[PATCH v5 38/45] fs: super: dynamically allocate the s_shrink

[Qi Zheng]

In preparation for implementing lockless slab shrink, use new APIs to
dynamically allocate the s_shrink, 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 super_block.

Signed-off-by: Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>
Reviewed-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
CC: Chris Mason <clm@xxxxxx>
CC: Josef Bacik <josef@xxxxxxxxxxxxxx>
CC: David Sterba <dsterba@xxxxxxxx>
CC: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx>
CC: Christian Brauner <brauner@xxxxxxxxxx>
CC: linux-btrfs@xxxxxxxxxxxxxxx
---
 fs/btrfs/super.c   |  2 +-
 fs/kernfs/mount.c  |  2 +-
 fs/proc/root.c     |  2 +-
 fs/super.c         | 34 +++++++++++++++++++---------------
 include/linux/fs.h |  2 +-
 5 files changed, 23 insertions(+), 19 deletions(-)

diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index 09bfe68d2ea3..3b165d9967bb 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -1519,7 +1519,7 @@ static struct dentry *btrfs_mount_root(struct file_system_type *fs_type,
 			error = -EBUSY;
 	} else {
 		snprintf(s->s_id, sizeof(s->s_id), "%pg", bdev);
-		shrinker_debugfs_rename(&s->s_shrink, "sb-%s:%s", fs_type->name,
+		shrinker_debugfs_rename(s->s_shrink, "sb-%s:%s", fs_type->name,
 					s->s_id);
 		btrfs_sb(s)->bdev_holder = fs_type;
 		error = btrfs_fill_super(s, fs_devices, data);
diff --git a/fs/kernfs/mount.c b/fs/kernfs/mount.c
index c4bf26142eec..79b96e74a8a0 100644
--- a/fs/kernfs/mount.c
+++ b/fs/kernfs/mount.c
@@ -265,7 +265,7 @@ static int kernfs_fill_super(struct super_block *sb, struct kernfs_fs_context *k
 	sb->s_time_gran = 1;
 
 	/* sysfs dentries and inodes don't require IO to create */
-	sb->s_shrink.seeks = 0;
+	sb->s_shrink->seeks = 0;
 
 	/* get root inode, initialize and unlock it */
 	down_read(&kf_root->kernfs_rwsem);
diff --git a/fs/proc/root.c b/fs/proc/root.c
index 9191248f2dac..b55dbc70287b 100644
--- a/fs/proc/root.c
+++ b/fs/proc/root.c
@@ -188,7 +188,7 @@ static int proc_fill_super(struct super_block *s, struct fs_context *fc)
 	s->s_stack_depth = FILESYSTEM_MAX_STACK_DEPTH;
 
 	/* procfs dentries and inodes don't require IO to create */
-	s->s_shrink.seeks = 0;
+	s->s_shrink->seeks = 0;
 
 	pde_get(&proc_root);
 	root_inode = proc_get_inode(s, &proc_root);
diff --git a/fs/super.c b/fs/super.c
index 719b67cd4a6b..5ce0c51bb445 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -191,7 +191,7 @@ static unsigned long super_cache_scan(struct shrinker *shrink,
 	long	dentries;
 	long	inodes;
 
-	sb = container_of(shrink, struct super_block, s_shrink);
+	sb = shrink->private_data;
 
 	/*
 	 * Deadlock avoidance.  We may hold various FS locks, and we don't want
@@ -244,7 +244,7 @@ static unsigned long super_cache_count(struct shrinker *shrink,
 	struct super_block *sb;
 	long	total_objects = 0;
 
-	sb = container_of(shrink, struct super_block, s_shrink);
+	sb = shrink->private_data;
 
 	/*
 	 * We don't call super_trylock_shared() here as it is a scalability
@@ -306,7 +306,7 @@ static void destroy_unused_super(struct super_block *s)
 	security_sb_free(s);
 	put_user_ns(s->s_user_ns);
 	kfree(s->s_subtype);
-	free_prealloced_shrinker(&s->s_shrink);
+	shrinker_free(s->s_shrink);
 	/* no delays needed */
 	destroy_super_work(&s->destroy_work);
 }
@@ -383,16 +383,20 @@ static struct super_block *alloc_super(struct file_system_type *type, int flags,
 	s->s_time_min = TIME64_MIN;
 	s->s_time_max = TIME64_MAX;
 
-	s->s_shrink.seeks = DEFAULT_SEEKS;
-	s->s_shrink.scan_objects = super_cache_scan;
-	s->s_shrink.count_objects = super_cache_count;
-	s->s_shrink.batch = 1024;
-	s->s_shrink.flags = SHRINKER_NUMA_AWARE | SHRINKER_MEMCG_AWARE;
-	if (prealloc_shrinker(&s->s_shrink, "sb-%s", type->name))
+	s->s_shrink = shrinker_alloc(SHRINKER_NUMA_AWARE | SHRINKER_MEMCG_AWARE,
+				     "sb-%s", type->name);
+	if (!s->s_shrink)
 		goto fail;
-	if (list_lru_init_memcg(&s->s_dentry_lru, &s->s_shrink))
+
+	s->s_shrink->seeks = DEFAULT_SEEKS;
+	s->s_shrink->scan_objects = super_cache_scan;
+	s->s_shrink->count_objects = super_cache_count;
+	s->s_shrink->batch = 1024;
+	s->s_shrink->private_data = s;
+
+	if (list_lru_init_memcg(&s->s_dentry_lru, s->s_shrink))
 		goto fail;
-	if (list_lru_init_memcg(&s->s_inode_lru, &s->s_shrink))
+	if (list_lru_init_memcg(&s->s_inode_lru, s->s_shrink))
 		goto fail;
 	return s;
 
@@ -450,7 +454,7 @@ void deactivate_locked_super(struct super_block *s)
 {
 	struct file_system_type *fs = s->s_type;
 	if (atomic_dec_and_test(&s->s_active)) {
-		unregister_shrinker(&s->s_shrink);
+		shrinker_free(s->s_shrink);
 		fs->kill_sb(s);
 
 		/*
@@ -808,7 +812,7 @@ struct super_block *sget_fc(struct fs_context *fc,
 	hlist_add_head(&s->s_instances, &s->s_type->fs_supers);
 	spin_unlock(&sb_lock);
 	get_filesystem(s->s_type);
-	register_shrinker_prepared(&s->s_shrink);
+	shrinker_register(s->s_shrink);
 	return s;
 
 share_extant_sb:
@@ -891,7 +895,7 @@ struct super_block *sget(struct file_system_type *type,
 	hlist_add_head(&s->s_instances, &type->fs_supers);
 	spin_unlock(&sb_lock);
 	get_filesystem(type);
-	register_shrinker_prepared(&s->s_shrink);
+	shrinker_register(s->s_shrink);
 	return s;
 }
 EXPORT_SYMBOL(sget);
@@ -1484,7 +1488,7 @@ int setup_bdev_super(struct super_block *sb, int sb_flags,
 	mutex_unlock(&bdev->bd_fsfreeze_mutex);
 
 	snprintf(sb->s_id, sizeof(sb->s_id), "%pg", bdev);
-	shrinker_debugfs_rename(&sb->s_shrink, "sb-%s:%s", sb->s_type->name,
+	shrinker_debugfs_rename(sb->s_shrink, "sb-%s:%s", sb->s_type->name,
 				sb->s_id);
 	sb_set_blocksize(sb, block_size(bdev));
 	return 0;
diff --git a/include/linux/fs.h b/include/linux/fs.h
index c8ff4156a0a1..82a0b5aca045 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1265,7 +1265,7 @@ struct super_block {
 
 	const struct dentry_operations *s_d_op; /* default d_op for dentries */
 
-	struct shrinker s_shrink;	/* per-sb shrinker handle */
+	struct shrinker *s_shrink;	/* per-sb shrinker handle */
 
 	/* Number of inodes with nlink == 0 but still referenced */
 	atomic_long_t s_remove_count;
-- 
2.30.2