linux-kernel - Re: [RFC PATCH 0/2] mm: multi-gen LRU: working set extensions

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Message-ID: <20230111141716.GA14685@blackbody.suse.cz>
Date:   Wed, 11 Jan 2023 15:17:17 +0100
From:   Michal Koutný <mkoutny@...e.com>
To:     Yuanchu Xie <yuanchu@...gle.com>
Cc:     Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Yu Zhao <yuzhao@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Shakeel Butt <shakeelb@...gle.com>,
        Muchun Song <songmuchun@...edance.com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        cgroups@...r.kernel.org
Subject: Re: [RFC PATCH 0/2] mm: multi-gen LRU: working set extensions

On Wed, Dec 14, 2022 at 02:51:21PM -0800, Yuanchu Xie <yuanchu@...gle.com> wrote:
> that's frequently used. The only missing pieces between MGLRU
> generations and working set estimation are a consistent aging cadence
> and an interface; we introduce the two additions.
> 
> Periodic aging
> ======
> MGLRU Aging is currently driven by reclaim, so the amount of time
> between generations is non-deterministic. With memcgs being aged
> regularly, MGLRU generations become time-based working set information.

Is this periodic aging specific to memcgs? IOW, periodic aging isn't
needed without memcgs (~with root only)
(Perhaps similar question to Aneeh's.)

> Use case: proactive reclaimer
> ======
> The proactive reclaimer sets the aging interval, and periodically reads
> the page idle age stats, forming a working set estimation, which it then
> calculates an amount to write to memory.reclaim.
> 
> With the page idle age stats, a proactive reclaimer could calculate a
> precise amount of memory to reclaim without continuously probing and
> inducing reclaim.

Could the aging be also made per-memcg? (Similar to memory.reclaim,
possibly without the new kthread (if global reclaim's aging is enough).)

Thanks,
Michal


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