[PATCH 3/5] mm: add pmd level THP COW judgement helpers

[Luka Bai <lukafocus@icloud.com>]

From: Luka Bai <lukabai@tencent.com>

We add hugepage_cow_always and hugepage_cow_madvise as two convenient
helpers to decide whether we want to do THP COW under each specific
circumstance.

Also, we add a helper hugepage_cow_enabled to help us know the setup
more easily. THP COW is only opened when hugepage is globally enabled
or madvise enabled.

Signed-off-by: Luka Bai <lukabai@tencent.com>
---
 include/linux/huge_mm.h | 32 ++++++++++++++++++++++++++++++++
 1 file changed, 32 insertions(+)

diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
index 2a62f0f92f68..3e5c6da3905b 100644
--- a/include/linux/huge_mm.h
+++ b/include/linux/huge_mm.h
@@ -203,6 +203,38 @@ static inline bool hugepage_global_always(void)
 			(1<<TRANSPARENT_HUGEPAGE_FLAG);
 }
 
+static inline bool hugepage_cow_always(void)
+{
+	return transparent_hugepage_flags &
+			(1<<TRANSPARENT_HUGEPAGE_COW_FLAG);
+}
+
+static inline bool hugepage_cow_madvise(void)
+{
+	return transparent_hugepage_flags &
+			(1<<TRANSPARENT_HUGEPAGE_REQ_MADV_COW_FLAG);
+}
+
+static inline bool hugepage_cow_enabled(struct vm_area_struct *vma)
+{
+	vm_flags_t vm_flags = vma->vm_flags;
+
+	/* anonymous THP need to be enabled first */
+	if (!hugepage_global_always() &&
+		(!hugepage_global_enabled() || !(vm_flags & VM_HUGEPAGE)))
+		return false;
+
+	/* always enables all the THP COW */
+	if (hugepage_cow_always())
+		return true;
+
+	/* madvise enables THP cow only when vm_flags says so */
+	if (hugepage_cow_madvise() && (vm_flags & VM_THP_COW))
+		return true;
+
+	return false;
+}
+
 static inline int highest_order(unsigned long orders)
 {
 	return fls_long(orders) - 1;

-- 
2.52.0