linux-kernel - Re: [PATCH] fs/address_space: move i_mmap_rwsem to mitigate a false sharing with i

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Message-ID: <20240205-harmlos-positionieren-ea42ccc90890@brauner>
Date: Mon,  5 Feb 2024 12:56:46 +0100
From: Christian Brauner <brauner@...nel.org>
To: JonasZhou-oc <JonasZhou-oc@...oxin.com>
Cc: Christian Brauner <brauner@...nel.org>,
	jack@...e.cz,
	linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	CobeChen@...oxin.com,
	LouisQi@...oxin.com,
	JonasZhou@...oxin.com,
	viro@...iv.linux.org.uk
Subject: Re: [PATCH] fs/address_space: move i_mmap_rwsem to mitigate a false sharing with i_mmap.

On Fri, 02 Feb 2024 16:33:04 +0800, JonasZhou-oc wrote:
> In the struct address_space, there is a 32-byte gap between i_mmap
> and i_mmap_rwsem. Due to the alignment of struct address_space
> variables to 8 bytes, in certain situations, i_mmap and i_mmap_rwsem
> may end up in the same CACHE line.
> 
> While running Unixbench/execl, we observe high false sharing issues
> when accessing i_mmap against i_mmap_rwsem. We move i_mmap_rwsem
> after i_private_list, ensuring a 64-byte gap between i_mmap and
> i_mmap_rwsem.
> 
> [...]

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.

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.misc

[1/1] fs/address_space: move i_mmap_rwsem to mitigate a false sharing with i_mmap.
      https://git.kernel.org/vfs/vfs/c/2a42e144dd0b