linux-kernel - Re: [PATCH] fs.h: Optimize file struct to prevent false sharing

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Message-Id: <20230605-polterabend-weggehen-44570d4b7429@brauner>
Date:   Mon,  5 Jun 2023 14:58:39 +0200
From:   Christian Brauner <brauner@...nel.org>
To:     chenzhiyin <zhiyin.chen@...el.com>
Cc:     Christian Brauner <brauner@...nel.org>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        nanhai.zou@...el.com, viro@...iv.linux.org.uk
Subject: Re: [PATCH] fs.h: Optimize file struct to prevent false sharing

On Thu, 01 Jun 2023 05:24:00 -0400, chenzhiyin wrote:
> In the syscall test of UnixBench, performance regression occurred due
> to false sharing.
> 
> The lock and atomic members, including file::f_lock, file::f_count and
> file::f_pos_lock are highly contended and frequently updated in the
> high-concurrency test scenarios. perf c2c indentified one affected
> read access, file::f_op.
> To prevent false sharing, the layout of file struct is changed as
> following
> (A) f_lock, f_count and f_pos_lock are put together to share the same
> cache line.
> (B) The read mostly members, including f_path, f_inode, f_op are put
> into a separate cache line.
> (C) f_mode is put together with f_count, since they are used frequently
>  at the same time.
> Due to '__randomize_layout' attribute of file struct, the updated layout
> only can be effective when CONFIG_RANDSTRUCT_NONE is 'y'.
> 
> [...]

Applied to the vfs.misc branch of the vfs/vfs.git tree.
Patches in the vfs.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.

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

[1/1] fs.h: Optimize file struct to prevent false sharing
      https://git.kernel.org/vfs/vfs/c/b63bfcf3c65d