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

Allison Henderson
2021-08-02T08:33:49Z

On 7/30/21 7:40 AM, Chandan Babu R wrote:
> On 27 Jul 2021 at 11:50, Allison Henderson wrote:
>> 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?
>>
>
> Apart from the issues pointed out by Darrick, the remaining changes seem to be
> fine.

Alrighty, thx for the reviews!
Allison

>
>> 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++;
>
>