[PATCH v3 1/5] ksm: abstract the function try_to_get_old_rmap_item

[xu . xin . sc]

From: xu xin <xu.xin16@xxxxxxxxxx>

A new function try_to_get_old_rmap_item is abstracted from
get_next_rmap_item. This function will be reused by the subsequent
patches about counting ksm_zero_pages.

The patch improves the readability and reusability of KSM code.

Signed-off-by: xu xin <xu.xin16@xxxxxxxxxx>
Cc: Claudio Imbrenda <imbrenda@xxxxxxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: Xuexin Jiang <jiang.xuexin@xxxxxxxxxx>
Cc: Xiaokai Ran <ran.xiaokai@xxxxxxxxxx>
Cc: Yang Yang <yang.yang29@xxxxxxxxxx>
---
 mm/ksm.c | 25 +++++++++++++++++++------
 1 file changed, 19 insertions(+), 6 deletions(-)

diff --git a/mm/ksm.c b/mm/ksm.c
index c19fcca9bc03..13c60f1071d8 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -2187,23 +2187,36 @@ static void cmp_and_merge_page(struct page *page, struct ksm_rmap_item *rmap_ite
 	}
 }
 
-static struct ksm_rmap_item *get_next_rmap_item(struct ksm_mm_slot *mm_slot,
-					    struct ksm_rmap_item **rmap_list,
-					    unsigned long addr)
+static struct ksm_rmap_item *try_to_get_old_rmap_item(unsigned long addr,
+					 struct ksm_rmap_item **rmap_list)
 {
-	struct ksm_rmap_item *rmap_item;
-
 	while (*rmap_list) {
-		rmap_item = *rmap_list;
+		struct ksm_rmap_item *rmap_item = *rmap_list;
 		if ((rmap_item->address & PAGE_MASK) == addr)
 			return rmap_item;
 		if (rmap_item->address > addr)
 			break;
 		*rmap_list = rmap_item->rmap_list;
+		/* Running here indicates it's vma has been UNMERGEABLE */
 		remove_rmap_item_from_tree(rmap_item);
 		free_rmap_item(rmap_item);
 	}
 
+	return NULL;
+}
+
+static struct ksm_rmap_item *get_next_rmap_item(struct ksm_mm_slot *mm_slot,
+					    struct ksm_rmap_item **rmap_list,
+					    unsigned long addr)
+{
+	struct ksm_rmap_item *rmap_item;
+
+	/* lookup if we have a old rmap_item matching the addr*/
+	rmap_item = try_to_get_old_rmap_item(addr, rmap_list);
+	if (rmap_item)
+		return rmap_item;
+
+	/* Need to allocate a new rmap_item */
 	rmap_item = alloc_rmap_item();
 	if (rmap_item) {
 		/* It has already been zeroed */
-- 
2.25.1