On Tue, May 20 2008, Jamie Lokier wrote:

Does WRITE_BARRIER always cause a flush?  It does not have to
according to Documentation/block/barrier.txt.  There are caveats about
tagged queuing "not yet implemented" in the text, but can we rely on
that?  The documentation is older than the current implementation;
those caveats might no longer apply.

It does, if you use ordered tags then that assumes write through
caching (or ordered tag + drain + flush after completion).

-- 
Jens Axboe