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

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Message-ID: <CAJD7tkam-Qbh-mJD3nTe1hX6JDtzS66Ej+1Fvo1kmg8WuwVfQA@mail.gmail.com>
Date: Wed, 25 Sep 2024 11:17:30 -0700
From: Yosry Ahmed <yosryahmed@...gle.com>
To: Johannes Weiner <hannes@...xchg.org>
Cc: Kanchana P Sridhar <kanchana.p.sridhar@...el.com>, linux-kernel@...r.kernel.org, 
	linux-mm@...ck.org, nphamcs@...il.com, chengming.zhou@...ux.dev, 
	usamaarif642@...il.com, shakeel.butt@...ux.dev, ryan.roberts@....com, 
	ying.huang@...el.com, 21cnbao@...il.com, akpm@...ux-foundation.org, 
	nanhai.zou@...el.com, wajdi.k.feghali@...el.com, vinodh.gopal@...el.com
Subject: Re: [PATCH v7 6/8] mm: zswap: Support mTHP swapout in zswap_store().

On Wed, Sep 25, 2024 at 7:27 AM Johannes Weiner <hannes@...xchg.org> wrote:
>
> On Mon, Sep 23, 2024 at 06:17:07PM -0700, Kanchana P Sridhar wrote:
> > zswap_store() will now store mTHP and PMD-size THP folios by compressing
>
> The hugepage terminology throughout the patches is a bit convoluted.
>
> There is no real distinction in this code between PMD-size THPs and
> sub-PMD-sized mTHPs e.g. In particular, I think "mTHP" made sense when
> they were added, to distinguish them from conventional THPs. But using
> this term going forward just causes confusion, IMO.
>
> We're going through a big effort in the codebase to call all of these
> things simply "folios" - which stands for "one or more pages". If you
> want to emphasize the "more than one page", the convention is to call
> it a "large folio". (If you need to emphasize that it's PMD size -
> which doesn't apply to these patches, but just for the record - the
> convention is "pmd-mappable folio".)
>
> So what this patch set does is "support large folios in zswap".

Agreed on all of this, except it should be "support large folios in
zswap _stores". We don't really support loading large folios.