[PATCH v6 23/45] dm: dynamically allocate the dm-bufio shrinker

[Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>]

In preparation for implementing lockless slab shrink, use new APIs to
dynamically allocate the dm-bufio shrinker, so that it can be freed
asynchronously via 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@xxxxxxxxxxxxx>
Reviewed-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
CC: Alasdair Kergon <agk@xxxxxxxxxx>
CC: Mike Snitzer <snitzer@xxxxxxxxxx>
CC: dm-devel@xxxxxxxxxx
---
 drivers/md/dm-bufio.c | 28 +++++++++++++++++-----------
 1 file changed, 17 insertions(+), 11 deletions(-)

diff --git a/drivers/md/dm-bufio.c b/drivers/md/dm-bufio.c
index bc309e41d074..62eb27639c9b 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;
 
@@ -2368,7 +2368,7 @@ 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);
 
@@ -2377,7 +2377,7 @@ 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);
@@ -2490,14 +2490,20 @@ 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)",
-			      MAJOR(bdev->bd_dev), MINOR(bdev->bd_dev));
-	if (r)
+	c->shrinker = shrinker_alloc(0, "dm-bufio:(%u:%u)",
+				     MAJOR(bdev->bd_dev), MINOR(bdev->bd_dev));
+	if (!c->shrinker) {
+		r = -ENOMEM;
 		goto bad;
+	}
+
+	c->shrinker->count_objects = dm_bufio_shrink_count;
+	c->shrinker->scan_objects = dm_bufio_shrink_scan;
+	c->shrinker->seeks = 1;
+	c->shrinker->batch = 0;
+	c->shrinker->private_data = c;
+
+	shrinker_register(c->shrinker);
 
 	mutex_lock(&dm_bufio_clients_lock);
 	dm_bufio_client_count++;
@@ -2537,7 +2543,7 @@ void dm_bufio_client_destroy(struct dm_bufio_client *c)
 
 	drop_buffers(c);
 
-	unregister_shrinker(&c->shrinker);
+	shrinker_free(c->shrinker);
 	flush_work(&c->shrink_work);
 
 	mutex_lock(&dm_bufio_clients_lock);
-- 
2.30.2