linux-kernel - RE: [PATCH v12 23/23] mm: zswap: Batched zswap_compress() with compress batching of large folios.

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Message-ID: <PH7PR11MB8121A3DB59F5D00279D08218C9F8A@PH7PR11MB8121.namprd11.prod.outlook.com>
Date: Fri, 31 Oct 2025 22:18:16 +0000
From: "Sridhar, Kanchana P" <kanchana.p.sridhar@...el.com>
To: Herbert Xu <herbert@...dor.apana.org.au>
CC: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>, "hannes@...xchg.org"
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	<kanchana.p.sridhar@...el.com>
Subject: RE: [PATCH v12 23/23] mm: zswap: Batched zswap_compress() with
 compress batching of large folios.


> -----Original Message-----
> From: Herbert Xu <herbert@...dor.apana.org.au>
> Sent: Tuesday, October 21, 2025 10:18 PM
> To: Sridhar, Kanchana P <kanchana.p.sridhar@...el.com>
> Cc: linux-kernel@...r.kernel.org; linux-mm@...ck.org;
> hannes@...xchg.org; yosry.ahmed@...ux.dev; 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; sj@...nel.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 v12 23/23] mm: zswap: Batched zswap_compress() with
> compress batching of large folios.
> 
> On Thu, Sep 25, 2025 at 08:35:02PM -0700, Kanchana P Sridhar wrote:
> >
> > Another initialization level optimization that happens in
> > zswap_cpu_comp_prepare() is, only for batching compressors, we allocate
> > extra memory for "batch-size" int pointers in the
> > @acomp_ctx->req->__ctx[] that are statically set to track the output SG
> > lists' lengths. This optimization was necessary to avoid the latency
> 
> There is no need for this allocation.  Just store the output lengths
> in each destination scatterlist entry.

Thanks Herbert, for this suggestion. I have included this in the v13 code
that I am currently validating and expect to post an updated patch-set
within a couple of days.

> 
> Before the call to acomp, the destination SG list should contain as
> many elements as the number of units.  On return, the dst lengths
> should be stored in each destination SG entry.

Yes, confirming that this is the case.

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