Add softrandommap and --alloc-size options

The softrandommap job option allows fio to continue if it cannot
allocate from the smalloc backing for the random map. Or the user
can specify --alloc-size with a size larger than the default of 1024k
to increase the size of the shared allocation pool.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/HOWTO b/HOWTO
index 3d92293..66ebebe 100644
--- a/HOWTO
+++ b/HOWTO
@@ -482,6 +482,12 @@
 		fio doesn't track potential block rewrites which may alter
 		the calculated checksum for that block.
 
+softrandommap	See norandommap. If fio runs with the random block map enabled
+		and it fails to allocate the map, if this option is set it
+		will continue without a random block map. As coverage will
+		not be as complete as with random maps, this option is
+		disabled by default.
+
 nice=int	Run the job with the given nice value. See man nice(2).
 
 prio=int	Set the io priority value of this job. Linux limits us to