linux-kernel - Re: [PATCH 1/2] zswap: implement a second chance algorithm for dynamic zswap shrinker

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Message-ID: <CAKEwX=Mzzs0kU4Fmw-hiyMT_6m37N6i=xWaEgZoCN+RAx6McSQ@mail.gmail.com>
Date: Tue, 30 Jul 2024 14:40:42 -0700
From: Nhat Pham <nphamcs@...il.com>
To: Yosry Ahmed <yosryahmed@...gle.com>
Cc: Johannes Weiner <hannes@...xchg.org>, akpm@...ux-foundation.org, shakeelb@...gle.com, 
	linux-mm@...ck.org, kernel-team@...a.com, linux-kernel@...r.kernel.org, 
	flintglass@...il.com
Subject: Re: [PATCH 1/2] zswap: implement a second chance algorithm for
 dynamic zswap shrinker

On Tue, Jul 30, 2024 at 11:46 AM Yosry Ahmed <yosryahmed@...gle.com> wrote:
>
>
> I still think the nr_deferred handling in the shrinker framework does
> not seem compatible with zswap. Entries could be double counted, and
> previously counted entries could go away during swapins. Unless I am
> missing something, it seems like the scanning can be arbitrary, and
> not truly proportional to the reclaim priority and zswap LRUs size.

We can do some investigation by the side. I did find the trace point
that collects deferred numbers, maybe that can illustrate the problem?

It'd be an orthogonal issue though. I don't think fixing the
nr_deferred part would be enough to handle the various cases Johannes
pointed out.