Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Date:   Tue, 8 Nov 2022 09:40:15 +0900
From:   Sergey Senozhatsky <senozhatsky@chromium.org>
To:     Minchan Kim <minchan@kernel.org>
Cc:     Sergey Senozhatsky <senozhatsky@chromium.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Nitin Gupta <ngupta@vflare.org>, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org
Subject: Re: [PATCHv4 2/9] zram: Add recompression algorithm sysfs knob
Message-ID: <Y2mlb6F7G8KskRch@google.com>
References: <20221018045533.2396670-3-senozhatsky@chromium.org>
 <Y2LP0OWF/WTnkSne@google.com>
 <Y2Mv4l+V9iCv9EMg@google.com>
 <Y2Ptq1GZISCD7Mor@google.com>
 <Y2SEkzKSWx2iQzLl@google.com>
 <Y2Sat1/FCCT0Lia/@google.com>
 <Y2VPQlnEiP75mY5O@google.com>
 <Y2WjMQeS2DihvPQF@google.com>
 <Y2WnoVJ+Tn5kYWot@google.com>
 <Y2lXt9E6YqB7fRbQ@google.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <Y2lXt9E6YqB7fRbQ@google.com>
Precedence: bulk

On (22/11/07 11:08), Minchan Kim wrote:
[..]
> I am thinking like this:
> 
> * Without recomp_algo setup, user can do whatever they want on the fly
> 
> 
>     echo "type=idle threshold=3000 algo=zstd" > recompress
> 
> Later they could do
> 
>     echo "type=idle threshold=3000 algo=deflate" > recompress

By "without recomp_algo setup" you mean that user doesn't configure
anything before `echo XG > zramX/disksize`? Currently algorithm and
recomp algorithm need to be selected at the same time - before zram
device is initialised, because we use the same code and same approaches:
we need to have zcomp back-ends in per-CPU data in zram read/write/recompress.

Creating per-CPU zcomps on the fly is probably going to be a little bit
intrusive to zram.


What I currently have is as follows.

A copy paste from my test script:

- init device
        echo "algo=lz4 priority=1" > /sys/block/zram0/recomp_algorithm
        echo "algo=zstd priority=2" > /sys/block/zram0/recomp_algorithm
        echo "algo=deflate priority=3" > /sys/block/zram0/recomp_algorithm
        echo 5G > /sys/block/zram0/disksize


Various recompression use cases:

- recompress huge pages using all secondary algos in order of priority
        echo "type=huge" > /sys/block/zram0/recompress

- recompress huge pages using zstd only
        echo "type=huge algo=zstd" > /sys/block/zram0/recompress

- recompress all pages using lz4
        echo "algo=lz4" > /sys/block/zram0/recompress

- recompress idle pages, use all algos in priority order, with threshold
        echo "type=idle threshold=3000" > /sys/block/zram0/recompress

- recompress idle pages, using zstd only, with threshold
        echo "algo=zstd type=idle threshold=2000" > /sys/block/zram0/recompress