debugobjects: Collect newly allocated objects in a list to reduce lock contention

Collect the newly allocated debug objects in a list outside the lock, so
that the lock held time and the potential lock contention is reduced.

Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/all/20240911083521.2257-3-thunder.leizhen@huawei.com
Link: https://lore.kernel.org/all/20241007164913.073653668@linutronix.de

Author: Zhen Lei

lib/debugobjects.c

@@ -161,23 +161,25 @@ static void fill_pool(void)
 		return;
 
 	while (READ_ONCE(obj_pool_free) < debug_objects_pool_min_level) {
-		struct debug_obj *new[ODEBUG_BATCH_SIZE];
+		struct debug_obj *new, *last = NULL;
+		HLIST_HEAD(head);
 		int cnt;
 
 		for (cnt = 0; cnt < ODEBUG_BATCH_SIZE; cnt++) {
-			new[cnt] = kmem_cache_zalloc(obj_cache, gfp);
-			if (!new[cnt])
+			new = kmem_cache_zalloc(obj_cache, gfp);
+			if (!new)
 				break;
+			hlist_add_head(&new->node, &head);
+			if (!last)
+				last = new;
 		}
 		if (!cnt)
 			return;
 
 		raw_spin_lock_irqsave(&pool_lock, flags);
-		while (cnt) {
-			hlist_add_head(&new[--cnt]->node, &obj_pool);
-			debug_objects_allocated++;
-			WRITE_ONCE(obj_pool_free, obj_pool_free + 1);
-		}
+		hlist_splice_init(&head, &last->node, &obj_pool);
+		debug_objects_allocated += cnt;
+		WRITE_ONCE(obj_pool_free, obj_pool_free + cnt);
 		raw_spin_unlock_irqrestore(&pool_lock, flags);
 	}
 }