linux-kernel - Re: [PATCH v7 6/8] mm: zswap: Support mTHP swapout in zswap

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Message-ID: <CAKEwX=PV4uwP7jyxYtThPGe8SFSchBXZGwxqvCr4YTWgYjtqYw@mail.gmail.com>
Date: Tue, 24 Sep 2024 15:16:00 -0700
From: Nhat Pham <nphamcs@...il.com>
To: Yosry Ahmed <yosryahmed@...gle.com>
Cc: "Sridhar, Kanchana P" <kanchana.p.sridhar@...el.com>, 
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "linux-mm@...ck.org" <linux-mm@...ck.org>, 
	"hannes@...xchg.org" <hannes@...xchg.org>, "chengming.zhou@...ux.dev" <chengming.zhou@...ux.dev>, 
	"usamaarif642@...il.com" <usamaarif642@...il.com>, "shakeel.butt@...ux.dev" <shakeel.butt@...ux.dev>, 
	"ryan.roberts@....com" <ryan.roberts@....com>, "Huang, Ying" <ying.huang@...el.com>, 
	"21cnbao@...il.com" <21cnbao@...il.com>, "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>, 
	"Zou, Nanhai" <nanhai.zou@...el.com>, "Feghali, Wajdi K" <wajdi.k.feghali@...el.com>, 
	"Gopal, Vinodh" <vinodh.gopal@...el.com>
Subject: Re: [PATCH v7 6/8] mm: zswap: Support mTHP swapout in zswap_store().

On Tue, Sep 24, 2024 at 2:34 PM Yosry Ahmed <yosryahmed@...gle.com> wrote:
>
>
> Why can't we just handle it the same way as we handle zswap
> disablement? If it is disabled, we invalidate any old entries for the
> offsets and return false to swapout to disk.

I think that was the suggestion.

>
> Taking a step back, why do we need the runtime knob and config option?
> Are there cases where we think zswapout of mTHPs will perform badly,
> or is it just due to lack of confidence in the feature?

Fair point. I think the reason why I suggested this knob was because
we observe so much regressions in earlier benchmarks, and especially
on the software compressor column.

But now that we've reworked the benchmark + use zstd for software
compressor, I think we can get rid of this knob/config option, and
simplify things.