[PATCH] mm/page_alloc: optimize the loop in find_suitable_fallback()

Yajun Deng
2023-02-09T02:44:58Z

There is no need to execute the next loop if it not return in the first
loop. So add a break at the end of the loop.

There are only three rows in fallbacks, so reduce the first index size
from MIGRATE_TYPES to MIGRATE_PCPTYPES.

Signed-off-by: Yajun Deng <yajun.deng@linux.dev>
---
mm/page_alloc.c | 11 +++++------
1 file changed, 5 insertions(+), 6 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 1113483fa6c5..536e8d838fb5 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -2603,7 +2603,7 @@ struct page *__rmqueue_smallest(struct zone *zone, unsigned int order,
*
* The other migratetypes do not have fallbacks.
*/
-static int fallbacks[MIGRATE_TYPES][MIGRATE_PCPTYPES - 1] = {
+static int fallbacks[MIGRATE_PCPTYPES][MIGRATE_PCPTYPES - 1] = {
[MIGRATE_UNMOVABLE] = { MIGRATE_RECLAIMABLE, MIGRATE_MOVABLE },
[MIGRATE_MOVABLE] = { MIGRATE_RECLAIMABLE, MIGRATE_UNMOVABLE },
[MIGRATE_RECLAIMABLE] = { MIGRATE_UNMOVABLE, MIGRATE_MOVABLE },
@@ -2861,7 +2861,7 @@ int find_suitable_fallback(struct free_area *area, unsigned int order,
int i;
int fallback_mt;

- if (area->nr_free == 0)
+ if (area->nr_free == 0 || !migratetype_is_mergeable(migratetype))
return -1;

*can_steal = false;
@@ -2873,11 +2873,10 @@ int find_suitable_fallback(struct free_area *area, unsigned int order,
if (can_steal_fallback(order, migratetype))
*can_steal = true;

- if (!only_stealable)
- return fallback_mt;
-
- if (*can_steal)
+ if (!only_stealable || *can_steal)
return fallback_mt;
+ else
+ break;
}

return -1;
--
2.25.1