X-Git-Url: https://git.kernel.dk/?p=fio.git;a=blobdiff_plain;f=HOWTO;h=6a7f58ed92d8fcc9e7a041e22b8a393c5786c425;hp=6ac744cd3d436124f8474ff135c7a842fb92136b;hb=c51074e7f095ad74114d7e0981f2e6f514b0f758;hpb=74b025b071b5bfbffa7ad7682b66b749e8d1f955

diff --git a/HOWTO b/HOWTO
index 6ac744cd..6a7f58ed 100644
--- a/HOWTO
+++ b/HOWTO
@@ -362,8 +362,34 @@ mem=str		Fio can use various types of memory as the io unit buffer.
 			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. Also see hugepage-size.
+
+		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.
+
+hugepage-size=siint
+		Defines the size of a huge page. Must at least be equal
+		to the system setting, see /proc/meminfo. Defaults to 4MiB.
+		Should probably always be a multiple of megabytes, so using
+		hugepage-size=Xm is the preferred way to set this to avoid
+		setting a non-pow-2 bad value.
 
 exitall		When one job finishes, terminate the rest. The default is
 		to wait for each job to finish, sometimes that is not the