linux-kernel - [PATCH 2/2] mm/mempolicy: Skip unnecessary synchronize

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Message-ID: <20250602162345.2595696-2-joshua.hahnjy@gmail.com>
Date: Mon,  2 Jun 2025 09:23:40 -0700
From: Joshua Hahn <joshua.hahnjy@...il.com>
To: Andrew Morton <akpm@...ux-foundation.org>,
	Gregory Price <gourry@...rry.net>
Cc: David Hildenbrand <david@...hat.com>,
	Zi Yan <ziy@...dia.com>,
	Matthew Brost <matthew.brost@...el.com>,
	Rakie Kim <rakie.kim@...com>,
	Byungchul Park <byungchul@...com>,
	Ying Huang <ying.huang@...ux.alibaba.com>,
	Alistair Popple <apopple@...dia.com>,
	linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	kernel-team@...a.com
Subject: [PATCH 2/2] mm/mempolicy: Skip unnecessary synchronize_rcu()

By unconditionally setting wi_state to NULL and conditionally calling
synchronize_rcu(), we can save an unncessary call when there is no
old_wi_state.

Suggested-by: David Hildenbrand <david@...hat.com>
Signed-off-by: Joshua Hahn <joshua.hahnjy@...il.com>
---
 mm/mempolicy.c | 13 +++++--------
 1 file changed, 5 insertions(+), 8 deletions(-)

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 3b1dfd08338b..b0619d0020c9 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -3703,18 +3703,15 @@ static void wi_state_free(void)
 	struct weighted_interleave_state *old_wi_state;
 
 	mutex_lock(&wi_state_lock);
-
 	old_wi_state = rcu_dereference_protected(wi_state,
 			lockdep_is_held(&wi_state_lock));
-	if (!old_wi_state) {
-		mutex_unlock(&wi_state_lock);
-		return;
-	}
-
 	rcu_assign_pointer(wi_state, NULL);
 	mutex_unlock(&wi_state_lock);
-	synchronize_rcu();
-	kfree(old_wi_state);
+
+	if (old_wi_state) {
+		synchronize_rcu();
+		kfree(old_wi_state);
+	}
 }
 
 static struct kobj_attribute wi_auto_attr =
-- 
2.47.1