Re: [PATCH 6/6] xfs: support lowmode allocations in xfs_bmap_exact_minlen_extent_alloc

["Darrick J. Wong" <djwong@kernel.org>]

On Tue, Aug 20, 2024 at 07:04:57PM +0200, Christoph Hellwig wrote:
> Currently the debug-only xfs_bmap_exact_minlen_extent_alloc allocation
> variant fails to drop into the lowmode last restor allocator, and

                                         last resort?

> thus can sometimes fail allocations for which the caller has a
> transaction block reservation.
> 
> Fix this by using xfs_bmap_btalloc_low_space to do the actual allocation.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>  fs/xfs/libxfs/xfs_bmap.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/xfs/libxfs/xfs_bmap.c b/fs/xfs/libxfs/xfs_bmap.c
> index b5eeaea164ee46..784dd5dda2a1a2 100644
> --- a/fs/xfs/libxfs/xfs_bmap.c
> +++ b/fs/xfs/libxfs/xfs_bmap.c
> @@ -3493,7 +3493,13 @@ xfs_bmap_exact_minlen_extent_alloc(
>  	 */
>  	ap->blkno = XFS_AGB_TO_FSB(ap->ip->i_mount, 0, 0);
>  
> -	return xfs_alloc_vextent_first_ag(args, ap->blkno);
> +	/*
> +	 * Use the low space allocator as it first does a "normal" AG iteration
> +	 * and then drops the reservation to minlen, which might be required to
> +	 * find an allocation for the transaction reservation when the file
> +	 * system is very full.

Isn't it already doing a minlen allocation?  Oh, that probably refers to
shrinking args->total, doesn't it.

If the answer to that is 'yes' then
Reviewed-by: Darrick J. Wong <djwong@kernel.org>

--D

> +	 */
> +	return xfs_bmap_btalloc_low_space(ap, args);
>  }
>  #else
>  
> -- 
> 2.43.0
> 
>