linux-kernel - Re: [mm-unstable v4 5/5] mm: memcg: restore subtree stats flushing

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Message-ID: <436e96d1-29eb-49ec-a463-2ed420757ce8@redhat.com>
Date:   Fri, 1 Dec 2023 21:56:47 -0500
From:   Waiman Long <longman@...hat.com>
To:     Bagas Sanjaya <bagasdotme@...il.com>,
        Yosry Ahmed <yosryahmed@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Shakeel Butt <shakeelb@...gle.com>,
        Muchun Song <muchun.song@...ux.dev>,
        Ivan Babrou <ivan@...udflare.com>, Tejun Heo <tj@...nel.org>,
        Michal Koutný <mkoutny@...e.com>,
        kernel-team@...udflare.com, Wei Xu <weixugc@...gle.com>,
        Greg Thelen <gthelen@...gle.com>,
        Domenico Cerasuolo <cerasuolodomenico@...il.com>,
        Attreyee M <tintinm2017@...il.com>,
        Linux Memory Management List <linux-mm@...ck.org>,
        Linux CGroups <cgroups@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [mm-unstable v4 5/5] mm: memcg: restore subtree stats flushing


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