linux-kernel - [PATCH 3/3] mm: optimize free_area_empty() check using per-migratetype counts

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Message-ID: <cd98e89b8b609bd2781b2d24c721a59feda83ec8.1764297987.git.zhanghongru@xiaomi.com>
Date: Fri, 28 Nov 2025 11:12:42 +0800
From: Hongru Zhang <zhanghongru06@...il.com>
To: akpm@...ux-foundation.org,
	vbabka@...e.cz,
	david@...nel.org
Cc: linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	surenb@...gle.com,
	mhocko@...e.com,
	jackmanb@...gle.com,
	hannes@...xchg.org,
	ziy@...dia.com,
	lorenzo.stoakes@...cle.com,
	Liam.Howlett@...cle.com,
	rppt@...nel.org,
	axelrasmussen@...gle.com,
	yuanchu@...gle.com,
	weixugc@...gle.com,
	Hongru Zhang <zhanghongru@...omi.com>
Subject: [PATCH 3/3] mm: optimize free_area_empty() check using per-migratetype counts

From: Hongru Zhang <zhanghongru@...omi.com>

Use per-migratetype counts instead of list_empty() helps reduce a
few cpu instructions.

Signed-off-by: Hongru Zhang <zhanghongru@...omi.com>
---
 mm/internal.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/internal.h b/mm/internal.h
index 1561fc2ff5b8..7759f8fdf445 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -954,7 +954,7 @@ int find_suitable_fallback(struct free_area *area, unsigned int order,
 
 static inline bool free_area_empty(struct free_area *area, int migratetype)
 {
-	return list_empty(&area->free_list[migratetype]);
+	return !READ_ONCE(area->mt_nr_free[migratetype]);
 }
 
 /* mm/util.c */
-- 
2.43.0