From mboxrd@z Thu Jan 1 00:00:00 1970 From: Yosry Ahmed Subject: [PATCH v3 3/8] memcg: do not flush stats in irq context Date: Thu, 30 Mar 2023 19:17:56 +0000 Message-ID: <20230330191801.1967435-4-yosryahmed@google.com> References: <20230330191801.1967435-1-yosryahmed@google.com> Mime-Version: 1.0 Return-path: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; t=1680203889; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=aVus0GFA9nzxOZ5lNIH1Nx8kHcLEa/aLkX98gl9HKOI=; b=Rb2fsB8aWLuAh/6UfhLacuvSldBOfVahXww4db+vgAZH6d8hHK5iS/Pb3yBuHu8zXu 8OHs3K+JgNd5BWKL8HmUqSNmeBMWOUfM93BgScQIJGiFyUTuS/OhqqsgB8B/zESgECWW id0La031n/vRfUHiqMH5ptV4ZUHLtuC1awDopegwUjfP8gYPSzkD9GboR6Sv+BT5F0il 4cP0p/kpaTUv9ECKBi7X6nDyHboM9b8Z+lLZ6iyDmkLsMIt+cWstg1DQo4e/ZnrIN56I iRBi8QgWvfbGxJTMXxv2zZuY7CwzGwzqEOEYe4XvyV9MRzo4MibTgBPKLkzWKa272DY9 IgGw== In-Reply-To: <20230330191801.1967435-1-yosryahmed-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org> List-ID: Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Tejun Heo , Josef Bacik , Jens Axboe , Zefan Li , Johannes Weiner , Michal Hocko , Roman Gushchin , Shakeel Butt , Muchun Song , Andrew Morton , =?UTF-8?q?Michal=20Koutn=C3=BD?= Cc: Vasily Averin , cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-block-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org, bpf-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Yosry Ahmed , Michal Hocko 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. Suggested-by: Johannes Weiner Suggested-by: Shakeel Butt Signed-off-by: Yosry Ahmed Acked-by: Shakeel Butt Acked-by: Johannes Weiner Acked-by: Michal Hocko --- mm/memcontrol.c | 16 +++++++++++++++- 1 file changed, 15 insertions(+), 1 deletion(-) diff --git a/mm/memcontrol.c b/mm/memcontrol.c index c3b6aae78901..ff39f78f962e 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -3669,7 +3669,21 @@ static unsigned long mem_cgroup_usage(struct mem_cgroup *memcg, bool swap) 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) -- 2.40.0.348.gf938b09366-goog