Re: [PATCH 11/21] fs: xfs: Don't use low-space allocator for alignment > 1

Darrick J. Wong
2023-10-03T03:00:14Z

On Tue, Oct 03, 2023 at 12:16:26PM +1100, Dave Chinner wrote:
> On Fri, Sep 29, 2023 at 10:27:16AM +0000, John Garry wrote:
> > The low-space allocator doesn't honour the alignment requirement, so don't
> > attempt to even use it (when we have an alignment requirement).
> >
> > Signed-off-by: John Garry <john.g.garry@oracle.com>
> > ---
> > fs/xfs/libxfs/xfs_bmap.c | 4 ++++
> > 1 file changed, 4 insertions(+)
> >
> > diff --git a/fs/xfs/libxfs/xfs_bmap.c b/fs/xfs/libxfs/xfs_bmap.c
> > index 30c931b38853..328134c22104 100644
> > --- a/fs/xfs/libxfs/xfs_bmap.c
> > +++ b/fs/xfs/libxfs/xfs_bmap.c
> > @@ -3569,6 +3569,10 @@ xfs_bmap_btalloc_low_space(
> > {
> > int error;
> >
> > + /* The allocator doesn't honour args->alignment */
> > + if (args->alignment > 1)
> > + return 0;
> > +
>
> How does this happen?
>
> The earlier failing aligned allocations will clear alignment before
> we get here....

I was thinking the predicate should be xfs_inode_force_align(ip) to save
me/us from thinking about all the other weird ways args->alignment could
end up 1.

/* forced-alignment means we don't use low mode */
if (xfs_inode_force_align(ip))
return -ENOSPC;

--D

> -Dave.
> --
> Dave Chinner
> david@fromorbit.com