Re: [PATCH] xfs: Correctly invert xfs_buftarg LRU isolation logic

[Darrick J. Wong]

On Tue, Mar 06, 2018 at 11:26:38AM +0100, Vratislav Bendel wrote:
> Due to an inverted logic mistake in xfs_buftarg_isolate()
> the xfs_buffers with zero b_lru_ref will take another trip
> around LRU, while isolating buffers with non-zero b_lru_ref.
> 
> Additionally those isolated buffers end up right back on the LRU
> once they are released, because b_lru_ref remains elevated.
> 
> Fix that circuitous route by leaving them on the LRU
> as originally intended.
> 
> Signed-off-by: Vratislav Bendel <vbendel@xxxxxxxxxx>
> Reviewed-by: Brian Foster <bfoster@xxxxxxxxxx>
> Reviewed-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>

Looks ok, tests ok...
Reviewed-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>

--D

> ---
>  fs/xfs/xfs_buf.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c
> index d1da2ee9e6db..ac669a10c62f 100644
> --- a/fs/xfs/xfs_buf.c
> +++ b/fs/xfs/xfs_buf.c
> @@ -1708,7 +1708,7 @@ xfs_buftarg_isolate(
>  	 * zero. If the value is already zero, we need to reclaim the
>  	 * buffer, otherwise it gets another trip through the LRU.
>  	 */
> -	if (!atomic_add_unless(&bp->b_lru_ref, -1, 0)) {
> +	if (atomic_add_unless(&bp->b_lru_ref, -1, 0)) {
>  		spin_unlock(&bp->b_lock);
>  		return LRU_ROTATE;
>  	}
> -- 
> 2.14.3
> 
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