[PATCH v8 03/17] mm: Assign id to every memcg-aware shrinker

[Kirill Tkhai <ktkhai@xxxxxxxxxxxxx>]

The patch introduces shrinker::id number, which is used to enumerate
memcg-aware shrinkers. The number start from 0, and the code tries
to maintain it as small as possible.

This will be used as to represent a memcg-aware shrinkers in memcg
shrinkers map.

Since all memcg-aware shrinkers are based on list_lru, which is per-memcg
in case of !CONFIG_MEMCG_KMEM only, the new functionality will be under
this config option.

Signed-off-by: Kirill Tkhai <ktkhai@xxxxxxxxxxxxx>
Acked-by: Vladimir Davydov <vdavydov.dev@xxxxxxxxx>
Tested-by: Shakeel Butt <shakeelb@xxxxxxxxxx>
---
 include/linux/shrinker.h |    4 +++
 mm/vmscan.c              |   62 ++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 66 insertions(+)

diff --git a/include/linux/shrinker.h b/include/linux/shrinker.h
index 6794490f25b2..7ca9c18cf130 100644
--- a/include/linux/shrinker.h
+++ b/include/linux/shrinker.h
@@ -66,6 +66,10 @@ struct shrinker {
 
 	/* These are for internal use */
 	struct list_head list;
+#ifdef CONFIG_MEMCG_KMEM
+	/* ID in shrinker_idr */
+	int id;
+#endif
 	/* objs pending delete, per node */
 	atomic_long_t *nr_deferred;
 };
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 8d2ffae4db28..f9ca6b57d72f 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -169,6 +169,49 @@ unsigned long vm_total_pages;
 static LIST_HEAD(shrinker_list);
 static DECLARE_RWSEM(shrinker_rwsem);
 
+#ifdef CONFIG_MEMCG_KMEM
+static DEFINE_IDR(shrinker_idr);
+static int shrinker_nr_max;
+
+static int prealloc_memcg_shrinker(struct shrinker *shrinker)
+{
+	int id, ret = -ENOMEM;
+
+	down_write(&shrinker_rwsem);
+	id = idr_alloc(&shrinker_idr, shrinker, 0, 0, GFP_KERNEL);
+	if (id < 0)
+		goto unlock;
+
+	if (id >= shrinker_nr_max)
+		shrinker_nr_max = id + 1;
+	shrinker->id = id;
+	ret = 0;
+unlock:
+	up_write(&shrinker_rwsem);
+	return ret;
+}
+
+static void unregister_memcg_shrinker(struct shrinker *shrinker)
+{
+	int id = shrinker->id;
+
+	BUG_ON(id < 0);
+
+	down_write(&shrinker_rwsem);
+	idr_remove(&shrinker_idr, id);
+	up_write(&shrinker_rwsem);
+}
+#else /* CONFIG_MEMCG_KMEM */
+static int prealloc_memcg_shrinker(struct shrinker *shrinker)
+{
+	return 0;
+}
+
+static void unregister_memcg_shrinker(struct shrinker *shrinker)
+{
+}
+#endif /* CONFIG_MEMCG_KMEM */
+
 #ifdef CONFIG_MEMCG
 static bool global_reclaim(struct scan_control *sc)
 {
@@ -313,13 +356,30 @@ int prealloc_shrinker(struct shrinker *shrinker)
 	shrinker->nr_deferred = kzalloc(size, GFP_KERNEL);
 	if (!shrinker->nr_deferred)
 		return -ENOMEM;
+
+	if (shrinker->flags & SHRINKER_MEMCG_AWARE) {
+		if (prealloc_memcg_shrinker(shrinker))
+			goto free_deferred;
+	}
+
 	return 0;
+
+free_deferred:
+	kfree(shrinker->nr_deferred);
+	shrinker->nr_deferred = NULL;
+	return -ENOMEM;
 }
 
 void free_prealloced_shrinker(struct shrinker *shrinker)
 {
+	if (!shrinker->nr_deferred)
+		return;
+
 	kfree(shrinker->nr_deferred);
 	shrinker->nr_deferred = NULL;
+
+	if (shrinker->flags & SHRINKER_MEMCG_AWARE)
+		unregister_memcg_shrinker(shrinker);
 }
 
 void register_shrinker_prepared(struct shrinker *shrinker)
@@ -347,6 +407,8 @@ void unregister_shrinker(struct shrinker *shrinker)
 {
 	if (!shrinker->nr_deferred)
 		return;
+	if (shrinker->flags & SHRINKER_MEMCG_AWARE)
+		unregister_memcg_shrinker(shrinker);
 	down_write(&shrinker_rwsem);
 	list_del(&shrinker->list);
 	up_write(&shrinker_rwsem);