linux-kernel - Re: [PATCH RFC 4/7] zram: Introduce recompress sysfs knob

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Date:   Mon, 5 Sep 2022 19:17:52 +0900
From:   Sergey Senozhatsky <senozhatsky@...omium.org>
To:     Barry Song <21cnbao@...il.com>
Cc:     Sergey Senozhatsky <senozhatsky@...omium.org>,
        Minchan Kim <minchan@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Nitin Gupta <ngupta@...are.org>, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org
Subject: Re: [PATCH RFC 4/7] zram: Introduce recompress sysfs knob

On (22/09/05 22:06), Barry Song wrote:
> 
> make sense! thanks! i assume you will have some benchmark data to compare
> three cases,
> 1. lzo with recompress zstd
> 2. always use lzo
> 3. always use zstd
> 
> such as power consumption, cpu utilization, available memory, benefits to user
> experiences especially to UI smoothness under memory pressure?

So I didn't want to include any benchmarks, because this is entirely
specific to device's data sets/patterns. In term of CPU usage, zstd
decompression is really fast [1]; and the way plan to use is battery
aware - e.g. when low on battery do not recompress at all, if AC is
plugged in then recompress more aggressively, etc.

In term of benchmarks... a copy paste from our internal tests. But
*do note* that this is relative only to our specific data sets.
Your millage may vary.

ZSTD recomp algorithm (5.10 kernel, so the last column is the number of
'zram huge pages'):

- Initial state of zram swap partition
localhost ~ # cat /sys/block/zram0/mm_stat 
8955662336 2180671776 2277711872        0 3179720704   798724   469474   118949

- Recompress HUGE objects only
localhost ~ # echo huge > /sys/block/zram0/recompress 
localhost ~ # cat /sys/block/zram0/mm_stat 
8944390144 2106998658 2211835904        0 3179720704   798617   469474    66821

- Recompress IDLE pages that are >= 3000 bytes in size
localhost ~ # echo 3000 > /sys/block/zram0/recompress 
localhost ~ # cat /sys/block/zram0/mm_stat 
8934166528 2085232505 2207690752        0 3179720704   798484   469474    66811

- Recompress the remaining IDLE pages that are >= 2000 bytes in size
localhost ~ # echo 2000 > /sys/block/zram0/recompress 
localhost ~ # cat /sys/block/zram0/mm_stat 
8913981440 1946488434 2145157120        0 3179720704   798130   469474    66498

- Recompress the remaining IDLE pages that are >= 1000 bytes in size
localhost ~ # echo 1000 > /sys/block/zram0/recompress 
localhost ~ # cat /sys/block/zram0/mm_stat 
8905592832 1711533182 1984495616        0 3179720704   797162   469474    66222

[1] https://facebook.github.io/zstd/