Re: [PATCH v24 05/11] RFC xfs: Skip flip flags for delayed attrs

[Allison Henderson <allison.henderson@xxxxxxxxxx>]

On 8/30/21 3:15 AM, Chandan Babu R wrote:
> On 25 Aug 2021 at 04:14, 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?
>
> Looks good to me.
>
> Reviewed-by: Chandan Babu R <chandanrlinux@xxxxxxxxx>
Ok, thank you!
Allison

> > Signed-off-by: Allison Henderson <allison.henderson@xxxxxxxxxx>
> > Reviewed-by: Darrick J. Wong <djwong@xxxxxxxxxx>
> > ---
> >   fs/xfs/libxfs/xfs_attr.c      | 54 +++++++++++++++++++++--------------
> >   fs/xfs/libxfs/xfs_attr_leaf.c |  3 +-
> >   2 files changed, 35 insertions(+), 22 deletions(-)
> >
> > diff --git a/fs/xfs/libxfs/xfs_attr.c b/fs/xfs/libxfs/xfs_attr.c
> > index dfff81024e46..fce67c717be2 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) {
> > @@ -477,16 +478,21 @@ 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_has_larp(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
> > @@ -589,17 +595,21 @@ 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_has_larp(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
> > @@ -1236,6 +1246,7 @@ xfs_attr_node_addname_clear_incomplete(
> >   {
> >   	struct xfs_da_args		*args = dac->da_args;
> >   	struct xfs_da_state		*state = NULL;
> > +	struct xfs_mount		*mp = args->dp->i_mount;
> >   	int				retval = 0;
> >   	int				error = 0;
> >   
> > @@ -1243,7 +1254,8 @@ 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;
> > +	if (!xfs_has_larp(mp))
> > +		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 e1d11e314228..a0a352bdea59 100644
> > --- a/fs/xfs/libxfs/xfs_attr_leaf.c
> > +++ b/fs/xfs/libxfs/xfs_attr_leaf.c
> > @@ -1487,7 +1487,8 @@ 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_has_larp(mp))
> > +			entry->flags |= XFS_ATTR_INCOMPLETE;
> >   		if ((args->blkno2 == args->blkno) &&
> >   		    (args->index2 <= args->index)) {
> >   			args->index2++;