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

[Darrick J. Wong]

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@xxxxxxxxxx>
> > ---
> >  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@xxxxxxxxxxxxx