From: Matthew Wilcox <willy@infradead.org>
To: Mateusz Guzik <mjguzik@gmail.com>
Cc: oleg@redhat.com, brauner@kernel.org,
linux-kernel@vger.kernel.org, akpm@linux-foundation.org,
linux-mm@kvack.org
Subject: Re: [PATCH 0/3] further damage-control lack of clone scalability
Date: Sun, 23 Nov 2025 15:00:31 +0000 [thread overview]
Message-ID: <aSMhj2Q6BTMNSsA4@casper.infradead.org> (raw)
In-Reply-To: <20251123063054.3502938-1-mjguzik@gmail.com>
On Sun, Nov 23, 2025 at 07:30:51AM +0100, Mateusz Guzik wrote:
> When spawning and killing threads in separate processes in parallel the
> primary bottleneck on the stock kernel is pidmap_lock, largely because
> of a back-to-back acquire in the common case.
>
> Benchmark code at the end.
>
> With this patchset alloc_pid() only takes the lock once and consequently
> alleviates the problem. While scalability improves, the lock remains the
> primary bottleneck by a large margin.
>
> I believe idr is a poor choice for the task at hand to begin with, but
> sorting out that out beyond the scope of this patchset. At the same time
> any replacement would be best evaluated against a state where the
> above relock problem is fixed.
Good news! The IDR is deprecated. Bad news! I'm not 100% sure that
the XArray is quite appropriate for this usecase. I am opposed to
introducing more IDR APIs. Have you looked at converting to the XArray?
Or do you have a better data structure in mind than the XArray?
next prev parent reply other threads:[~2025-11-23 15:00 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-11-23 6:30 Mateusz Guzik
2025-11-23 6:30 ` [PATCH 1/3] idr: add idr_prealloc_many Mateusz Guzik
2025-11-23 6:30 ` [PATCH 2/3] ns: pad refcount Mateusz Guzik
2025-11-23 18:58 ` Oleg Nesterov
2025-11-23 19:47 ` Mateusz Guzik
2025-11-24 18:25 ` Oleg Nesterov
2025-11-23 6:30 ` [PATCH 3/3] pid: only take pidmap_lock once on alloc Mateusz Guzik
2025-11-23 20:09 ` Oleg Nesterov
2025-11-23 22:48 ` Mateusz Guzik
2025-11-23 15:00 ` Matthew Wilcox [this message]
2025-11-23 16:39 ` [PATCH 0/3] further damage-control lack of clone scalability Mateusz Guzik
2025-11-23 21:45 ` Matthew Wilcox
2025-11-23 22:33 ` Mateusz Guzik
2025-11-24 4:03 ` Mateusz Guzik
2025-12-03 8:37 ` Mateusz Guzik
2025-12-03 9:18 ` Mateusz Guzik
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