From: Matthew Wilcox <willy@infradead.org>
To: JonasZhou-oc <JonasZhou-oc@zhaoxin.com>
Cc: viro@zeniv.linux.org.uk, brauner@kernel.org, jack@suse.cz,
linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
CobeChen@zhaoxin.com, LouisQi@zhaoxin.com, JonasZhou@zhaoxin.com
Subject: Re: [PATCH] fs/address_space: move i_mmap_rwsem to mitigate a false sharing with i_mmap.
Date: Fri, 2 Feb 2024 15:03:51 +0000 [thread overview]
Message-ID: <Zb0EV8rTpfJVNAJA@casper.infradead.org> (raw)
In-Reply-To: <20240202093407.12536-1-JonasZhou-oc@zhaoxin.com>
On Fri, Feb 02, 2024 at 05:34:07PM +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.
I'm confused. i_mmap_rwsem protects i_mmap. Usually you want the lock
and the thing it's protecting in the same cacheline. Why is that not
the case here?
next prev parent reply other threads:[~2024-02-02 15:03 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-02-02 9:34 [PATCH] fs/address_space: move i_mmap_rwsem to mitigate a false sharing with i_mmap JonasZhou-oc
2024-02-02 10:18 ` Christian Brauner
2024-02-02 15:03 ` Matthew Wilcox [this message]
2024-02-02 19:32 ` Matthew Wilcox
2024-02-05 3:22 ` Dave Chinner
2024-02-05 23:28 ` Matthew Wilcox
2024-02-06 21:35 ` Dave Chinner
2024-02-06 23:33 ` Matthew Wilcox
2024-02-05 6:22 ` JonasZhou
2024-02-05 23:08 ` Matthew Wilcox
2024-02-06 13:06 ` Christian Brauner
2024-02-05 23:15 ` Dave Chinner
2024-03-06 6:16 ` JonasZhou
-- strict thread matches above, loose matches on Subject: below --
2024-02-02 8:33 JonasZhou-oc
2024-02-02 16:20 ` Al Viro
2024-02-05 11:56 ` Christian Brauner
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