f2fs: speed up shrinking extent tree entries

If there is no candidates for shrinking slab entries, we don't need to traverse
any trees at all.
Reviewed-by: Chao Yu <chao2.yu@samsung.com>
[Jaegeuk Kim: fix missing initialization reported by Yunlei He]
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/extent_cache.c

@@ -71,6 +71,8 @@ static struct extent_tree *__grab_extent_tree(struct inode *inode)
 		atomic_set(&et->refcount, 0);
 		et->count = 0;
 		atomic_inc(&sbi->total_ext_tree);
+	} else {
+		atomic_dec(&sbi->total_zombie_tree);
 	}
 	atomic_inc(&et->refcount);
 	up_write(&sbi->extent_tree_lock);
@@ -547,10 +549,14 @@ unsigned int f2fs_shrink_extent_tree(struct f2fs_sb_info *sbi, int nr_shrink)
 	unsigned int found;
 	unsigned int node_cnt = 0, tree_cnt = 0;
 	int remained;
+	bool do_free = false;
 
 	if (!test_opt(sbi, EXTENT_CACHE))
 		return 0;
 
+	if (!atomic_read(&sbi->total_zombie_tree))
+		goto free_node;
+
 	if (!down_write_trylock(&sbi->extent_tree_lock))
 		goto out;
 
@@ -571,6 +577,7 @@ unsigned int f2fs_shrink_extent_tree(struct f2fs_sb_info *sbi, int nr_shrink)
 				radix_tree_delete(root, et->ino);
 				kmem_cache_free(extent_tree_slab, et);
 				atomic_dec(&sbi->total_ext_tree);
+				atomic_dec(&sbi->total_zombie_tree);
 				tree_cnt++;
 
 				if (node_cnt + tree_cnt >= nr_shrink)
@@ -580,6 +587,7 @@ unsigned int f2fs_shrink_extent_tree(struct f2fs_sb_info *sbi, int nr_shrink)
 	}
 	up_write(&sbi->extent_tree_lock);
 
+free_node:
 	/* 2. remove LRU extent entries */
 	if (!down_write_trylock(&sbi->extent_tree_lock))
 		goto out;
@@ -591,9 +599,13 @@ unsigned int f2fs_shrink_extent_tree(struct f2fs_sb_info *sbi, int nr_shrink)
 		if (!remained--)
 			break;
 		list_del_init(&en->list);
+		do_free = true;
 	}
 	spin_unlock(&sbi->extent_lock);
 
+	if (do_free == false)
+		goto unlock_out;
+
 	/*
 	 * reset ino for searching victims from beginning of global extent tree.
 	 */
@@ -651,6 +663,7 @@ void f2fs_destroy_extent_tree(struct inode *inode)
 
 	if (inode->i_nlink && !is_bad_inode(inode) && et->count) {
 		atomic_dec(&et->refcount);
+		atomic_inc(&sbi->total_zombie_tree);
 		return;
 	}
 
@@ -716,6 +729,7 @@ void init_extent_cache_info(struct f2fs_sb_info *sbi)
 	INIT_LIST_HEAD(&sbi->extent_list);
 	spin_lock_init(&sbi->extent_lock);
 	atomic_set(&sbi->total_ext_tree, 0);
+	atomic_set(&sbi->total_zombie_tree, 0);
 	atomic_set(&sbi->total_ext_node, 0);
 }
 

fs/f2fs/f2fs.h

@@ -763,6 +763,7 @@ struct f2fs_sb_info {
 	struct list_head extent_list;		/* lru list for shrinker */
 	spinlock_t extent_lock;			/* locking extent lru list */
 	atomic_t total_ext_tree;		/* extent tree count */
+	atomic_t total_zombie_tree;		/* extent zombie tree count */
 	atomic_t total_ext_node;		/* extent info count */
 
 	/* basic filesystem units */

fs/f2fs/shrinker.c

@@ -32,7 +32,7 @@ static unsigned long __count_free_nids(struct f2fs_sb_info *sbi)
 
 static unsigned long __count_extent_cache(struct f2fs_sb_info *sbi)
 {
-	return atomic_read(&sbi->total_ext_tree) +
+	return atomic_read(&sbi->total_zombie_tree) +
 				atomic_read(&sbi->total_ext_node);
 }