2023-09-29 16:55:20

by John Garry

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

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 <[email protected]>
---
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;
+
if (args->minlen > ap->minlen) {
args->minlen = ap->minlen;
error = xfs_alloc_vextent_start_ag(args, ap->blkno);
--
2.31.1

2023-10-03 01:16:40

by Dave Chinner

Subject: Re: [PATCH 11/21] fs: xfs: Don't use low-space allocator for alignment > 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 <[email protected]>
> ---
> 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.
--
Dave Chinner
[email protected]

2023-10-03 03:00:51

by Darrick J. Wong

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

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 <[email protected]>
> > ---
> > 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
> [email protected]

2023-10-03 04:34:38

by Dave Chinner

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

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 <[email protected]>
> > > ---
> > > 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.
--
Dave Chinner
[email protected]

2023-10-03 10:24:14

by John Garry

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

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