linux-kernel - Re: [PATCH 7/8] mm/vmscan: Increase the timeout if page reclaim is not making progress

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Date:   Fri, 22 Oct 2021 12:07:43 +1100
From:   "NeilBrown" <neilb@...e.de>
To:     "Mel Gorman" <mgorman@...hsingularity.net>
Cc:     "Andrew Morton" <akpm@...ux-foundation.org>,
        "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>,
        "Vlastimil Babka" <vbabka@...e.cz>,
        "Johannes Weiner" <hannes@...xchg.org>,
        "Jonathan Corbet" <corbet@....net>,
        "Linux-MM" <linux-mm@...ck.org>,
        "Linux-fsdevel" <linux-fsdevel@...r.kernel.org>,
        "LKML" <linux-kernel@...r.kernel.org>,
        "Mel Gorman" <mgorman@...hsingularity.net>
Subject: Re: [PATCH 7/8] mm/vmscan: Increase the timeout if page reclaim is
 not making progress

On Tue, 19 Oct 2021, Mel Gorman wrote:
> Tracing of the stutterp workload showed the following delays
> 
>       1 usect_delayed=124000 reason=VMSCAN_THROTTLE_NOPROGRESS
>       1 usect_delayed=128000 reason=VMSCAN_THROTTLE_NOPROGRESS
>       1 usect_delayed=176000 reason=VMSCAN_THROTTLE_NOPROGRESS
>       1 usect_delayed=536000 reason=VMSCAN_THROTTLE_NOPROGRESS
>       1 usect_delayed=544000 reason=VMSCAN_THROTTLE_NOPROGRESS
>       1 usect_delayed=556000 reason=VMSCAN_THROTTLE_NOPROGRESS
>       1 usect_delayed=624000 reason=VMSCAN_THROTTLE_NOPROGRESS
>       1 usect_delayed=716000 reason=VMSCAN_THROTTLE_NOPROGRESS
>       1 usect_delayed=772000 reason=VMSCAN_THROTTLE_NOPROGRESS
>       2 usect_delayed=512000 reason=VMSCAN_THROTTLE_NOPROGRESS
>      16 usect_delayed=120000 reason=VMSCAN_THROTTLE_NOPROGRESS
>      53 usect_delayed=116000 reason=VMSCAN_THROTTLE_NOPROGRESS
>     116 usect_delayed=112000 reason=VMSCAN_THROTTLE_NOPROGRESS
>    5907 usect_delayed=108000 reason=VMSCAN_THROTTLE_NOPROGRESS
>   71741 usect_delayed=104000 reason=VMSCAN_THROTTLE_NOPROGRESS
> 
> All the throttling hit the full timeout and then there was wakeup delays
> meaning that the wakeups are premature as no other reclaimer such as
> kswapd has made progress. This patch increases the maximum timeout.

Would love to see the comparable tracing results for after the patch.

Thanks,
NeilBrown


> 
> Signed-off-by: Mel Gorman <mgorman@...hsingularity.net>
> Acked-by: Vlastimil Babka <vbabka@...e.cz>
> ---
>  mm/vmscan.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 1f5c467dc83c..ec2006680242 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -1033,6 +1033,8 @@ void reclaim_throttle(pg_data_t *pgdat, enum vmscan_throttle_state reason)
>  	 */
>  	switch(reason) {
>  	case VMSCAN_THROTTLE_NOPROGRESS:
> +		timeout = HZ/2;
> +		break;
>  	case VMSCAN_THROTTLE_WRITEBACK:
>  		timeout = HZ/10;
>  
> -- 
> 2.31.1
> 
>