linux-kernel - Re: [PATCH v4 2/6] mm/zswap: reuse dstmem when decompress

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Date: Wed,  3 Jan 2024 15:57:59 +1300
From: Barry Song <21cnbao@...il.com>
To: herbert@...dor.apana.org.au,
	davem@...emloft.net,
	akpm@...ux-foundation.org,
	chriscli@...gle.com,
	chrisl@...nel.org,
	ddstreet@...e.org,
	hannes@...xchg.org,
	linux-mm@...ck.org,
	nphamcs@...il.com,
	sjenning@...hat.com,
	vitaly.wool@...sulko.com,
	yosryahmed@...gle.com,
	zhouchengming@...edance.com
Cc: linux-kernel@...r.kernel.org,
	linux-crypto@...r.kernel.org
Subject: Re: [PATCH v4 2/6] mm/zswap: reuse dstmem when decompress

>>
>> for CPU-based alg, we have completed the compr/decompr within
>> crypto_acomp_decompress()
>> synchronously. they won't return EINPROGRESS, EBUSY.
>>
>> The problem is that crypto_acomp won't expose this information to its
>> users. if it does,
>> we can use this info, we will totally avoid the code of copying
>> zsmalloc's data to a tmp
>> buffer for the most majority users of zswap.
>>
>> But I am not sure if we can find a way to convince Herbert(+To)  :-)

> What would you like to expose? The async status of the underlying
> algorithm?

Right. followed by a rfc patchset, please help take a look.

> 
> We could certainly do that.  But I wonder if it might actually be
> better for you to allocate a second sync-only algorithm for such
> cases.  I'd like to see some real numbers.

some hardware might want to use an accelerator to help offload CPU's
work. their drivers are working in async mode, for example, hisilicon
and intel.

I don't have the exact number we can save by removing the redundant
memcpy, nor do i have a proper hardware to test and get the number.
As Chengming is actually working in zswap, i wonder if you can test
my patches and post some data?

> 
> Cheers,
> --
> Email: Herbert Xu <herbert@...dor.apana.org.au>

Thanks
Barry