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

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Message-ID: <ZRtrap9v9xJrf6nq@dread.disaster.area>
Date:   Tue, 3 Oct 2023 12:16:26 +1100
From:   Dave Chinner <david@...morbit.com>
To:     John Garry <john.g.garry@...cle.com>
Cc:     axboe@...nel.dk, kbusch@...nel.org, hch@....de, sagi@...mberg.me,
        jejb@...ux.ibm.com, martin.petersen@...cle.com, djwong@...nel.org,
        viro@...iv.linux.org.uk, brauner@...nel.org,
        chandan.babu@...cle.com, dchinner@...hat.com,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-nvme@...ts.infradead.org, linux-xfs@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, tytso@....edu, jbongio@...gle.com,
        linux-api@...r.kernel.org
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 <john.g.garry@...cle.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.
-- 
Dave Chinner
david@...morbit.com