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

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Message-ID: <aDmHMLpMBTPCdRBN@tiehlicka>
Date: Fri, 30 May 2025 12:23:44 +0200
From: Michal Hocko <mhocko@...e.com>
To: Aboorva Devarajan <aboorvad@...ux.ibm.com>
Cc: Baolin Wang <baolin.wang@...ux.alibaba.com>, 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, 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 23-05-25 15:44:37, Aboorva Devarajan wrote:
> While this change may introduce some lock contention, it only affects
> the task_mem function which is invoked only when reading
> /proc/[pid]/status. Since this is not on a performance critical path,
> it will be good to have this change in order to get accurate memory
> stats.

This particular function might not be performance critical but you are
exposing a lock contention to the userspace that could be abused and
cause contention controlled by unprivileged user. I do not think we want
that without any control. Or is the pcp lock not really affecting any
actual kernel code path?

So while precision is nice it should be weight against potential side
effects. 
-- 
Michal Hocko
SUSE Labs