[merged mm-stable] memcg-do-not-flush-stats-in-irq-context.patch removed from -mm tree

[Andrew Morton <akpm@linux-foundation.org>]

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The quilt patch titled
     Subject: memcg: do not flush stats in irq context
has been removed from the -mm tree.  Its filename was
     memcg-do-not-flush-stats-in-irq-context.patch

This patch was dropped because it was merged into the mm-stable branch
of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

------------------------------------------------------
From: Yosry Ahmed <yosryahmed@google.com>
Subject: memcg: do not flush stats in irq context
Date: Thu, 30 Mar 2023 19:17:56 +0000

Currently, the only context in which we can invoke an rstat flush from irq
context is through mem_cgroup_usage() on the root memcg when called from
memcg_check_events().  An rstat flush is an expensive operation that
should not be done in irq context, so do not flush stats and use the stale
stats in this case.

Arguably, usage threshold events are not reliable on the root memcg anyway
since its usage is ill-defined.

Link: https://lkml.kernel.org/r/20230330191801.1967435-4-yosryahmed@google.com
Signed-off-by: Yosry Ahmed <yosryahmed@google.com>
Suggested-by: Johannes Weiner <hannes@cmpxchg.org>
Suggested-by: Shakeel Butt <shakeelb@google.com>
Acked-by: Shakeel Butt <shakeelb@google.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Josef Bacik <josef@toxicpanda.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Michal Koutný <mkoutny@suse.com>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Tejun Heo <tj@kernel.org>
Cc: Vasily Averin <vasily.averin@linux.dev>
Cc: Zefan Li <lizefan.x@bytedance.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/memcontrol.c |   16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

--- a/mm/memcontrol.c~memcg-do-not-flush-stats-in-irq-context
+++ a/mm/memcontrol.c
@@ -3670,7 +3670,21 @@ static unsigned long mem_cgroup_usage(st
 	unsigned long val;
 
 	if (mem_cgroup_is_root(memcg)) {
-		mem_cgroup_flush_stats();
+		/*
+		 * We can reach here from irq context through:
+		 * uncharge_batch()
+		 * |--memcg_check_events()
+		 *    |--mem_cgroup_threshold()
+		 *       |--__mem_cgroup_threshold()
+		 *          |--mem_cgroup_usage
+		 *
+		 * rstat flushing is an expensive operation that should not be
+		 * done from irq context; use stale stats in this case.
+		 * Arguably, usage threshold events are not reliable on the root
+		 * memcg anyway since its usage is ill-defined.
+		 */
+		if (in_task())
+			mem_cgroup_flush_stats();
 		val = memcg_page_state(memcg, NR_FILE_PAGES) +
 			memcg_page_state(memcg, NR_ANON_MAPPED);
 		if (swap)
_

Patches currently in -mm which might be from yosryahmed@google.com are

memcg-replace-stats_flush_lock-with-an-atomic.patch
memcg-sleep-during-flushing-stats-in-safe-contexts.patch
workingset-memcg-sleep-when-flushing-stats-in-workingset_refault.patch
vmscan-memcg-sleep-when-flushing-stats-during-reclaim.patch
memcg-do-not-modify-rstat-tree-for-zero-updates.patch
memcg-page_cgroup_ino-get-memcg-from-the-pages-folio.patch
mm-vmscan-ignore-non-lru-based-reclaim-in-memcg-reclaim.patch
mm-vmscan-move-set_task_reclaim_state-near-flush_reclaim_state.patch
mm-vmscan-refactor-updating-current-reclaim_state.patch