[PATCH 12/29] mbcache: dynamically allocate the mbcache shrinker

[Qi Zheng]

In preparation for implementing lockless slab shrink,
we need to dynamically allocate the mbcache 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 mb_cache.

Signed-off-by: Qi Zheng <zhengqi.arch at bytedance.com>
---
 fs/mbcache.c | 39 +++++++++++++++++++++------------------
 1 file changed, 21 insertions(+), 18 deletions(-)

diff --git a/fs/mbcache.c b/fs/mbcache.c
index 2a4b8b549e93..fec393e55a66 100644
--- a/fs/mbcache.c
+++ b/fs/mbcache.c
@@ -37,7 +37,7 @@ struct mb_cache {
 	struct list_head	c_list;
 	/* Number of entries in cache */
 	unsigned long		c_entry_count;
-	struct shrinker		c_shrink;
+	struct shrinker		*c_shrink;
 	/* Work for shrinking when the cache has too many entries */
 	struct work_struct	c_shrink_work;
 };
@@ -293,8 +293,7 @@ EXPORT_SYMBOL(mb_cache_entry_touch);
 static unsigned long mb_cache_count(struct shrinker *shrink,
 				    struct shrink_control *sc)
 {
-	struct mb_cache *cache = container_of(shrink, struct mb_cache,
-					      c_shrink);
+	struct mb_cache *cache = shrink->private_data;
 
 	return cache->c_entry_count;
 }
@@ -333,8 +332,8 @@ static unsigned long mb_cache_shrink(struct mb_cache *cache,
 static unsigned long mb_cache_scan(struct shrinker *shrink,
 				   struct shrink_control *sc)
 {
-	struct mb_cache *cache = container_of(shrink, struct mb_cache,
-					      c_shrink);
+	struct mb_cache *cache = shrink->private_data;
+
 	return mb_cache_shrink(cache, sc->nr_to_scan);
 }
 
@@ -370,26 +369,30 @@ struct mb_cache *mb_cache_create(int bucket_bits)
 	cache->c_hash = kmalloc_array(bucket_count,
 				      sizeof(struct hlist_bl_head),
 				      GFP_KERNEL);
-	if (!cache->c_hash) {
-		kfree(cache);
-		goto err_out;
-	}
+	if (!cache->c_hash)
+		goto err_c_hash;
+
 	for (i = 0; i < bucket_count; i++)
 		INIT_HLIST_BL_HEAD(&cache->c_hash[i]);
 
-	cache->c_shrink.count_objects = mb_cache_count;
-	cache->c_shrink.scan_objects = mb_cache_scan;
-	cache->c_shrink.seeks = DEFAULT_SEEKS;
-	if (register_shrinker(&cache->c_shrink, "mbcache-shrinker")) {
-		kfree(cache->c_hash);
-		kfree(cache);
-		goto err_out;
-	}
+	cache->c_shrink = shrinker_alloc_and_init(mb_cache_count, mb_cache_scan,
+						  0, DEFAULT_SEEKS, 0, cache);
+	if (!cache->c_shrink)
+		goto err_shrinker;
+
+	if (register_shrinker(cache->c_shrink, "mbcache-shrinker"))
+		goto err_register;
 
 	INIT_WORK(&cache->c_shrink_work, mb_cache_shrink_worker);
 
 	return cache;
 
+err_register:
+	shrinker_free(cache->c_shrink);
+err_shrinker:
+	kfree(cache->c_hash);
+err_c_hash:
+	kfree(cache);
 err_out:
 	return NULL;
 }
@@ -406,7 +409,7 @@ void mb_cache_destroy(struct mb_cache *cache)
 {
 	struct mb_cache_entry *entry, *next;
 
-	unregister_shrinker(&cache->c_shrink);
+	unregister_and_free_shrinker(cache->c_shrink);
 
 	/*
 	 * We don't bother with any locking. Cache must not be used at this
-- 
2.30.2