linux-kernel - Re: [PATCH v4 3/4] mm: memcg: let non-unified root stats flushes help unified flushes

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Message-ID: <hrpw2bjsrs3pzxympb7cz4nohyeztnxkmdtzbzlfdba6ugkken@dhcdbbbrv4fn>
Date:   Tue, 5 Sep 2023 16:10:10 +0200
From:   Michal Koutný <mkoutny@...e.com>
To:     Michal Hocko <mhocko@...e.com>
Cc:     Yosry Ahmed <yosryahmed@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Johannes Weiner <hannes@...xchg.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>,
        Waiman Long <longman@...hat.com>, linux-mm@...ck.org,
        cgroups@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 3/4] mm: memcg: let non-unified root stats flushes
 help unified flushes

On Mon, Sep 04, 2023 at 05:41:10PM +0200, Michal Hocko <mhocko@...e.com> wrote:
> So it also creates an undocumented but userspace visible behavior.
> Something that userspace might start depending on, right?

Yes but -
- depending on undocumented behavior is a mistake,
- breaking the dependency would manifest (in the case I imagine) as a
  performance regression (and if there are some users, the future can
  allow them configuring periodic kernel flush to compensate for that).

Or do you suggest these effects should be documented (that would require
deeper analysis of the actual effect)? 


Thanks,
Michal

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