linux-kernel - [RFC PATCH 1/4] lib/percpu_counter: Split out a helper to insert into hotplug list

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Message-ID: <20251127233635.4170047-2-krisman@suse.de>
Date: Thu, 27 Nov 2025 18:36:28 -0500
From: Gabriel Krisman Bertazi <krisman@...e.de>
To: linux-mm@...ck.org
Cc: Gabriel Krisman Bertazi <krisman@...e.de>,
	linux-kernel@...r.kernel.org,
	jack@...e.cz,
	Mateusz Guzik <mjguzik@...il.com>,
	Shakeel Butt <shakeel.butt@...ux.dev>,
	Michal Hocko <mhocko@...nel.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Dennis Zhou <dennis@...nel.org>,
	Tejun Heo <tj@...nel.org>,
	Christoph Lameter <cl@...two.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	David Hildenbrand <david@...hat.com>,
	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
	"Liam R. Howlett" <Liam.Howlett@...cle.com>,
	Vlastimil Babka <vbabka@...e.cz>,
	Mike Rapoport <rppt@...nel.org>,
	Suren Baghdasaryan <surenb@...gle.com>
Subject: [RFC PATCH 1/4] lib/percpu_counter: Split out a helper to insert into hotplug list

In preparation to using it with the lazy pcpu counter.

Signed-off-by: Gabriel Krisman Bertazi <krisman@...e.de>
---
 lib/percpu_counter.c | 28 +++++++++++++++++-----------
 1 file changed, 17 insertions(+), 11 deletions(-)

diff --git a/lib/percpu_counter.c b/lib/percpu_counter.c
index 2891f94a11c6..c2322d53f3b1 100644
--- a/lib/percpu_counter.c
+++ b/lib/percpu_counter.c
@@ -185,11 +185,26 @@ s64 __percpu_counter_sum(struct percpu_counter *fbc)
 }
 EXPORT_SYMBOL(__percpu_counter_sum);
 
+static int cpu_hotplug_add_watchlist(struct percpu_counter *fbc, int nr_counters)
+{
+#ifdef CONFIG_HOTPLUG_CPU
+	unsigned long flags;
+	int i;
+
+	spin_lock_irqsave(&percpu_counters_lock, flags);
+	for (i = 0; i < nr_counters; i++) {
+		INIT_LIST_HEAD(&fbc[i].list);
+		list_add(&fbc[i].list, &percpu_counters);
+	}
+	spin_unlock_irqrestore(&percpu_counters_lock, flags);
+#endif
+	return 0;
+}
+
 int __percpu_counter_init_many(struct percpu_counter *fbc, s64 amount,
 			       gfp_t gfp, u32 nr_counters,
 			       struct lock_class_key *key)
 {
-	unsigned long flags __maybe_unused;
 	size_t counter_size;
 	s32 __percpu *counters;
 	u32 i;
@@ -205,21 +220,12 @@ int __percpu_counter_init_many(struct percpu_counter *fbc, s64 amount,
 	for (i = 0; i < nr_counters; i++) {
 		raw_spin_lock_init(&fbc[i].lock);
 		lockdep_set_class(&fbc[i].lock, key);
-#ifdef CONFIG_HOTPLUG_CPU
-		INIT_LIST_HEAD(&fbc[i].list);
-#endif
 		fbc[i].count = amount;
 		fbc[i].counters = (void __percpu *)counters + i * counter_size;
 
 		debug_percpu_counter_activate(&fbc[i]);
 	}
-
-#ifdef CONFIG_HOTPLUG_CPU
-	spin_lock_irqsave(&percpu_counters_lock, flags);
-	for (i = 0; i < nr_counters; i++)
-		list_add(&fbc[i].list, &percpu_counters);
-	spin_unlock_irqrestore(&percpu_counters_lock, flags);
-#endif
+	cpu_hotplug_add_watchlist(fbc, nr_counters);
 	return 0;
 }
 EXPORT_SYMBOL(__percpu_counter_init_many);
-- 
2.51.0