linux-block.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Xiao Ni <xni@redhat.com>
To: Wang Shanker <shankerwangmiao@gmail.com>
Cc: Ming Lei <ming.lei@redhat.com>,
	linux-raid@vger.kernel.org, linux-block@vger.kernel.org
Subject: Re: [Bug Report] Discard bios cannot be correctly merged in blk-mq
Date: Fri, 18 Jun 2021 20:49:21 +0800	[thread overview]
Message-ID: <CALTww29rcAwSfbpsBzM_pnVSuVTYyt-YJryeUaNkHetCjXktCg@mail.gmail.com> (raw)
In-Reply-To: <13C1B2E3-B177-4B05-9FF3-AEE57E964605@gmail.com>

Hi Miao

So you plan to fix this problem now? The plan is to submit the discard
bio directly to disk similar with raid0/raid10.
As we talked, it needs to consider the discard region. It should be
larger than chunk_sectors * nr_data_disks. It needs
to split the bio when its size not aligned with chunk_sectors *
nr_data_disks. And it needs to consider the start address
of the bio too. If it's not aligned with a start address of
chunk_sectors, it's better to split this part too.

I'm working on another job. So I don't have time to do this now. If
you submit the patches, I can help to review :)

Regards
Xiao

On Fri, Jun 18, 2021 at 2:28 PM Wang Shanker <shankerwangmiao@gmail.com> wrote:
>
> Hi, Xiao
>
> Any ideas on this issue?
>
> Cheers,
>
> Miao Wang
>
> > 2021年06月09日 17:03,Wang Shanker <shankerwangmiao@gmail.com> 写道:
> >
> >>
> >> 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:[~2021-06-18 12:49 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
2021-06-18  6:28             ` Wang Shanker
2021-06-18 12:49               ` Xiao Ni [this message]
2021-06-21  7:49                 ` Wang Shanker
2021-06-22  1:48                   ` Xiao Ni

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=CALTww29rcAwSfbpsBzM_pnVSuVTYyt-YJryeUaNkHetCjXktCg@mail.gmail.com \
    --to=xni@redhat.com \
    --cc=linux-block@vger.kernel.org \
    --cc=linux-raid@vger.kernel.org \
    --cc=ming.lei@redhat.com \
    --cc=shankerwangmiao@gmail.com \
    --subject='Re: [Bug Report] Discard bios cannot be correctly merged in blk-mq' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).