linux-kernel - Re: [PATCHv4 2/9] zram: Add recompression algorithm sysfs knob

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Message-ID: <Y2mlb6F7G8KskRch@google.com>
Date:   Tue, 8 Nov 2022 09:40:15 +0900
From:   Sergey Senozhatsky <senozhatsky@...omium.org>
To:     Minchan Kim <minchan@...nel.org>
Cc:     Sergey Senozhatsky <senozhatsky@...omium.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Nitin Gupta <ngupta@...are.org>, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org
Subject: Re: [PATCHv4 2/9] zram: Add recompression algorithm sysfs knob

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