linux-kernel - Re: [PATCH v2] mm: zswap: multiple zpools support

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Date:   Wed, 31 May 2023 16:20:28 -0600
From:   Yu Zhao <yuzhao@...gle.com>
To:     Yosry Ahmed <yosryahmed@...gle.com>
Cc:     Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Seth Jennings <sjenning@...hat.com>,
        Dan Streetman <ddstreet@...e.org>,
        Vitaly Wool <vitaly.wool@...sulko.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Nhat Pham <nphamcs@...il.com>,
        Domenico Cerasuolo <cerasuolodomenico@...il.com>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] mm: zswap: multiple zpools support

On Wed, May 31, 2023 at 4:13 PM Yosry Ahmed <yosryahmed@...gle.com> wrote:
>
> Support using multiple zpools of the same type in zswap, for concurrency
> purposes. Add CONFIG_ZSWAP_NR_ZPOOLS_ORDER to control the number of
> zpools. The order is specific by the config rather than the absolute
> number to guarantee a power of 2. This is useful so that we can use
> deterministically link each entry to a zpool by hashing the zswap_entry
> pointer.
>
> On a setup with zswap and zsmalloc, comparing a single zpool (current
> default) to 32 zpools (by setting CONFIG_ZSWAP_NR_ZPOOLS_ORDER=32) shows
> improvements in the zsmalloc lock contention, especially on the swap out
> path.
>
> The following shows the perf analysis of the swapout path when 10
> workloads are simulatenously reclaiming and refaulting tmpfs pages.

simultaneously

> There are some improvements on the swap in path as well, but much less
> significant.

...

> ---
>  mm/Kconfig | 12 +++++++
>  mm/zswap.c | 91 ++++++++++++++++++++++++++++++++++++------------------
>  2 files changed, 73 insertions(+), 30 deletions(-)
>
> diff --git a/mm/Kconfig b/mm/Kconfig
> index 92c30879bf67..de1da56d2c07 100644
> --- a/mm/Kconfig
> +++ b/mm/Kconfig
> @@ -59,6 +59,18 @@ config ZSWAP_EXCLUSIVE_LOADS
>           The cost is that if the page was never dirtied and needs to be
>           swapped out again, it will be re-compressed.
>
> +config ZSWAP_NR_ZPOOLS_ORDER
> +       int "Number of zpools in zswap, as power of 2"
> +       default 0
> +       depends on ZSWAP
> +       help
> +         This options determines the number of zpools to use for zswap, it

option