linux-kernel - Re: [PATCH v4] mm/zswap: store <PAGE_SIZE compression failed page as-is

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Message-ID: <CAGsJ_4xR3bvWTEfbu_navPHGiVacAJTY-87BvOH2QQd4xAM4VA@mail.gmail.com>
Date: Fri, 22 Aug 2025 15:30:07 +0800
From: Barry Song <21cnbao@...il.com>
To: Herbert Xu <herbert@...dor.apana.org.au>
Cc: SeongJae Park <sj@...nel.org>, Chris Li <chrisl@...nel.org>, Nhat Pham <nphamcs@...il.com>, 
	Andrew Morton <akpm@...ux-foundation.org>, Chengming Zhou <chengming.zhou@...ux.dev>, 
	Johannes Weiner <hannes@...xchg.org>, Yosry Ahmed <yosry.ahmed@...ux.dev>, kernel-team@...a.com, 
	linux-kernel@...r.kernel.org, linux-mm@...ck.org, 
	Takero Funaki <flintglass@...il.com>, David Hildenbrand <david@...hat.com>, Baoquan He <bhe@...hat.com>, 
	Kairui Song <kasong@...cent.com>
Subject: Re: [PATCH v4] mm/zswap: store <PAGE_SIZE compression failed page as-is

On Fri, Aug 22, 2025 at 1:54 PM Herbert Xu <herbert@...dor.apana.org.au> wrote:
>
> On Fri, Aug 22, 2025 at 12:48:27PM +1200, Barry Song wrote:
> >
> > Is it even possible for crypto_wait_req() to return -EINPROGRESS, since
> > crypto_req_done() will not call complete(&wait->completion) in that case at
> > all?
>
> Of course crypto_wait_req cannot return -EINPROGRESS.  However,
> I was responding to a request to make the crypto_acomp_compress
> call return a boolean instead of an error code.  That is not
> possible because it has to be able to return -EINPROGRESS.
>
> Nor is it possible to change crypto_wait_req to be boolean since
> other Crypto API operations (including decompression) can indeed
> fail.
>

Ok. zswap only cares about the return value of crypto_wait_req(),
not crypto_acomp_compress(). So it’s clear now—any error return
means the page is incompressible.

Thanks
Barry