linux-kernel - Re: [PATCH v5 02/12] crypto: acomp - Define new interfaces for compress/decompress batching.

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Message-ID: <CAJD7tkbSXWp+yU8z-djTSounTh1Pq2MMRqo69=1d_aDAO3wrow@mail.gmail.com>
Date: Tue, 7 Jan 2025 17:43:34 -0800
From: Yosry Ahmed <yosryahmed@...gle.com>
To: Herbert Xu <herbert@...dor.apana.org.au>
Cc: Eric Biggers <ebiggers@...nel.org>, 
	"Sridhar, Kanchana P" <kanchana.p.sridhar@...el.com>, 
	"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>, "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>, 
	"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>, 
	"Feghali, Wajdi K" <wajdi.k.feghali@...el.com>, "Gopal, Vinodh" <vinodh.gopal@...el.com>
Subject: Re: [PATCH v5 02/12] crypto: acomp - Define new interfaces for
 compress/decompress batching.

On Tue, Jan 7, 2025 at 5:39 PM Herbert Xu <herbert@...dor.apana.org.au> wrote:
>
> On Mon, Jan 06, 2025 at 07:10:53PM -0800, Yosry Ahmed wrote:
> >
> > The main problem is memory usage. Zswap needs a PAGE_SIZE*2-sized
> > buffer for each request on each CPU. We preallocate these buffers to
> > avoid trying to allocate this much memory in the reclaim path (i.e.
> > potentially allocating two pages to reclaim one).
>
> What if we allowed each acomp request to take a whole folio?
> That would mean you'd only need to allocate one request per
> folio, regardless of how big it is.

Hmm this means we need to allocate a single request instead of N
requests, but the source of overhead is the output buffers not the
requests. We need PAGE_SIZE*2 for each page in the folio in the output
buffer on each CPU. Preallocating this unnecessarily adds up to a lot
of memory.

Did I miss something?

>
> Eric, we could do something similar with ahash.  Allow the
> user to supply a folio (or scatterlist entry) instead of a
> single page, and then cut it up based on a unit-size supplied
> by the user (e.g., 512 bytes for sector-based users).  That
> would mean just a single request object as long as your input
> is a folio or something similar.
>
> Is this something that you could use in fs/verity? You'd still
> need to allocate enough memory to store the output hashes.
>
> 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
>