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From:   Barry Song <song.bao.hua@hisilicon.com>
To:     <herbert@gondor.apana.org.au>, <sjenning@redhat.com>,
        <ddstreet@ieee.org>, <vitaly.wool@konsulko.com>
CC:     <mahipalreddy2006@gmail.com>, <linux-mm@kvack.org>,
        <linux-crypto@vger.kernel.org>, <linuxarm@huawei.com>,
        Barry Song <song.bao.hua@hisilicon.com>
Subject: [PATCH 0/1] mm/zswap: move to use crypto_acomp APIs
Date:   Sat, 2 May 2020 14:04:18 +1200
Message-ID: <20200502020419.11616-1-song.bao.hua@hisilicon.com>
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Sender: linux-crypto-owner@vger.kernel.org
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Hi Seth, Dan, Vitaly, Herbert,

Using crypto_comp APIs, zswap is not able to use the hardware accelators which
are only ported to cryto_acomp nowadays. So Mahipal Challa tried to solve this
problem by the below patch a long time ago:
mm: zswap - Add crypto acomp/scomp framework support [1]

At that time, the test was based on acomp with scomp backend. It was not a real
async platform. On a platform with real acomp support like hisilicon-zip, the
patch will lead to serious "sleep on atomic" issues.

To leverage the power of hardware accelerator, right now, I am sending a new patch
which will remove the atomic context and permit crypto to sleep in zswap.

Literally, using an async compressor, people can dynamically allocate acomp_req and
queue those requests to acrytp drivers, and finally use the callback to notify
the completion of compression/decompression. but this will require dynamic memory
allocation and various synchronizations in zswap, and it is too complex.

Alternatively, this patch pre-allocates the acomp_req with the same number of CPUs.
For each acomp_req, one mutex and one wait are bound with it. The mutex is used
for the race protection of the acomp_req and other percpu resources. Even though
the preempt-disabled atomic context is replaced by sleepable context, threads
might migrate, but the mutex can still protect the race between CPUs for same
resources.

Tested on hisilicon zip driver on a SMP enviorment and on lz4 scomp-based acomp
as well. To use scomp-based acomp, another patch I sent before is needed:
crypto: acomp - search acomp with scomp backend in crypto_has_acomp [2]

[1] https://www.spinics.net/lists/linux-mm/msg122455.html
[2] https://marc.info/?l=linux-crypto-vger&m=158822346227760&w=2

Barry Song (1):
  mm/zswap: move to use crypto_acomp API for hardware acceleration

 mm/zswap.c | 150 ++++++++++++++++++++++++++++++++++++++---------------
 1 file changed, 108 insertions(+), 42 deletions(-)

-- 
2.23.0