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

[Barry Song <21cnbao@gmail.com>]

On Mon, Sep 5, 2022 at 10:17 PM Sergey Senozhatsky
<senozhatsky@chromium.org> wrote:
>
> 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/

Thanks very much. I guess the difficulty is that we need to
comprehensively evaluate its
effect on a real product such as android. there is always a trade-off
between cpu utilization
and more available memory.

Best Regards
Barry