diff mbox series

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

Message ID 20230929102726.2985188-12-john.g.garry@oracle.com
State New
Headers
Series block atomic writes |

Commit Message

John Garry Sept. 29, 2023, 10:27 a.m. UTC 
  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(+)

Comments

Dave Chinner Oct. 3, 2023, 1:16 a.m. UTC | #1 
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....

-Dave.
Darrick J. Wong Oct. 3, 2023, 3 a.m. UTC | #2 
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
Dave Chinner Oct. 3, 2023, 4:34 a.m. UTC | #3 
On Mon, Oct 02, 2023 at 08:00:10PM -0700, Darrick J. Wong wrote:
> 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;

See the email I just wrote about not needing per-inode on-disk state
or even extent size hints for doing allocation for atomic IO. Atomic
write unit alignment is a device parameter (similar to stripe unit)
that applies to context specific allocation requests - it's not an
inode property as such....

Cheers,

Dave.
John Garry Oct. 3, 2023, 10:22 a.m. UTC | #4 
On 03/10/2023 04:00, Darrick J. Wong wrote:
>> 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))

My idea was that if we add another feature which requires 
args->alignment > 1 be honoured, then we would need to change this code 
to cover both features, so better just check args->alignment > 1.

> 		return -ENOSPC;
Thanks,
John
diff mbox series

Patch

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;
+
 	if (args->minlen > ap->minlen) {
 		args->minlen = ap->minlen;
 		error = xfs_alloc_vextent_start_ag(args, ap->blkno);