linux-kernel - Re: [PATCH 12/23] md/md-bitmap: add macros for lockless bitmap

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Message-ID: <40af768d-373c-4a56-8af5-82aeabe49515@huaweicloud.com>
Date: Mon, 26 May 2025 16:12:06 +0800
From: Yu Kuai <yukuai1@...weicloud.com>
To: Christoph Hellwig <hch@....de>, Yu Kuai <yukuai1@...weicloud.com>
Cc: xni@...hat.com, colyli@...nel.org, song@...nel.org,
 linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-raid@...r.kernel.org, yi.zhang@...wei.com, yangerkun@...wei.com,
 johnny.chenyi@...wei.com, "yukuai (C)" <yukuai3@...wei.com>
Subject: Re: [PATCH 12/23] md/md-bitmap: add macros for lockless bitmap

Hi,

在 2025/05/26 14:40, Christoph Hellwig 写道:
> On Sat, May 24, 2025 at 02:13:09PM +0800, Yu Kuai wrote:
>> From: Yu Kuai <yukuai3@...wei.com>
>>
>> Also move other values to md-bitmap.h and update comments.
> 
> Hmm.  The commit message looks very confusing to me.
> 
> I think this should be two patches:
> 
>   1) move defines relevant to the disk format from md-bitmap.c to md-bitmap.h
>   2) add new bits for llbitmap (and explain what they are).

OK.

> 
>> +#define BITMAP_SB_SIZE 1024
> 
> And while we're at it: this is still duplicated in llbitmap.c later.
> But shouldn't it simply be replaced with a sizeof on struct bitmap_super_s?

Sorry that I forgot to explain why it's still in .c

sizeof(struct bitmap_super_s) is actually 256 bytes, while by default,
1k is reserved, perhaps I can name it as BITMAP_DATA_OFFSET ?

0-255B		bitmap_super_s
256-1023B	hole
1024-[space]	bitmap
[space] - 128k	hole

BTW, the new bitmap only support the default offset and space, user
can't configure it manually.

Thanks,
Kuai

> 
> (and when cleaning thing up, rename that to bitmap_super without
> the _s and use it instead of the typedef at least for all new code)?
> .
>