linux-kernel - [PATCH] mm/page_alloc: optimize the loop in find_suitable

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Date:   Thu,  9 Feb 2023 10:44:35 +0800
From:   Yajun Deng <yajun.deng@...ux.dev>
To:     akpm@...ux-foundation.org
Cc:     ziy@...dia.com, mgorman@...hsingularity.net, david@...hat.com,
        vbabka@...e.cz, rppt@...ux.ibm.com, osalvador@...e.de,
        rppt@...nel.org, linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Yajun Deng <yajun.deng@...ux.dev>
Subject: [PATCH] mm/page_alloc: optimize the loop in find_suitable_fallback()

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@...ux.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