Sometimes bcache_writebac task consumes 100% CPU during normal operation, but after a while (like a minute) this drops to normal.
It can be triggered in a reproducable fashion on my system by: echo 0 > /sys/block/bcache0/bcache/writeback_percent After this bcache_writebac starts to burn CPU cycles, and it never seems to stop doing so. changing the writeback_percent value back to 25 doesn't change anything. Apart from a busy CPU there appear to be no problem (e.g. no "task bcache_writebac:286 blocked for more than 120 seconds" messages). I filed this issue also on: https://bugzilla.kernel.org/show_bug.cgi?id=76391 [rolf.fokkens@home07 ~]$ bcache-status -s --- bcache --- UUID 4892b3d5-fd49-4d71-adb6-d7b0a799e913 Block Size 512 B Bucket Size 512.00 KiB Congested? False Read Congestion 0.0ms Write Congestion 0.0ms Total Cache Size 30 GiB Total Cache Used 2 GiB (6%) Total Cache Unused 28 GiB (94%) Evictable Cache 30 GiB (100%) Replacement Policy [lru] fifo random Cache Mode writethrough [writeback] writearound none Total Hits 31727 (99%) Total Misses 76 Total Bypass Hits 3569 (100%) Total Bypass Misses 0 Total Bypassed 27.5 MiB --- Backing Device --- Device File /dev/md2 (9:2) bcache Device File /dev/bcache0 (252:0) Size 140 GiB Cache Mode writethrough [writeback] writearound none Readahead 0 Sequential Cutoff 0 B Merge sequential? False State dirty Writeback? True Dirty Data 6.1 MiB Total Hits 31727 (99%) Total Misses 76 Total Bypass Hits 3569 (100%) Total Bypass Misses 0 Total Bypassed 27.5 MiB --- Cache Device --- Device File /dev/sdd1 (8:49) Size 30 GiB Block Size 512 B Bucket Size 512.00 KiB Replacement Policy [lru] fifo random Discard? True I/O Errors 0 Metadata Written 906.00 KiB Data Written 52.3 MiB Buckets 61440 Cache Used 2 GiB (6%) Cache Unused 28 GiB (94%) [rolf.fokkens@home07 ~]$ -- To unsubscribe from this list: send the line "unsubscribe linux-bcache" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
