linux-kernel - [PATCH v3 4/7] xfs: don't bump the i_version on an atime update in xfs_vn_update

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Date:   Fri, 26 Aug 2022 17:47:00 -0400
From:   Jeff Layton <jlayton@...nel.org>
To:     tytso@....edu, adilger.kernel@...ger.ca, djwong@...nel.org,
        david@...morbit.com, trondmy@...merspace.com, neilb@...e.de,
        viro@...iv.linux.org.uk, zohar@...ux.ibm.com, xiubli@...hat.com,
        chuck.lever@...cle.com, lczerner@...hat.com, jack@...e.cz,
        brauner@...nel.org
Cc:     linux-api@...r.kernel.org, linux-btrfs@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-ceph@...r.kernel.org, linux-ext4@...r.kernel.org,
        linux-nfs@...r.kernel.org, linux-xfs@...r.kernel.org,
        David Wysochanski <dwysocha@...hat.com>
Subject: [PATCH v3 4/7] xfs: don't bump the i_version on an atime update in xfs_vn_update_time

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.

Cc: Dave Chinner <david@...morbit.com>
Cc: NeilBrown <neilb@...e.de>
Cc: Trond Myklebust <trondmy@...merspace.com>
Cc: David Wysochanski <dwysocha@...hat.com>
Signed-off-by: Jeff Layton <jlayton@...nel.org>
---
 fs/xfs/libxfs/xfs_log_format.h  |  2 +-
 fs/xfs/libxfs/xfs_trans_inode.c |  2 +-
 fs/xfs/xfs_iops.c               | 11 +++++++++--
 3 files changed, 11 insertions(+), 4 deletions(-)

Dave has NACK'ed this patch, but I'm sending it as a way to illustrate
the problem. I still think this approach should at least fix the worst
problems with atime updates being counted. We can look to carve out
other "spurious" i_version updates as we identify them.

If however there are offline analysis tools that require atime updates
to be counted, then we won't be able to do this. If that's the case, how
can we fix this such that serving xfs via NFSv4 doesn't suck?

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..94f14d96641b 100644
--- a/fs/xfs/xfs_iops.c
+++ b/fs/xfs/xfs_iops.c
@@ -1041,10 +1041,17 @@ xfs_vn_update_time(
 		return error;
 
 	xfs_ilock(ip, XFS_ILOCK_EXCL);
-	if (flags & S_CTIME)
+
+	if (!(flags & S_VERSION))
+		log_flags |= XFS_ILOG_NOIVER;
+	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