docs: update discussion of huge page sizes

[fio.git] / fio.1

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