linux-kernel - Re: [PATCH v7 md-6.18 11/11] md/md-llbitmap: introduce new lockless bitmap

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Message-ID: <e4da9027-abb4-76d1-04df-fff9798baae1@huaweicloud.com>
Date: Thu, 4 Sep 2025 17:19:45 +0800
From: Li Nan <linan666@...weicloud.com>
To: Yu Kuai <yukuai1@...weicloud.com>, hch@...radead.org, xni@...hat.com,
 colyli@...nel.org, corbet@....net, agk@...hat.com, snitzer@...nel.org,
 mpatocka@...hat.com, song@...nel.org, yukuai3@...wei.com, hare@...e.de
Cc: linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
 dm-devel@...ts.linux.dev, linux-raid@...r.kernel.org, yi.zhang@...wei.com,
 yangerkun@...wei.com, johnny.chenyi@...wei.com, hailan@...uai.org.cn
Subject: Re: [PATCH v7 md-6.18 11/11] md/md-llbitmap: introduce new lockless
 bitmap



在 2025/8/29 16:04, Yu Kuai 写道:
> From: Yu Kuai <yukuai3@...wei.com>
> 
> Redundant data is used to enhance data fault tolerance, and the storage
> method for redundant data vary depending on the RAID levels. And it's
> important to maintain the consistency of redundant data.
> 
> Bitmap is used to record which data blocks have been synchronized and which
> ones need to be resynchronized or recovered. Each bit in the bitmap
> represents a segment of data in the array. When a bit is set, it indicates
> that the multiple redundant copies of that data segment may not be
> consistent. Data synchronization can be performed based on the bitmap after
> power failure or readding a disk. If there is no bitmap, a full disk
> synchronization is required.
> 
> Due to known performance issues with md-bitmap and the unreasonable
> implementations:
> 
>   - self-managed IO submitting like filemap_write_page();
>   - global spin_lock
> 
> I have decided not to continue optimizing based on the current bitmap
> implementation, this new bitmap is invented without locking from IO fast
> path and can be used with fast disks.
> 
> For designs and details, see the comments in drivers/md-llbitmap.c.
> 
> Signed-off-by: Yu Kuai <yukuai3@...wei.com>

LGTM

Reviewed-by: Li Nan <linan122@...wei.com>

-- 
Thanks,
Nan