linux-kernel - Re: [PATCH 2/2] memcg: periodically flush the memcg stats

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Message-ID: <YLriZxiWo+2hMI7g@slm.duckdns.org>
Date:   Fri, 4 Jun 2021 22:33:11 -0400
From:   Tejun Heo <tj@...nel.org>
To:     Hillf Danton <hdanton@...a.com>
Cc:     Shakeel Butt <shakeelb@...gle.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Muchun Song <songmuchun@...edance.com>,
        Michal Hocko <mhocko@...nel.org>, Roman Gushchin <guro@...com>,
        Michal Koutný <mkoutny@...e.com>,
        Huang Ying <ying.huang@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        cgroups@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] memcg: periodically flush the memcg stats

On Sat, Jun 05, 2021 at 09:54:21AM +0800, Hillf Danton wrote:
> The cond_resched() in cgroup_rstat_flush_locked() matches its appearence in
> your post [1]. So does unbound IMHO.

Ah yeah, this either needs CPU_INTENSIVE or UNBOUND, prolly the latter is
better.

> And the short stuff [2] looks to me like it is incorrect to queue a work
> acquiring mutex lock on to the system_wq. IOW the unbound wq is the right
> thing for any work that might sleep.

This part doesn't make sense. Blocking from per-cpu workqueue is completely
fine. What's not fine is consuming a lot of CPU cycles.

Thanks.

-- 
tejun