[PATCH v4 41/48] fs: super: dynamically allocate the s_shrink

[Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>]

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

Signed-off-by: Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>
Reviewed-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
---
 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 5ca07b41b4cd..c6980fc6fe02 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -1514,7 +1514,7 @@ static struct dentry *btrfs_mount_root(struct 
file_system_type *fs_type,
 
                snprintf(s->s_id, sizeof(s->s_id), "%pg",
                         fs_devices->latest_dev->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);
                fs_info->bdev_holder = s;
                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 2354bcab6fff..a28193045345 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -67,7 +67,7 @@ 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
@@ -120,7 +120,7 @@ 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 trylock_super() here as it is a scalability bottleneck,
@@ -182,7 +182,7 @@ 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);
 }
@@ -259,16 +259,20 @@ 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;
 
@@ -326,7 +330,7 @@ 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);
 
                /*
@@ -610,7 +614,7 @@ 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:
@@ -693,7 +697,7 @@ 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);
@@ -1312,7 +1316,7 @@ 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 9515d3688f71..1464afd41164 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1263,7 +1263,7 @@ 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