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Subject[RFC PATCH 20/24] mm/hugetlb: Add a kernel parameter hugetlb_free_vmemmap
Date
Add a kernel parameter hugetlb_free_vmemmap to disable the feature of
freeing unused vmemmap pages associated with each hugetlb page on boot.

Signed-off-by: Muchun Song <songmuchun@bytedance.com>
---
.../admin-guide/kernel-parameters.txt | 9 ++++++++
Documentation/admin-guide/mm/hugetlbpage.rst | 3 +++
mm/hugetlb.c | 23 +++++++++++++++++++
3 files changed, 35 insertions(+)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 5debfe238027..69d18ef6f66b 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -1551,6 +1551,15 @@
Documentation/admin-guide/mm/hugetlbpage.rst.
Format: size[KMG]

+ hugetlb_free_vmemmap=
+ [KNL] When CONFIG_HUGETLB_PAGE_FREE_VMEMMAP is set,
+ this disables freeing unused vmemmap pages associated
+ each HugeTLB page.
+ Format: { on (default) | off }
+
+ on: enable the feature
+ off: dosable the feature
+
hung_task_panic=
[KNL] Should the hung task detector generate panics.
Format: 0 | 1
diff --git a/Documentation/admin-guide/mm/hugetlbpage.rst b/Documentation/admin-guide/mm/hugetlbpage.rst
index f7b1c7462991..7d6129ee97dd 100644
--- a/Documentation/admin-guide/mm/hugetlbpage.rst
+++ b/Documentation/admin-guide/mm/hugetlbpage.rst
@@ -145,6 +145,9 @@ default_hugepagesz

will all result in 256 2M huge pages being allocated. Valid default
huge page size is architecture dependent.
+hugetlb_free_vmemmap
+ When CONFIG_HUGETLB_PAGE_FREE_VMEMMAP is set, this disables freeing
+ unused vmemmap pages associated each HugeTLB page.

When multiple huge page sizes are supported, ``/proc/sys/vm/nr_hugepages``
indicates the current number of pre-allocated huge pages of the default size.
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 56c0bf2370ed..28c154679838 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -1310,6 +1310,8 @@ static void __free_hugepage(struct hstate *h, struct page *page);
(__boundary - 1 < (end) - 1) ? __boundary : (end); \
})

+static bool hugetlb_free_vmemmap_disabled __initdata;
+
static inline unsigned int nr_free_vmemmap(struct hstate *h)
{
return h->nr_free_vmemmap_pages;
@@ -1457,6 +1459,13 @@ static void __init hugetlb_vmemmap_init(struct hstate *h)
unsigned int order = huge_page_order(h);
unsigned int vmemmap_pages;

+ if (hugetlb_free_vmemmap_disabled) {
+ h->nr_free_vmemmap_pages = 0;
+ pr_info("HugeTLB: disable free vmemmap pages for %s\n",
+ h->name);
+ return;
+ }
+
vmemmap_pages = ((1 << order) * sizeof(struct page)) >> PAGE_SHIFT;
/*
* The head page and the first tail page not free to buddy system,
@@ -1867,6 +1876,20 @@ static inline void clear_subpage_hwpoison(struct page *head)
{
set_page_private(head + 4, 0);
}
+
+static int __init early_hugetlb_free_vmemmap_param(char *buf)
+{
+ if (!buf)
+ return -EINVAL;
+
+ if (!strcmp(buf, "off"))
+ hugetlb_free_vmemmap_disabled = true;
+ else if (strcmp(buf, "on"))
+ return -EINVAL;
+
+ return 0;
+}
+early_param("hugetlb_free_vmemmap", early_hugetlb_free_vmemmap_param);
#else
static inline void hugetlb_vmemmap_init(struct hstate *h)
{
--
2.20.1
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