linux-kernel - Re: [RFC PATCH 1/2] mm/swap, memcg: basic structure and logic for per cgroup swap priority control

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Message-ID: <rivwhhhkuqy7p4r6mmuhpheaj3c7vcw4w4kavp42avpz7es5vp@hbnvrmgzb5tr>
Date: Wed, 18 Jun 2025 11:11:32 +0200
From: Michal Koutný <mkoutny@...e.com>
To: YoungJun Park <youngjun.park@....com>
Cc: linux-mm@...ck.org, akpm@...ux-foundation.org, hannes@...xchg.org, 
	mhocko@...nel.org, roman.gushchin@...ux.dev, shakeel.butt@...ux.dev, 
	cgroups@...r.kernel.org, linux-kernel@...r.kernel.org, shikemeng@...weicloud.com, 
	kasong@...cent.com, nphamcs@...il.com, bhe@...hat.com, baohua@...nel.org, 
	chrisl@...nel.org, muchun.song@...ux.dev, iamjoonsoo.kim@....com, 
	taejoon.song@....com, gunho.lee@....com
Subject: Re: [RFC PATCH 1/2] mm/swap, memcg: basic structure and logic for
 per cgroup swap priority control

On Wed, Jun 18, 2025 at 09:32:13AM +0900, YoungJun Park <youngjun.park@....com> wrote:
> What issue is the question assuming the existence of competitors in two
> cgroups trying to address? Could you explain it a bit more specifically?

I'm after how this mechanism is supposed to honor hierarchical
structure. (I thought the numeric example was the most specific.)

> 
> To answer your question for now,
> Each cgroup just prefers devices according to their priority values.
> until swap device is exhausted.
> 
> cg1 prefer /dev/sda than /dev/sdb.
> cg2 prefer /dev/sdb than /dev/sda.
> cg3 prefer /dev/sdb than /dev/sda.
> cg4 prefer /dev/sda than /dev/sdb.

Hm, than means the settigs from cg1 (or cg2) don't apply to descendant
cg3 (or cg4) :-/

When referring to that document
(Documentation/admin-guide/cgroup-v2.rst) again, which of the "Resource
Distribution Models" do you find the most fitting for this scenario?

Thanks,
Michal

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