linux-kernel - Re: [PATCH 7/9] mm, swap: remove contention workaround for swap cache

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Message-ID: <CAGsJ_4xNydZqSx7GJ9GfUGaSVERZ2Nj82D5eefMN_Q-OUjnoyw@mail.gmail.com>
Date: Tue, 2 Sep 2025 18:06:59 +0800
From: Barry Song <21cnbao@...il.com>
To: Kairui Song <kasong@...cent.com>
Cc: linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>, 
	Matthew Wilcox <willy@...radead.org>, Hugh Dickins <hughd@...gle.com>, Chris Li <chrisl@...nel.org>, 
	Baoquan He <bhe@...hat.com>, Nhat Pham <nphamcs@...il.com>, 
	Kemeng Shi <shikemeng@...weicloud.com>, Baolin Wang <baolin.wang@...ux.alibaba.com>, 
	Ying Huang <ying.huang@...ux.alibaba.com>, Johannes Weiner <hannes@...xchg.org>, 
	David Hildenbrand <david@...hat.com>, Yosry Ahmed <yosryahmed@...gle.com>, 
	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, Zi Yan <ziy@...dia.com>, 
	linux-kernel@...r.kernel.org, kernel test robot <oliver.sang@...el.com>
Subject: Re: [PATCH 7/9] mm, swap: remove contention workaround for swap cache

On Sat, Aug 23, 2025 at 3:21 AM Kairui Song <ryncsn@...il.com> wrote:
>
> From: Kairui Song <kasong@...cent.com>
>
> Swap cluster setup will try to shuffle the clusters on initialization.
> It was helpful to avoid contention for the swap cache space. The cluster
> size (2M) was much smaller than each swap cache space (64M), so shuffling
> the cluster means the allocator will try to allocate swap slots that are
> in different swap cache spaces for each CPU, reducing the chance of two
> CPUs using the same swap cache space, and hence reducing the contention.
>
> Now, swap cache is managed by swap clusters, this shuffle is pointless.
> Just remove it, and clean up related macros.
>
> This should also improve the HDD swap performance as shuffling IO is a
> bad idea for HDD, and now the shuffling is gone.
>
> Reported-by: kernel test robot <oliver.sang@...el.com>
> Closes: https://lore.kernel.org/oe-lkp/202504241621.f27743ec-lkp@intel.com
> Signed-off-by: Kairui Song <kasong@...cent.com>
> ---

Reviewed-by: Barry Song <baohua@...nel.org>