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

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Message-ID: <j7rqzweklga72b7hdebljs7nziz7bs7kzvevkuhnbwi3uespkt@rmkdqlpku2gh>
Date: Tue, 9 Dec 2025 16:55:01 +0000
From: Yosry Ahmed <yosry.ahmed@...ux.dev>
To: Herbert Xu <herbert@...dor.apana.org.au>
Cc: "Sridhar, Kanchana P" <kanchana.p.sridhar@...el.com>, 
	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>, 
	"usamaarif642@...il.com" <usamaarif642@...il.com>, "ryan.roberts@....com" <ryan.roberts@....com>, 
	"21cnbao@...il.com" <21cnbao@...il.com>, "ying.huang@...ux.alibaba.com" <ying.huang@...ux.alibaba.com>, 
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>, "senozhatsky@...omium.org" <senozhatsky@...omium.org>, 
	"kasong@...cent.com" <kasong@...cent.com>, "linux-crypto@...r.kernel.org" <linux-crypto@...r.kernel.org>, 
	"davem@...emloft.net" <davem@...emloft.net>, "clabbe@...libre.com" <clabbe@...libre.com>, 
	"ardb@...nel.org" <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>
Subject: Re: [PATCH v13 22/22] mm: zswap: Batched zswap_compress() with
 compress batching of large folios.

On Tue, Dec 09, 2025 at 10:32:20AM +0800, Herbert Xu wrote:
> On Tue, Dec 09, 2025 at 01:15:02AM +0000, Yosry Ahmed wrote:
> > 
> > Just to clarify, does this mean that zswap can pass a batch of (eight)
> > pages to the acomp API, and get the results for the batch uniformly
> > whether or not the underlying compressor supports batching?
> 
> Correct.  In fact I'd like to remove the batch size exposure to zswap
> altogether.  zswap should just pass along whatever maximum number of
> pages that is convenient to itself.

I think exposing the batch size is still useful as a hint for zswap. In
the current series, zswap allocates as many per-CPU buffers as the
compressor's batch size, so no extra buffers for non-batching
compressors (including SW compressors).

If we use the same batch size regardless, we'll have to always allocate
8 (or N) per-CPU buffers, for little to no benefit on non-batching
compressors.

So we still want the batch size on the zswap side, but we want the
crypto API to be uniform whether or not the compressor supports
batching.

> 
> 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