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

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Message-ID: <r5rbfskjjhkp5pjlwi7xqluc5lxq7bxo44gmxwhihn62ea75wp@iljnpiqo5dcr>
Date:   Tue, 5 Sep 2023 18:07:04 +0200
From:   Michal Koutný <mkoutny@...e.com>
To:     Yosry Ahmed <yosryahmed@...gle.com>
Cc:     Michal Hocko <mhocko@...e.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 Tue, Sep 05, 2023 at 08:54:46AM -0700, Yosry Ahmed <yosryahmed@...gle.com> wrote:
> How would that create a userspace visible behavior that a dependency
> can be formed on?

A userspace process reading out root memory.stat more frequently than
in-kernel periodic flusher.

> Users expecting reclaim to be faster right after reading root stats?

Yes, that is what I had in mind.

> I would guess that would be too flaky to cause a behavior that people
> can depend on tbh.

I agree it's a weird dependency. As I wrote, nothing that would be hard
to take away.


Michal

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