linux-kernel - Re: [PATCH RFC -next 00/26] md/md-bitmap: introduce bitmap

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Message-ID: <9607d43d-5196-6a2a-dcd6-6471baaa3d70@huaweicloud.com>
Date: Tue, 13 Aug 2024 15:36:25 +0800
From: Yu Kuai <yukuai1@...weicloud.com>
To: Christoph Hellwig <hch@...radead.org>, Yu Kuai <yukuai1@...weicloud.com>
Cc: song@...nel.org, linux-kernel@...r.kernel.org,
 linux-raid@...r.kernel.org, yi.zhang@...wei.com, yangerkun@...wei.com,
 "yukuai (C)" <yukuai3@...wei.com>
Subject: Re: [PATCH RFC -next 00/26] md/md-bitmap: introduce bitmap_operations



在 2024/08/13 15:21, Christoph Hellwig 写道:
> On Sat, Aug 10, 2024 at 10:08:28AM +0800, Yu Kuai wrote:
>> From: Yu Kuai <yukuai3@...wei.com>
>>
>> The background is that currently bitmap is using a global spin_lock,
>> cauing lock contention and huge IO performance degration for all raid
>> levels.
>>
>> However, it's impossible to implement a new lock free bitmap with
>> current situation that md-bitmap exposes the internal implementation
>> with lots of exported apis. Hence bitmap_operations is invented, to
>> describe bitmap core implementation, and a new bitmap can be introduced
>> with a new bitmap_operations, we only need to switch to the new one
>> during initialization.
>>
>> And with this we can build bitmap as kernel module, but that's not
>> our concern for now.
>>
>> Noted I just compile this patchset, not tested yet.
> 
> Refactoring the bitmap code to be modular seems like a good idea.
> 
> But I'd just turn this into plain function calls and maybe a hidden
> data structure if you feel really fancy.  No need to introduce expensive
> indirect calls and a separate module.

Got it, and will make the struct bitmap a hidden structure in the next
version. This is exactly what I'm doing now locally, get rid of bitmap
direct dereference :).

Thanks for the review!
Kuai
> 
> .
>