[PATCH 11/29] virtio_balloon: dynamically allocate the virtio-balloon shrinker

[Qi Zheng <qi.zheng@xxxxxxxxx>]

From: Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>

In preparation for implementing lockless slab shrink,
we need to dynamically allocate the virtio-balloon shrinker,
so that it can be freed asynchronously using kfree_rcu().
Then it doesn't need to wait for RCU read-side critical
section when releasing the struct virtio_balloon.

Signed-off-by: Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>
---
 drivers/virtio/virtio_balloon.c | 26 ++++++++++++++++----------
 1 file changed, 16 insertions(+), 10 deletions(-)

diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
index 5b15936a5214..fa051bff8d90 100644
--- a/drivers/virtio/virtio_balloon.c
+++ b/drivers/virtio/virtio_balloon.c
@@ -111,7 +111,7 @@ struct virtio_balloon {
 	struct virtio_balloon_stat stats[VIRTIO_BALLOON_S_NR];
 
 	/* Shrinker to return free pages - VIRTIO_BALLOON_F_FREE_PAGE_HINT */
-	struct shrinker shrinker;
+	struct shrinker *shrinker;
 
 	/* OOM notifier to deflate on OOM - VIRTIO_BALLOON_F_DEFLATE_ON_OOM */
 	struct notifier_block oom_nb;
@@ -816,8 +816,7 @@ static unsigned long shrink_free_pages(struct virtio_balloon *vb,
 static unsigned long virtio_balloon_shrinker_scan(struct shrinker *shrinker,
 						  struct shrink_control *sc)
 {
-	struct virtio_balloon *vb = container_of(shrinker,
-					struct virtio_balloon, shrinker);
+	struct virtio_balloon *vb = shrinker->private_data;
 
 	return shrink_free_pages(vb, sc->nr_to_scan);
 }
@@ -825,8 +824,7 @@ static unsigned long virtio_balloon_shrinker_scan(struct shrinker *shrinker,
 static unsigned long virtio_balloon_shrinker_count(struct shrinker *shrinker,
 						   struct shrink_control *sc)
 {
-	struct virtio_balloon *vb = container_of(shrinker,
-					struct virtio_balloon, shrinker);
+	struct virtio_balloon *vb = shrinker->private_data;
 
 	return vb->num_free_page_blocks * VIRTIO_BALLOON_HINT_BLOCK_PAGES;
 }
@@ -847,16 +845,24 @@ static int virtio_balloon_oom_notify(struct notifier_block *nb,
 
 static void virtio_balloon_unregister_shrinker(struct virtio_balloon *vb)
 {
-	unregister_shrinker(&vb->shrinker);
+	unregister_and_free_shrinker(vb->shrinker);
 }
 
 static int virtio_balloon_register_shrinker(struct virtio_balloon *vb)
 {
-	vb->shrinker.scan_objects = virtio_balloon_shrinker_scan;
-	vb->shrinker.count_objects = virtio_balloon_shrinker_count;
-	vb->shrinker.seeks = DEFAULT_SEEKS;
+	int ret;
+
+	vb->shrinker = shrinker_alloc_and_init(virtio_balloon_shrinker_count,
+					       virtio_balloon_shrinker_scan,
+					       0, DEFAULT_SEEKS, 0, vb);
+	if (!vb->shrinker)
+		return -ENOMEM;
+
+	ret = register_shrinker(vb->shrinker, "virtio-balloon");
+	if (ret)
+		shrinker_free(vb->shrinker);
 
-	return register_shrinker(&vb->shrinker, "virtio-balloon");
+	return ret;
 }
 
 static int virtballoon_probe(struct virtio_device *vdev)
-- 
2.30.2