linux-kernel - Re: [PATCH -next v3 2/2] memcg: remove mem_cgroup

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <o3hmzratjkcxms3ylnjiuashclllf7mvz6ttkfrz4lybdiwhhp@yeo5my374trx>
Date: Mon, 15 Dec 2025 17:28:20 +0100
From: Michal Koutný <mkoutny@...e.com>
To: Chen Ridong <chenridong@...weicloud.com>
Cc: hannes@...xchg.org, mhocko@...nel.org, roman.gushchin@...ux.dev, 
	shakeel.butt@...ux.dev, muchun.song@...ux.dev, akpm@...ux-foundation.org, 
	axelrasmussen@...gle.com, yuanchu@...gle.com, weixugc@...gle.com, david@...nel.org, 
	zhengqi.arch@...edance.com, lorenzo.stoakes@...cle.com, cgroups@...r.kernel.org, 
	linux-mm@...ck.org, linux-kernel@...r.kernel.org, lujialin4@...wei.com
Subject: Re: [PATCH -next v3 2/2] memcg: remove mem_cgroup_size()

Hi Ridong.

On Thu, Dec 11, 2025 at 01:30:19AM +0000, Chen Ridong <chenridong@...weicloud.com> wrote:
> From: Chen Ridong <chenridong@...wei.com>
> 
> The mem_cgroup_size helper is used only in apply_proportional_protection
> to read the current memory usage. Its semantics are unclear and
> inconsistent with other sites, which directly call page_counter_read for
> the same purpose.
> 
> Remove this helper and get its usage via mem_cgroup_protection for
> clarity. Additionally, rename the local variable 'cgroup_size' to 'usage'
> to better reflect its meaning.
> 
> No functional changes intended.
> 
> Signed-off-by: Chen Ridong <chenridong@...wei.com>

Why does mem_cgroup_calculate_protection "calculate" usage for its
callers? Couldn't you just the change source in
apply_proportional_protection()?

Thanks,
Michal

> @@ -2485,7 +2485,6 @@ static unsigned long apply_proportional_protection(struct mem_cgroup *memcg,
>  		 * again by how much of the total memory used is under
>  		 * hard protection.
>  		 */
> -		unsigned long cgroup_size = mem_cgroup_size(memcg);
+		unsigned long cgroup_size = page_counter_read(memcg);

>  		unsigned long protection;
>  
>  		/* memory.low scaling, make sure we retry before OOM */
> @@ -2497,9 +2496,9 @@ static unsigned long apply_proportional_protection(struct mem_cgroup *memcg,
>  		}
>  
>  		/* Avoid TOCTOU with earlier protection check */
> -		cgroup_size = max(cgroup_size, protection);
> +		usage = max(usage, protection);
>  
> -		scan -= scan * protection / (cgroup_size + 1);
> +		scan -= scan * protection / (usage + 1);
>  
>  		/*
>  		 * Minimally target SWAP_CLUSTER_MAX pages to keep

Download attachment "signature.asc" of type "application/pgp-signature" (266 bytes)