linux-kernel - Re: [RFC PATCH v2] mm/zswap: store <PAGE

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Message-Id: <20250807165037.53199-1-sj@kernel.org>
Date: Thu,  7 Aug 2025 09:50:37 -0700
From: SeongJae Park <sj@...nel.org>
To: David Hildenbrand <david@...hat.com>
Cc: SeongJae Park <sj@...nel.org>,
	Shakeel Butt <shakeel.butt@...ux.dev>,
	Nhat Pham <nphamcs@...il.com>,
	"Liam R. Howlett" <Liam.Howlett@...cle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Chengming Zhou <chengming.zhou@...ux.dev>,
	Johannes Weiner <hannes@...xchg.org>,
	Jonathan Corbet <corbet@....net>,
	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
	Michal Hocko <mhocko@...e.com>,
	Mike Rapoport <rppt@...nel.org>,
	Suren Baghdasaryan <surenb@...gle.com>,
	Vlastimil Babka <vbabka@...e.cz>,
	Yosry Ahmed <yosry.ahmed@...ux.dev>,
	kernel-team@...a.com,
	linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linux-mm@...ck.org,
	Takero Funaki <flintglass@...il.com>
Subject: Re: [RFC PATCH v2] mm/zswap: store <PAGE_SIZE compression failed page as-is

On Thu, 7 Aug 2025 07:55:27 +0200 David Hildenbrand <david@...hat.com> wrote:

> On 07.08.25 01:48, Shakeel Butt wrote:
> > On Wed, Aug 06, 2025 at 10:14:39PM +0200, David Hildenbrand wrote:
> >>
> >> But yeah, whether these "as is" pages are movable or not is a good question
> >> as well -- in particular when zsmalloc supports page migration and the "as
> >> is" pages would not.
> > 
> > By "as is" page, do you mean the page which the reclaim code is trying
> > to reclaim or the page within zsmalloc on which the content of original
> > pages are copied as is?
> 
> I mean whatever the "dst" is here.
> 
> +	if (zswap_save_as_is(comp_ret, dlen, page)) {
> +		comp_ret = 0;
> +		dlen = PAGE_SIZE;
> +		memcpy_from_page(dst, page, 0, dlen);
> 
> IIUC SJ correctly, in case of zsmalloc "dst" is just the same page that 
> would have stored encrypted data.

You correctly understood me.

> 
> If that is the case, nothing should change, really.
> 
> Thanks for clarifying, all!

Thank you for asking this important question, too, David! :)


Thanks,
SJ

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