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

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Message-ID: <36659c34-08bf-2103-a762-ce9e75e8262e@huaweicloud.com>
Date: Sat, 9 Nov 2024 09:43:54 +0800
From: Yu Kuai <yukuai1@...weicloud.com>
To: Dragan Milivojević <galileo@...-inc.com>,
 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

Hi,

在 2024/11/09 6:19, Dragan Milivojević 写道:
> 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

This is not what I expected, can you give the tests procedures in
details? Including test machine, create the array and test scrpits.

> 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.

Bitmap file will be removed, the way it's implemented is problematic. If
you have plans to upgrade kernel to v6.13+, I can keep it for now,
untill the other lockless bitmap is ready.

Thanks,
Kuai

> .
>