diff options
Diffstat (limited to '0004-mm-vmscan-fix-extreme-overreclaim-and-swap-floods.patch')
| -rw-r--r-- | 0004-mm-vmscan-fix-extreme-overreclaim-and-swap-floods.patch | 131 |
1 files changed, 0 insertions, 131 deletions
diff --git a/0004-mm-vmscan-fix-extreme-overreclaim-and-swap-floods.patch b/0004-mm-vmscan-fix-extreme-overreclaim-and-swap-floods.patch deleted file mode 100644 index 6109ad0eaa6e..000000000000 --- a/0004-mm-vmscan-fix-extreme-overreclaim-and-swap-floods.patch +++ /dev/null @@ -1,131 +0,0 @@ -From fa7daa6069c323ea75d85e0e1c33eecd148a4ea8 Mon Sep 17 00:00:00 2001 -From: Johannes Weiner <hannes@cmpxchg.org> -Date: Tue, 2 Aug 2022 12:28:11 -0400 -Subject: [PATCH 4/8] 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. - -Signed-off-by: Johannes Weiner <hannes@cmpxchg.org> ---- - mm/vmscan.c | 10 ++++------ - 1 file changed, 4 insertions(+), 6 deletions(-) - -diff --git a/mm/vmscan.c b/mm/vmscan.c -index f7d9a683e3a7..1cc0c6666787 100644 ---- a/mm/vmscan.c -+++ b/mm/vmscan.c -@@ -2897,8 +2897,8 @@ 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); - -@@ -2916,8 +2916,8 @@ 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] || -@@ -2937,7 +2937,7 @@ 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; - - /* -@@ -2988,8 +2988,6 @@ 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; --- -2.37.3 - |