Re: [RFC PATCH] xfs: don't bump the i_version on an atime update in xfs_vn_update_time

[Dave Chinner <david@fromorbit.com>]

On Wed, Aug 17, 2022 at 09:00:02AM -0400, Jeff Layton wrote:
> xfs will update the i_version when updating only the atime value, which
> is not desirable for any of the current consumers of i_version. Doing so
> leads to unnecessary cache invalidations on NFS and extra measurement
> activity in IMA.
> 
> Add a new XFS_ILOG_NOIVER flag, and use that to indicate that the
> transaction should not update the i_version. Set that value in
> xfs_vn_update_time if we're only updating the atime.
> 
> Signed-off-by: Jeff Layton <jlayton@kernel.org>
> ---
>  fs/xfs/libxfs/xfs_log_format.h  |  2 +-
>  fs/xfs/libxfs/xfs_trans_inode.c |  2 +-
>  fs/xfs/xfs_iops.c               | 10 +++++++---
>  3 files changed, 9 insertions(+), 5 deletions(-)
> 
> Dave,
> 
> How about this for an alternate approach? This just explicitly ensures
> that we don't bump the i_version on an atime-only update, and seems to
> fix the testcase I have.

This just duplicates lazytime functionality, only now users
can't opt-in or out.

atime update filtering is a VFS function so behaviour is common
across all filesystems. Deficiencies in VFS filtering behaviour
should not be hacked around by individual filesystems, the VFS
filtering should be fixed.

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com