linux-kernel - Re: [PATCH v3 0/2] further damage-control lack of clone scalability

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Message-ID: <20260119-wohlmeinend-hebamme-1a9c418f3e8d@brauner>
Date: Mon, 19 Jan 2026 12:09:10 +0100
From: Christian Brauner <brauner@...nel.org>
To: Mateusz Guzik <mjguzik@...il.com>
Cc: Christian Brauner <brauner@...nel.org>,
	linux-kernel@...r.kernel.org,
	akpm@...ux-foundation.org,
	linux-mm@...ck.org,
	willy@...radead.org,
	oleg@...hat.com
Subject: Re: [PATCH v3 0/2] further damage-control lack of clone scalability

On Sat, 06 Dec 2025 14:19:53 +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.
> 
> [...]

Applied to the kernel-7.0.misc branch of the vfs/vfs.git tree.
Patches in the kernel-7.0.misc branch should appear in linux-next soon.

Please report any outstanding bugs that were missed during review in a
new review to the original patch series allowing us to drop it.

It's encouraged to provide Acked-bys and Reviewed-bys even though the
patch has now been applied. If possible patch trailers will be updated.

Note that commit hashes shown below are subject to change due to rebase,
trailer updates or similar. If in doubt, please check the listed branch.

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs.git
branch: kernel-7.0.misc

[1/2] ns: pad refcount
      https://git.kernel.org/vfs/vfs/c/0832219c84f2
[2/2] pid: only take pidmap_lock once on alloc
      https://git.kernel.org/vfs/vfs/c/fb374f0d6fc6