Re: [PATCH V2 0/5] md/raid10: Improve handling raid10 discard request

[Xiao Ni <xni@redhat.com>]

Hi Song

Please ignore the v2 version. There is a place that needs to be fix. 
I'll re-send
v2 version again.

Regards
Xiao

On 02/04/2021 01:57 PM, Xiao Ni wrote:
> Hi all
>
> Now mkfs on raid10 which is combined with ssd/nvme disks takes a long time.
> This patch set tries to resolve this problem.
>
> This patch set had been reverted because of a data corruption problem. This
> version fix this problem. The root cause which causes the data corruption is
> the wrong calculation of start address of near copies disks.
>
> Now we use a similar way with raid0 to handle discard request for raid10.
> Because the discard region is very big, we can calculate the start/end
> address for each disk. Then we can submit the discard request to each disk.
> But for raid10, it has copies. For near layout, if the discard request
> doesn't align with chunk size, we calculate a start_disk_offset. Now we only
> use start_disk_offset for the first disk, but it should be used for the
> near copies disks too.
>
> [  789.709501] discard bio start : 70968, size : 191176
> [  789.709507] first stripe index 69, start disk index 0, start disk offset 70968
> [  789.709509] last stripe index 256, end disk index 0, end disk offset 262144
> [  789.709511] disk 0, dev start : 70968, dev end : 262144
> [  789.709515] disk 1, dev start : 70656, dev end : 262144
>
> For example, in this test case, it has 2 near copies. The start_disk_offset
> for the first disk is 70968. It should use the same offset address for second disk.
> But it uses the start address of this chunk. It discard more region. This version
> simply spilt the un-aligned part with strip size.
>
> And it fixes another problem. The calculation of stripe_size is wrong in reverted version.
>
> V2: Fix problems pointed by Christoph Hellwig.
>
> Xiao Ni (5):
>    md: add md_submit_discard_bio() for submitting discard bio
>    md/raid10: extend r10bio devs to raid disks
>    md/raid10: pull the code that wait for blocked dev into one function
>    md/raid10: improve raid10 discard request
>    md/raid10: improve discard request for far layout
>
>   drivers/md/md.c     |  20 +++
>   drivers/md/md.h     |   2 +
>   drivers/md/raid0.c  |  14 +-
>   drivers/md/raid10.c | 434 +++++++++++++++++++++++++++++++++++++++++++++-------
>   drivers/md/raid10.h |   1 +
>   5 files changed, 402 insertions(+), 69 deletions(-)
>