From mboxrd@z Thu Jan  1 00:00:00 1970
From: Johannes Weiner <hannes@cmpxchg.org>
Subject: Re: [RFC PATCH 4/7] memcg: sleep during flushing stats in safe
 contexts
Date: Thu, 23 Mar 2023 11:56:13 -0400
Message-ID: <20230323155613.GC739026@cmpxchg.org>
References: <20230323040037.2389095-1-yosryahmed@google.com>
 <20230323040037.2389095-5-yosryahmed@google.com>
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To: Yosry Ahmed <yosryahmed@google.com>
Cc: Tejun Heo <tj@kernel.org>, Josef Bacik <josef@toxicpanda.com>, Jens Axboe <axboe@kernel.dk>, Zefan Li <lizefan.x@bytedance.com>, Michal Hocko <mhocko@kernel.org>, Roman Gushchin <roman.gushchin@linux.dev>, Shakeel Butt <shakeelb@google.com>, Muchun Song <muchun.song@linux.dev>, Andrew Morton <akpm@linux-foundation.org>, Vasily Averin <vasily.averin@linux.dev>, cgroups@vger.kernel.org, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, bpf@vger.kernel.org

On Thu, Mar 23, 2023 at 04:00:34AM +0000, Yosry Ahmed wrote:
> @@ -644,26 +644,26 @@ static void __mem_cgroup_flush_stats(void)
>  		return;
>  
>  	flush_next_time = jiffies_64 + 2*FLUSH_TIME;
> -	cgroup_rstat_flush(root_mem_cgroup->css.cgroup, false);
> +	cgroup_rstat_flush(root_mem_cgroup->css.cgroup, may_sleep);

How is it safe to call this with may_sleep=true when it's holding the
stats_flush_lock?

>  	atomic_set(&stats_flush_threshold, 0);
>  	spin_unlock(&stats_flush_lock);
>  }