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References: <20240210-zswap-global-lru-v1-0-853473d7b0da@bytedance.com> <20240210-zswap-global-lru-v1-2-853473d7b0da@bytedance.com>
In-Reply-To: <20240210-zswap-global-lru-v1-2-853473d7b0da@bytedance.com>
From: Yosry Ahmed <yosryahmed@google.com>
Date: Mon, 12 Feb 2024 14:42:09 -0800
Message-ID: <CAJD7tkYdEWrrQj+MFNpDR6FHc60czXcuawh3dd1rSF=QQm6+yg@mail.gmail.com>
Subject: Re: [PATCH 2/2] mm/zswap: change zswap_pool kref to percpu_ref
To: Chengming Zhou <zhouchengming@bytedance.com>
Cc: Andrew Morton <akpm@linux-foundation.org>, Johannes Weiner <hannes@cmpxchg.org>, 
	Nhat Pham <nphamcs@gmail.com>, linux-mm@kvack.org, linux-kernel@vger.kernel.org
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On Sun, Feb 11, 2024 at 5:58=E2=80=AFAM Chengming Zhou
<zhouchengming@bytedance.com> wrote:
>
> All zswap entries will take a reference of zswap_pool when
> zswap_store(), and drop it when free. Change it to use the
> percpu_ref is better for scalability performance.
>
> Testing kernel build in tmpfs with memory.max=3D2GB
> (zswap shrinker and writeback enabled with one 50GB swapfile).
>
>         mm-unstable  zswap-global-lru
> real    63.20        63.12
> user    1061.75      1062.95
> sys     268.74       264.44

Are these numbers from a single run or the average of multiple runs?
It just seems that the improvement is small, and percpu refcnt is
slightly less intuitive (and uses a bit more memory), so let's make
sure there is a real performance gain first.

It would also be useful to mention how many threads/CPUs are being used her=
e.