[PATCH RFC 1/4] mm/ksm: introduce ksm_enter() helper

[Oleksandr Natalenko <oleksandr@redhat.com>]

Move MADV_MERGEABLE part of ksm_madvise() into a dedicated helper since
it will be further used in do_anonymous_page().

This does not bring any functional changes.

Signed-off-by: Oleksandr Natalenko <oleksandr@redhat.com>
---
 include/linux/ksm.h |  2 ++
 mm/ksm.c            | 66 ++++++++++++++++++++++++++-------------------
 2 files changed, 41 insertions(+), 27 deletions(-)

diff --git a/include/linux/ksm.h b/include/linux/ksm.h
index e48b1e453ff5..bc13f228e2ed 100644
--- a/include/linux/ksm.h
+++ b/include/linux/ksm.h
@@ -21,6 +21,8 @@ struct mem_cgroup;
 #ifdef CONFIG_KSM
 int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
 		unsigned long end, int advice, unsigned long *vm_flags);
+int ksm_enter(struct mm_struct *mm, struct vm_area_struct *vma,
+		unsigned long *vm_flags);
 int __ksm_enter(struct mm_struct *mm);
 void __ksm_exit(struct mm_struct *mm);
 
diff --git a/mm/ksm.c b/mm/ksm.c
index fc64874dc6f4..a6b0788a3a22 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -2450,33 +2450,9 @@ int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
 
 	switch (advice) {
 	case MADV_MERGEABLE:
-		/*
-		 * Be somewhat over-protective for now!
-		 */
-		if (*vm_flags & (VM_MERGEABLE | VM_SHARED  | VM_MAYSHARE   |
-				 VM_PFNMAP    | VM_IO      | VM_DONTEXPAND |
-				 VM_HUGETLB | VM_MIXEDMAP))
-			return 0;		/* just ignore the advice */
-
-		if (vma_is_dax(vma))
-			return 0;
-
-#ifdef VM_SAO
-		if (*vm_flags & VM_SAO)
-			return 0;
-#endif
-#ifdef VM_SPARC_ADI
-		if (*vm_flags & VM_SPARC_ADI)
-			return 0;
-#endif
-
-		if (!test_bit(MMF_VM_MERGEABLE, &mm->flags)) {
-			err = __ksm_enter(mm);
-			if (err)
-				return err;
-		}
-
-		*vm_flags |= VM_MERGEABLE;
+		err = ksm_enter(mm, vma, vm_flags);
+		if (err)
+			return err;
 		break;
 
 	case MADV_UNMERGEABLE:
@@ -2496,6 +2472,42 @@ int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
 	return 0;
 }
 
+int ksm_enter(struct mm_struct *mm, struct vm_area_struct *vma,
+		unsigned long *vm_flags)
+{
+	int err;
+
+	/*
+	 * Be somewhat over-protective for now!
+	 */
+	if (*vm_flags & (VM_MERGEABLE | VM_SHARED  | VM_MAYSHARE   |
+			 VM_PFNMAP    | VM_IO      | VM_DONTEXPAND |
+			 VM_HUGETLB | VM_MIXEDMAP))
+		return 0;		/* just ignore the advice */
+
+	if (vma_is_dax(vma))
+		return 0;
+
+#ifdef VM_SAO
+	if (*vm_flags & VM_SAO)
+		return 0;
+#endif
+#ifdef VM_SPARC_ADI
+	if (*vm_flags & VM_SPARC_ADI)
+		return 0;
+#endif
+
+	if (!test_bit(MMF_VM_MERGEABLE, &mm->flags)) {
+		err = __ksm_enter(mm);
+		if (err)
+			return err;
+	}
+
+	*vm_flags |= VM_MERGEABLE;
+
+	return 0;
+}
+
 int __ksm_enter(struct mm_struct *mm)
 {
 	struct mm_slot *mm_slot;
-- 
2.21.0