Re: [PATCH 37/39] xfs: avoid cil push lock if possible

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

On Wed, May 19, 2021 at 10:13:15PM +1000, Dave Chinner wrote:
> From: Dave Chinner <dchinner@redhat.com>
> 
> Because now it hurts when the CIL fills up.
> 
>   - 37.20% __xfs_trans_commit
>       - 35.84% xfs_log_commit_cil
>          - 19.34% _raw_spin_lock
>             - do_raw_spin_lock
>                  19.01% __pv_queued_spin_lock_slowpath
>          - 4.20% xfs_log_ticket_ungrant
>               0.90% xfs_log_space_wake
> 
> 
> Signed-off-by: Dave Chinner <dchinner@redhat.com>

Looks good,
Reviewed-by: Darrick J. Wong <djwong@kernel.org>

--D

> ---
>  fs/xfs/xfs_log_cil.c | 14 +++++++++++---
>  1 file changed, 11 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/xfs/xfs_log_cil.c b/fs/xfs/xfs_log_cil.c
> index cfd3128399f6..672cbaa4606c 100644
> --- a/fs/xfs/xfs_log_cil.c
> +++ b/fs/xfs/xfs_log_cil.c
> @@ -1125,10 +1125,18 @@ xlog_cil_push_background(
>  	ASSERT(!test_bit(XLOG_CIL_EMPTY, &cil->xc_flags));
>  
>  	/*
> -	 * Don't do a background push if we haven't used up all the
> -	 * space available yet.
> +	 * We are done if:
> +	 * - we haven't used up all the space available yet; or
> +	 * - we've already queued up a push; and
> +	 * - we're not over the hard limit; and
> +	 * - nothing has been over the hard limit.
> +	 *
> +	 * If so, we don't need to take the push lock as there's nothing to do.
>  	 */
> -	if (space_used < XLOG_CIL_SPACE_LIMIT(log)) {
> +	if (space_used < XLOG_CIL_SPACE_LIMIT(log) ||
> +	    (cil->xc_push_seq == cil->xc_current_sequence &&
> +	     space_used < XLOG_CIL_BLOCKING_SPACE_LIMIT(log) &&
> +	     !waitqueue_active(&cil->xc_push_wait))) {
>  		up_read(&cil->xc_ctx_lock);
>  		return;
>  	}
> -- 
> 2.31.1
>