f2fs: introduce infra macro and data structure of rb-tree extent cache

#define MAX_DIR_RA_PAGES	4	/* maximum ra pages of dir */

/* vector size for gang look-up from extent cache that consists of radix tree */

#define EXT_TREE_VEC_SIZE	64

/* for in-memory extent cache entry */

#define F2FS_MIN_EXTENT_LEN	16	/* minimum extent length */

#define F2FS_MIN_EXTENT_LEN	64	/* minimum extent length */

/* number of extent info in extent cache we try to shrink */

#define EXTENT_CACHE_SHRINK_NUMBER	128

struct extent_info {

	unsigned int fofs;		/* start offset in a file */

	unsigned int len;		/* length of the extent */

};

struct extent_node {

	struct rb_node rb_node;		/* rb node located in rb-tree */

	struct list_head list;		/* node in global extent list of sbi */

	struct extent_info ei;		/* extent info */

};

struct extent_tree {

	nid_t ino;			/* inode number */

	struct rb_root root;		/* root of extent info rb-tree */

	rwlock_t lock;			/* protect extent info rb-tree */

	atomic_t refcount;		/* reference count of rb-tree */

	unsigned int count;		/* # of extent node in rb-tree*/

};

/*

 * i_advise uses FADVISE_XXX_BIT. We can add additional hints later.

 */

	struct list_head dir_inode_list;	/* dir inode list */

	spinlock_t dir_inode_lock;		/* for dir inode list lock */

	/* for extent tree cache */

	struct radix_tree_root extent_tree_root;/* cache extent cache entries */

	struct rw_semaphore extent_tree_lock;	/* locking extent radix tree */

	struct list_head extent_list;		/* lru list for shrinker */

	spinlock_t extent_lock;			/* locking extent lru list */

	int total_ext_tree;			/* extent tree count */

	atomic_t total_ext_node;		/* extent info count */

	/* basic filesystem units */

	unsigned int log_sectors_per_block;	/* log2 sectors per block */

	unsigned int log_blocksize;		/* log2 block size */

	NAT_ENTRIES,	/* indicates the cached nat entry */

	DIRTY_DENTS,	/* indicates dirty dentry pages */

	INO_ENTRIES,	/* indicates inode entries */

	EXTENT_CACHE,	/* indicates extent cache */

	BASE_CHECK,	/* check kernel status */

};