_FEAT_INCOMPAT_32BIT_AEXT_CNTR (1 << 3)
> > 
> > If you're going to introduce an INCOMPAT feature, please also use the
> > opportunity to convert xattrs to something resembling the dir v3 format,
> > where we index free space within each block so that we can speed up attr
> > setting with 100 million attrs.
> 
> Not necessary. Chandan has already spent a lot of time investigating
> that - I suggested doing the investigation probably a year ago when
> he was looking for stuff to do knowing that this could be a problem
> parent pointers hit. Long story short - there's no degradation in
> performance in the dabtree out to tens of millions of records with
> different fixed size or random sized attributes, nor does various
> combinations of insert/lookup/remove/replace operations seem to
> impact the tree performance at scale. IOWs, we hit the 16 bit extent
> limits of the attribute trees without finding any degradation in
> performance.

My benchmarking was limited to working with a maximum of 1,000,000 xattrs. I
will address the review comments provided on this patchset and then run the
benchmarks once again ... but this time I will increase the upper limit to 100
million xattrs (since we will have a 32-bit extent counter). I will post the
results of the benchmarking (along with the benchmarking programs/scripts) to
the mailing list before I post the patchset itself.

-- 
chandan