linux-kernel - Re: [PATCH 8/8] mm/vmscan: Delay waking of tasks throttled on NOPROGRESS

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Date:   Thu, 14 Oct 2021 17:41:17 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Mel Gorman <mgorman@...hsingularity.net>,
        Linux-MM <linux-mm@...ck.org>
Cc:     NeilBrown <neilb@...e.de>, Theodore Ts'o <tytso@....edu>,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        "Darrick J . Wong" <djwong@...nel.org>,
        Matthew Wilcox <willy@...radead.org>,
        Michal Hocko <mhocko@...e.com>,
        Dave Chinner <david@...morbit.com>,
        Rik van Riel <riel@...riel.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Jonathan Corbet <corbet@....net>,
        Linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 8/8] mm/vmscan: Delay waking of tasks throttled on
 NOPROGRESS

On 10/8/21 15:53, Mel Gorman wrote:
> Tracing indicates that tasks throttled on NOPROGRESS are woken
> prematurely resulting in occasional massive spikes in direct
> reclaim activity. This patch wakes tasks throttled on NOPROGRESS
> if reclaim efficiency is at least 12%.
> 
> Signed-off-by: Mel Gorman <mgorman@...hsingularity.net>

Acked-by: Vlastimil Babka <vbabka@...e.cz>

> ---
>  mm/vmscan.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 7b54fec4072c..80a9a26f701f 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -3338,8 +3338,11 @@ static inline bool compaction_ready(struct zone *zone, struct scan_control *sc)
>  
>  static void consider_reclaim_throttle(pg_data_t *pgdat, struct scan_control *sc)
>  {
> -	/* If reclaim is making progress, wake any throttled tasks. */
> -	if (sc->nr_reclaimed) {
> +	/*
> +	 * If reclaim is making progress greater than 12% efficiency then
> +	 * wake all the NOPROGRESS throttled tasks.
> +	 */
> +	if (sc->nr_reclaimed > (sc->nr_scanned >> 3)) {
>  		wait_queue_head_t *wqh;
>  
>  		wqh = &pgdat->reclaim_wait[VMSCAN_THROTTLE_NOPROGRESS];
>