On Mon, Jun 30, 2025 at 10:34 AM Yu Kuai <yukuai1@xxxxxxxxxxxxxxx> wrote: > > Hi, > > 在 2025/06/30 9:59, Xiao Ni 写道: > > > > After reading other patches, I want to check if I understand right. > > > > The first write sets the bitmap bit. The second write which hits the > > same block (one sector, 512 bits) will call llbitmap_infect_dirty_bits > > to set all other bits. Then the third write doesn't need to set bitmap > > bits. If I'm right, the comments above should say only the first two > > writes have additional overhead? > > Yes, for the same bit, it's twice; For different bit in the same block, > it's third, by infect all bits in the block in the second. For different bits in the same block, test_and_set_bit(bit, pctl->dirty) should be true too, right? So it infects other bits when second write hits the same block too. [946761.035079] llbitmap_set_page_dirty:390 page[0] offset 2024, block 3 [946761.035430] llbitmap_state_machine:646 delay raid456 initial recovery [946761.035802] llbitmap_state_machine:652 bit 1001 state from 0 to 3 [946761.036498] llbitmap_set_page_dirty:390 page[0] offset 2025, block 3 [946761.036856] llbitmap_set_page_dirty:403 call llbitmap_infect_dirty_bits As the debug logs show, different bits in the same block, the second write (offset 2025) infects other bits. > > For Reload action, if the bitmap bit is > > NeedSync, the changed status will be x. It can't trigger resync/recovery. > > This is not expected, see llbitmap_state_machine(), if old or new state > is need_sync, it will trigger a resync. > > c = llbitmap_read(llbitmap, start); > if (c == BitNeedSync) > need_resync = true; > -> for RELOAD case, need_resync is still set. > > state = state_machine[c][action]; > if (state == BitNone) > continue If bitmap bit is BitNeedSync, state_machine[BitNeedSync][BitmapActionReload] returns BitNone, so if (state == BitNone) is true, it can't set MD_RECOVERY_NEEDED and it can't start sync after assembling the array. > if (state == BitNeedSync) > need_resync = true; > > > > > For example: > > > > cat /sys/block/md127/md/llbitmap/bits > > unwritten 3480 > > clean 2 > > dirty 0 > > need sync 510 > > > > It doesn't do resync after aseembling the array. Does it need to modify > > the changed status from x to NeedSync? > > Can you explain in detail how to reporduce this? Aseembling in my VM is > fine. I added many debug logs, so the sync request runs slowly. The test I do: mdadm -CR /dev/md0 -l5 -n3 /dev/loop[0-2] --bitmap=lockless -x 1 /dev/loop3 dd if=/dev/zero of=/dev/md0 bs=1M count=1 seek=500 oflag=direct mdadm --stop /dev/md0 (the sync thread finishes the region that two bitmap bits represent, so you can see llbitmap/bits has 510 bits (need sync)) mdadm -As Regards Xiao > > Thanks, > Kuai > >
