linux-kernel - Re: [PATCH v3 2/2] mm/zswap: use only one pool in zswap

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Date: Tue, 25 Jun 2024 02:53:33 -0700
From: Yosry Ahmed <yosryahmed@...gle.com>
To: Chengming Zhou <chengming.zhou@...ux.dev>
Cc: Minchan Kim <minchan@...nel.org>, Sergey Senozhatsky <senozhatsky@...omium.org>, 
	Andrew Morton <akpm@...ux-foundation.org>, Johannes Weiner <hannes@...xchg.org>, 
	Nhat Pham <nphamcs@...il.com>, Yu Zhao <yuzhao@...gle.com>, 
	Takero Funaki <flintglass@...il.com>, Chengming Zhou <zhouchengming@...edance.com>, 
	Dan Carpenter <dan.carpenter@...aro.org>, linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 2/2] mm/zswap: use only one pool in zswap

On Mon, Jun 24, 2024 at 9:40 PM Chengming Zhou <chengming.zhou@...ux.dev> wrote:
>
> Zswap uses 32 pools to workaround the locking scalability problem in
> zswap backends (mainly zsmalloc nowadays), which brings its own problems
> like memory waste and more memory fragmentation.
>
> Testing results show that we can have near performance with only one
> pool in zswap after changing zsmalloc to use per-size_class lock instead
> of pool spinlock.
>
> Testing kernel build (make bzImage -j32) on tmpfs with memory.max=1GB,
> and zswap shrinker enabled with 10GB swapfile on ext4.
>
>                                 real    user    sys
> 6.10.0-rc3                      138.18  1241.38 1452.73
> 6.10.0-rc3-onepool              149.45  1240.45 1844.69
> 6.10.0-rc3-onepool-perclass     138.23  1242.37 1469.71
>
> And do the same testing using zbud, which shows a little worse performance
> as expected since we don't do any locking optimization for zbud. I think
> it's acceptable since zsmalloc became a lot more popular than other
> backends, and we may want to support only zsmalloc in the future.
>
>                                 real    user    sys
> 6.10.0-rc3-zbud                 138.23  1239.58 1430.09
> 6.10.0-rc3-onepool-zbud         139.64  1241.37 1516.59
>
> Reviewed-by: Nhat Pham <nphamcs@...il.com>
> Signed-off-by: Chengming Zhou <chengming.zhou@...ux.dev>

Acked-by: Yosry Ahmed <yosryahmed@...gle.com>