[PATCH RFC 2/5] mm/ksm: introduce ksm_madvise_merge() helper

[Oleksandr Natalenko <oleksandr@redhat.com>]

Move MADV_MERGEABLE part of ksm_madvise() into a dedicated helper since
it will be further used for marking VMAs to be merged forcibly.

This does not bring any functional changes.

Signed-off-by: Oleksandr Natalenko <oleksandr@redhat.com>
---
 include/linux/ksm.h |  2 ++
 mm/ksm.c            | 60 +++++++++++++++++++++++++++------------------
 2 files changed, 38 insertions(+), 24 deletions(-)

diff --git a/include/linux/ksm.h b/include/linux/ksm.h
index e48b1e453ff5..e824b3141677 100644
--- a/include/linux/ksm.h
+++ b/include/linux/ksm.h
@@ -19,6 +19,8 @@ struct stable_node;
 struct mem_cgroup;
 
 #ifdef CONFIG_KSM
+int ksm_madvise_merge(struct mm_struct *mm, struct vm_area_struct *vma,
+		unsigned long *vm_flags);
 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);
diff --git a/mm/ksm.c b/mm/ksm.c
index fc64874dc6f4..1fdcf2fbd58d 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -2442,41 +2442,53 @@ static int ksm_scan_thread(void *nothing)
 	return 0;
 }
 
-int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
-		unsigned long end, int advice, unsigned long *vm_flags)
+int ksm_madvise_merge(struct mm_struct *mm, struct vm_area_struct *vma,
+		unsigned long *vm_flags)
 {
-	struct mm_struct *mm = vma->vm_mm;
 	int err;
 
-	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 */
+	/*
+	 * 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;
+	if (vma_is_dax(vma))
+		return 0;
 
 #ifdef VM_SAO
-		if (*vm_flags & VM_SAO)
-			return 0;
+	if (*vm_flags & VM_SAO)
+		return 0;
 #endif
 #ifdef VM_SPARC_ADI
-		if (*vm_flags & VM_SPARC_ADI)
-			return 0;
+	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;
-		}
+	if (!test_bit(MMF_VM_MERGEABLE, &mm->flags)) {
+		err = __ksm_enter(mm);
+		if (err)
+			return err;
+	}
+
+	*vm_flags |= VM_MERGEABLE;
+
+	return 0;
+}
 
-		*vm_flags |= VM_MERGEABLE;
+int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
+		unsigned long end, int advice, unsigned long *vm_flags)
+{
+	struct mm_struct *mm = vma->vm_mm;
+	int err;
+
+	switch (advice) {
+	case MADV_MERGEABLE:
+		err = ksm_madvise_merge(mm, vma, vm_flags);
+		if (err)
+			return err;
 		break;
 
 	case MADV_UNMERGEABLE:
-- 
2.21.0