linux-kernel - Re: [PATCH v6] zswap: memcontrol: implement zswap writeback disabling

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Message-ID: <CAKEwX=OM0-auqDz9E1=_tC9n=KMFCs7JBYM1OhcZsOiH6cJmHw@mail.gmail.com>
Date: Wed, 20 Dec 2023 16:50:20 -0800
From: Nhat Pham <nphamcs@...il.com>
To: Yosry Ahmed <yosryahmed@...gle.com>
Cc: Johannes Weiner <hannes@...xchg.org>, akpm@...ux-foundation.org, tj@...nel.org, 
	lizefan.x@...edance.com, cerasuolodomenico@...il.com, sjenning@...hat.com, 
	ddstreet@...e.org, vitaly.wool@...sulko.com, mhocko@...nel.org, 
	roman.gushchin@...ux.dev, shakeelb@...gle.com, muchun.song@...ux.dev, 
	hughd@...gle.com, corbet@....net, konrad.wilk@...cle.com, 
	senozhatsky@...omium.org, rppt@...nel.org, linux-mm@...ck.org, 
	kernel-team@...a.com, linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org, 
	david@...t.cz, chrisl@...nel.org, Wei Xu <weixugc@...gle.com>, 
	Yu Zhao <yuzhao@...gle.com>
Subject: Re: [PATCH v6] zswap: memcontrol: implement zswap writeback disabling

On Wed, Dec 20, 2023 at 4:24 PM Yosry Ahmed <yosryahmed@...gle.com> wrote:
>
> We can agree to disagree here, I am not trying to block this anyway.
> But let's at least document this in the commit message/docs/code
> (wherever it makes sense) -- that recurrent failures (e.g.
> incompressible memory) may keep going back to zswap only to get
> rejected, so workloads prone to this may observe some reclaim
> inefficiency.

I'll add the following caveat:

Note that if the store failures are recurring (for e.g if the pages are
incompressible), users can observe reclaim inefficiency after disabling
writeback (because the same pages might be rejected again and again).

to the zswap documentation and the cgroup documentation then? I'll
repeat this caveat in both places for self-containment purposes.