docs: update discussion of huge page sizes

Note that the default huge page size is either 2 or 4 MiB, depending on
the platform. Also mention /sys/kernel/mm/hugepages/ as another place to
see the supported huge page sizes.

Signed-off-by: Vincent Fu <vincent.fu@samsung.com>
Link: https://lore.kernel.org/r/20220524142229.135808-6-vincent.fu@samsung.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

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
 

diff --git a/fio.1 b/fio.1
index ded7bbfc993bd431a10a034a1c63e14d765d44e1..5f0575742cc91c3eef542a7fe49f0c8fecf03940 100644 (file)
--- a/fio.1
+++ b/fio.1
@@ -1631,11 +1631,11 @@ multiplied by the I/O depth given. Note that for \fBshmhuge\fR and
 \fBmmaphuge\fR 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 I/O depth of all jobs (normally one unless
-\fBiodepth\fR 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
+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 \fBiodepth\fR 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 \fBmmaphuge\fR or \fBshmhuge\fR will fail. Also
 see \fBhugepage\-size\fR.
 .P
@@ -1655,10 +1655,11 @@ of subsequent I/O memory buffers is the sum of the \fBiomem_align\fR and
 \fBbs\fR used.
 .TP
 .BI hugepage\-size \fR=\fPint
-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.
+Defines the size of a huge page. Must at least be equal to the system setting,
+see `/proc/meminfo' and `/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.
 .TP
 .BI lockmem \fR=\fPint
 Pin the specified amount of memory with \fBmlock\fR\|(2). Can be used to