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

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Message-ID: <SJ0PR11MB5678B1F845444D6620491700C9682@SJ0PR11MB5678.namprd11.prod.outlook.com>
Date: Tue, 24 Sep 2024 22:18:57 +0000
From: "Sridhar, Kanchana P" <kanchana.p.sridhar@...el.com>
To: Nhat Pham <nphamcs@...il.com>, Yosry Ahmed <yosryahmed@...gle.com>
CC: "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>,
	"Sridhar, Kanchana P" <kanchana.p.sridhar@...el.com>
Subject: RE: [PATCH v7 6/8] mm: zswap: Support mTHP swapout in zswap_store().

> -----Original Message-----
> From: Nhat Pham <nphamcs@...il.com>
> Sent: Tuesday, September 24, 2024 3:16 PM
> To: Yosry Ahmed <yosryahmed@...gle.com>
> Cc: Sridhar, Kanchana P <kanchana.p.sridhar@...el.com>; linux-
> kernel@...r.kernel.org; linux-mm@...ck.org; hannes@...xchg.org;
> chengming.zhou@...ux.dev; usamaarif642@...il.com;
> shakeel.butt@...ux.dev; ryan.roberts@....com; Huang, Ying
> <ying.huang@...el.com>; 21cnbao@...il.com; 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.

I agree, thanks Nhat! Will fix this in v8.

Thanks,
Kanchana