Re: [PATCH] xfs: speed up parent pointer operations

["Darrick J. Wong" <djwong@kernel.org>]

On Tue, Jan 06, 2026 at 12:16:59AM -0800, Christoph Hellwig wrote:
> On Fri, Dec 19, 2025 at 07:41:54AM -0800, Darrick J. Wong wrote:
> > Now parent pointers only increase the system time by 8% for creation and
> > 19% for deletion.  Wall time increases by 5% and 9%.
> 
> Nice!
> 
> > @@ -202,6 +203,16 @@ xfs_parent_addname(
> >  	xfs_inode_to_parent_rec(&ppargs->rec, dp);
> >  	xfs_parent_da_args_init(&ppargs->args, tp, &ppargs->rec, child,
> >  			child->i_ino, parent_name);
> > +
> > +	if (xfs_inode_has_attr_fork(child) &&
> > +	    xfs_attr_is_shortform(child)) {
> > +		ppargs->args.op_flags |= XFS_DA_OP_ADDNAME;
> > +
> > +		error = xfs_attr_try_sf_addname(&ppargs->args);
> > +		if (error != -ENOSPC)
> > +			return error;
> > +	}
> > +
> >  	xfs_attr_defer_add(&ppargs->args, XFS_ATTR_DEFER_SET);
> 
> We should be able to do this for all attrs, not just parent pointers,
> right?

In principle, yes.  For a generic xattr version you'd probably want to
check for a large valuelen on the set side so that we don't waste time
scanning the sf structure when we're just going to end up in remote
value territory anyway.

>         It might be nice to just do this for set and remove in
> xfs_attr_defer_add and have it handle all attr operations.

Yeah.  I think it's more logical to put these new shortcut calls in
xfs_attr_set because we're be deciding /not/ to invoke the deferred
xattr mechanism.

> > +	if (xfs_attr_is_shortform(child)) {
> > +		ppargs->args.op_flags |= XFS_DA_OP_ADDNAME | XFS_DA_OP_REPLACE;
> > +
> > +		error = xfs_attr_sf_removename(&ppargs->args);
> > +		if (error)
> > +			return error;
> > +
> > +		xfs_parent_da_args_init(&ppargs->args, tp, &ppargs->new_rec,
> > +				child, child->i_ino, new_name);
> > +		ppargs->args.op_flags |= XFS_DA_OP_ADDNAME;
> > +
> > +		error = xfs_attr_try_sf_addname(&ppargs->args);
> > +		if (error == -ENOSPC) {
> > +			xfs_attr_defer_add(&ppargs->args, XFS_ATTR_DEFER_SET);
> > +			return 0;
> > +		}
> 
> And for replace we should be able to optimize this even further
> by adding a new xfs_attr_sf_replacename that just checks if the new
> version would fit, and then memmove everything behind the changed
> attr and update it in place.  This should improve the operation a lot
> more.

That would depends on the frequency of non-parent pointer xattr
operations where the value doesn't change size modulo the rounding
factor.

I also wonder how much benefit anyone really gets from doing this to
regular xattrs, but once I'm more convinced that it's solid w.r.t.
parent pointers it's trivial to move it to xattrs too.

--D