Hello! I noticed, that bcache is no longer caching reads on my system which makes it behave like if there were only hdds. I'm using two hdds in a raid 1 as the backing device and a single ssd as cache device: sda 8:0 0 111,8G 0 disk └─bcache0 252:0 0 921,9G 0 disk / sdb 8:16 0 931,5G 0 disk ├─sdb1 8:17 0 922G 0 part │ └─md0 9:0 0 921,9G 0 raid1 │ └─bcache0 252:0 0 921,9G 0 disk / ├─sdb2 8:18 0 1K 0 part ├─sdb5 8:21 0 1,9G 0 part │ └─md1 9:1 0 1,9G 0 raid1 /boot └─sdb6 8:22 0 7,6G 0 part [SWAP] sdc 8:32 0 931,5G 0 disk ├─sdc1 8:33 0 922G 0 part │ └─md0 9:0 0 921,9G 0 raid1 │ └─bcache0 252:0 0 921,9G 0 disk / ├─sdc2 8:34 0 1K 0 part ├─sdc5 8:37 0 1,9G 0 part │ └─md1 9:1 0 1,9G 0 raid1 /boot └─sdc6 8:38 0 7,6G 0 part [SWAP] For benchmarking every time I detach the cache device, stop the bcache device, do a wipefs on the cache device, then make-bcache -C /dev/sda and finally reattach the cache. After that, I'm using the following script to repeatedly read a 1gb file: #!/bin/sh echo 0 > /sys/block/bcache0/bcache/sequential_cutoff echo 0 > /sys/block/bcache0/bcache/cache/congested_read_threshold_us echo 0 > /sys/block/bcache0/bcache/cache/congested_write_threshold_us uname -a echo bcache-status echo echo "1st pass" sync; echo 3 > /proc/sys/vm/drop_caches (time cat 1GB.bin > /dev/null) echo echo "2nd pass" sync; echo 3 > /proc/sys/vm/drop_caches (time cat 1GB.bin > /dev/null) echo echo "3rd pass" sync; echo 3 > /proc/sys/vm/drop_caches (time cat 1GB.bin > /dev/null) bcache-status As you can see from the results below, kernel 4.18.20 is the last kernel, where the cache grows and the performance goes up. I also compiled 4.19.0 with the bcache files from 4.18.20 and much to my suprise, that didn't change 4.19's behavior - still no caching. So some other changes must be the culprit or I did something wrong. I'm not that much into compiling the kernel, but I checked out the 4.19.0 and 4.18.20 commits and replaced the 4.19.0 drivers/md/bcache directory with the one from 4.18.20 - then recompiled and installed the new kernel. So i am at my wits end. Any help would be appreciated. Thanks Flo Linux kkb 4.18.20-041820-generic #201812030624 SMP Mon Dec 3 11:25:55 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux --- bcache --- Device /dev/md0 (9:0) UUID 8275bf01-f0b3-423e-87fa-48336ce33068 Block Size 0.50KiB Bucket Size 512.00KiB Congested? False Read Congestion 0.0ms Write Congestion 0.0ms Total Cache Size 111.79GiB Total Cache Used 1.12GiB (0%) Total Cache Unused 110.67GiB (99%) Evictable Cache 111.79GiB (100%) Replacement Policy [lru] fifo random Cache Mode writethrough [writeback] writearound none Total Hits 0 (0%) Total Misses 6 Total Bypass Hits 0 Total Bypass Misses 0 Total Bypassed 0B 1st pass 0.00user 0.36system 0:08.58elapsed 4%CPU (0avgtext+0avgdata 2196maxresident)k 2097608inputs+0outputs (1major+113minor)pagefaults 0swaps 2nd pass 0.00user 0.32system 0:03.29elapsed 9%CPU (0avgtext+0avgdata 2100maxresident)k 2097184inputs+0outputs (1major+110minor)pagefaults 0swaps 3rd pass 0.00user 0.32system 0:02.64elapsed 12%CPU (0avgtext+0avgdata 2092maxresident)k 2097280inputs+0outputs (1major+111minor)pagefaults 0swaps --- bcache --- Device /dev/md0 (9:0) UUID 8275bf01-f0b3-423e-87fa-48336ce33068 Block Size 0.50KiB Bucket Size 512.00KiB Congested? False Read Congestion 0.0ms Write Congestion 0.0ms Total Cache Size 111.79GiB Total Cache Used 2.24GiB (2%) Total Cache Unused 109.55GiB (98%) Evictable Cache 110.67GiB (99%) Replacement Policy [lru] fifo random Cache Mode writethrough [writeback] writearound none Total Hits 5 (0%) Total Misses 4079 Total Bypass Hits 0 (0%) Total Bypass Misses 615 Total Bypassed 2.40MiB Linux kkb 4.19.0-041900-generic #201810221809 SMP Mon Oct 22 22:11:45 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux --- bcache --- Device /dev/md0 (9:0) UUID 67269654-92e8-4c3b-a524-8e8910082146 Block Size 0.50KiB Bucket Size 512.00KiB Congested? False Read Congestion 0.0ms Write Congestion 0.0ms Total Cache Size 111.79GiB Total Cache Used 1.12GiB (0%) Total Cache Unused 110.67GiB (99%) Evictable Cache 111.79GiB (100%) Replacement Policy [lru] fifo random Cache Mode writethrough [writeback] writearound none Total Hits 0 (0%) Total Misses 1 Total Bypass Hits 0 Total Bypass Misses 0 Total Bypassed 0B 1st pass 0.00user 0.33system 0:09.29elapsed 3%CPU (0avgtext+0avgdata 2280maxresident)k 2097624inputs+0outputs (1major+113minor)pagefaults 0swaps 2nd pass 0.00user 0.33system 0:08.47elapsed 4%CPU (0avgtext+0avgdata 2248maxresident)k 2097280inputs+0outputs (1major+111minor)pagefaults 0swaps 3rd pass 0.00user 0.37system 0:10.46elapsed 3%CPU (0avgtext+0avgdata 2220maxresident)k 2097616inputs+0outputs (1major+114minor)pagefaults 0swaps --- bcache --- Device /dev/md0 (9:0) UUID 67269654-92e8-4c3b-a524-8e8910082146 Block Size 0.50KiB Bucket Size 512.00KiB Congested? False Read Congestion 0.0ms Write Congestion 0.0ms Total Cache Size 111.79GiB Total Cache Used 1.12GiB (0%) Total Cache Unused 110.67GiB (99%) Evictable Cache 111.79GiB (100%) Replacement Policy [lru] fifo random Cache Mode writethrough [writeback] writearound none Total Hits 132 (23%) Total Misses 436 Total Bypass Hits 51 (0%) Total Bypass Misses 17399 Total Bypassed 43.50MiB Linux kkb 5.5.2-050502-generic #202002041931 SMP Tue Feb 4 19:33:15 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux --- bcache --- Device /dev/md0 (9:0) UUID 38a8b675-e332-4076-b0cf-44e4be72c300 Block Size 0.50KiB Bucket Size 512.00KiB Congested? False Read Congestion 0.0ms Write Congestion 0.0ms Total Cache Size 111.79GiB Total Cache Used 1.12GiB (0%) Total Cache Unused 110.67GiB (99%) Evictable Cache 111.79GiB (100%) Replacement Policy [lru] fifo random Cache Mode writethrough [writeback] writearound none Total Hits 0 (0%) Total Misses 1 Total Bypass Hits 0 (0%) Total Bypass Misses 3 Total Bypassed 52.00KiB 1st pass 0.00user 0.42system 0:09.21elapsed 4%CPU (0avgtext+0avgdata 2216maxresident)k 2097608inputs+0outputs (1major+112minor)pagefaults 0swaps 2nd pass 0.00user 0.42system 0:09.62elapsed 4%CPU (0avgtext+0avgdata 2248maxresident)k 2097280inputs+0outputs (1major+112minor)pagefaults 0swaps 3rd pass 0.00user 0.43system 0:08.75elapsed 5%CPU (0avgtext+0avgdata 2220maxresident)k 2097224inputs+0outputs (1major+114minor)pagefaults 0swaps --- bcache --- Device /dev/md0 (9:0) UUID 38a8b675-e332-4076-b0cf-44e4be72c300 Block Size 0.50KiB Bucket Size 512.00KiB Congested? False Read Congestion 0.0ms Write Congestion 0.0ms Total Cache Size 111.79GiB Total Cache Used 1.12GiB (0%) Total Cache Unused 110.67GiB (99%) Evictable Cache 111.79GiB (100%) Replacement Policy [lru] fifo random Cache Mode writethrough [writeback] writearound none Total Hits 121 (32%) Total Misses 246 Total Bypass Hits 15 (0%) Total Bypass Misses 12811 Total Bypassed 39.70MiB
