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diff --git a/HOWTO b/HOWTO
index 2616156d..996da23a 100644
--- a/HOWTO
+++ b/HOWTO
@@ -218,22 +218,22 @@ size=siint	The total size of file io for this job. This may describe
 		size if larger than the current file size. If this parameter
 		is not given and the file exists, the file size will be used.
 
-bs=siint	The block size used for the io units. Defaults to 4k.
-
-read_bs=siint
-write_bs=siint	If the workload is a mixed read-write workload, you can use
-		these options to set separate block sizes.
+bs=siint	The block size used for the io units. Defaults to 4k. Values
+		can be given for both read and writes. If a single siint is
+		given, it will apply to both. If a second siint is specified
+		after a comma, it will apply to writes only. In other words,
+		the format is either bs=read_and_write or bs=read,write.
+		bs=4k,8k will thus use 4k blocks for reads, and 8k blocks
+		for writes. If you only wish to set the write size, you
+		can do so by passing an empty read size - bs=,8k will set
+		8k for writes and leave the read default value.
 
 bsrange=irange	Instead of giving a single block size, specify a range
 		and fio will mix the issued io block sizes. The issued
 		io unit will always be a multiple of the minimum value
-		given (also see bs_unaligned).
-
-read_bsrange=irange
-write_bsrange=irange
-		If the workload is a mixed read-write workload, you can use
-		one of these options to set separate block size ranges for
-		reads and writes.
+		given (also see bs_unaligned). Applies to both reads and
+		writes, however a second range can be given after a comma.
+		See bs=.
 
 bs_unaligned	If this option is given, any byte size value within bsrange
 		may be used as a block range. This typically wont work with
@@ -264,6 +264,10 @@ ioengine=str	Defines how the job issues io to the file. The following
 				we use read(2) and write(2) for asynchronous
 				io.
 
+			null	Doesn't transfer any data, just pretends
+				to. This is mainly used to exercise fio
+				itself and for debugging/testing purposes.
+
 iodepth=int	This defines how many io units to keep in flight against
 		the file. The default is 1 for each file defined in this
 		job, can be overridden with a larger value for higher
@@ -353,11 +357,32 @@ mem=str		Fio can use various types of memory as the io unit buffer.
 			shm	Use shared memory as the buffers. Allocated
 				through shmget(2).
 
+			shmhuge	Same as shm, but use huge pages as backing.
+
 			mmap	Use anonymous memory maps as the buffers.
 				Allocated through mmap(2).
 
+			mmaphuge Use a memory mapped huge file as the buffer
+				backing. Append filename after mmaphuge, ala
+				mem=mmaphuge:/hugetlbfs/file
+
 		The area allocated is a function of the maximum allowed
-		bs size for the job, multiplied by the io depth given.
+		bs size for the job, multiplied by the io depth given. Note
+		that for shmhuge and mmaphuge to work, the system must have
+		free huge pages allocated. This can normally be checked
+		and set by reading/writing /proc/sys/vm/nr_hugepages on a
+		Linux system. Fio assumes a huge page is 4MiB in size. So
+		to calculate the number of huge pages you need for a given
+		job file, add up the io depth of all jobs (normally one unless
+		iodepth= is used) and multiply by the maximum bs set. Then
+		divide that number by the huge page size. You can see the
+		size of the huge pages in /proc/meminfo. If no huge pages
+		are allocated by having a non-zero number in nr_hugepages,
+		using mmaphuge or shmhuge will fail.
+
+		mmaphuge also needs to have hugetlbfs mounted and the file
+		location should point there. So if it's mounted in /huge,
+		you would use mem=mmaphuge:/huge/somefile.
 
 exitall		When one job finishes, terminate the rest. The default is
 		to wait for each job to finish, sometimes that is not the