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Date:   Fri, 1 Dec 2023 21:56:47 -0500
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Subject: Re: [mm-unstable v4 5/5] mm: memcg: restore subtree stats flushing
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To:     Bagas Sanjaya <bagasdotme@gmail.com>,
        Yosry Ahmed <yosryahmed@google.com>,
        Andrew Morton <akpm@linux-foundation.org>
Cc:     Johannes Weiner <hannes@cmpxchg.org>,
        Michal Hocko <mhocko@kernel.org>,
        Roman Gushchin <roman.gushchin@linux.dev>,
        Shakeel Butt <shakeelb@google.com>,
        Muchun Song <muchun.song@linux.dev>,
        Ivan Babrou <ivan@cloudflare.com>, Tejun Heo <tj@kernel.org>,
        =?UTF-8?Q?Michal_Koutn=C3=BD?= <mkoutny@suse.com>,
        kernel-team@cloudflare.com, Wei Xu <weixugc@google.com>,
        Greg Thelen <gthelen@google.com>,
        Domenico Cerasuolo <cerasuolodomenico@gmail.com>,
        Attreyee M <tintinm2017@gmail.com>,
        Linux Memory Management List <linux-mm@kvack.org>,
        Linux CGroups <cgroups@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
References: <20231129032154.3710765-1-yosryahmed@google.com>
 <20231129032154.3710765-6-yosryahmed@google.com> <ZWqPBHCXz4nBIQFN@archie.me>
From:   Waiman Long <longman@redhat.com>
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On 12/1/23 20:57, Bagas Sanjaya wrote:
>> -void mem_cgroup_flush_stats(void)
>> +/*
>> + * mem_cgroup_flush_stats - flush the stats of a memory cgroup subtree
>> + * @memcg: root of the subtree to flush
>> + *
>> + * Flushing is serialized by the underlying global rstat lock. There is also a
>> + * minimum amount of work to be done even if there are no stat updates to flush.
>> + * Hence, we only flush the stats if the updates delta exceeds a threshold. This
>> + * avoids unnecessary work and contention on the underlying lock.
>> + */
> What is global rstat lock?

It is the cgroup_rstat_lock in kernel/cgroup/rstat.c.

Cheers,
Longman