Re: [PATCH 1/1] mm: vmscan: Reduce throttling due to a failure to make progress

Vlastimil Babka
2021-11-26T10:16:37Z

On 11/25/21 16:18, Mel Gorman wrote:
> Mike Galbraith, Alexey Avramov and Darrick Wong all reported similar
> problems due to reclaim throttling for excessive lengths of time.
> In Alexey's case, a memory hog that should go OOM quickly stalls for
> several minutes before stalling. In Mike and Darrick's cases, a small
> memcg environment stalled excessively even though the system had enough
> memory overall.
>
> Commit 69392a403f49 ("mm/vmscan: throttle reclaim when no progress is being
> made") introduced the problem although commit a19594ca4a8b ("mm/vmscan:
> increase the timeout if page reclaim is not making progress") made it
> worse. Systems at or near an OOM state that cannot be recovered must
> reach OOM quickly and memcg should kill tasks if a memcg is near OOM.
>
> To address this, only stall for the first zone in the zonelist, reduce
> the timeout to 1 tick for VMSCAN_THROTTLE_NOPROGRESS and only stall if
> the scan control nr_reclaimed is 0 and kswapd is still active. If kswapd
> has stopped reclaiming due to excessive failures, do not stall at all so
> that OOM triggers relatively quickly.
>
> Alexey's test case was the most straight forward
>
> for i in {1..3}; do tail /dev/zero; done
>
> On vanilla 5.16-rc1, this test stalled and was reset after 10 minutes.
> After the patch, the test gets killed after roughly 15 seconds which is
> the same length of time taken in 5.15.
>
> Link: https://lore.kernel.org/r/99e779783d6c7fce96448a3402061b9dc1b3b602.camel@gmx.de
> Link: https://lore.kernel.org/r/20211124011954.7cab9bb4@mail.inbox.lv
> Link: https://lore.kernel.org/r/20211022144651.19914-1-mgorman@techsingularity.net

Should probably include Reported-by: tags too?

> Fixes: 69392a403f49 ("mm/vmscan: throttle reclaim when no progress is being made")
> Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
> Tested-by: Darrick J. Wong <djwong@kernel.org>

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

> ---
> mm/vmscan.c | 21 ++++++++++++++++++---
> 1 file changed, 18 insertions(+), 3 deletions(-)
>
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index fb9584641ac7..176ddd28df21 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -1057,7 +1057,17 @@ void reclaim_throttle(pg_data_t *pgdat, enum vmscan_throttle_state reason)
>
> break;
> case VMSCAN_THROTTLE_NOPROGRESS:
> - timeout = HZ/2;
> + timeout = 1;
> +
> + /*
> + * If kswapd is disabled, reschedule if necessary but do not
> + * throttle as the system is likely near OOM.
> + */
> + if (pgdat->kswapd_failures >= MAX_RECLAIM_RETRIES) {
> + cond_resched();
> + return;
> + }
> +
> break;
> case VMSCAN_THROTTLE_ISOLATED:
> timeout = HZ/50;
> @@ -3395,7 +3405,7 @@ static void consider_reclaim_throttle(pg_data_t *pgdat, struct scan_control *sc)
> return;
>
> /* Throttle if making no progress at high prioities. */
> - if (sc->priority < DEF_PRIORITY - 2)
> + if (sc->priority < DEF_PRIORITY - 2 && !sc->nr_reclaimed)
> reclaim_throttle(pgdat, VMSCAN_THROTTLE_NOPROGRESS);
> }
>
> @@ -3415,6 +3425,7 @@ static void shrink_zones(struct zonelist *zonelist, struct scan_control *sc)
> unsigned long nr_soft_scanned;
> gfp_t orig_mask;
> pg_data_t *last_pgdat = NULL;
> + pg_data_t *first_pgdat = NULL;
>
> /*
> * If the number of buffer_heads in the machine exceeds the maximum
> @@ -3478,14 +3489,18 @@ static void shrink_zones(struct zonelist *zonelist, struct scan_control *sc)
> /* need some check for avoid more shrink_zone() */
> }
>
> + if (!first_pgdat)
> + first_pgdat = zone->zone_pgdat;
> +
> /* See comment about same check for global reclaim above */
> if (zone->zone_pgdat == last_pgdat)
> continue;
> last_pgdat = zone->zone_pgdat;
> shrink_node(zone->zone_pgdat, sc);
> - consider_reclaim_throttle(zone->zone_pgdat, sc);
> }
>
> + consider_reclaim_throttle(first_pgdat, sc);
> +
> /*
> * Restore to original mask to avoid the impact on the caller if we
> * promoted it to __GFP_HIGHMEM.
>