From: Pedro Falcato <pfalcato@suse.de>
To: Dennis Zhou <dennis@kernel.org>
Cc: Kaitao Cheng <kaitao.cheng@linux.dev>,
akpm@linux-foundation.org, tj@kernel.org, cl@gentwo.org,
mhocko@suse.com, vbabka@kernel.org, linux-mm@kvack.org,
linux-kernel@vger.kernel.org, muchun.song@linux.dev,
Kaitao Cheng <chengkaitao@kylinos.cn>
Subject: Re: [PATCH 1/2] mm/percpu: Preserve NOFS/NOIO scope during chunk create and populate
Date: Tue, 2 Jun 2026 14:46:57 +0100 [thread overview]
Message-ID: <ah7eYOb5YU0Jhs-Y@pedro-suse.lan> (raw)
In-Reply-To: <ahrm4x2ubbjs4An1@palisades.local>
On Sat, May 30, 2026 at 03:32:19PM +0200, Dennis Zhou wrote:
<snip>
> >
> > I’ll try to do it.
> >
> > Following your suggestion, including in [PATCH 2/2], I will also try a
> > different approach and fix the issue by reducing the scope of the
> > pcpu_alloc_mutex critical section.
> >
>
> No please don't. The point of the percpu mutex is to ensure that only
> one person is ever possibly creating a new chunk. If you drop the mutex,
> then you have to deal with concurrent callers when available percpu
> memory is low. Percpu memory is expensive and unmovable so the cost is
> in the control plane to avoid excess fragmentation.
And so is slab memory, yet this is not a problem. We shouldn't keep
problematic locks just because they may aid fragmentation slightly.
--
Pedro
next prev parent reply other threads:[~2026-06-02 13:47 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-05-28 13:29 [PATCH 0/2] mm/percpu: Fix possible NOFS/NOIO reclaim recursion Kaitao Cheng
2026-05-28 13:29 ` [PATCH 1/2] mm/percpu: Preserve NOFS/NOIO scope during chunk create and populate Kaitao Cheng
2026-05-29 9:25 ` Pedro Falcato
2026-05-29 9:38 ` Pedro Falcato
2026-05-30 12:47 ` Kaitao Cheng
2026-05-30 13:32 ` Dennis Zhou
2026-06-01 2:27 ` Kaitao Cheng
2026-06-01 15:45 ` Michal Hocko
2026-06-02 3:03 ` Kaitao Cheng
2026-06-02 7:16 ` Vlastimil Babka (SUSE)
2026-06-02 8:05 ` Michal Hocko
2026-06-02 9:02 ` Kaitao Cheng
2026-06-02 7:17 ` Michal Hocko
2026-06-02 13:46 ` Pedro Falcato [this message]
2026-05-28 13:29 ` [PATCH 2/2] mm/percpu: Avoid pcpu_alloc_mutex recursion from reclaim Kaitao Cheng
2026-05-29 9:34 ` Pedro Falcato
2026-05-28 21:09 ` [PATCH 0/2] mm/percpu: Fix possible NOFS/NOIO reclaim recursion Andrew Morton
2026-05-28 21:10 ` Andrew Morton
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