Re: [PATCH v15 17/22] xfs: Skip flip flags for delayed attrs

[Allison Henderson <allison.henderson@xxxxxxxxxx>]

On 2/25/21 10:02 PM, Darrick J. Wong wrote:
> On Thu, Feb 18, 2021 at 09:53:43AM -0700, 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
> >
> > Signed-off-by: Allison Henderson <allison.henderson@xxxxxxxxxx>
>
> I wonder, have you done much performance analysis of the old vs. new
> xattr code paths?  Does skipping the extra step + roll make attr
> operations faster?
I dont have any analysis right now, but maybe I could put some together. 
 I'm sure there's some impact, but not sure how much.  If it does, I 
suspect it will become of more interest when we bring in pptrs since the 
code path with be in heavier use then.

> This looks pretty straightforward though:
> Reviewed-by: Darrick J. Wong <djwong@xxxxxxxxxx>
Thank you!

Allison

> --D
>
> > ---
> >   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 e4c1b4b..666cc69 100644
> > --- a/fs/xfs/libxfs/xfs_attr.c
> > +++ b/fs/xfs/libxfs/xfs_attr.c
> > @@ -337,6 +337,7 @@ xfs_attr_set_iter(
> >   	struct xfs_da_state		*state = NULL;
> >   	int				forkoff, error = 0;
> >   	int				retval = 0;
> > +	struct xfs_mount		*mp = args->dp->i_mount;
> >   
> >   	/* State machine switch */
> >   	switch (dac->dela_state) {
> > @@ -470,16 +471,21 @@ xfs_attr_set_iter(
> >   		 * "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
> > @@ -588,17 +594,21 @@ 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
> > @@ -1277,7 +1287,6 @@ int xfs_attr_node_addname_work(
> >   	 * 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 3780141..ec707bd 100644
> > --- a/fs/xfs/libxfs/xfs_attr_leaf.c
> > +++ b/fs/xfs/libxfs/xfs_attr_leaf.c
> > @@ -1486,7 +1486,8 @@ 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