linux-kernel - Re: [PATCH] zram: support asynchronous writeback

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Message-ID: <CALC_0q-aRtNS8c00nCD0key27UH9-_2kW=PoXQKrLQ5bg6MU_A@mail.gmail.com>
Date: Fri, 20 Jun 2025 13:56:36 +0800
From: Richard Chang <richardycc@...gle.com>
To: Sergey Senozhatsky <senozhatsky@...omium.org>
Cc: Minchan Kim <minchan@...nel.org>, Jens Axboe <axboe@...nel.dk>, bgeffon@...gle.com, 
	liumartin@...gle.com, linux-kernel@...r.kernel.org, 
	linux-block@...r.kernel.org
Subject: Re: [PATCH] zram: support asynchronous writeback

Hi Sergey,
I copied three linux-6.16-rc2.tar.gz tarball files as the data set.

Test Flow:
- mkfs on the zram device, mount it
- cp tarball files
- do idle writeback
- check bd_stat writes 185072 pages

On Fri, Jun 20, 2025 at 12:15 PM Sergey Senozhatsky
<senozhatsky@...omium.org> wrote:
>
> Hi,
>
> On (25/06/20 12:09), Richard Chang wrote:
> > Hi Sergey,
> > The main idea is to replace submit_bio_wait() to submit_bio(), remove
> > the one-by-one IO, and rely on the underlying backing device to handle
> > the asynchronous IO requests.
> > From my testing results on Android, the idle writeback speed increased 27%.
> >
> > idle writeback for 185072 4k-pages (~723 MiB)
> > $ echo all > /sys/block/zram0/idle
> > $ time echo idle > /sys/block/zram0/writeback
> >
> > Async writeback:
> > 0m02.49s real     0m00.00s user     0m01.19s system
> > 0m02.32s real     0m00.00s user     0m00.89s system
> > 0m02.35s real     0m00.00s user     0m00.93s system
> > 0m02.29s real     0m00.00s user     0m00.88s system
> >
> > Sync writeback:
> > 0m03.09s real     0m00.00s user     0m01.07s system
> > 0m03.18s real     0m00.00s user     0m01.12s system
> > 0m03.47s real     0m00.00s user     0m01.16s system
> > 0m03.36s real     0m00.00s user     0m01.27s system
>
> Has this been tested on exactly same data sets? page-to-page comparable?
> We decompress before writeback, so if the data had different compression
> ratios, different number of incompressible objects, etc. then the results
> are not directly comparable.