[PATCH 2/4] mm, migrate: allocation new page lazyily in unmap_and_move()

Joonsoo Kim
2013-08-02T02:08:47Z

We don't need a new page and then go out immediately if some condition
is met. Allocation has overhead in comparison with some condition check,
so allocating lazyily is preferable solution.

Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>

diff --git a/mm/migrate.c b/mm/migrate.c
index 6f0c244..86db87e 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -864,10 +864,7 @@ static int unmap_and_move(new_page_t get_new_page, unsigned long private,
{
int rc = 0;
int *result = NULL;
- struct page *newpage = get_new_page(page, private, &result);
-
- if (!newpage)
- return -ENOMEM;
+ struct page *newpage = NULL;

if (page_count(page) == 1) {
/* page was freed from under us. So we are done. */
@@ -878,6 +875,10 @@ static int unmap_and_move(new_page_t get_new_page, unsigned long private,
if (unlikely(split_huge_page(page)))
goto out;

+ newpage = get_new_page(page, private, &result);
+ if (!newpage)
+ return -ENOMEM;
+
rc = __unmap_and_move(page, newpage, force, mode);

if (unlikely(rc == MIGRATEPAGE_BALLOON_SUCCESS)) {
@@ -908,7 +909,8 @@ out:
* Move the new page to the LRU. If migration was not successful
* then this will free the page.
*/
- putback_lru_page(newpage);
+ if (newpage)
+ putback_lru_page(newpage);
if (result) {
if (rc)
*result = rc;
--
1.7.9.5