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

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Message-ID: <CALC_0q8-98y0v_jV6QOFTKRAGhJ4nCXZ=q9wutLZPCE0KnKymw@mail.gmail.com>
Date: Fri, 20 Jun 2025 12:09:51 +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,
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

On Thu, Jun 19, 2025 at 10:28 AM Sergey Senozhatsky
<senozhatsky@...omium.org> wrote:
>
> On (25/06/18 13:26), Richard Chang wrote:
> > This commit introduces asynchronous writeback to zram, improving the
> > idle writeback speed.
>
> Can I please ask for significantly more details here?
> Justification, rationale, testing data/results, etc.