linux-kernel - RE: [PATCH v13 22/22] mm: zswap: Batched zswap_compress() with compress batching of large folios.

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Message-ID: <SJ2PR11MB8472529E92EC003D956DF530C9A2A@SJ2PR11MB8472.namprd11.prod.outlook.com>
Date: Mon, 8 Dec 2025 04:17:38 +0000
From: "Sridhar, Kanchana P" <kanchana.p.sridhar@...el.com>
To: Herbert Xu <herbert@...dor.apana.org.au>
CC: Yosry Ahmed <yosry.ahmed@...ux.dev>, SeongJae Park <sj@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>, "hannes@...xchg.org"
	<hannes@...xchg.org>, "nphamcs@...il.com" <nphamcs@...il.com>,
	"chengming.zhou@...ux.dev" <chengming.zhou@...ux.dev>,
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	<ryan.roberts@....com>, "21cnbao@...il.com" <21cnbao@...il.com>,
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	<ardb@...nel.org>, "ebiggers@...gle.com" <ebiggers@...gle.com>,
	"surenb@...gle.com" <surenb@...gle.com>, "Accardi, Kristen C"
	<kristen.c.accardi@...el.com>, "Gomes, Vinicius" <vinicius.gomes@...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 v13 22/22] mm: zswap: Batched zswap_compress() with
 compress batching of large folios.


> -----Original Message-----
> From: Herbert Xu <herbert@...dor.apana.org.au>
> Sent: Sunday, December 7, 2025 7:24 PM
> To: Sridhar, Kanchana P <kanchana.p.sridhar@...el.com>
> Cc: Yosry Ahmed <yosry.ahmed@...ux.dev>; SeongJae Park <sj@...nel.org>;
> linux-kernel@...r.kernel.org; linux-mm@...ck.org; hannes@...xchg.org;
> nphamcs@...il.com; chengming.zhou@...ux.dev;
> usamaarif642@...il.com; ryan.roberts@....com; 21cnbao@...il.com;
> ying.huang@...ux.alibaba.com; akpm@...ux-foundation.org;
> senozhatsky@...omium.org; kasong@...cent.com; linux-
> crypto@...r.kernel.org; davem@...emloft.net; clabbe@...libre.com;
> ardb@...nel.org; ebiggers@...gle.com; surenb@...gle.com; Accardi,
> Kristen C <kristen.c.accardi@...el.com>; Gomes, Vinicius
> <vinicius.gomes@...el.com>; Feghali, Wajdi K <wajdi.k.feghali@...el.com>;
> Gopal, Vinodh <vinodh.gopal@...el.com>
> Subject: Re: [PATCH v13 22/22] mm: zswap: Batched zswap_compress() with
> compress batching of large folios.
> 
> On Wed, Nov 26, 2025 at 08:05:40PM +0000, Sridhar, Kanchana P wrote:
> >
> > Herbert, to make sure I understand, will you be implementing all of these
> > features in crypto_acomp for software compressors? I would appreciate it
> > if you can clarify:
> >
> > 1) Error & compressed length propagation to the dst sg->length only for
> >     non-batching compressors.
> >     a) For batching compressors, this wouldn't apply since errors could occur
> >         for any page in the batch, and the first page (dst sg->length) could have
> >         successfully compressed.
> 
> This would be the first step.

Hi Herbert,

Thanks for these clarifications! This sounds like a great first step.

> 
> > 2) Will you also be handling the case where zswap can send an SG list batch
> >      with multiple pages to a non-batching compressor, and the crypto_acomp
> >      API will internally compress each page sequentially, propagate
> >      errors/compress lengths before returning?
> >
> > If so, this would really standardize the code in zswap for batching and
> > non-batching compressors.
> 
> Yes this will be done as the next step.  My understanding is that
> your patch-set doesn't require this yet as all non-batching compressors
> will have a batch size of 1.

I see. So the way my patch-set tries to standardize batching in
zswap_compress() is to call it with a batch of 8 pages, regardless of batching
or non-batching compressors. In zswap_compress(), I presently iterate
through each page in the batch for sequential processing for non-batching
compressors whose batch size is 1. For batching compressors, the iteration
happens just once: the whole batch is compressed in one call to
crypto_acomp_compress().

When the next step is ready, I will no longer need this for loop that
iterates over the batch in "batch_size" increments. If Yosry and Nhat are
Ok with staging it as you've described, this should all be good.

Also, I have incorporated your suggestion to implement batching within
iaa_crypto in a manner that adheres to the acomp API. I was planning to
start creating an updated patch-set with this. Please let me know if it would
be a good idea to wait to sync with the first step you are working on before
submitting the updated patch-set. Thanks for collaboration!

> 
> But yes this certainly will be extended, not just with sequential
> processing, but we could also use pcrypt/cryptd to parallelise the
> compression across CPUs.

Sounds great!

Best regards,
Kanchana

> 
> Cheers,
> --
> Email: Herbert Xu <herbert@...dor.apana.org.au>
> Home Page: http://gondor.apana.org.au/~herbert/
> PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt