mm/list_lru: introduce list_lru_shrink_walk_irq()

Provide list_lru_shrink_walk_irq() and let it behave like
list_lru_walk_one() except that it locks the spinlock with
spin_lock_irq(). This is used by scan_shadow_nodes() because its lock
nests within the i_pages lock which is acquired with IRQ. This change
allows to use proper locking promitives instead hand crafted
lock_irq_disable() plus spin_lock().

There is no EXPORT_SYMBOL provided because the current user is in-kernel
only.

Add list_lru_shrink_walk_irq() which acquires the spinlock with the
proper locking primitives.

Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Sebastian Andrzej Siewior <[e-mail]>
Reviewed-by: Vladimir Davydov <[e-mail]>
Cc: Thomas Gleixner <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

include/linux/list_lru.h

···
 				int nid, struct mem_cgroup *memcg,
 				list_lru_walk_cb isolate, void *cb_arg,
 				unsigned long *nr_to_walk);
+/**
+ * list_lru_walk_one_irq: walk a list_lru, isolating and disposing freeable items.
+ * @lru: the lru pointer.
+ * @nid: the node id to scan from.
+ * @memcg: the cgroup to scan from.
+ * @isolate: callback function that is resposible for deciding what to do with
+ *  the item currently being scanned
+ * @cb_arg: opaque type that will be passed to @isolate
+ * @nr_to_walk: how many items to scan.
+ *
+ * Same as @list_lru_walk_one except that the spinlock is acquired with
+ * spin_lock_irq().
+ */
+unsigned long list_lru_walk_one_irq(struct list_lru *lru,
+				    int nid, struct mem_cgroup *memcg,
+				    list_lru_walk_cb isolate, void *cb_arg,
+				    unsigned long *nr_to_walk);
 unsigned long list_lru_walk_node(struct list_lru *lru, int nid,
 				 list_lru_walk_cb isolate, void *cb_arg,
 				 unsigned long *nr_to_walk);
···
 {
 	return list_lru_walk_one(lru, sc->nid, sc->memcg, isolate, cb_arg,
 				 &sc->nr_to_scan);
+}
+
+static inline unsigned long
+list_lru_shrink_walk_irq(struct list_lru *lru, struct shrink_control *sc,
+			 list_lru_walk_cb isolate, void *cb_arg)
+{
+	return list_lru_walk_one_irq(lru, sc->nid, sc->memcg, isolate, cb_arg,
+				     &sc->nr_to_scan);
 }
 
 static inline unsigned long

mm/list_lru.c

···
 }
 EXPORT_SYMBOL_GPL(list_lru_walk_one);
 
+unsigned long
+list_lru_walk_one_irq(struct list_lru *lru, int nid, struct mem_cgroup *memcg,
+		      list_lru_walk_cb isolate, void *cb_arg,
+		      unsigned long *nr_to_walk)
+{
+	struct list_lru_node *nlru = &lru->node[nid];
+	unsigned long ret;
+
+	spin_lock_irq(&nlru->lock);
+	ret = __list_lru_walk_one(nlru, memcg_cache_id(memcg), isolate, cb_arg,
+				  nr_to_walk);
+	spin_unlock_irq(&nlru->lock);
+	return ret;
+}
+
 unsigned long list_lru_walk_node(struct list_lru *lru, int nid,
 				 list_lru_walk_cb isolate, void *cb_arg,
 				 unsigned long *nr_to_walk)

mm/workingset.c

···
 static unsigned long scan_shadow_nodes(struct shrinker *shrinker,
 				       struct shrink_control *sc)
 {
-	unsigned long ret;
-
 	/* list_lru lock nests inside the IRQ-safe i_pages lock */
-	local_irq_disable();
-	ret = list_lru_shrink_walk(&shadow_nodes, sc, shadow_lru_isolate, NULL);
-	local_irq_enable();
-	return ret;
+	return list_lru_shrink_walk_irq(&shadow_nodes, sc, shadow_lru_isolate,
+					NULL);
 }
 
 static struct shrinker workingset_shadow_shrinker = {