linux-kernel - Re: [RFC PATCH] mm: fix the inaccurate memory statistics issue for users

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: <20250523172029.57745-1-sj@kernel.org>
Date: Fri, 23 May 2025 10:20:29 -0700
From: SeongJae Park <sj@...nel.org>
To: Baolin Wang <baolin.wang@...ux.alibaba.com>
Cc: SeongJae Park <sj@...nel.org>,
	akpm@...ux-foundation.org,
	david@...hat.com,
	shakeelb@...gle.com,
	lorenzo.stoakes@...cle.com,
	Liam.Howlett@...cle.com,
	vbabka@...e.cz,
	rppt@...nel.org,
	surenb@...gle.com,
	mhocko@...e.com,
	linux-mm@...ck.org,
	linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH] mm: fix the inaccurate memory statistics issue for users

On Fri, 23 May 2025 11:16:13 +0800 Baolin Wang <baolin.wang@...ux.alibaba.com> wrote:

> On some large machines with a high number of CPUs running a 64K kernel,

What does 64K kernel means?

> we found that the 'RES' field is always 0 displayed by the top command
> for some processes, which will cause a lot of confusion for users.
> 
>     PID USER      PR  NI    VIRT    RES    SHR S  %CPU  %MEM     TIME+ COMMAND
>  875525 root      20   0   12480      0      0 R   0.3   0.0   0:00.08 top
>       1 root      20   0  172800      0      0 S   0.0   0.0   0:04.52 systemd
> 
> The main reason is that the batch size of the percpu counter is quite large
> on these machines, caching a significant percpu value, since converting mm's
> rss stats into percpu_counter by commit f1a7941243c1 ("mm: convert mm's rss
> stats into percpu_counter"). Intuitively, the batch number should be optimized,
> but on some paths, performance may take precedence over statistical accuracy.
> Therefore, introducing a new interface to add the percpu statistical count
> and display it to users, which can remove the confusion. In addition, this
> change is not expected to be on a performance-critical path, so the modification
> should be acceptable.
> 
> Signed-off-by: Baolin Wang <baolin.wang@...ux.alibaba.com>

Acked-by: SeongJae Park <sj@...nel.org>


Thanks,
SJ

[...]