diff options
Diffstat (limited to '0102-mm_vmscan_fix_extreme_overreclaim_and_swap_floods.patch')
-rw-r--r-- | 0102-mm_vmscan_fix_extreme_overreclaim_and_swap_floods.patch | 134 |
1 files changed, 134 insertions, 0 deletions
diff --git a/0102-mm_vmscan_fix_extreme_overreclaim_and_swap_floods.patch b/0102-mm_vmscan_fix_extreme_overreclaim_and_swap_floods.patch new file mode 100644 index 000000000000..7a771a2a0fc2 --- /dev/null +++ b/0102-mm_vmscan_fix_extreme_overreclaim_and_swap_floods.patch @@ -0,0 +1,134 @@ +From 2535fbde890f14c78b750139fcf87d1143850626 Mon Sep 17 00:00:00 2001 +From: Johannes Weiner <hannes@cmpxchg.org> +Date: Tue, 2 Aug 2022 12:28:11 -0400 +Subject: [PATCH] mm: vmscan: fix extreme overreclaim and swap floods + +During proactive reclaim, we sometimes observe severe overreclaim, with +several thousand times more pages reclaimed than requested. + +This trace was obtained from shrink_lruvec() during such an instance: + + prio:0 anon_cost:1141521 file_cost:7767 + nr_reclaimed:4387406 nr_to_reclaim:1047 (or_factor:4190) + nr=[7161123 345 578 1111] + +While he reclaimer requested 4M, vmscan reclaimed close to 16G, most of it +by swapping. These requests take over a minute, during which the write() +to memory.reclaim is unkillably stuck inside the kernel. + +Digging into the source, this is caused by the proportional reclaim +bailout logic. This code tries to resolve a fundamental conflict: to +reclaim roughly what was requested, while also aging all LRUs fairly and +in accordance to their size, swappiness, refault rates etc. The way it +attempts fairness is that once the reclaim goal has been reached, it stops +scanning the LRUs with the smaller remaining scan targets, and adjusts the +remainder of the bigger LRUs according to how much of the smaller LRUs was +scanned. It then finishes scanning that remainder regardless of the +reclaim goal. + +This works fine if priority levels are low and the LRU lists are +comparable in size. However, in this instance, the cgroup that is +targeted by proactive reclaim has almost no files left - they've already +been squeezed out by proactive reclaim earlier - and the remaining anon +pages are hot. Anon rotations cause the priority level to drop to 0, +which results in reclaim targeting all of anon (a lot) and all of file +(almost nothing). By the time reclaim decides to bail, it has scanned +most or all of the file target, and therefor must also scan most or all of +the enormous anon target. This target is thousands of times larger than +the reclaim goal, thus causing the overreclaim. + +The bailout code hasn't changed in years, why is this failing now? The +most likely explanations are two other recent changes in anon reclaim: + +1. Before the series starting with commit 5df741963d52 ("mm: fix LRU + balancing effect of new transparent huge pages"), the VM was + overall relatively reluctant to swap at all, even if swap was + configured. This means the LRU balancing code didn't come into play + as often as it does now, and mostly in high pressure situations + where pronounced swap activity wouldn't be as surprising. + +2. For historic reasons, shrink_lruvec() loops on the scan targets of + all LRU lists except the active anon one, meaning it would bail if + the only remaining pages to scan were active anon - even if there + were a lot of them. + + Before the series starting with commit ccc5dc67340c ("mm/vmscan: + make active/inactive ratio as 1:1 for anon lru"), most anon pages + would live on the active LRU; the inactive one would contain only a + handful of preselected reclaim candidates. After the series, anon + gets aged similarly to file, and the inactive list is the default + for new anon pages as well, making it often the much bigger list. + + As a result, the VM is now more likely to actually finish large + anon targets than before. + +Change the code such that only one SWAP_CLUSTER_MAX-sized nudge toward the +larger LRU lists is made before bailing out on a met reclaim goal. + +This fixes the extreme overreclaim problem. + +Fairness is more subtle and harder to evaluate. No obvious misbehavior +was observed on the test workload, in any case. Conceptually, fairness +should primarily be a cumulative effect from regular, lower priority +scans. Once the VM is in trouble and needs to escalate scan targets to +make forward progress, fairness needs to take a backseat. This is also +acknowledged by the myriad exceptions in get_scan_count(). This patch +makes fairness decrease gradually, as it keeps fairness work static over +increasing priority levels with growing scan targets. This should make +more sense - although we may have to re-visit the exact values. + +Link: https://lkml.kernel.org/r/20220802162811.39216-1-hannes@cmpxchg.org +Signed-off-by: Johannes Weiner <hannes@cmpxchg.org> +Reviewed-by: Rik van Riel <riel@surriel.com> +Acked-by: Mel Gorman <mgorman@techsingularity.net> +Cc: Hugh Dickins <hughd@google.com> +Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com> +Cc: <stable@vger.kernel.org> +Signed-off-by: Andrew Morton <akpm@linux-foundation.org> +--- + mm/vmscan.c | 10 ++++------ + 1 file changed, 4 insertions(+), 6 deletions(-) + +diff --git a/mm/vmscan.c b/mm/vmscan.c +index 382dbe97329f33..266eb8cfe93a67 100644 +--- a/mm/vmscan.c ++++ b/mm/vmscan.c +@@ -2955,8 +2955,8 @@ static void shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc) + enum lru_list lru; + unsigned long nr_reclaimed = 0; + unsigned long nr_to_reclaim = sc->nr_to_reclaim; ++ bool proportional_reclaim; + struct blk_plug plug; +- bool scan_adjusted; + + get_scan_count(lruvec, sc, nr); + +@@ -2974,8 +2974,8 @@ static void shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc) + * abort proportional reclaim if either the file or anon lru has already + * dropped to zero at the first pass. + */ +- scan_adjusted = (!cgroup_reclaim(sc) && !current_is_kswapd() && +- sc->priority == DEF_PRIORITY); ++ proportional_reclaim = (!cgroup_reclaim(sc) && !current_is_kswapd() && ++ sc->priority == DEF_PRIORITY); + + blk_start_plug(&plug); + while (nr[LRU_INACTIVE_ANON] || nr[LRU_ACTIVE_FILE] || +@@ -2995,7 +2995,7 @@ static void shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc) + + cond_resched(); + +- if (nr_reclaimed < nr_to_reclaim || scan_adjusted) ++ if (nr_reclaimed < nr_to_reclaim || proportional_reclaim) + continue; + + /* +@@ -3046,8 +3046,6 @@ static void shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc) + nr_scanned = targets[lru] - nr[lru]; + nr[lru] = targets[lru] * (100 - percentage) / 100; + nr[lru] -= min(nr[lru], nr_scanned); +- +- scan_adjusted = true; + } + blk_finish_plug(&plug); + sc->nr_reclaimed += nr_reclaimed; |