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. > 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 ? Thanks. Coly Li
