linux-kernel - Re: [PATCH v13 2/3] mm: Fix OOM killer inaccuracy on large many-core systems

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Message-ID: <aWZSqIrbJW9q824H@tiehlicka>
Date: Tue, 13 Jan 2026 15:11:52 +0100
From: Michal Hocko <mhocko@...e.com>
To: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>, linux-kernel@...r.kernel.org,
	"Paul E. McKenney" <paulmck@...nel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Dennis Zhou <dennis@...nel.org>, Tejun Heo <tj@...nel.org>,
	Christoph Lameter <cl@...ux.com>, Martin Liu <liumartin@...gle.com>,
	David Rientjes <rientjes@...gle.com>, christian.koenig@....com,
	Shakeel Butt <shakeel.butt@...ux.dev>,
	SeongJae Park <sj@...nel.org>, Johannes Weiner <hannes@...xchg.org>,
	Sweet Tea Dorminy <sweettea-kernel@...miny.me>,
	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
	"Liam R . Howlett" <liam.howlett@...cle.com>,
	Mike Rapoport <rppt@...nel.org>,
	Suren Baghdasaryan <surenb@...gle.com>,
	Vlastimil Babka <vbabka@...e.cz>,
	Christian Brauner <brauner@...nel.org>,
	Wei Yang <richard.weiyang@...il.com>,
	David Hildenbrand <david@...hat.com>,
	Miaohe Lin <linmiaohe@...wei.com>,
	Al Viro <viro@...iv.linux.org.uk>, linux-mm@...ck.org,
	linux-trace-kernel@...r.kernel.org, Yu Zhao <yuzhao@...gle.com>,
	Roman Gushchin <roman.gushchin@...ux.dev>,
	Mateusz Guzik <mjguzik@...il.com>,
	Matthew Wilcox <willy@...radead.org>,
	Baolin Wang <baolin.wang@...ux.alibaba.com>,
	Aboorva Devarajan <aboorvad@...ux.ibm.com>
Subject: Re: [PATCH v13 2/3] mm: Fix OOM killer inaccuracy on large many-core
 systems

On Tue 13-01-26 08:51:45, Mathieu Desnoyers wrote:
> On 2026-01-13 04:24, Michal Hocko wrote:
[...]
> - Introduce new proc files, e.g.
> 
>   /proc/<pid>/rss/approximate
>   /proc/<pid>/rss/precise
> 
> Where the "approximate" file would export the following lines for each
> page type (MM_FILEPAGES, MM_ANONPAGES, MM_SWAPENTS, MM_SHMPAGES,
> allowing future additions):
> 
> <page type> <approximate> <precise_sum_min> <precise_sum_max>
> 
> And "precise" would export lines for each page type:
> 
> <page type> <precise_sum>
> 
> The key thing here is to have different files to query approximated
> vs precise values, so we don't have the overhead of the precise sum
> when all we need is an approximation.
> 
> This would expose all the bits and pieces needed to allow userspace to
> implement something similar to the 2-pass algorithm I'm proposing for
> the OOM killer, but tweaked for other use-cases.
> 
> This proposed ABI is purely hypothetical at this stage. Please let me
> know if you have something different in mind.

TBH, I am not convinced this is really needed. I would simply use the
new more-precise interface for /proc/<pid>/stat with numbers of
potential overhead payed by an increased precision. If we need to revert
to low precision then we can do that based on a specific report.

> When you mention "highlevel doc", which document do you have in mind ?
> Something related to lib/percpu_counter_tree.c or to the /proc ABI ?

Documentation/core-api/percpu_counter_tree.rst

-- 
Michal Hocko
SUSE Labs