[RFC PATCH v2 25/30] mm: vma: add VM_HUGEPAGE_PUD to vm_flags at bit 37.

[Zi Yan <zi.yan@sent.com>]

From: Zi Yan <ziy@nvidia.com>

madvise can set this bit via MADV_HUGEPAGE | MADV_HUGEPAGE_1GB and unset
it via MADV_NOHUGEPAGE | MADV_HUGEPAGE_1GB. Later, kernel will check
this bit to decide whether to allocate PUD THPs or not on a VMA when the
global PUD THP is set to madvise.

Signed-off-by: Zi Yan <ziy@nvidia.com>
---
 include/linux/mm.h | 6 ++++++
 mm/khugepaged.c    | 9 +++++++++
 2 files changed, 15 insertions(+)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 51b75ffa6a6c..78bee63c64da 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -305,11 +305,13 @@ extern unsigned int kobjsize(const void *objp);
 #define VM_HIGH_ARCH_BIT_2	34	/* bit only usable on 64-bit architectures */
 #define VM_HIGH_ARCH_BIT_3	35	/* bit only usable on 64-bit architectures */
 #define VM_HIGH_ARCH_BIT_4	36	/* bit only usable on 64-bit architectures */
+#define VM_HIGH_ARCH_BIT_5	37	/* bit only usable on 64-bit architectures */
 #define VM_HIGH_ARCH_0	BIT(VM_HIGH_ARCH_BIT_0)
 #define VM_HIGH_ARCH_1	BIT(VM_HIGH_ARCH_BIT_1)
 #define VM_HIGH_ARCH_2	BIT(VM_HIGH_ARCH_BIT_2)
 #define VM_HIGH_ARCH_3	BIT(VM_HIGH_ARCH_BIT_3)
 #define VM_HIGH_ARCH_4	BIT(VM_HIGH_ARCH_BIT_4)
+#define VM_HIGH_ARCH_5	BIT(VM_HIGH_ARCH_BIT_5)
 #endif /* CONFIG_ARCH_USES_HIGH_VMA_FLAGS */
 
 #ifdef CONFIG_ARCH_HAS_PKEYS
@@ -325,6 +327,10 @@ extern unsigned int kobjsize(const void *objp);
 #endif
 #endif /* CONFIG_ARCH_HAS_PKEYS */
 
+#ifdef CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD
+#define VM_HUGEPAGE_PUD VM_HIGH_ARCH_5
+#endif /* CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD */
+
 #if defined(CONFIG_X86)
 # define VM_PAT		VM_ARCH_1	/* PAT reserves whole VMA at once (x86) */
 #elif defined(CONFIG_PPC)
diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index b34c78085017..f085c218ea84 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -345,6 +345,9 @@ struct attribute_group khugepaged_attr_group = {
 int hugepage_madvise(struct vm_area_struct *vma,
 		     unsigned long *vm_flags, int advice)
 {
+	/* only support 1GB PUD THP on x86 now */
+	bool use_pud_page = advice & MADV_HUGEPAGE_1GB;
+
 	advice = advice & MADV_BEHAVIOR_MASK;
 	switch (advice) {
 	case MADV_HUGEPAGE:
@@ -359,6 +362,9 @@ int hugepage_madvise(struct vm_area_struct *vma,
 #endif
 		*vm_flags &= ~VM_NOHUGEPAGE;
 		*vm_flags |= VM_HUGEPAGE;
+
+		if (use_pud_page)
+			*vm_flags |= VM_HUGEPAGE_PUD;
 		/*
 		 * If the vma become good for khugepaged to scan,
 		 * register it here without waiting a page fault that
@@ -371,6 +377,9 @@ int hugepage_madvise(struct vm_area_struct *vma,
 	case MADV_NOHUGEPAGE:
 		*vm_flags &= ~VM_HUGEPAGE;
 		*vm_flags |= VM_NOHUGEPAGE;
+
+		if (use_pud_page)
+			*vm_flags &= ~VM_HUGEPAGE_PUD;
 		/*
 		 * Setting VM_NOHUGEPAGE will prevent khugepaged from scanning
 		 * this vma even if we leave the mm registered in khugepaged if
-- 
2.28.0