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From: Wang Shanker <shankerwangmiao@gmail.com>
To: Xiao Ni <xni@redhat.com>
Cc: Ming Lei <ming.lei@redhat.com>,
	linux-block@vger.kernel.org, linux-raid@vger.kernel.org
Subject: Re: [Bug Report] Discard bios cannot be correctly merged in blk-mq
Date: Wed, 9 Jun 2021 17:03:22 +0800	[thread overview]
Message-ID: <ED5B1993-9D44-4B9C-A7DF-72BD2375A216@gmail.com> (raw)
In-Reply-To: <CALTww28L7afRdVdBf-KsyF6Hvf-8-CORSCpZJAvnVbDRo6chDQ@mail.gmail.com>


> 2021年06月09日 16:44,Xiao Ni <xni@redhat.com> 写道:
> 
> Hi all
> 
> Thanks for reporting about this. I did a test in my environment.
> time blkdiscard /dev/nvme5n1  (477GB)
> real    0m0.398s
> time blkdiscard /dev/md0
> real    9m16.569s
> 
> I'm not familiar with the block layer codes. I'll try to understand
> the codes related with discard request and
> try to fix this problem.
> 
> I have a question for raid5 discard, it needs to consider more than
> raid0 and raid10. For example, there is a raid5 with 3 disks.
> D11 D21 P1 (stripe size is 4KB)
> D12 D22 P2
> D13 D23 P3
> D14 D24 P4
> ...  (chunk size is 512KB)
> If there is a discard request on D13 and D14, and there is no discard
> request on D23 D24. It can't send
> discard request to D13 and D14, right? P3 = D23 xor D13. If we discard
> D13 and disk2 is broken, it can't
> get the right data from D13 and P3. The discard request on D13 can
> write 0 to the discard region, right?

Yes. It can be seen at the beginning of make_discard_request(), where
the requested range being discarded is aligned to ``stripe_sectors", 
which should be chunk_sectors * nr_data_disks.

Cheers,

Miao Wang


  reply	other threads:[~2021-06-09  9:04 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-06-05 20:54 Wang Shanker
2021-06-05 22:38 ` antlists
2021-06-06  3:44   ` Wang Shanker
2021-06-07 13:07 ` Ming Lei
2021-06-08 15:49   ` Wang Shanker
2021-06-09  0:41     ` Ming Lei
2021-06-09  2:40       ` Wang Shanker
2021-06-09  8:44         ` Xiao Ni
2021-06-09  9:03           ` Wang Shanker [this message]
2021-06-18  6:28             ` Wang Shanker
2021-06-18 12:49               ` Xiao Ni
2021-06-21  7:49                 ` Wang Shanker
2021-06-22  1:48                   ` Xiao Ni

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