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Date: Sat, 1 Jun 2024 09:24:15 +0900
From: Sergey Senozhatsky <senozhatsky@chromium.org>
To: Herbert Xu <herbert@gondor.apana.org.au>
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>,
	Linux Crypto Mailing List <linux-crypto@vger.kernel.org>
Subject: Re: [PATCH 1/3] crypto: scomp - Add setparam interface
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On (24/05/31 16:29), Herbert Xu wrote:
> On Fri, May 31, 2024 at 03:34:44PM +0900, Sergey Senozhatsky wrote:
> >
> > So passing "raw" algorithm parameters to crypto_scomp_setparam(tfm) can be
> > suboptimal, depending on the compression driver. For instance, for zstd
> > (what is currently done in zram [1]) we pre-process "raw" parameters:
> > parse dictionary in order to get zstd_cdict and zstd_ddict which are then
> > shared by all tfm-s (as they access C/D dictionaries in read-only mode).
> > For zram/zswap doing this per-tfm would result in extra per-CPU
> > zstd_cdict/zstd_ddict allocations, which is a significant overhead.
> 
> If they share the dictionary, why can't they just share the
> tfm directly? Or do you actually need to vary the other parameters
> while keeping the dictionary the same?

Is it possible to share a tfm? I thought that tfm-s carry some state
(compression workmem/scratch buffer) so one cannot do parallel compressions
on different CPUs using the same tfm.