linux-kernel - Re: [PATCH md-6.13] md: remove bitmap file support

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Message-ID: <CALtW_ajYN4byY_hWLyKadAyLa9Rmi==j6yCYjLLUuR_nttKMrQ@mail.gmail.com>
Date: Fri, 8 Nov 2024 23:19:40 +0100
From: Dragan Milivojević <galileo@...-inc.com>
To: Yu Kuai <yukuai1@...weicloud.com>
Cc: Song Liu <song@...nel.org>, linux-raid@...r.kernel.org, 
	linux-kernel@...r.kernel.org, yi.zhang@...wei.com, yangerkun@...wei.com, 
	"yukuai (C)" <yukuai3@...wei.com>
Subject: Re: [PATCH md-6.13] md: remove bitmap file support

On Fri, 8 Nov 2024 at 07:07, Yu Kuai <yukuai1@...weicloud.com> wrote:


> I don't think external bitmap can workaround the performance degradation
> problem, because the global lock for the bitmap are the one to blame for
> this, it's the same for external or internal bitmap.

Not according to my tests:

5 disk RAID5, 64K chunk



Test                   BW         IOPS
bitmap internal 64M    700KiB/s   174
bitmap internal 128M   702KiB/s   175
bitmap internal 512M   1142KiB/s  285
bitmap internal 1024M  40.4MiB/s  10.3k
bitmap internal 2G     66.5MiB/s  17.0k
bitmap external 64M    67.8MiB/s  17.3k
bitmap external 1024M  76.5MiB/s  19.6k
bitmap none            80.6MiB/s  20.6k
Single disk 1K         54.1MiB/s  55.4k
Single disk 4K         269MiB/s   68.8k



Full test logs with system details at: pastebin. com/raw/TK4vWjQu


>
> Do you know that is there anyone using external bitmap in the real
> world? And is there numbers for performance? We'll have to consider
> to keep it untill the new lockless bitmap is ready if so.

Well I am and it's a royal pain but there isn't much of an alternative.