[PATCH v2 5/7] mm: Introduce may_mmap_overlapped_region() helper

[Kirill Tkhai <ktkhai@virtuozzo.com>]

Extract address space limit check for overlapped regions
in a separate helper.

v2: New

Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com>
---
 mm/mmap.c |   33 ++++++++++++++++++++-------------
 1 file changed, 20 insertions(+), 13 deletions(-)

diff --git a/mm/mmap.c b/mm/mmap.c
index e4ced5366643..260e47e917e6 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -583,6 +583,24 @@ static unsigned long count_vma_pages_range(struct mm_struct *mm,
 	return nr_pages;
 }
 
+/*
+ * Check against address space limit, whether we may expand mm
+ * with a new mapping. Currently mapped in the given range pages
+ * are not accounted in the limit.
+ */
+static bool may_mmap_overlapped_region(struct mm_struct *mm,
+		unsigned long vm_flags, unsigned long addr, unsigned long len)
+{
+	unsigned long nr_pages = len >> PAGE_SHIFT;
+
+	if (!may_expand_vm(mm, vm_flags, nr_pages)) {
+		nr_pages -= count_vma_pages_range(mm, addr, addr + len);
+		if (!may_expand_vm(mm, vm_flags, nr_pages))
+			return false;
+	}
+	return true;
+}
+
 void __vma_link_rb(struct mm_struct *mm, struct vm_area_struct *vma,
 		struct rb_node **rb_link, struct rb_node *rb_parent)
 {
@@ -1697,19 +1715,8 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
 	unsigned long charged = 0;
 
 	/* Check against address space limit. */
-	if (!may_expand_vm(mm, vm_flags, len >> PAGE_SHIFT)) {
-		unsigned long nr_pages;
-
-		/*
-		 * MAP_FIXED may remove pages of mappings that intersects with
-		 * requested mapping. Account for the pages it would unmap.
-		 */
-		nr_pages = count_vma_pages_range(mm, addr, addr + len);
-
-		if (!may_expand_vm(mm, vm_flags,
-					(len >> PAGE_SHIFT) - nr_pages))
-			return -ENOMEM;
-	}
+	if (!may_mmap_overlapped_region(mm, vm_flags, addr, len))
+		return -ENOMEM;
 
 	/* Clear old maps */
 	while (find_vma_links(mm, addr, addr + len, &prev, &rb_link,