linux-kernel - Re: [RFC PATCH v5 2/2] mm: Fix OOM killer inaccuracy on large many-core systems

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Message-ID: <a6d9f99c-dbf7-4871-a7cd-cdd857bb1951@efficios.com>
Date: Thu, 3 Jul 2025 15:44:52 -0400
From: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: 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>,
 Johannes Weiner <hannes@...xchg.org>, Sweet Tea Dorminy
 <sweettea@...gle.com>, Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
 "Liam R . Howlett" <Liam.Howlett@...cle.com>,
 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>
Subject: Re: [RFC PATCH v5 2/2] mm: Fix OOM killer inaccuracy on large
 many-core systems

On 2025-07-03 13:38, Mathieu Desnoyers wrote:
[...]
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index e51dba8398f7..18ccb51dad88 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -2705,28 +2705,30 @@ static inline bool get_user_page_fast_only(unsigned long addr,
>    */
>   static inline unsigned long get_mm_counter(struct mm_struct *mm, int member)
>   {
> -	return percpu_counter_read_positive(&mm->rss_stat[member]);
> +	int v = percpu_counter_tree_approximate_sum(&mm->rss_stat[member]);
> +
> +	return v > 0 ? v : 0;
>   }

In a follow up version, I plan to introduce a new
percpu_counter_tree_approximate_sum_positive() to wrap this
 >= 0 logic.

Thanks,

Mathieu

-- 
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com