Description of problem:
Current implementation of map function in dm-crypt waits for
earlies items to complete to solve insufficient memory situations.
/* out of memory -> run queues */
This will not work after reduce stack changes in generic_make_request()
which will not process IOs immediately.
Processing of map request and most of its workload should be moved
to dm-crypt workqueue.
Already in RHEL5beta2 (from upstream).