The patch titled
Subject: hugetlb: document the demote sysfs interfaces
has been added to the -mm tree. Its filename is
hugetlb-document-the-demote-sysfs-interfaces.patch
This patch should soon appear at
https://ozlabs.org/~akpm/mmots/broken-out/hugetlb-document-the-demote-sysfs-interfaces.patch
and later at
https://ozlabs.org/~akpm/mmotm/broken-out/hugetlb-document-the-demote-sysfs-interfaces.patch
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------------------------------------------------------
From: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Subject: hugetlb: document the demote sysfs interfaces
Describe demote and demote_size interfaces.
Link: https://lkml.kernel.org/r/20210816224953.157796-6-mike.kravetz@xxxxxxxxxx
Signed-off-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Muchun Song <songmuchun@xxxxxxxxxxxxx>
Cc: Naoya Horiguchi <naoya.horiguchi@xxxxxxxxx>
Cc: Oscar Salvador <osalvador@xxxxxxx>
Cc: Zi Yan <ziy@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
Documentation/admin-guide/mm/hugetlbpage.rst | 29 +++++++++++++++--
1 file changed, 27 insertions(+), 2 deletions(-)
--- a/Documentation/admin-guide/mm/hugetlbpage.rst~hugetlb-document-the-demote-sysfs-interfaces
+++ a/Documentation/admin-guide/mm/hugetlbpage.rst
@@ -234,8 +234,12 @@ 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 will exist::
+ demote
+ demote_size
nr_hugepages
nr_hugepages_mempolicy
nr_overcommit_hugepages
@@ -243,7 +247,28 @@ Inside each of these directories, the sa
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. 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. For huge pages
+ of the smallest supported size (2MB on x86), demote_size will be the
+ system page size (PAGE_SIZE). If demote_size is the system page size
+ then demoting a page will simply free the huge page. demote_size is
+ a read only interface.
+
+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`` function as described
+above for the default huge page-sized case.
.. _mem_policy_and_hp_alloc:
_
Patches currently in -mm which might be from mike.kravetz@xxxxxxxxxx are
hugetlb-simplify-prep_compound_gigantic_page-ref-count-racing-code.patch
hugetlb-drop-ref-count-earlier-after-page-allocation.patch
hugetlb-before-freeing-hugetlb-page-set-dtor-to-appropriate-value.patch
hugetlb-add-demote-hugetlb-page-sysfs-interfaces.patch
hugetlb-add-hpagecma-flag-and-code-to-free-non-gigantic-pages-in-cma.patch
hugetlb-add-demote-bool-to-gigantic-page-routines.patch
hugetlb-add-hugetlb-demote-page-support.patch
hugetlb-document-the-demote-sysfs-interfaces.patch
hugetlb-vmemmap-optimizations-when-demoting-hugetlb-pages.patch
hugetlb-prepare-destroy-and-prep-routines-for-vmemmap-optimized-pages.patch
hugetlb-optimized-demote-vmemmap-optimizatized-pages.patch
