[PATCH v22 10/16] RFC xfs: Skip flip flags for delayed attrs

Allison Henderson
2021-07-27T06:21:19Z

This is a clean up patch that skips the flip flag logic for delayed attr
renames. Since the log replay keeps the inode locked, we do not need to
worry about race windows with attr lookups. So we can skip over
flipping the flag and the extra transaction roll for it

RFC: In the last review, folks asked for some performance analysis, so I
did a few perf captures with and with out this patch. What I found was
that there wasnt very much difference at all between having the patch or
not having it. Of the time we do spend in the affected code, the
percentage is small. Most of the time we spend about %0.03 of the time
in this function, with or with out the patch. Occasionally we get a
0.02%, though not often. So I think this starts to challenge needing
this patch at all. This patch was requested some number of reviews ago,
be perhaps in light of the findings, it may no longer be of interest.

0.03% 0.00% fsstress [xfs] [k] xfs_attr_set_iter

Keep it or drop it?

Signed-off-by: Allison Henderson <allison.henderson@oracle.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
---
fs/xfs/libxfs/xfs_attr.c | 51 +++++++++++++++++++++++++------------------
fs/xfs/libxfs/xfs_attr_leaf.c | 3 ++-
2 files changed, 32 insertions(+), 22 deletions(-)

diff --git a/fs/xfs/libxfs/xfs_attr.c b/fs/xfs/libxfs/xfs_attr.c
index 11d8081..eee219c6 100644
--- a/fs/xfs/libxfs/xfs_attr.c
+++ b/fs/xfs/libxfs/xfs_attr.c
@@ -355,6 +355,7 @@ xfs_attr_set_iter(
struct xfs_inode *dp = args->dp;
struct xfs_buf *bp = NULL;
int forkoff, error = 0;
+ struct xfs_mount *mp = args->dp->i_mount;

/* State machine switch */
switch (dac->dela_state) {
@@ -476,16 +477,21 @@ xfs_attr_set_iter(
* In a separate transaction, set the incomplete flag on the
* "old" attr and clear the incomplete flag on the "new" attr.
*/
- error = xfs_attr3_leaf_flipflags(args);
- if (error)
- return error;
- /*
- * Commit the flag value change and start the next trans in
- * series.
- */
- dac->dela_state = XFS_DAS_FLIP_LFLAG;
- trace_xfs_attr_set_iter_return(dac->dela_state, args->dp);
- return -EAGAIN;
+ if (!xfs_hasdelattr(mp)) {
+ error = xfs_attr3_leaf_flipflags(args);
+ if (error)
+ return error;
+ /*
+ * Commit the flag value change and start the next trans
+ * in series.
+ */
+ dac->dela_state = XFS_DAS_FLIP_LFLAG;
+ trace_xfs_attr_set_iter_return(dac->dela_state,
+ args->dp);
+ return -EAGAIN;
+ }
+
+ /* fallthrough */
case XFS_DAS_FLIP_LFLAG:
/*
* Dismantle the "old" attribute/value pair by removing a
@@ -587,17 +593,21 @@ xfs_attr_set_iter(
* In a separate transaction, set the incomplete flag on the
* "old" attr and clear the incomplete flag on the "new" attr.
*/
- error = xfs_attr3_leaf_flipflags(args);
- if (error)
- goto out;
- /*
- * Commit the flag value change and start the next trans in
- * series
- */
- dac->dela_state = XFS_DAS_FLIP_NFLAG;
- trace_xfs_attr_set_iter_return(dac->dela_state, args->dp);
- return -EAGAIN;
+ if (!xfs_hasdelattr(mp)) {
+ error = xfs_attr3_leaf_flipflags(args);
+ if (error)
+ goto out;
+ /*
+ * Commit the flag value change and start the next trans
+ * in series
+ */
+ dac->dela_state = XFS_DAS_FLIP_NFLAG;
+ trace_xfs_attr_set_iter_return(dac->dela_state,
+ args->dp);
+ return -EAGAIN;
+ }

+ /* fallthrough */
case XFS_DAS_FLIP_NFLAG:
/*
* Dismantle the "old" attribute/value pair by removing a
@@ -1241,7 +1251,6 @@ xfs_attr_node_addname_clear_incomplete(
* Re-find the "old" attribute entry after any split ops. The INCOMPLETE
* flag means that we will find the "old" attr, not the "new" one.
*/
- args->attr_filter |= XFS_ATTR_INCOMPLETE;
state = xfs_da_state_alloc(args);
state->inleaf = 0;
error = xfs_da3_node_lookup_int(state, &retval);
diff --git a/fs/xfs/libxfs/xfs_attr_leaf.c b/fs/xfs/libxfs/xfs_attr_leaf.c
index b910bd2..a9116ee 100644
--- a/fs/xfs/libxfs/xfs_attr_leaf.c
+++ b/fs/xfs/libxfs/xfs_attr_leaf.c
@@ -1482,7 +1482,8 @@ xfs_attr3_leaf_add_work(
if (tmp)
entry->flags |= XFS_ATTR_LOCAL;
if (args->op_flags & XFS_DA_OP_RENAME) {
- entry->flags |= XFS_ATTR_INCOMPLETE;
+ if (!xfs_hasdelattr(mp))
+ entry->flags |= XFS_ATTR_INCOMPLETE;
if ((args->blkno2 == args->blkno) &&
(args->index2 <= args->index)) {
args->index2++;
--
2.7.4