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-rw-r--r--Documentation/admin-guide/mm/hugetlbpage.rst42
1 files changed, 39 insertions, 3 deletions
diff --git a/Documentation/admin-guide/mm/hugetlbpage.rst b/Documentation/admin-guide/mm/hugetlbpage.rst
index 8abaeb144e44..0166f9de3428 100644
--- a/Documentation/admin-guide/mm/hugetlbpage.rst
+++ b/Documentation/admin-guide/mm/hugetlbpage.rst
@@ -128,7 +128,9 @@ hugepages
implicitly specifies the number of huge pages of default size to
allocate. If the number of huge pages of default size is implicitly
specified, it can not be overwritten by a hugepagesz,hugepages
- parameter pair for the default size.
+ parameter pair for the default size. This parameter also has a
+ node format. The node format specifies the number of huge pages
+ to allocate on specific nodes.
For example, on an architecture with 2M default huge page size::
@@ -138,6 +140,14 @@ hugepages
indicating that the hugepages=512 parameter is ignored. If a hugepages
parameter is preceded by an invalid hugepagesz parameter, it will
be ignored.
+
+ Node format example::
+
+ hugepagesz=2M hugepages=0:1,1:2
+
+ It will allocate 1 2M hugepage on node0 and 2 2M hugepages on node1.
+ If the node number is invalid, the parameter will be ignored.
+
default_hugepagesz
Specify the default huge page size. This parameter can
only be specified once on the command line. default_hugepagesz can
@@ -234,8 +244,12 @@ will exist, of the form::
hugepages-${size}kB
-Inside each of these directories, the same set of files will exist::
+Inside each of these directories, the set of files contained in ``/proc``
+will exist. In addition, two additional interfaces for demoting huge
+pages may exist::
+ demote
+ demote_size
nr_hugepages
nr_hugepages_mempolicy
nr_overcommit_hugepages
@@ -243,7 +257,29 @@ Inside each of these directories, the same set of files will exist::
resv_hugepages
surplus_hugepages
-which function as described above for the default huge page-sized case.
+The demote interfaces provide the ability to split a huge page into
+smaller huge pages. For example, the x86 architecture supports both
+1GB and 2MB huge pages sizes. A 1GB huge page can be split into 512
+2MB huge pages. Demote interfaces are not available for the smallest
+huge page size. The demote interfaces are:
+
+demote_size
+ is the size of demoted pages. When a page is demoted a corresponding
+ number of huge pages of demote_size will be created. By default,
+ demote_size is set to the next smaller huge page size. If there are
+ multiple smaller huge page sizes, demote_size can be set to any of
+ these smaller sizes. Only huge page sizes less than the current huge
+ pages size are allowed.
+
+demote
+ is used to demote a number of huge pages. A user with root privileges
+ can write to this file. It may not be possible to demote the
+ requested number of huge pages. To determine how many pages were
+ actually demoted, compare the value of nr_hugepages before and after
+ writing to the demote interface. demote is a write only interface.
+
+The interfaces which are the same as in ``/proc`` (all except demote and
+demote_size) function as described above for the default huge page-sized case.
.. _mem_policy_and_hp_alloc: