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

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Message-ID: <x54netqswex6fpv46nlmeea3ebnm32xnwask4zxw7nmcn7tqdz@4mu4hwsa7hsb>
Date: Fri, 20 Jun 2025 13:15:38 +0900
From: Sergey Senozhatsky <senozhatsky@...omium.org>
To: Richard Chang <richardycc@...gle.com>
Cc: Sergey Senozhatsky <senozhatsky@...omium.org>, 
	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,

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.