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

Darrick J. Wong
2022-08-18T00:05:03Z

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.

I suppose that would work, since explicit atime updates from futimens()
go through notify_change/setattr and not ->update_time.

--D

> 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.
>
> diff --git a/fs/xfs/libxfs/xfs_log_format.h b/fs/xfs/libxfs/xfs_log_format.h
> index b351b9dc6561..866a4c5cf70c 100644
> --- a/fs/xfs/libxfs/xfs_log_format.h
> +++ b/fs/xfs/libxfs/xfs_log_format.h
> @@ -323,7 +323,7 @@ struct xfs_inode_log_format_32 {
> #define XFS_ILOG_ABROOT 0x100 /* log i_af.i_broot */
> #define XFS_ILOG_DOWNER 0x200 /* change the data fork owner on replay */
> #define XFS_ILOG_AOWNER 0x400 /* change the attr fork owner on replay */
> -
> +#define XFS_ILOG_NOIVER 0x800 /* don't bump i_version */
>
> /*
> * The timestamps are dirty, but not necessarily anything else in the inode
> diff --git a/fs/xfs/libxfs/xfs_trans_inode.c b/fs/xfs/libxfs/xfs_trans_inode.c
> index 8b5547073379..ffe6d296e7f9 100644
> --- a/fs/xfs/libxfs/xfs_trans_inode.c
> +++ b/fs/xfs/libxfs/xfs_trans_inode.c
> @@ -126,7 +126,7 @@ xfs_trans_log_inode(
> * unconditionally.
> */
> if (!test_and_set_bit(XFS_LI_DIRTY, &iip->ili_item.li_flags)) {
> - if (IS_I_VERSION(inode) &&
> + if (!(flags & XFS_ILOG_NOIVER) && IS_I_VERSION(inode) &&
> inode_maybe_inc_iversion(inode, flags & XFS_ILOG_CORE))
> iversion_flags = XFS_ILOG_CORE;
> }
> diff --git a/fs/xfs/xfs_iops.c b/fs/xfs/xfs_iops.c
> index 45518b8c613c..54db85a43dfb 100644
> --- a/fs/xfs/xfs_iops.c
> +++ b/fs/xfs/xfs_iops.c
> @@ -1021,7 +1021,7 @@ xfs_vn_update_time(
> {
> struct xfs_inode *ip = XFS_I(inode);
> struct xfs_mount *mp = ip->i_mount;
> - int log_flags = XFS_ILOG_TIMESTAMP;
> + int log_flags = XFS_ILOG_TIMESTAMP|XFS_ILOG_NOIVER;
> struct xfs_trans *tp;
> int error;
>
> @@ -1041,10 +1041,14 @@ xfs_vn_update_time(
> return error;
>
> xfs_ilock(ip, XFS_ILOCK_EXCL);
> - if (flags & S_CTIME)
> + if (flags & S_CTIME) {
> inode->i_ctime = *now;
> - if (flags & S_MTIME)
> + log_flags &= ~XFS_ILOG_NOIVER;
> + }
> + if (flags & S_MTIME) {
> inode->i_mtime = *now;
> + log_flags &= ~XFS_ILOG_NOIVER;
> + }
> if (flags & S_ATIME)
> inode->i_atime = *now;
>
> --
> 2.37.2
>