Add a kernel parameter hugetlb_free_vmemmap to enable the feature of
freeing unused vmemmap pages associated with each hugetlb page on boot.
We disables PMD mapping of vmemmap pages for x86-64 arch when this
feature is enabled. Because vmemmap_remap_free() depends on vmemmap
being base page mapped.
Signed-off-by: Muchun Song
Reviewed-by: Oscar Salvador
Reviewed-by: Barry Song
Reviewed-by: Miaohe Lin
Tested-by: Chen Huang
Tested-by: Bodeddula Balasubramaniam
---
Documentation/admin-guide/kernel-parameters.txt | 17 +
Documentation/admin-guide/mm/hugetlbpage.rst| 3 +++
arch/x86/mm/init_64.c | 8 ++--
include/linux/hugetlb.h | 19 +++
mm/hugetlb_vmemmap.c| 24
5 files changed, 69 insertions(+), 2 deletions(-)
diff --git a/Documentation/admin-guide/kernel-parameters.txt
b/Documentation/admin-guide/kernel-parameters.txt
index 3bf052d14504..9e655f5206ac 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -1611,6 +1611,23 @@
Documentation/admin-guide/mm/hugetlbpage.rst.
Format: size[KMG]
+ hugetlb_free_vmemmap=
+ [KNL] Reguires CONFIG_HUGETLB_PAGE_FREE_VMEMMAP
+ enabled.
+ Allows heavy hugetlb users to free up some more
+ memory (6 * PAGE_SIZE for each 2MB hugetlb page).
+ This feauture is not free though. Large page
+ tables are not used to back vmemmap pages which
+ can lead to a performance degradation for some
+ workloads. Also there will be memory allocation
+ required when hugetlb pages are freed from the
+ pool which can lead to corner cases under heavy
+ memory pressure.
+ Format: { on | off (default) }
+
+ on: enable the feature
+ off: disable 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 6988895d09a8..8abaeb144e44 100644
--- a/Documentation/admin-guide/mm/hugetlbpage.rst
+++ b/Documentation/admin-guide/mm/hugetlbpage.rst
@@ -153,6 +153,9 @@ 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 enables freeing
+ unused vmemmap pages associated with 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/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
index 65ea58527176..9d9d18d0c2a1 100644
--- a/arch/x86/mm/init_64.c
+++ b/arch/x86/mm/init_64.c
@@ -34,6 +34,7 @@
#include
#include
#include
+#include
#include
#include
@@ -1609,7 +1610,8 @@ int __meminit vmemmap_populate(unsigned long start,
unsigned long end, int node,
VM_BUG_ON(!IS_ALIGNED(start, PAGE_SIZE));
VM_BUG_ON(!IS_ALIGNED(end, PAGE_SIZE));
- if (end - start < PAGES_PER_SECTION * sizeof(struct page))
+ if ((is_hugetlb_free_vmemmap_enabled() && !altmap) ||
+ end - start < PAGES_PER_SECTION * sizeof(struct page))
err = vmemmap_populate_basepages(start, end, node, NULL);
else if (boot_cpu_has(X86_FEATURE_PSE))
err = vmemmap_populate_hugepages(start, end, node, altmap);
@@ -1637,6 +1639,8 @@ void register_page_bootmem_memmap(unsigned long
section_nr,
pmd_t *pmd;
unsigned int nr_pmd_pages;
struct page *page;
+ bool base_mapping = !boot_cpu_has(X86_FEATURE_PSE) ||
+ is_hugetlb_free_vmemmap_enabled();
for (; addr < end; addr = next) {
pte_t *pte = NULL;
@@ -1662,7 +1666,7 @@ void register_page_bootmem_memmap(unsigned long
section_nr,
}
get_page_bootmem(section_nr, pud_page(*pud), MIX_SECTION_INFO);
- if (!boot_cpu_has(X86_FEATURE_PSE)) {
+ if (base_mapping) {
next = (addr + PAGE_SIZE) & PAGE_MASK;
pmd = pmd_offset(pud, addr);
if (pmd_none(*pmd))
diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index 6e970a7d3480..4015cedacf91 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -894,6 +894,20 @@ static inline void huge_ptep_modify_prot_commit(struct
vm_area_struct *vma,
}
#endif
+#ifdef CONFIG_HUGETLB_PAGE_FREE_VM
