This section is bit misleading because the user process blocks forever if it doesn't do suspend and resume to drop transient data. drop_caches only drops data in the caching device to the backing store, not care about the transient data in rambuf.
Remove cache device
-------------------
If you want to detach your cache device for some reasons (you don't like
dm-writeboost anymore or you try to upgrade the cache device to a newly
perchased device) the safest way to do this is clean the dirty data up from your
cache device first and then deconstrust the dm-writeboost'd device.
You can use drop_caches message to forcibly clean up your cache device.
e.g.
dmsetup message wbdev 0 drop_caches
dmsetup remove wbdev
This section is bit misleading because the user process blocks forever if it doesn't do suspend and resume to drop transient data. drop_caches only drops data in the caching device to the backing store, not care about the transient data in rambuf.