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: <pcji4n5tjsgjwbp7r65gfevkr3wyghlbi2vi4mndafzs4w7zs4@2k4citaugdz2>
Date: Tue, 17 Jun 2025 14:23:07 +0200
From: Michal Koutný <mkoutny@...e.com>
To: 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

Hello.

On Thu, Jun 12, 2025 at 07:37:43PM +0900, youngjun.park@....com wrote:
> Example:
> cat memory.swap.priority
> Inactive
> /dev/sdb	unique:1	 prio:10
> /dev/sdc	unique:2	 prio:5
> 
> - Creation
> echo  "unique id of swapdev 1: priority, unique id of swapdev 2: priority ..."
> > memory.swap.priority
> 
> - Destruction
> Reset through the memory.swap.priority interface.
> Example: echo "" > memory.swap.priority
> 
> And also be destroyed when the mem_cgroup is removed.
> 
> 3. Priority Mechanism
> 
> - Follows the original concept of swap priority.
> (This includes automatic binding of swap devices to NUMA nodes.)

How is this supposed to work
cg1     /dev/sda	prio:10
        /dev/sdb	prio:5
` cg3     /dev/sda	  prio:5
   	  /dev/sdb	  prio:10
cg2     /dev/sda	prio:5
        /dev/sdb	prio:10
` cg4     /dev/sda	  prio:10
   	  /dev/sdb	  prio:5

when there are competitors from cg3 and cg4? Which device should be
preferred by each cgroup?

Interface note -- try to make it "Nested keyed" or "Flat keyed" as
described in Documentation/admin-guide/cgroup-v2.rst (like io.max or
io.weight), so that it is consistent with other cgroup v2 APIs.


HTH,
Michal

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