linux-kernel - Re: [PATCH v9 1/2] lib: Introduce hierarchical per-cpu counters

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Message-Id: <20251122111336.56b060c86ff6ba41fe76bfd4@linux-foundation.org>
Date: Sat, 22 Nov 2025 11:13:36 -0800
From: Andrew Morton <akpm@...ux-foundation.org>
To: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
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>, SeongJae
 Park <sj@...nel.org>, Michal Hocko <mhocko@...e.com>, 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 v9 1/2] lib: Introduce hierarchical per-cpu counters

On Sat, 22 Nov 2025 12:15:02 -0500 Mathieu Desnoyers <mathieu.desnoyers@...icios.com> wrote:

> > 
> >>   include/linux/percpu_counter_tree.h | 239 +++++++++++++++
> >>   init/main.c                         |   2 +
> >>   lib/Makefile                        |   1 +
> >>   lib/percpu_counter_tree.c           | 443 ++++++++++++++++++++++++++++
> >>   4 files changed, 685 insertions(+)
> >>   create mode 100644 include/linux/percpu_counter_tree.h
> >>   create mode 100644 lib/percpu_counter_tree.c
> > 
> > An in-kernel test suite would be great.  Like lib/*test*.c or
> > tools/testing/.
> 
> I'll keep a note to port the tests from my userspace librseq
> percpu counters feature branch to the kernel. I did not do it
> initially because I wanted to see if the overall approach was
> deemed interesting for the kernel.

It deems interesting to me - certainly seems useful in addressing some
nasty problems.

If it hasn't been massacred by reviewers, please poke me in a week or
so and I'll look at giving it some exposure in mm.git's mm-new branch
(which isn't included in linux-next).