Re: [PATCH 3/4] xfs: improve busy extent sorting

[Brian Foster <bfoster@redhat.com>]

On Sun, Jan 29, 2017 at 07:43:40PM +0100, Christoph Hellwig wrote:
> Sort busy extents by the full block number instead of just the AGNO so
> that we can issue consecutive discard requests that the block layer could
> merge (although we'll need additional block layer fixes for fast devices).
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>  fs/xfs/xfs_extent_busy.c | 12 ++++++++----
>  1 file changed, 8 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/xfs/xfs_extent_busy.c b/fs/xfs/xfs_extent_busy.c
> index 8251359..d64dd4c 100644
> --- a/fs/xfs/xfs_extent_busy.c
> +++ b/fs/xfs/xfs_extent_busy.c
> @@ -629,9 +629,13 @@ xfs_extent_busy_flush(
>  int
>  xfs_extent_busy_ag_cmp(
>  	void			*priv,
> -	struct list_head	*a,
> -	struct list_head	*b)
> +	struct list_head	*l1,
> +	struct list_head	*l2)
>  {
> -	return container_of(a, struct xfs_extent_busy, list)->agno -
> -		container_of(b, struct xfs_extent_busy, list)->agno;
> +	struct xfs_extent_busy	*b1 =
> +		container_of(l1, struct xfs_extent_busy, list);
> +	struct xfs_extent_busy	*b2 =
> +		container_of(l2, struct xfs_extent_busy, list);
> +
> +	return b1->agno - b2->agno || b1->bno - b2->bno;

When will this ever return negative?

Brian

>  }
> -- 
> 2.1.4
> 
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