[PATCH v4 31/48] virtio_balloon: dynamically allocate the virtio-balloon shrinker

[Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>]

In preparation for implementing lockless slab shrink, use new APIs 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>
Reviewed-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
---
 drivers/virtio/virtio_balloon.c | 25 +++++++++++++++----------
 1 file changed, 15 insertions(+), 10 deletions(-)

diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
index 5b15936a5214..82e6087073a9 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 +845,23 @@ static int virtio_balloon_oom_notify(struct 
notifier_block *nb,
 
 static void virtio_balloon_unregister_shrinker(struct virtio_balloon *vb)
 {
-       unregister_shrinker(&vb->shrinker);
+       shrinker_free(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;
+       vb->shrinker = shrinker_alloc(0, "virtio-balloon");
+       if (!vb->shrinker)
+               return -ENOMEM;
 
-       return register_shrinker(&vb->shrinker, "virtio-balloon");
+       vb->shrinker->scan_objects = virtio_balloon_shrinker_scan;
+       vb->shrinker->count_objects = virtio_balloon_shrinker_count;
+       vb->shrinker->seeks = DEFAULT_SEEKS;
+       vb->shrinker->private_data = vb;
+
+       shrinker_register(vb->shrinker);
+
+       return 0;
 }
 
 static int virtballoon_probe(struct virtio_device *vdev)
-- 
2.30.2