docs: update discussion of huge page sizes

[fio.git] / HOWTO.rst

diff --git a/HOWTO.rst b/HOWTO.rst
index eee386c146cb88ce4110b18afa7ba1bb917773c7..58d02fa24c89cce5e1f6f1a9bf39c4c39dde99b8 100644 (file)
--- a/HOWTO.rst
+++ b/HOWTO.rst
@@ -1823,13 +1823,14 @@ Buffers and memory
        **mmaphuge** to work, the system must have free huge pages allocated. This
        can normally be checked and set by reading/writing
        :file:`/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 I/O depth of all jobs (normally one unless
-       :option:`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
-       :file:`/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 :option:`hugepage-size`.
+        is 2 or 4MiB in size depending on the platform. So to calculate the
+        number of huge pages you need for a given job file, add up the I/O
+        depth of all jobs (normally one unless :option:`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
+        :file:`/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 :option:`hugepage-size`.
 
        **mmaphuge** also needs to have hugetlbfs mounted and the file location
        should point there. So if it's mounted in :file:`/huge`, you would use
@@ -1848,10 +1849,12 @@ Buffers and memory
 
 .. option:: hugepage-size=int
 
-       Defines the size of a huge page. Must at least be equal to the system
-       setting, see :file:`/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.
+        Defines the size of a huge page. Must at least be equal to the system
+        setting, see :file:`/proc/meminfo` and
+        :file:`/sys/kernel/mm/hugepages/`. Defaults to 2 or 4MiB depending on
+        the platform.  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.
 
 .. option:: lockmem=int