By calling the device driver to write the page directly, we avoid
allocating a BIO, which allows us to free memory without allocating
memory.

[akpm@linux-foundation.org: fix used-uninitialized bug]
Signed-off-by: NMatthew Wilcox <matthew.r.wilcox@intel.com>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Dheeraj Reddy <dheeraj.reddy@intel.com>
Cc: Hugh Dickins <hughd@google.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>