We must add "hugetlb_free_vmemmap=on" to boot cmdline and reboot the
server to enable the feature of freeing vmemmap pages of HugeTLB
pages. Rebooting usually taske a long time. Add a sysctl to enable
the feature at runtime and do not need to reboot.
Signed-off-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
---
Documentation/admin-guide/sysctl/vm.rst | 13 +++++++++++++
include/linux/hugetlb.h | 5 +++++
include/linux/memory_hotplug.h | 1 +
kernel/sysctl.c | 11 +++++++++++
mm/hugetlb_vmemmap.c | 23 +++++++++++++++++------
mm/hugetlb_vmemmap.h | 4 +++-
mm/memory_hotplug.c | 2 +-
7 files changed, 51 insertions(+), 8 deletions(-)
diff --git a/Documentation/admin-guide/sysctl/vm.rst b/Documentation/admin-guide/sysctl/vm.rst
index f4804ce37c58..01f18e6cc227 100644
--- a/Documentation/admin-guide/sysctl/vm.rst
+++ b/Documentation/admin-guide/sysctl/vm.rst
@@ -561,6 +561,19 @@ Change the minimum size of the hugepage pool.
See Documentation/admin-guide/mm/hugetlbpage.rst
+hugetlb_free_vmemmap
+====================
+
+A toggle value indicating if vmemmap pages are allowed to be optimized.
+If it is off (0), then it can be set true (1). Once true, the vmemmap
+pages associated with each HugeTLB page will be optimized, and the toggle
+cannot be set back to false. It only optimizes the subsequent allocation
+of HugeTLB pages from buddy system, while already allocated HugeTLB pages
+will not be optimized.
+
+See Documentation/admin-guide/mm/hugetlbpage.rst
+
+
nr_hugepages_mempolicy
======================
diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index 53c1b6082a4c..cc4ab21892f5 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -1080,6 +1080,11 @@ static inline void set_huge_swap_pte_at(struct mm_struct *mm, unsigned long addr
}
#endif /* CONFIG_HUGETLB_PAGE */
+#ifdef CONFIG_HUGETLB_PAGE_FREE_VMEMMAP
+int hugetlb_vmemmap_sysctl_handler(struct ctl_table *table, int write,
+ void *buffer, size_t *length, loff_t *ppos);
+#endif
+
static inline spinlock_t *huge_pte_lock(struct hstate *h,
struct mm_struct *mm, pte_t *pte)
{
diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h
index e0b2209ab71c..b30f9fdaed73 100644
--- a/include/linux/memory_hotplug.h
+++ b/include/linux/memory_hotplug.h
@@ -349,6 +349,7 @@ extern int arch_create_linear_mapping(int nid, u64 start, u64 size,
struct mhp_params *params);
void arch_remove_linear_mapping(u64 start, u64 size);
extern bool mhp_supports_memmap_on_memory(unsigned long size);
+extern bool memmap_on_memory;
#endif /* CONFIG_MEMORY_HOTPLUG */
#endif /* __LINUX_MEMORY_HOTPLUG_H */
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index ab3e9c937268..77f039849b2a 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -2223,6 +2223,17 @@ static struct ctl_table vm_table[] = {
.mode = 0644,
.proc_handler = hugetlb_sysctl_handler,
},
+#ifdef CONFIG_HUGETLB_PAGE_FREE_VMEMMAP
+ {
+ .procname = "hugetlb_free_vmemmap",
+ .data = &hugetlb_free_vmemmap_enabled_key.key,
+ .maxlen = sizeof(hugetlb_free_vmemmap_enabled_key.key),
+ .mode = 0644,
+ /* only handle a transition from default "0" to "1" */
+ .proc_handler = hugetlb_vmemmap_sysctl_handler,
+ .extra1 = SYSCTL_ONE,
+ },
+#endif
#ifdef CONFIG_NUMA
{
.procname = "nr_hugepages_mempolicy",
diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c
index 836d1117f08b..3167021055d6 100644
--- a/mm/hugetlb_vmemmap.c
+++ b/mm/hugetlb_vmemmap.c
@@ -10,6 +10,7 @@
#define pr_fmt(fmt) "HugeTLB: " fmt
+#include <linux/memory_hotplug.h>
#include "hugetlb_vmemmap.h"
/*
@@ -118,17 +119,14 @@ void __init hugetlb_vmemmap_init(struct hstate *h)
BUILD_BUG_ON(__NR_USED_SUBPAGE >=
RESERVE_VMEMMAP_SIZE / sizeof(struct page));
- if (!hugetlb_free_vmemmap_enabled())
- return;
-
- if (IS_ENABLED(CONFIG_HUGETLB_PAGE_FREE_VMEMMAP_DEFAULT_ON) &&
- !is_power_of_2(sizeof(struct page))) {
+ if (!is_power_of_2(sizeof(struct page))) {
/*
* The hugetlb_free_vmemmap_enabled_key can be enabled when
* CONFIG_HUGETLB_PAGE_FREE_VMEMMAP_DEFAULT_ON. It should
* be disabled if "struct page" crosses page boundaries.
*/
- static_branch_disable(&hugetlb_free_vmemmap_enabled_key);
+ if (IS_ENABLED(CONFIG_HUGETLB_PAGE_FREE_VMEMMAP_DEFAULT_ON))
+ static_branch_disable(&hugetlb_free_vmemmap_enabled_key);
return;
}
@@ -147,3 +145,16 @@ void __init hugetlb_vmemmap_init(struct hstate *h)
pr_info("can free %d vmemmap pages for %s\n", h->nr_free_vmemmap_pages,
h->name);
}
+
+int hugetlb_vmemmap_sysctl_handler(struct ctl_table *table, int write,
+ void *buffer, size_t *length, loff_t *ppos)
+{
+ /*
+ * The vmemmap pages cannot be optimized if a "struct page" crosses page
+ * boundaries or memory_hotplug.memmap_on_memory is enabled.
+ */
+ if (write && (!is_power_of_2(sizeof(struct page)) || memmap_on_memory))
+ return -EPERM;
+
+ return proc_do_static_key(table, write, buffer, length, ppos);
+}
diff --git a/mm/hugetlb_vmemmap.h b/mm/hugetlb_vmemmap.h
index cb2bef8f9e73..b67a159027f4 100644
--- a/mm/hugetlb_vmemmap.h
+++ b/mm/hugetlb_vmemmap.h
@@ -21,7 +21,9 @@ void hugetlb_vmemmap_init(struct hstate *h);
*/
static inline unsigned int free_vmemmap_pages_per_hpage(struct hstate *h)
{
- return h->nr_free_vmemmap_pages;
+ if (hugetlb_free_vmemmap_enabled())
+ return h->nr_free_vmemmap_pages;
+ return 0;
}
#else
static inline int alloc_huge_page_vmemmap(struct hstate *h, struct page *head)
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index c226a337c1ef..b5cc5abde05a 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -46,7 +46,7 @@
/*
* memory_hotplug.memmap_on_memory parameter
*/
-static bool memmap_on_memory __ro_after_init;
+bool memmap_on_memory __ro_after_init;
#ifdef CONFIG_MHP_MEMMAP_ON_MEMORY
module_param(memmap_on_memory, bool, 0444);
MODULE_PARM_DESC(memmap_on_memory, "Enable memmap on memory for memory hotplug");
--
2.11.0
