linux-kernel - Re: [RFC PATCH v3 0/4] avoid the extra atomic on a ref when closing a fd

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Message-ID: <20250305-angepackt-berggipfel-c4d21f1db4b3@brauner>
Date: Wed,  5 Mar 2025 18:31:36 +0100
From: Christian Brauner <brauner@...nel.org>
To: Mateusz Guzik <mjguzik@...il.com>
Cc: Christian Brauner <brauner@...nel.org>,
	viro@...iv.linux.org.uk,
	jack@...e.cz,
	linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org
Subject: Re: [RFC PATCH v3 0/4] avoid the extra atomic on a ref when closing a fd

On Wed, 05 Mar 2025 13:36:40 +0100, Mateusz Guzik wrote:
> The stock kernel transitioning the file to no refs held penalizes the
> caller with an extra atomic to block any increments.
> 
> For cases where the file is highly likely to be going away this is
> easily avoidable.
> 
> In the open+close case the win is very modest because of the following
> problems:
> - kmem and memcg having terrible performance
> - putname using an atomic (I have a wip to whack that)
> - open performing an extra ref/unref on the dentry (there are patches to
>   do it, including by Al. I mailed about them in [1])
> - creds using atomics (I have a wip to whack that)
> - apparmor using atomics (ditto, same mechanism)
> 
> [...]

Applied to the vfs-6.15.file branch of the vfs/vfs.git tree.
Patches in the vfs-6.15.file 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: vfs-6.15.file

[1/4] file: add fput and file_ref_put routines optimized for use when closing a fd
      https://git.kernel.org/vfs/vfs/c/e83588458f65
[2/4] fs: use fput_close_sync() in close()
      https://git.kernel.org/vfs/vfs/c/3e46a92a27c2
[3/4] fs: use fput_close() in filp_close()
      https://git.kernel.org/vfs/vfs/c/a914bd93f3ed
[4/4] fs: use fput_close() in path_openat()
      https://git.kernel.org/vfs/vfs/c/606623de503f