[dm-devel] [PATCH 0/2 v2] Fix fallout from changes to FUA and PREFLUSH definitions

[Jan Kara]

Hello,

here are patches for DM/MD that address a possible performance issue caused by
commit b685d3d65ac7 "block: treat REQ_FUA and REQ_PREFLUSH as synchronous".

The core of the problem is that above mentioned commit removed REQ_SYNC flag
from WRITE_{FUA|PREFLUSH|...} definitions.  generic_make_request_checks()
however strips REQ_FUA and REQ_PREFLUSH flags from a bio when the storage
doesn't report volatile write cache and thus write effectively becomes
asynchronous which can lead to performance regressions.

DM/MD guys, can you please have a look at patches and take them through your
trees? Thanks!

								Honza