Dear DM Developers, I stumbled on a weird (and annoing) behaviour of dm-cache: after unclean reboot (sysrq + s,u,b) it marks all the cache as dirty and starts to write it back. This takes a few hours every time (cache data is on SSD, but backing storage is very slow for random access) and mostly kills interactivity for anything that touches the cached volume. This seems to ignore cache mode: write-through is also affected, even when it should not ever have a dirty state. Switching from write-through to write-back also resets cache to all-dirty and generates the same situation. Why is write-through cache considered dirty when switching to write-back? Is there a way to sort the requests, so the writes are monotonic wrt sector number? Can the dirty state be written to metadata storage on SysRq+S? Best Regards, Michał Mirosław --- # uname -a Linux qmqm 5.1.13mq+ #321 SMP PREEMPT Sun Jun 23 03:14:18 CEST 2019 x86_64 GNU/Linux # dmsetup table |grep sources fox-sources_corig: 0 335544320 linear 253:6 209717248 fox-sources_corig: 335544320 83886080 linear 253:6 1048578048 fox-sources_corig: 419430400 104857600 linear 253:6 1174407168 fox-c_sources_cdata: 0 31350784 linear 253:4 116736 fox-sources: 0 524288000 cache 253:12 253:11 253:13 64 2 metadata2 writethrough smq 0 fox-c_sources_cmeta: 0 57344 linear 253:4 59392 # lvmcache-stats fox/sources start 0 end 524288000 segment_type cache md_block_size 8 md_utilization 1480/7168 cache_block_size 64 cache_utilization 489856/489856 read_hits 2027069 read_misses 144887 read_hit_ratio 93.33% write_hits 331428 write_misses 112870 write_hit_ratio 74.60% demotions 0 promotions 0 dirty 314362 features 3 -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel