Re: [PATCH 2/2] mm/zswap: change zswap_pool kref to percpu_ref

From: Yosry Ahmed
Date: Mon Feb 12 2024 - 17:43:05 EST

On Sun, Feb 11, 2024 at 5:58 AM Chengming Zhou
<zhouchengming@xxxxxxxxxxxxx> 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=2GB
> (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 here.