On 2021/3/2 下午9:20, Coly Li wrote: > On 3/2/21 6:20 PM, Norman.Kern wrote: >> Sorry for creating a new mail thread(the origin is so long...) >> >> >> I made a test again and get more infomation: >> >> root@WXS0089:~# cat /sys/block/bcache0/bcache/dirty_data >> 0.0k >> root@WXS0089:~# lsblk /dev/sda >> NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT >> sda 8:0 0 447.1G 0 disk >> `-bcache0 252:0 0 10.9T 0 disk >> root@WXS0089:~# cat /sys/block/sda/bcache/priority_stats >> Unused: 1% >> Clean: 29% >> Dirty: 70% >> Metadata: 0% >> Average: 49 >> Sectors per Q: 29184768 >> Quantiles: [1 2 3 5 6 8 9 11 13 14 16 19 21 23 26 29 32 36 39 43 48 53 59 65 73 83 94 109 129 156 203] >> root@WXS0089:~# cat /sys/fs/bcache/066319e1-8680-4b5b-adb8-49596319154b/internal/gc_after_writeback >> 1 >> You have new mail in /var/mail/root >> root@WXS0089:~# cat /sys/fs/bcache/066319e1-8680-4b5b-adb8-49596319154b/cache_available_percent >> 28 >> >> I read the source codes and found if cache_available_percent > 50, it should wakeup gc while doing writeback, but it seemed not work right. >> > If gc_after_writeback is enabled, and after it is enabled and the cache > usage > 50%, a tag BCH_DO_AUTO_GC will be set to c->gc_after_writeback. > Then when the writeback completed the gc thread will wake up in force. > > so the auto gc after writeback will be triggered when, > 1, the bcache device is in writeback mode > 2, gc_after_writeback set to 1 > 3, After 2) done, the cache usage exceeds 50% threshold. > 4, writeback rate set to maximum rate when the bcache device is idle (no > regular I/O request) > 5, after the writeback accomplished, the gc thread will be waken up. > > But /sys/block/bcache0/bcache/dirty_data is 0.0k doesn't mean the > writeback is accomplished. It is possible the writeback thread still > goes through all btree keys for the last try even all the dirty data are > flushed. Therefore you should check whether the writeback thread is > still active before a conclusion is made that the writeback is completed. > > BTW, do you try a Linux v5.8+ kernel and see how things are ? I stoped all rw tests for almost the whole day and no iops from iostat. When I echo 1 to trigger_gc the cache_available_percent changed for 29 to 100 in seconds. I will have a test on 5.8.0-44. > > Thanks. > > Coly Li
