linux-kernel - RE: [PATCH v4 0/4] mm: ZSWAP swap-out of mTHP folios

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Message-ID: <SJ0PR11MB567847468457F7B094AF3AE5C9892@SJ0PR11MB5678.namprd11.prod.outlook.com>
Date: Sat, 24 Aug 2024 06:24:14 +0000
From: "Sridhar, Kanchana P" <kanchana.p.sridhar@...el.com>
To: Yosry Ahmed <yosryahmed@...gle.com>, Nhat Pham <nphamcs@...il.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>, "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 v4 0/4] mm: ZSWAP swap-out of mTHP folios

Hi Yosry,

> -----Original Message-----
> From: Yosry Ahmed <yosryahmed@...gle.com>
> Sent: Friday, August 23, 2024 8:10 PM
> To: Nhat Pham <nphamcs@...il.com>
> Cc: Sridhar, Kanchana P <kanchana.p.sridhar@...el.com>; linux-
> kernel@...r.kernel.org; linux-mm@...ck.org; hannes@...xchg.org;
> 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 v4 0/4] mm: ZSWAP swap-out of mTHP folios
> 
> [..]
> >
> > I'm not trying to delay this patch - I fully believe in supporting
> > zswap for larger pages (both mTHP and THP - whatever the memory
> > reclaim subsystem throws at us).
> >
> > But we need to get to the bottom of this :) These are very suspicious
> > and concerning data. If this is something urgent, I can live with a
> > gate to enable/disable this, but I'd much prefer we understand what's
> > going on here.
> 
> Agreed. I don't think merging this support is urgent, so I think we
> should better understand what is happening here. If there is a problem
> with how we charge compressed memory today (temporary double charges),
> we need to sort this out before the the mTHP support, as it will only
> make things worse.
> 
> I have to admit I didn't take a deep look at the discussion and data,
> so there may be other problems that I didn't notice. It seems to me
> like Kanchana is doing more debugging to understand what is happening,
> so that's great!

This sounds good. I just shared the data and my learnings from some
debugging experiments. I would appreciate it if you can review this and
suggest next steps.

> 
> As for the patches, we should sort out the impact on a higher level
> before discussing implementation details. From a quick look though it
> seems like the first patch can be dropped after Usama's patches that
> remove the same-filled handling from zswap land, and the last two
> patches can be squashed.

Sure, this sounds good.

Thanks,
Kanchana