On 2021/3/5 下午6:03, Coly Li wrote: > On 3/5/21 5:00 PM, Norman.Kern wrote: >> 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 have test on 5.8.X, but it doesn't help. I test on the same config on another server(480G SSD + 8T HDD), >> > What do you mean on "doesn't help" ? Do you mean the force gc does not > trigger, or something else. The cache_available_percent didn't reset to 100 automatically after all I/O done for a very long time. I must echo 1 to trigger_gc to help it recovered. > >> it can't reproduce, this really made me confused. I will compare the configs and try to find out the diffs. > For which behavior that it don't reproduce ? The problem of cache_available_percent not being recovered automatically. > > Thanks. > > Coly Li
