[PATCH] Allow mem=mmap to also use a file backing

[fio.git] / HOWTO

diff --git a/HOWTO b/HOWTO
index 996da23a1ce998665d1f9af7d65faaf064eced64..19182019f7020389e6e5e48391e8f2b6f58b5871 100644 (file)
--- a/HOWTO
+++ b/HOWTO
@@ -359,8 +359,10 @@ mem=str            Fio can use various types of memory as the io unit buffer.
 
                        shmhuge Same as shm, but use huge pages as backing.
 
-                       mmap    Use anonymous memory maps as the buffers.
-                               Allocated through mmap(2).
+                       mmap    Use mmap to allocate buffers. May either be
+                               anonymous memory, or can be file backed if
+                               a filename is given after the option. The
+                               format is mem=mmap:/path/to/file.
 
                        mmaphuge Use a memory mapped huge file as the buffer
                                backing. Append filename after mmaphuge, ala
@@ -378,12 +380,19 @@ mem=str           Fio can use various types of memory as the io unit buffer.
                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.
+               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
                desired action.