+ mm-mempolicy-skip-unnecessary-synchronize_rcu.patch added to mm-hotfixes-unstable branch

+ mm-mempolicy-skip-unnecessary-synchronize_rcu.patch added to mm-hotfixes-unstable branch

[Andrew Morton]

The patch titled
     Subject: mm/mempolicy: Skip unnecessary synchronize_rcu()
has been added to the -mm mm-hotfixes-unstable branch.  Its filename is
     mm-mempolicy-skip-unnecessary-synchronize_rcu.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-mempolicy-skip-unnecessary-synchronize_rcu.patch

This patch will later appear in the mm-hotfixes-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

Before you just go and hit "reply", please:
   a) Consider who else should be cc'ed
   b) Prefer to cc a suitable mailing list as well
   c) Ideally: find the original patch on the mailing list and do a
      reply-to-all to that, adding suitable additional cc's

*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***

The -mm tree is included into linux-next via the mm-everything
branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there every 2-3 working days

------------------------------------------------------
From: Joshua Hahn <joshua.hahnjy@gmail.com>
Subject: mm/mempolicy: Skip unnecessary synchronize_rcu()
Date: Mon, 2 Jun 2025 09:23:40 -0700

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.

Link: https://lkml.kernel.org/r/20250602162345.2595696-2-joshua.hahnjy@gmail.com
Signed-off-by: Joshua Hahn <joshua.hahnjy@gmail.com>
Suggested-by: David Hildenbrand <david@redhat.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Byungchul Park <byungchul@sk.com>
Cc: Gregory Price <gourry@gourry.net>
Cc: "Huang, Ying" <ying.huang@linux.alibaba.com>
Cc: kernel test robot <lkp@intel.com>
Cc: Mathew Brost <matthew.brost@intel.com>
Cc: Rakie Kim <rakie.kim@sk.com>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/mempolicy.c |   13 +++++--------
 1 file changed, 5 insertions(+), 8 deletions(-)

--- a/mm/mempolicy.c~mm-mempolicy-skip-unnecessary-synchronize_rcu
+++ a/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 =
_

Patches currently in -mm which might be from joshua.hahnjy@gmail.com are

mm-mempolicy-fix-incorrect-freeing-of-wi_kobj.patch
mm-mempolicy-skip-unnecessary-synchronize_rcu.patch