[PATCH 06/29] dm: dynamically allocate the dm-bufio shrinker

[Qi Zheng]

In preparation for implementing lockless slab shrink,
we need to dynamically allocate the dm-bufio 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 dm_bufio_client.

Signed-off-by: Qi Zheng <zhengqi.arch at bytedance.com>
---
 drivers/md/dm-bufio.c | 23 +++++++++++++----------
 1 file changed, 13 insertions(+), 10 deletions(-)

diff --git a/drivers/md/dm-bufio.c b/drivers/md/dm-bufio.c
index eea977662e81..9472470d456d 100644
--- a/drivers/md/dm-bufio.c
+++ b/drivers/md/dm-bufio.c
@@ -963,7 +963,7 @@ struct dm_bufio_client {
 
 	sector_t start;
 
-	struct shrinker shrinker;
+	struct shrinker *shrinker;
 	struct work_struct shrink_work;
 	atomic_long_t need_shrink;
 
@@ -2385,7 +2385,7 @@ static unsigned long dm_bufio_shrink_scan(struct shrinker *shrink, struct shrink
 {
 	struct dm_bufio_client *c;
 
-	c = container_of(shrink, struct dm_bufio_client, shrinker);
+	c = shrink->private_data;
 	atomic_long_add(sc->nr_to_scan, &c->need_shrink);
 	queue_work(dm_bufio_wq, &c->shrink_work);
 
@@ -2394,7 +2394,7 @@ static unsigned long dm_bufio_shrink_scan(struct shrinker *shrink, struct shrink
 
 static unsigned long dm_bufio_shrink_count(struct shrinker *shrink, struct shrink_control *sc)
 {
-	struct dm_bufio_client *c = container_of(shrink, struct dm_bufio_client, shrinker);
+	struct dm_bufio_client *c = shrink->private_data;
 	unsigned long count = cache_total(&c->cache);
 	unsigned long retain_target = get_retain_buffers(c);
 	unsigned long queued_for_cleanup = atomic_long_read(&c->need_shrink);
@@ -2507,14 +2507,15 @@ struct dm_bufio_client *dm_bufio_client_create(struct block_device *bdev, unsign
 	INIT_WORK(&c->shrink_work, shrink_work);
 	atomic_long_set(&c->need_shrink, 0);
 
-	c->shrinker.count_objects = dm_bufio_shrink_count;
-	c->shrinker.scan_objects = dm_bufio_shrink_scan;
-	c->shrinker.seeks = 1;
-	c->shrinker.batch = 0;
-	r = register_shrinker(&c->shrinker, "dm-bufio:(%u:%u)",
+	c->shrinker = shrinker_alloc_and_init(dm_bufio_shrink_count,
+					      dm_bufio_shrink_scan, 0, 1, 0, c);
+	if (!c->shrinker)
+		goto bad;
+
+	r = register_shrinker(c->shrinker, "dm-bufio:(%u:%u)",
 			      MAJOR(bdev->bd_dev), MINOR(bdev->bd_dev));
 	if (r)
-		goto bad;
+		goto bad_shrinker;
 
 	mutex_lock(&dm_bufio_clients_lock);
 	dm_bufio_client_count++;
@@ -2524,6 +2525,8 @@ struct dm_bufio_client *dm_bufio_client_create(struct block_device *bdev, unsign
 
 	return c;
 
+bad_shrinker:
+	shrinker_free(c->shrinker);
 bad:
 	while (!list_empty(&c->reserved_buffers)) {
 		struct dm_buffer *b = list_to_buffer(c->reserved_buffers.next);
@@ -2554,7 +2557,7 @@ void dm_bufio_client_destroy(struct dm_bufio_client *c)
 
 	drop_buffers(c);
 
-	unregister_shrinker(&c->shrinker);
+	unregister_and_free_shrinker(c->shrinker);
 	flush_work(&c->shrink_work);
 
 	mutex_lock(&dm_bufio_clients_lock);
-- 
2.30.2