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

[Allison Henderson <allison.henderson@oracle.com>]

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++;
> 
>