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@xxxxxxxxx> wrote: > > Hi, Xiao > > Any ideas on this issue? > > Cheers, > > Miao Wang > > > 2021年06月09日 17:03，Wang Shanker <shankerwangmiao@xxxxxxxxx> 写道： > > > >> > >> 2021年06月09日 16:44，Xiao Ni <xni@xxxxxxxxxx> 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 >
