/*
   * f2fs extent cache support
   *
   * Copyright (c) 2015 Motorola Mobility
   * Copyright (c) 2015 Samsung Electronics
   * Authors: Jaegeuk Kim <jaegeuk@kernel.org>
   *          Chao Yu <chao2.yu@samsung.com>
   *
   * This program is free software; you can redistribute it and/or modify
   * it under the terms of the GNU General Public License version 2 as
   * published by the Free Software Foundation.
   */
  
  #include <linux/fs.h>
  #include <linux/f2fs_fs.h>
  
  #include "f2fs.h"
  #include "node.h"
  #include <trace/events/f2fs.h>
  
  static struct kmem_cache *extent_tree_slab;
  static struct kmem_cache *extent_node_slab;
  
  static struct extent_node *__attach_extent_node(struct f2fs_sb_info *sbi,
  				struct extent_tree *et, struct extent_info *ei,
  				struct rb_node *parent, struct rb_node **p)
  {
  	struct extent_node *en;
  
  	en = kmem_cache_alloc(extent_node_slab, GFP_ATOMIC);
  	if (!en)
  		return NULL;
  
  	en->ei = *ei;
  	INIT_LIST_HEAD(&en->list);

  	en->et = et;

  
  	rb_link_node(&en->rb_node, parent, p);
  	rb_insert_color(&en->rb_node, &et->root);

  	atomic_inc(&et->node_cnt);

  	atomic_inc(&sbi->total_ext_node);
  	return en;
  }
  
  static void __detach_extent_node(struct f2fs_sb_info *sbi,
  				struct extent_tree *et, struct extent_node *en)
  {
  	rb_erase(&en->rb_node, &et->root);

  	atomic_dec(&et->node_cnt);

  	atomic_dec(&sbi->total_ext_node);
  
  	if (et->cached_en == en)
  		et->cached_en = NULL;

  	kmem_cache_free(extent_node_slab, en);
  }
  
  /*
   * Flow to release an extent_node:
   * 1. list_del_init
   * 2. __detach_extent_node
   * 3. kmem_cache_free.
   */
  static void __release_extent_node(struct f2fs_sb_info *sbi,
  			struct extent_tree *et, struct extent_node *en)
  {
  	spin_lock(&sbi->extent_lock);

  	f2fs_bug_on(sbi, list_empty(&en->list));
  	list_del_init(&en->list);

  	spin_unlock(&sbi->extent_lock);
  
  	__detach_extent_node(sbi, et, en);

  }
  
  static struct extent_tree *__grab_extent_tree(struct inode *inode)
  {
  	struct f2fs_sb_info *sbi = F2FS_I_SB(inode);
  	struct extent_tree *et;
  	nid_t ino = inode->i_ino;
  
  	down_write(&sbi->extent_tree_lock);
  	et = radix_tree_lookup(&sbi->extent_tree_root, ino);
  	if (!et) {
  		et = f2fs_kmem_cache_alloc(extent_tree_slab, GFP_NOFS);
  		f2fs_radix_tree_insert(&sbi->extent_tree_root, ino, et);
  		memset(et, 0, sizeof(struct extent_tree));
  		et->ino = ino;
  		et->root = RB_ROOT;
  		et->cached_en = NULL;
  		rwlock_init(&et->lock);

  		INIT_LIST_HEAD(&et->list);

  		atomic_set(&et->node_cnt, 0);

  		atomic_inc(&sbi->total_ext_tree);

  	} else {
  		atomic_dec(&sbi->total_zombie_tree);

  		list_del_init(&et->list);

  	}

  	up_write(&sbi->extent_tree_lock);
  
  	/* never died until evict_inode */
  	F2FS_I(inode)->extent_tree = et;
  
  	return et;
  }

  static struct extent_node *__lookup_extent_tree(struct f2fs_sb_info *sbi,
  				struct extent_tree *et, unsigned int fofs)

  {
  	struct rb_node *node = et->root.rb_node;

  	struct extent_node *en = et->cached_en;

  	if (en) {
  		struct extent_info *cei = &en->ei;

  		if (cei->fofs <= fofs && cei->fofs + cei->len > fofs) {
  			stat_inc_cached_node_hit(sbi);

  			return en;

  		}

  	}
  
  	while (node) {
  		en = rb_entry(node, struct extent_node, rb_node);

  		if (fofs < en->ei.fofs) {

  			node = node->rb_left;

  		} else if (fofs >= en->ei.fofs + en->ei.len) {

  			node = node->rb_right;

  		} else {
  			stat_inc_rbtree_node_hit(sbi);

  			return en;

  		}

  	}
  	return NULL;
  }

  static struct extent_node *__init_extent_tree(struct f2fs_sb_info *sbi,
  				struct extent_tree *et, struct extent_info *ei)

  {
  	struct rb_node **p = &et->root.rb_node;

  	struct extent_node *en;

  	en = __attach_extent_node(sbi, et, ei, NULL, p);

  	if (!en)
  		return NULL;

  
  	et->largest = en->ei;

  	et->cached_en = en;
  	return en;
  }
  
  static unsigned int __free_extent_tree(struct f2fs_sb_info *sbi,

  					struct extent_tree *et)

  {
  	struct rb_node *node, *next;
  	struct extent_node *en;

  	unsigned int count = atomic_read(&et->node_cnt);

  
  	node = rb_first(&et->root);
  	while (node) {
  		next = rb_next(node);
  		en = rb_entry(node, struct extent_node, rb_node);

  		__release_extent_node(sbi, et, en);

  		node = next;
  	}

  	return count - atomic_read(&et->node_cnt);

  }

  static void __drop_largest_extent(struct inode *inode,
  					pgoff_t fofs, unsigned int len)

  {
  	struct extent_info *largest = &F2FS_I(inode)->extent_tree->largest;

  	if (fofs < largest->fofs + largest->len && fofs + len > largest->fofs) {

  		largest->len = 0;

  		f2fs_mark_inode_dirty_sync(inode);

  	}

  }

  /* return true, if inode page is changed */
  bool f2fs_init_extent_tree(struct inode *inode, struct f2fs_extent *i_ext)

  {
  	struct f2fs_sb_info *sbi = F2FS_I_SB(inode);
  	struct extent_tree *et;
  	struct extent_node *en;
  	struct extent_info ei;

  	if (!f2fs_may_extent_tree(inode)) {
  		/* drop largest extent */
  		if (i_ext && i_ext->len) {
  			i_ext->len = 0;
  			return true;
  		}
  		return false;
  	}

  
  	et = __grab_extent_tree(inode);

  	if (!i_ext || !i_ext->len)
  		return false;

  	get_extent_info(&ei, i_ext);

  
  	write_lock(&et->lock);

  	if (atomic_read(&et->node_cnt))

  		goto out;

  	en = __init_extent_tree(sbi, et, &ei);

  	if (en) {
  		spin_lock(&sbi->extent_lock);
  		list_add_tail(&en->list, &sbi->extent_list);
  		spin_unlock(&sbi->extent_lock);
  	}
  out:
  	write_unlock(&et->lock);

  	return false;

  }
  
  static bool f2fs_lookup_extent_tree(struct inode *inode, pgoff_t pgofs,
  							struct extent_info *ei)
  {
  	struct f2fs_sb_info *sbi = F2FS_I_SB(inode);
  	struct extent_tree *et = F2FS_I(inode)->extent_tree;
  	struct extent_node *en;
  	bool ret = false;
  
  	f2fs_bug_on(sbi, !et);
  
  	trace_f2fs_lookup_extent_tree_start(inode, pgofs);
  
  	read_lock(&et->lock);
  
  	if (et->largest.fofs <= pgofs &&
  			et->largest.fofs + et->largest.len > pgofs) {
  		*ei = et->largest;
  		ret = true;

  		stat_inc_largest_node_hit(sbi);

  		goto out;
  	}

  	en = __lookup_extent_tree(sbi, et, pgofs);

  	if (en) {
  		*ei = en->ei;
  		spin_lock(&sbi->extent_lock);

  		if (!list_empty(&en->list)) {

  			list_move_tail(&en->list, &sbi->extent_list);

  			et->cached_en = en;
  		}

  		spin_unlock(&sbi->extent_lock);
  		ret = true;

  	}
  out:

  	stat_inc_total_hit(sbi);

  	read_unlock(&et->lock);
  
  	trace_f2fs_lookup_extent_tree_end(inode, pgofs, ei);
  	return ret;
  }

  
  /*
   * lookup extent at @fofs, if hit, return the extent
   * if not, return NULL and
   * @prev_ex: extent before fofs
   * @next_ex: extent after fofs
   * @insert_p: insert point for new extent at fofs
   * in order to simpfy the insertion after.
   * tree must stay unchanged between lookup and insertion.
   */
  static struct extent_node *__lookup_extent_tree_ret(struct extent_tree *et,

  				unsigned int fofs,
  				struct extent_node **prev_ex,

  				struct extent_node **next_ex,
  				struct rb_node ***insert_p,
  				struct rb_node **insert_parent)
  {
  	struct rb_node **pnode = &et->root.rb_node;
  	struct rb_node *parent = NULL, *tmp_node;

  	struct extent_node *en = et->cached_en;

  	*insert_p = NULL;
  	*insert_parent = NULL;
  	*prev_ex = NULL;
  	*next_ex = NULL;
  
  	if (RB_EMPTY_ROOT(&et->root))
  		return NULL;
  
  	if (en) {
  		struct extent_info *cei = &en->ei;

  
  		if (cei->fofs <= fofs && cei->fofs + cei->len > fofs)

  			goto lookup_neighbors;

  	}
  
  	while (*pnode) {
  		parent = *pnode;
  		en = rb_entry(*pnode, struct extent_node, rb_node);
  
  		if (fofs < en->ei.fofs)
  			pnode = &(*pnode)->rb_left;
  		else if (fofs >= en->ei.fofs + en->ei.len)
  			pnode = &(*pnode)->rb_right;
  		else

  			goto lookup_neighbors;

  	}
  
  	*insert_p = pnode;
  	*insert_parent = parent;
  
  	en = rb_entry(parent, struct extent_node, rb_node);
  	tmp_node = parent;
  	if (parent && fofs > en->ei.fofs)
  		tmp_node = rb_next(parent);
  	*next_ex = tmp_node ?
  		rb_entry(tmp_node, struct extent_node, rb_node) : NULL;
  
  	tmp_node = parent;
  	if (parent && fofs < en->ei.fofs)
  		tmp_node = rb_prev(parent);
  	*prev_ex = tmp_node ?
  		rb_entry(tmp_node, struct extent_node, rb_node) : NULL;

  	return NULL;

  
  lookup_neighbors:
  	if (fofs == en->ei.fofs) {
  		/* lookup prev node for merging backward later */
  		tmp_node = rb_prev(&en->rb_node);
  		*prev_ex = tmp_node ?
  			rb_entry(tmp_node, struct extent_node, rb_node) : NULL;
  	}
  	if (fofs == en->ei.fofs + en->ei.len - 1) {
  		/* lookup next node for merging frontward later */
  		tmp_node = rb_next(&en->rb_node);
  		*next_ex = tmp_node ?
  			rb_entry(tmp_node, struct extent_node, rb_node) : NULL;
  	}
  	return en;

  }

  static struct extent_node *__try_merge_extent_node(struct inode *inode,

  				struct extent_tree *et, struct extent_info *ei,

  				struct extent_node *prev_ex,

  				struct extent_node *next_ex)

  {

  	struct f2fs_sb_info *sbi = F2FS_I_SB(inode);

  	struct extent_node *en = NULL;

  
  	if (prev_ex && __is_back_mergeable(ei, &prev_ex->ei)) {

  		prev_ex->ei.len += ei->len;
  		ei = &prev_ex->ei;
  		en = prev_ex;
  	}

  	if (next_ex && __is_front_mergeable(ei, &next_ex->ei)) {

  		if (en)
  			__release_extent_node(sbi, et, prev_ex);

  		next_ex->ei.fofs = ei->fofs;
  		next_ex->ei.blk = ei->blk;
  		next_ex->ei.len += ei->len;
  		en = next_ex;
  	}

  	if (!en)
  		return NULL;

  	__try_update_largest_extent(inode, et, en);

  
  	spin_lock(&sbi->extent_lock);

  	if (!list_empty(&en->list)) {

  		list_move_tail(&en->list, &sbi->extent_list);

  		et->cached_en = en;
  	}

  	spin_unlock(&sbi->extent_lock);

  	return en;
  }

  static struct extent_node *__insert_extent_tree(struct inode *inode,

  				struct extent_tree *et, struct extent_info *ei,
  				struct rb_node **insert_p,
  				struct rb_node *insert_parent)
  {

  	struct f2fs_sb_info *sbi = F2FS_I_SB(inode);

  	struct rb_node **p = &et->root.rb_node;
  	struct rb_node *parent = NULL;
  	struct extent_node *en = NULL;

  
  	if (insert_p && insert_parent) {
  		parent = insert_parent;
  		p = insert_p;
  		goto do_insert;
  	}
  
  	while (*p) {
  		parent = *p;
  		en = rb_entry(parent, struct extent_node, rb_node);
  
  		if (ei->fofs < en->ei.fofs)
  			p = &(*p)->rb_left;
  		else if (ei->fofs >= en->ei.fofs + en->ei.len)
  			p = &(*p)->rb_right;
  		else
  			f2fs_bug_on(sbi, 1);
  	}
  do_insert:
  	en = __attach_extent_node(sbi, et, ei, parent, p);
  	if (!en)
  		return NULL;

  	__try_update_largest_extent(inode, et, en);

  
  	/* update in global extent list */
  	spin_lock(&sbi->extent_lock);
  	list_add_tail(&en->list, &sbi->extent_list);

  	et->cached_en = en;

  	spin_unlock(&sbi->extent_lock);

  	return en;
  }

  static unsigned int f2fs_update_extent_tree_range(struct inode *inode,

  				pgoff_t fofs, block_t blkaddr, unsigned int len)

  {
  	struct f2fs_sb_info *sbi = F2FS_I_SB(inode);
  	struct extent_tree *et = F2FS_I(inode)->extent_tree;

  	struct extent_node *en = NULL, *en1 = NULL;

  	struct extent_node *prev_en = NULL, *next_en = NULL;

  	struct extent_info ei, dei, prev;

  	struct rb_node **insert_p = NULL, *insert_parent = NULL;

  	unsigned int end = fofs + len;
  	unsigned int pos = (unsigned int)fofs;

  
  	if (!et)
  		return false;

  	trace_f2fs_update_extent_tree_range(inode, fofs, blkaddr, len);

  	write_lock(&et->lock);

  	if (is_inode_flag_set(inode, FI_NO_EXTENT)) {

  		write_unlock(&et->lock);
  		return false;
  	}
  
  	prev = et->largest;
  	dei.len = 0;

  	/*
  	 * drop largest extent before lookup, in case it's already
  	 * been shrunk from extent tree
  	 */

  	__drop_largest_extent(inode, fofs, len);

  	/* 1. lookup first extent node in range [fofs, fofs + len - 1] */
  	en = __lookup_extent_tree_ret(et, fofs, &prev_en, &next_en,

  					&insert_p, &insert_parent);

  	if (!en)
  		en = next_en;

  
  	/* 2. invlidate all extent nodes in range [fofs, fofs + len - 1] */

  	while (en && en->ei.fofs < end) {
  		unsigned int org_end;
  		int parts = 0;	/* # of parts current extent split into */

  		next_en = en1 = NULL;

  
  		dei = en->ei;

  		org_end = dei.fofs + dei.len;
  		f2fs_bug_on(sbi, pos >= org_end);

  		if (pos > dei.fofs &&	pos - dei.fofs >= F2FS_MIN_EXTENT_LEN) {
  			en->ei.len = pos - en->ei.fofs;
  			prev_en = en;
  			parts = 1;
  		}

  		if (end < org_end && org_end - end >= F2FS_MIN_EXTENT_LEN) {
  			if (parts) {
  				set_extent_info(&ei, end,
  						end - dei.fofs + dei.blk,
  						org_end - end);

  				en1 = __insert_extent_tree(inode, et, &ei,

  							NULL, NULL);
  				next_en = en1;
  			} else {
  				en->ei.fofs = end;
  				en->ei.blk += end - dei.fofs;
  				en->ei.len -= end - dei.fofs;
  				next_en = en;

  			}

  			parts++;

  		}

  		if (!next_en) {
  			struct rb_node *node = rb_next(&en->rb_node);

  			next_en = node ?
  				rb_entry(node, struct extent_node, rb_node)
  				: NULL;

  		}

  		if (parts)

  			__try_update_largest_extent(inode, et, en);

  		else

  			__release_extent_node(sbi, et, en);

  
  		/*

  		 * if original extent is split into zero or two parts, extent
  		 * tree has been altered by deletion or insertion, therefore
  		 * invalidate pointers regard to tree.

  		 */

  		if (parts != 1) {
  			insert_p = NULL;
  			insert_parent = NULL;

  		}

  		en = next_en;

  	}

  	/* 3. update extent in extent cache */
  	if (blkaddr) {

  
  		set_extent_info(&ei, fofs, blkaddr, len);

  		if (!__try_merge_extent_node(inode, et, &ei, prev_en, next_en))
  			__insert_extent_tree(inode, et, &ei,

  						insert_p, insert_parent);

  
  		/* give up extent_cache, if split and small updates happen */
  		if (dei.len >= 1 &&
  				prev.len < F2FS_MIN_EXTENT_LEN &&
  				et->largest.len < F2FS_MIN_EXTENT_LEN) {

  			__drop_largest_extent(inode, 0, UINT_MAX);

  			set_inode_flag(inode, FI_NO_EXTENT);

  		}

  	}

  	if (is_inode_flag_set(inode, FI_NO_EXTENT))

  		__free_extent_tree(sbi, et);

  
  	write_unlock(&et->lock);
  
  	return !__is_extent_same(&prev, &et->largest);
  }
  
  unsigned int f2fs_shrink_extent_tree(struct f2fs_sb_info *sbi, int nr_shrink)
  {

  	struct extent_tree *et, *next;

  	struct extent_node *en;

  	unsigned int node_cnt = 0, tree_cnt = 0;
  	int remained;
  
  	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;
  
  	/* 1. remove unreferenced extent tree */

  	list_for_each_entry_safe(et, next, &sbi->zombie_list, list) {

  		if (atomic_read(&et->node_cnt)) {
  			write_lock(&et->lock);

  			node_cnt += __free_extent_tree(sbi, et);

  			write_unlock(&et->lock);
  		}

  		f2fs_bug_on(sbi, atomic_read(&et->node_cnt));

  		list_del_init(&et->list);
  		radix_tree_delete(&sbi->extent_tree_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)
  			goto unlock_out;

  		cond_resched();

  	}
  	up_write(&sbi->extent_tree_lock);

  free_node:

  	/* 2. remove LRU extent entries */
  	if (!down_write_trylock(&sbi->extent_tree_lock))
  		goto out;
  
  	remained = nr_shrink - (node_cnt + tree_cnt);
  
  	spin_lock(&sbi->extent_lock);

  	for (; remained > 0; remained--) {
  		if (list_empty(&sbi->extent_list))

  			break;

  		en = list_first_entry(&sbi->extent_list,
  					struct extent_node, list);
  		et = en->et;
  		if (!write_trylock(&et->lock)) {
  			/* refresh this extent node's position in extent list */
  			list_move_tail(&en->list, &sbi->extent_list);
  			continue;
  		}

  		list_del_init(&en->list);
  		spin_unlock(&sbi->extent_lock);

  		__detach_extent_node(sbi, et, en);

  		write_unlock(&et->lock);
  		node_cnt++;
  		spin_lock(&sbi->extent_lock);

  	}

  	spin_unlock(&sbi->extent_lock);

  unlock_out:
  	up_write(&sbi->extent_tree_lock);
  out:
  	trace_f2fs_shrink_extent_tree(sbi, node_cnt, tree_cnt);
  
  	return node_cnt + tree_cnt;
  }
  
  unsigned int f2fs_destroy_extent_node(struct inode *inode)
  {
  	struct f2fs_sb_info *sbi = F2FS_I_SB(inode);
  	struct extent_tree *et = F2FS_I(inode)->extent_tree;
  	unsigned int node_cnt = 0;

  	if (!et || !atomic_read(&et->node_cnt))

  		return 0;
  
  	write_lock(&et->lock);

  	node_cnt = __free_extent_tree(sbi, et);

  	write_unlock(&et->lock);
  
  	return node_cnt;
  }

  void f2fs_drop_extent_tree(struct inode *inode)
  {
  	struct f2fs_sb_info *sbi = F2FS_I_SB(inode);
  	struct extent_tree *et = F2FS_I(inode)->extent_tree;
  
  	set_inode_flag(inode, FI_NO_EXTENT);
  
  	write_lock(&et->lock);
  	__free_extent_tree(sbi, et);
  	__drop_largest_extent(inode, 0, UINT_MAX);
  	write_unlock(&et->lock);
  }

  void f2fs_destroy_extent_tree(struct inode *inode)
  {
  	struct f2fs_sb_info *sbi = F2FS_I_SB(inode);
  	struct extent_tree *et = F2FS_I(inode)->extent_tree;
  	unsigned int node_cnt = 0;
  
  	if (!et)
  		return;

  	if (inode->i_nlink && !is_bad_inode(inode) &&
  					atomic_read(&et->node_cnt)) {

  		down_write(&sbi->extent_tree_lock);
  		list_add_tail(&et->list, &sbi->zombie_list);

  		atomic_inc(&sbi->total_zombie_tree);

  		up_write(&sbi->extent_tree_lock);

  		return;
  	}
  
  	/* free all extent info belong to this extent tree */
  	node_cnt = f2fs_destroy_extent_node(inode);
  
  	/* delete extent tree entry in radix tree */
  	down_write(&sbi->extent_tree_lock);

  	f2fs_bug_on(sbi, atomic_read(&et->node_cnt));

  	radix_tree_delete(&sbi->extent_tree_root, inode->i_ino);
  	kmem_cache_free(extent_tree_slab, et);

  	atomic_dec(&sbi->total_ext_tree);

  	up_write(&sbi->extent_tree_lock);
  
  	F2FS_I(inode)->extent_tree = NULL;
  
  	trace_f2fs_destroy_extent_tree(inode, node_cnt);
  }
  
  bool f2fs_lookup_extent_cache(struct inode *inode, pgoff_t pgofs,
  					struct extent_info *ei)
  {
  	if (!f2fs_may_extent_tree(inode))
  		return false;
  
  	return f2fs_lookup_extent_tree(inode, pgofs, ei);
  }
  
  void f2fs_update_extent_cache(struct dnode_of_data *dn)
  {

  	pgoff_t fofs;

  	block_t blkaddr;

  
  	if (!f2fs_may_extent_tree(dn->inode))
  		return;

  	if (dn->data_blkaddr == NEW_ADDR)
  		blkaddr = NULL_ADDR;
  	else
  		blkaddr = dn->data_blkaddr;

  	fofs = start_bidx_of_node(ofs_of_node(dn->node_page), dn->inode) +
  								dn->ofs_in_node;

  	f2fs_update_extent_tree_range(dn->inode, fofs, blkaddr, 1);

  }
  
  void f2fs_update_extent_cache_range(struct dnode_of_data *dn,
  				pgoff_t fofs, block_t blkaddr, unsigned int len)
  
  {
  	if (!f2fs_may_extent_tree(dn->inode))
  		return;

  	f2fs_update_extent_tree_range(dn->inode, fofs, blkaddr, len);

  }
  
  void init_extent_cache_info(struct f2fs_sb_info *sbi)
  {
  	INIT_RADIX_TREE(&sbi->extent_tree_root, GFP_NOIO);
  	init_rwsem(&sbi->extent_tree_lock);
  	INIT_LIST_HEAD(&sbi->extent_list);
  	spin_lock_init(&sbi->extent_lock);

  	atomic_set(&sbi->total_ext_tree, 0);

  	INIT_LIST_HEAD(&sbi->zombie_list);

  	atomic_set(&sbi->total_zombie_tree, 0);

  	atomic_set(&sbi->total_ext_node, 0);
  }
  
  int __init create_extent_cache(void)
  {
  	extent_tree_slab = f2fs_kmem_cache_create("f2fs_extent_tree",
  			sizeof(struct extent_tree));
  	if (!extent_tree_slab)
  		return -ENOMEM;
  	extent_node_slab = f2fs_kmem_cache_create("f2fs_extent_node",
  			sizeof(struct extent_node));
  	if (!extent_node_slab) {
  		kmem_cache_destroy(extent_tree_slab);
  		return -ENOMEM;
  	}
  	return 0;
  }
  
  void destroy_extent_cache(void)
  {
  	kmem_cache_destroy(extent_node_slab);
  	kmem_cache_destroy(extent_tree_slab);
  }