/*
   *  fs/ext4/extents_status.c
   *
   * Written by Yongqiang Yang <xiaoqiangnk@gmail.com>
   * Modified by
   *	Allison Henderson <achender@linux.vnet.ibm.com>
   *	Hugh Dickins <hughd@google.com>
   *	Zheng Liu <wenqing.lz@taobao.com>
   *
   * Ext4 extents status tree core functions.
   */
  #include <linux/list_sort.h>
  #include <linux/proc_fs.h>
  #include <linux/seq_file.h>
  #include "ext4.h"
  
  #include <trace/events/ext4.h>
  
  /*
   * According to previous discussion in Ext4 Developer Workshop, we
   * will introduce a new structure called io tree to track all extent
   * status in order to solve some problems that we have met
   * (e.g. Reservation space warning), and provide extent-level locking.
   * Delay extent tree is the first step to achieve this goal.  It is
   * original built by Yongqiang Yang.  At that time it is called delay
   * extent tree, whose goal is only track delayed extents in memory to
   * simplify the implementation of fiemap and bigalloc, and introduce
   * lseek SEEK_DATA/SEEK_HOLE support.  That is why it is still called
   * delay extent tree at the first commit.  But for better understand
   * what it does, it has been rename to extent status tree.
   *
   * Step1:
   * Currently the first step has been done.  All delayed extents are
   * tracked in the tree.  It maintains the delayed extent when a delayed
   * allocation is issued, and the delayed extent is written out or
   * invalidated.  Therefore the implementation of fiemap and bigalloc
   * are simplified, and SEEK_DATA/SEEK_HOLE are introduced.
   *
   * The following comment describes the implemenmtation of extent
   * status tree and future works.
   *
   * Step2:
   * In this step all extent status are tracked by extent status tree.
   * Thus, we can first try to lookup a block mapping in this tree before
   * finding it in extent tree.  Hence, single extent cache can be removed
   * because extent status tree can do a better job.  Extents in status
   * tree are loaded on-demand.  Therefore, the extent status tree may not
   * contain all of the extents in a file.  Meanwhile we define a shrinker
   * to reclaim memory from extent status tree because fragmented extent
   * tree will make status tree cost too much memory.  written/unwritten/-
   * hole extents in the tree will be reclaimed by this shrinker when we
   * are under high memory pressure.  Delayed extents will not be
   * reclimed because fiemap, bigalloc, and seek_data/hole need it.
   */
  
  /*
   * Extent status tree implementation for ext4.
   *
   *
   * ==========================================================================
   * Extent status tree tracks all extent status.
   *
   * 1. Why we need to implement extent status tree?
   *
   * Without extent status tree, ext4 identifies a delayed extent by looking
   * up page cache, this has several deficiencies - complicated, buggy,
   * and inefficient code.
   *
   * FIEMAP, SEEK_HOLE/DATA, bigalloc, and writeout all need to know if a
   * block or a range of blocks are belonged to a delayed extent.
   *
   * Let us have a look at how they do without extent status tree.
   *   --	FIEMAP
   *	FIEMAP looks up page cache to identify delayed allocations from holes.
   *
   *   --	SEEK_HOLE/DATA
   *	SEEK_HOLE/DATA has the same problem as FIEMAP.
   *
   *   --	bigalloc
   *	bigalloc looks up page cache to figure out if a block is
   *	already under delayed allocation or not to determine whether
   *	quota reserving is needed for the cluster.
   *
   *   --	writeout
   *	Writeout looks up whole page cache to see if a buffer is
   *	mapped, If there are not very many delayed buffers, then it is
   *	time comsuming.
   *
   * With extent status tree implementation, FIEMAP, SEEK_HOLE/DATA,
   * bigalloc and writeout can figure out if a block or a range of
   * blocks is under delayed allocation(belonged to a delayed extent) or
   * not by searching the extent tree.
   *
   *
   * ==========================================================================
   * 2. Ext4 extent status tree impelmentation
   *
   *   --	extent
   *	A extent is a range of blocks which are contiguous logically and
   *	physically.  Unlike extent in extent tree, this extent in ext4 is
   *	a in-memory struct, there is no corresponding on-disk data.  There
   *	is no limit on length of extent, so an extent can contain as many
   *	blocks as they are contiguous logically and physically.
   *
   *   --	extent status tree
   *	Every inode has an extent status tree and all allocation blocks
   *	are added to the tree with different status.  The extent in the
   *	tree are ordered by logical block no.
   *
   *   --	operations on a extent status tree
   *	There are three important operations on a delayed extent tree: find
   *	next extent, adding a extent(a range of blocks) and removing a extent.
   *
   *   --	race on a extent status tree
   *	Extent status tree is protected by inode->i_es_lock.
   *
   *   --	memory consumption
   *      Fragmented extent tree will make extent status tree cost too much
   *      memory.  Hence, we will reclaim written/unwritten/hole extents from
   *      the tree under a heavy memory pressure.
   *
   *
   * ==========================================================================
   * 3. Performance analysis
   *
   *   --	overhead
   *	1. There is a cache extent for write access, so if writes are
   *	not very random, adding space operaions are in O(1) time.
   *
   *   --	gain
   *	2. Code is much simpler, more readable, more maintainable and
   *	more efficient.
   *
   *
   * ==========================================================================
   * 4. TODO list
   *
   *   -- Refactor delayed space reservation
   *
   *   -- Extent-level locking
   */
  
  static struct kmem_cache *ext4_es_cachep;
  
  static int __es_insert_extent(struct inode *inode, struct extent_status *newes);
  static int __es_remove_extent(struct inode *inode, ext4_lblk_t lblk,
  			      ext4_lblk_t end);
  static int es_reclaim_extents(struct ext4_inode_info *ei, int *nr_to_scan);
  static int __es_shrink(struct ext4_sb_info *sbi, int nr_to_scan,
  		       struct ext4_inode_info *locked_ei);
  
  int __init ext4_init_es(void)
  {
  	ext4_es_cachep = kmem_cache_create("ext4_extent_status",
  					   sizeof(struct extent_status),
  					   0, (SLAB_RECLAIM_ACCOUNT), NULL);
  	if (ext4_es_cachep == NULL)
  		return -ENOMEM;
  	return 0;
  }
  
  void ext4_exit_es(void)
  {
  	if (ext4_es_cachep)
  		kmem_cache_destroy(ext4_es_cachep);
  }
  
  void ext4_es_init_tree(struct ext4_es_tree *tree)
  {
  	tree->root = RB_ROOT;
  	tree->cache_es = NULL;
  }
  
  #ifdef ES_DEBUG__
  static void ext4_es_print_tree(struct inode *inode)
  {
  	struct ext4_es_tree *tree;
  	struct rb_node *node;
  
  	printk(KERN_DEBUG "status extents for inode %lu:", inode->i_ino);
  	tree = &EXT4_I(inode)->i_es_tree;
  	node = rb_first(&tree->root);
  	while (node) {
  		struct extent_status *es;
  		es = rb_entry(node, struct extent_status, rb_node);
  		printk(KERN_DEBUG " [%u/%u) %llu %x",
  		       es->es_lblk, es->es_len,
  		       ext4_es_pblock(es), ext4_es_status(es));
  		node = rb_next(node);
  	}
  	printk(KERN_DEBUG "
  ");
  }
  #else
  #define ext4_es_print_tree(inode)
  #endif
  
  static inline ext4_lblk_t ext4_es_end(struct extent_status *es)
  {
  	BUG_ON(es->es_lblk + es->es_len < es->es_lblk);
  	return es->es_lblk + es->es_len - 1;
  }
  
  /*
   * search through the tree for an delayed extent with a given offset.  If
   * it can't be found, try to find next extent.
   */
  static struct extent_status *__es_tree_search(struct rb_root *root,
  					      ext4_lblk_t lblk)
  {
  	struct rb_node *node = root->rb_node;
  	struct extent_status *es = NULL;
  
  	while (node) {
  		es = rb_entry(node, struct extent_status, rb_node);
  		if (lblk < es->es_lblk)
  			node = node->rb_left;
  		else if (lblk > ext4_es_end(es))
  			node = node->rb_right;
  		else
  			return es;
  	}
  
  	if (es && lblk < es->es_lblk)
  		return es;
  
  	if (es && lblk > ext4_es_end(es)) {
  		node = rb_next(&es->rb_node);
  		return node ? rb_entry(node, struct extent_status, rb_node) :
  			      NULL;
  	}
  
  	return NULL;
  }
  
  /*
   * ext4_es_find_delayed_extent_range: find the 1st delayed extent covering
   * @es->lblk if it exists, otherwise, the next extent after @es->lblk.
   *
   * @inode: the inode which owns delayed extents
   * @lblk: the offset where we start to search
   * @end: the offset where we stop to search
   * @es: delayed extent that we found
   */
  void ext4_es_find_delayed_extent_range(struct inode *inode,
  				 ext4_lblk_t lblk, ext4_lblk_t end,
  				 struct extent_status *es)
  {
  	struct ext4_es_tree *tree = NULL;
  	struct extent_status *es1 = NULL;
  	struct rb_node *node;
  
  	BUG_ON(es == NULL);
  	BUG_ON(end < lblk);
  	trace_ext4_es_find_delayed_extent_range_enter(inode, lblk);
  
  	read_lock(&EXT4_I(inode)->i_es_lock);
  	tree = &EXT4_I(inode)->i_es_tree;
  
  	/* find extent in cache firstly */
  	es->es_lblk = es->es_len = es->es_pblk = 0;
  	if (tree->cache_es) {
  		es1 = tree->cache_es;
  		if (in_range(lblk, es1->es_lblk, es1->es_len)) {
  			es_debug("%u cached by [%u/%u) %llu %x
  ",
  				 lblk, es1->es_lblk, es1->es_len,
  				 ext4_es_pblock(es1), ext4_es_status(es1));
  			goto out;
  		}
  	}
  
  	es1 = __es_tree_search(&tree->root, lblk);
  
  out:
  	if (es1 && !ext4_es_is_delayed(es1)) {
  		while ((node = rb_next(&es1->rb_node)) != NULL) {
  			es1 = rb_entry(node, struct extent_status, rb_node);
  			if (es1->es_lblk > end) {
  				es1 = NULL;
  				break;
  			}
  			if (ext4_es_is_delayed(es1))
  				break;
  		}
  	}
  
  	if (es1 && ext4_es_is_delayed(es1)) {
  		tree->cache_es = es1;
  		es->es_lblk = es1->es_lblk;
  		es->es_len = es1->es_len;
  		es->es_pblk = es1->es_pblk;
  	}
  
  	read_unlock(&EXT4_I(inode)->i_es_lock);
  
  	trace_ext4_es_find_delayed_extent_range_exit(inode, es);
  }
  
  static void ext4_es_list_add(struct inode *inode)
  {
  	struct ext4_inode_info *ei = EXT4_I(inode);
  	struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
  
  	if (!list_empty(&ei->i_es_list))
  		return;
  
  	spin_lock(&sbi->s_es_lock);
  	if (list_empty(&ei->i_es_list)) {
  		list_add_tail(&ei->i_es_list, &sbi->s_es_list);
  		sbi->s_es_nr_inode++;
  	}
  	spin_unlock(&sbi->s_es_lock);
  }
  
  static void ext4_es_list_del(struct inode *inode)
  {
  	struct ext4_inode_info *ei = EXT4_I(inode);
  	struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
  
  	spin_lock(&sbi->s_es_lock);
  	if (!list_empty(&ei->i_es_list)) {
  		list_del_init(&ei->i_es_list);
  		sbi->s_es_nr_inode--;
  		WARN_ON_ONCE(sbi->s_es_nr_inode < 0);
  	}
  	spin_unlock(&sbi->s_es_lock);
  }
  
  static struct extent_status *
  ext4_es_alloc_extent(struct inode *inode, ext4_lblk_t lblk, ext4_lblk_t len,
  		     ext4_fsblk_t pblk)
  {
  	struct extent_status *es;
  	es = kmem_cache_alloc(ext4_es_cachep, GFP_ATOMIC);
  	if (es == NULL)
  		return NULL;
  	es->es_lblk = lblk;
  	es->es_len = len;
  	es->es_pblk = pblk;
  
  	/*
  	 * We don't count delayed extent because we never try to reclaim them
  	 */
  	if (!ext4_es_is_delayed(es)) {
  		if (!EXT4_I(inode)->i_es_shk_nr++)
  			ext4_es_list_add(inode);
  		percpu_counter_inc(&EXT4_SB(inode->i_sb)->
  					s_es_stats.es_stats_shk_cnt);
  	}
  
  	EXT4_I(inode)->i_es_all_nr++;
  	percpu_counter_inc(&EXT4_SB(inode->i_sb)->s_es_stats.es_stats_all_cnt);
  
  	return es;
  }
  
  static void ext4_es_free_extent(struct inode *inode, struct extent_status *es)
  {
  	EXT4_I(inode)->i_es_all_nr--;
  	percpu_counter_dec(&EXT4_SB(inode->i_sb)->s_es_stats.es_stats_all_cnt);
  
  	/* Decrease the shrink counter when this es is not delayed */
  	if (!ext4_es_is_delayed(es)) {
  		BUG_ON(EXT4_I(inode)->i_es_shk_nr == 0);
  		if (!--EXT4_I(inode)->i_es_shk_nr)
  			ext4_es_list_del(inode);
  		percpu_counter_dec(&EXT4_SB(inode->i_sb)->
  					s_es_stats.es_stats_shk_cnt);
  	}
  
  	kmem_cache_free(ext4_es_cachep, es);
  }
  
  /*
   * Check whether or not two extents can be merged
   * Condition:
   *  - logical block number is contiguous
   *  - physical block number is contiguous
   *  - status is equal
   */
  static int ext4_es_can_be_merged(struct extent_status *es1,
  				 struct extent_status *es2)
  {
  	if (ext4_es_type(es1) != ext4_es_type(es2))
  		return 0;
  
  	if (((__u64) es1->es_len) + es2->es_len > EXT_MAX_BLOCKS) {
  		pr_warn("ES assertion failed when merging extents. "
  			"The sum of lengths of es1 (%d) and es2 (%d) "
  			"is bigger than allowed file size (%d)
  ",
  			es1->es_len, es2->es_len, EXT_MAX_BLOCKS);
  		WARN_ON(1);
  		return 0;
  	}
  
  	if (((__u64) es1->es_lblk) + es1->es_len != es2->es_lblk)
  		return 0;
  
  	if ((ext4_es_is_written(es1) || ext4_es_is_unwritten(es1)) &&
  	    (ext4_es_pblock(es1) + es1->es_len == ext4_es_pblock(es2)))
  		return 1;
  
  	if (ext4_es_is_hole(es1))
  		return 1;
  
  	/* we need to check delayed extent is without unwritten status */
  	if (ext4_es_is_delayed(es1) && !ext4_es_is_unwritten(es1))
  		return 1;
  
  	return 0;
  }
  
  static struct extent_status *
  ext4_es_try_to_merge_left(struct inode *inode, struct extent_status *es)
  {
  	struct ext4_es_tree *tree = &EXT4_I(inode)->i_es_tree;
  	struct extent_status *es1;
  	struct rb_node *node;
  
  	node = rb_prev(&es->rb_node);
  	if (!node)
  		return es;
  
  	es1 = rb_entry(node, struct extent_status, rb_node);
  	if (ext4_es_can_be_merged(es1, es)) {
  		es1->es_len += es->es_len;
  		if (ext4_es_is_referenced(es))
  			ext4_es_set_referenced(es1);
  		rb_erase(&es->rb_node, &tree->root);
  		ext4_es_free_extent(inode, es);
  		es = es1;
  	}
  
  	return es;
  }
  
  static struct extent_status *
  ext4_es_try_to_merge_right(struct inode *inode, struct extent_status *es)
  {
  	struct ext4_es_tree *tree = &EXT4_I(inode)->i_es_tree;
  	struct extent_status *es1;
  	struct rb_node *node;
  
  	node = rb_next(&es->rb_node);
  	if (!node)
  		return es;
  
  	es1 = rb_entry(node, struct extent_status, rb_node);
  	if (ext4_es_can_be_merged(es, es1)) {
  		es->es_len += es1->es_len;
  		if (ext4_es_is_referenced(es1))
  			ext4_es_set_referenced(es);
  		rb_erase(node, &tree->root);
  		ext4_es_free_extent(inode, es1);
  	}
  
  	return es;
  }
  
  #ifdef ES_AGGRESSIVE_TEST
  #include "ext4_extents.h"	/* Needed when ES_AGGRESSIVE_TEST is defined */
  
  static void ext4_es_insert_extent_ext_check(struct inode *inode,
  					    struct extent_status *es)
  {
  	struct ext4_ext_path *path = NULL;
  	struct ext4_extent *ex;
  	ext4_lblk_t ee_block;
  	ext4_fsblk_t ee_start;
  	unsigned short ee_len;
  	int depth, ee_status, es_status;
  
  	path = ext4_find_extent(inode, es->es_lblk, NULL, EXT4_EX_NOCACHE);
  	if (IS_ERR(path))
  		return;
  
  	depth = ext_depth(inode);
  	ex = path[depth].p_ext;
  
  	if (ex) {
  
  		ee_block = le32_to_cpu(ex->ee_block);
  		ee_start = ext4_ext_pblock(ex);
  		ee_len = ext4_ext_get_actual_len(ex);
  
  		ee_status = ext4_ext_is_unwritten(ex) ? 1 : 0;
  		es_status = ext4_es_is_unwritten(es) ? 1 : 0;
  
  		/*
  		 * Make sure ex and es are not overlap when we try to insert
  		 * a delayed/hole extent.
  		 */
  		if (!ext4_es_is_written(es) && !ext4_es_is_unwritten(es)) {
  			if (in_range(es->es_lblk, ee_block, ee_len)) {
  				pr_warn("ES insert assertion failed for "
  					"inode: %lu we can find an extent "
  					"at block [%d/%d/%llu/%c], but we "
  					"want to add a delayed/hole extent "
  					"[%d/%d/%llu/%x]
  ",
  					inode->i_ino, ee_block, ee_len,
  					ee_start, ee_status ? 'u' : 'w',
  					es->es_lblk, es->es_len,
  					ext4_es_pblock(es), ext4_es_status(es));
  			}
  			goto out;
  		}
  
  		/*
  		 * We don't check ee_block == es->es_lblk, etc. because es
  		 * might be a part of whole extent, vice versa.
  		 */
  		if (es->es_lblk < ee_block ||
  		    ext4_es_pblock(es) != ee_start + es->es_lblk - ee_block) {
  			pr_warn("ES insert assertion failed for inode: %lu "
  				"ex_status [%d/%d/%llu/%c] != "
  				"es_status [%d/%d/%llu/%c]
  ", inode->i_ino,
  				ee_block, ee_len, ee_start,
  				ee_status ? 'u' : 'w', es->es_lblk, es->es_len,
  				ext4_es_pblock(es), es_status ? 'u' : 'w');
  			goto out;
  		}
  
  		if (ee_status ^ es_status) {
  			pr_warn("ES insert assertion failed for inode: %lu "
  				"ex_status [%d/%d/%llu/%c] != "
  				"es_status [%d/%d/%llu/%c]
  ", inode->i_ino,
  				ee_block, ee_len, ee_start,
  				ee_status ? 'u' : 'w', es->es_lblk, es->es_len,
  				ext4_es_pblock(es), es_status ? 'u' : 'w');
  		}
  	} else {
  		/*
  		 * We can't find an extent on disk.  So we need to make sure
  		 * that we don't want to add an written/unwritten extent.
  		 */
  		if (!ext4_es_is_delayed(es) && !ext4_es_is_hole(es)) {
  			pr_warn("ES insert assertion failed for inode: %lu "
  				"can't find an extent at block %d but we want "
  				"to add a written/unwritten extent "
  				"[%d/%d/%llu/%x]
  ", inode->i_ino,
  				es->es_lblk, es->es_lblk, es->es_len,
  				ext4_es_pblock(es), ext4_es_status(es));
  		}
  	}
  out:
  	ext4_ext_drop_refs(path);
  	kfree(path);
  }
  
  static void ext4_es_insert_extent_ind_check(struct inode *inode,
  					    struct extent_status *es)
  {
  	struct ext4_map_blocks map;
  	int retval;
  
  	/*
  	 * Here we call ext4_ind_map_blocks to lookup a block mapping because
  	 * 'Indirect' structure is defined in indirect.c.  So we couldn't
  	 * access direct/indirect tree from outside.  It is too dirty to define
  	 * this function in indirect.c file.
  	 */
  
  	map.m_lblk = es->es_lblk;
  	map.m_len = es->es_len;
  
  	retval = ext4_ind_map_blocks(NULL, inode, &map, 0);
  	if (retval > 0) {
  		if (ext4_es_is_delayed(es) || ext4_es_is_hole(es)) {
  			/*
  			 * We want to add a delayed/hole extent but this
  			 * block has been allocated.
  			 */
  			pr_warn("ES insert assertion failed for inode: %lu "
  				"We can find blocks but we want to add a "
  				"delayed/hole extent [%d/%d/%llu/%x]
  ",
  				inode->i_ino, es->es_lblk, es->es_len,
  				ext4_es_pblock(es), ext4_es_status(es));
  			return;
  		} else if (ext4_es_is_written(es)) {
  			if (retval != es->es_len) {
  				pr_warn("ES insert assertion failed for "
  					"inode: %lu retval %d != es_len %d
  ",
  					inode->i_ino, retval, es->es_len);
  				return;
  			}
  			if (map.m_pblk != ext4_es_pblock(es)) {
  				pr_warn("ES insert assertion failed for "
  					"inode: %lu m_pblk %llu != "
  					"es_pblk %llu
  ",
  					inode->i_ino, map.m_pblk,
  					ext4_es_pblock(es));
  				return;
  			}
  		} else {
  			/*
  			 * We don't need to check unwritten extent because
  			 * indirect-based file doesn't have it.
  			 */
  			BUG_ON(1);
  		}
  	} else if (retval == 0) {
  		if (ext4_es_is_written(es)) {
  			pr_warn("ES insert assertion failed for inode: %lu "
  				"We can't find the block but we want to add "
  				"a written extent [%d/%d/%llu/%x]
  ",
  				inode->i_ino, es->es_lblk, es->es_len,
  				ext4_es_pblock(es), ext4_es_status(es));
  			return;
  		}
  	}
  }
  
  static inline void ext4_es_insert_extent_check(struct inode *inode,
  					       struct extent_status *es)
  {
  	/*
  	 * We don't need to worry about the race condition because
  	 * caller takes i_data_sem locking.
  	 */
  	BUG_ON(!rwsem_is_locked(&EXT4_I(inode)->i_data_sem));
  	if (ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS))
  		ext4_es_insert_extent_ext_check(inode, es);
  	else
  		ext4_es_insert_extent_ind_check(inode, es);
  }
  #else
  static inline void ext4_es_insert_extent_check(struct inode *inode,
  					       struct extent_status *es)
  {
  }
  #endif
  
  static int __es_insert_extent(struct inode *inode, struct extent_status *newes)
  {
  	struct ext4_es_tree *tree = &EXT4_I(inode)->i_es_tree;
  	struct rb_node **p = &tree->root.rb_node;
  	struct rb_node *parent = NULL;
  	struct extent_status *es;
  
  	while (*p) {
  		parent = *p;
  		es = rb_entry(parent, struct extent_status, rb_node);
  
  		if (newes->es_lblk < es->es_lblk) {
  			if (ext4_es_can_be_merged(newes, es)) {
  				/*
  				 * Here we can modify es_lblk directly
  				 * because it isn't overlapped.
  				 */
  				es->es_lblk = newes->es_lblk;
  				es->es_len += newes->es_len;
  				if (ext4_es_is_written(es) ||
  				    ext4_es_is_unwritten(es))
  					ext4_es_store_pblock(es,
  							     newes->es_pblk);
  				es = ext4_es_try_to_merge_left(inode, es);
  				goto out;
  			}
  			p = &(*p)->rb_left;
  		} else if (newes->es_lblk > ext4_es_end(es)) {
  			if (ext4_es_can_be_merged(es, newes)) {
  				es->es_len += newes->es_len;
  				es = ext4_es_try_to_merge_right(inode, es);
  				goto out;
  			}
  			p = &(*p)->rb_right;
  		} else {
  			BUG_ON(1);
  			return -EINVAL;
  		}
  	}
  
  	es = ext4_es_alloc_extent(inode, newes->es_lblk, newes->es_len,
  				  newes->es_pblk);
  	if (!es)
  		return -ENOMEM;
  	rb_link_node(&es->rb_node, parent, p);
  	rb_insert_color(&es->rb_node, &tree->root);
  
  out:
  	tree->cache_es = es;
  	return 0;
  }
  
  /*
   * ext4_es_insert_extent() adds information to an inode's extent
   * status tree.
   *
   * Return 0 on success, error code on failure.
   */
  int ext4_es_insert_extent(struct inode *inode, ext4_lblk_t lblk,
  			  ext4_lblk_t len, ext4_fsblk_t pblk,
  			  unsigned int status)
  {
  	struct extent_status newes;
  	ext4_lblk_t end = lblk + len - 1;
  	int err = 0;
  
  	es_debug("add [%u/%u) %llu %x to extent status tree of inode %lu
  ",
  		 lblk, len, pblk, status, inode->i_ino);
  
  	if (!len)
  		return 0;
  
  	BUG_ON(end < lblk);
  
  	if ((status & EXTENT_STATUS_DELAYED) &&
  	    (status & EXTENT_STATUS_WRITTEN)) {
  		ext4_warning(inode->i_sb, "Inserting extent [%u/%u] as "
  				" delayed and written which can potentially "
  				" cause data loss.
  ", lblk, len);
  		WARN_ON(1);
  	}
  
  	newes.es_lblk = lblk;
  	newes.es_len = len;
  	ext4_es_store_pblock_status(&newes, pblk, status);
  	trace_ext4_es_insert_extent(inode, &newes);
  
  	ext4_es_insert_extent_check(inode, &newes);
  
  	write_lock(&EXT4_I(inode)->i_es_lock);
  	err = __es_remove_extent(inode, lblk, end);
  	if (err != 0)
  		goto error;
  retry:
  	err = __es_insert_extent(inode, &newes);
  	if (err == -ENOMEM && __es_shrink(EXT4_SB(inode->i_sb),
  					  128, EXT4_I(inode)))
  		goto retry;
  	if (err == -ENOMEM && !ext4_es_is_delayed(&newes))
  		err = 0;
  
  error:
  	write_unlock(&EXT4_I(inode)->i_es_lock);
  
  	ext4_es_print_tree(inode);
  
  	return err;
  }
  
  /*
   * ext4_es_cache_extent() inserts information into the extent status
   * tree if and only if there isn't information about the range in
   * question already.
   */
  void ext4_es_cache_extent(struct inode *inode, ext4_lblk_t lblk,
  			  ext4_lblk_t len, ext4_fsblk_t pblk,
  			  unsigned int status)
  {
  	struct extent_status *es;
  	struct extent_status newes;
  	ext4_lblk_t end = lblk + len - 1;
  
  	newes.es_lblk = lblk;
  	newes.es_len = len;
  	ext4_es_store_pblock_status(&newes, pblk, status);
  	trace_ext4_es_cache_extent(inode, &newes);
  
  	if (!len)
  		return;
  
  	BUG_ON(end < lblk);
  
  	write_lock(&EXT4_I(inode)->i_es_lock);
  
  	es = __es_tree_search(&EXT4_I(inode)->i_es_tree.root, lblk);
  	if (!es || es->es_lblk > end)
  		__es_insert_extent(inode, &newes);
  	write_unlock(&EXT4_I(inode)->i_es_lock);
  }
  
  /*
   * ext4_es_lookup_extent() looks up an extent in extent status tree.
   *
   * ext4_es_lookup_extent is called by ext4_map_blocks/ext4_da_map_blocks.
   *
   * Return: 1 on found, 0 on not
   */
  int ext4_es_lookup_extent(struct inode *inode, ext4_lblk_t lblk,
  			  struct extent_status *es)
  {
  	struct ext4_es_tree *tree;
  	struct ext4_es_stats *stats;
  	struct extent_status *es1 = NULL;
  	struct rb_node *node;
  	int found = 0;
  
  	trace_ext4_es_lookup_extent_enter(inode, lblk);
  	es_debug("lookup extent in block %u
  ", lblk);
  
  	tree = &EXT4_I(inode)->i_es_tree;
  	read_lock(&EXT4_I(inode)->i_es_lock);
  
  	/* find extent in cache firstly */
  	es->es_lblk = es->es_len = es->es_pblk = 0;
  	if (tree->cache_es) {
  		es1 = tree->cache_es;
  		if (in_range(lblk, es1->es_lblk, es1->es_len)) {
  			es_debug("%u cached by [%u/%u)
  ",
  				 lblk, es1->es_lblk, es1->es_len);
  			found = 1;
  			goto out;
  		}
  	}
  
  	node = tree->root.rb_node;
  	while (node) {
  		es1 = rb_entry(node, struct extent_status, rb_node);
  		if (lblk < es1->es_lblk)
  			node = node->rb_left;
  		else if (lblk > ext4_es_end(es1))
  			node = node->rb_right;
  		else {
  			found = 1;
  			break;
  		}
  	}
  
  out:
  	stats = &EXT4_SB(inode->i_sb)->s_es_stats;
  	if (found) {
  		BUG_ON(!es1);
  		es->es_lblk = es1->es_lblk;
  		es->es_len = es1->es_len;
  		es->es_pblk = es1->es_pblk;
  		if (!ext4_es_is_referenced(es))
  			ext4_es_set_referenced(es);
  		stats->es_stats_cache_hits++;
  	} else {
  		stats->es_stats_cache_misses++;
  	}
  
  	read_unlock(&EXT4_I(inode)->i_es_lock);
  
  	trace_ext4_es_lookup_extent_exit(inode, es, found);
  	return found;
  }
  
  static int __es_remove_extent(struct inode *inode, ext4_lblk_t lblk,
  			      ext4_lblk_t end)
  {
  	struct ext4_es_tree *tree = &EXT4_I(inode)->i_es_tree;
  	struct rb_node *node;
  	struct extent_status *es;
  	struct extent_status orig_es;
  	ext4_lblk_t len1, len2;
  	ext4_fsblk_t block;
  	int err;
  
  retry:
  	err = 0;
  	es = __es_tree_search(&tree->root, lblk);
  	if (!es)
  		goto out;
  	if (es->es_lblk > end)
  		goto out;
  
  	/* Simply invalidate cache_es. */
  	tree->cache_es = NULL;
  
  	orig_es.es_lblk = es->es_lblk;
  	orig_es.es_len = es->es_len;
  	orig_es.es_pblk = es->es_pblk;
  
  	len1 = lblk > es->es_lblk ? lblk - es->es_lblk : 0;
  	len2 = ext4_es_end(es) > end ? ext4_es_end(es) - end : 0;
  	if (len1 > 0)
  		es->es_len = len1;
  	if (len2 > 0) {
  		if (len1 > 0) {
  			struct extent_status newes;
  
  			newes.es_lblk = end + 1;
  			newes.es_len = len2;
  			block = 0x7FDEADBEEFULL;
  			if (ext4_es_is_written(&orig_es) ||
  			    ext4_es_is_unwritten(&orig_es))
  				block = ext4_es_pblock(&orig_es) +
  					orig_es.es_len - len2;
  			ext4_es_store_pblock_status(&newes, block,
  						    ext4_es_status(&orig_es));
  			err = __es_insert_extent(inode, &newes);
  			if (err) {
  				es->es_lblk = orig_es.es_lblk;
  				es->es_len = orig_es.es_len;
  				if ((err == -ENOMEM) &&
  				    __es_shrink(EXT4_SB(inode->i_sb),
  							128, EXT4_I(inode)))
  					goto retry;
  				goto out;
  			}
  		} else {
  			es->es_lblk = end + 1;
  			es->es_len = len2;
  			if (ext4_es_is_written(es) ||
  			    ext4_es_is_unwritten(es)) {
  				block = orig_es.es_pblk + orig_es.es_len - len2;
  				ext4_es_store_pblock(es, block);
  			}
  		}
  		goto out;
  	}
  
  	if (len1 > 0) {
  		node = rb_next(&es->rb_node);
  		if (node)
  			es = rb_entry(node, struct extent_status, rb_node);
  		else
  			es = NULL;
  	}
  
  	while (es && ext4_es_end(es) <= end) {
  		node = rb_next(&es->rb_node);
  		rb_erase(&es->rb_node, &tree->root);
  		ext4_es_free_extent(inode, es);
  		if (!node) {
  			es = NULL;
  			break;
  		}
  		es = rb_entry(node, struct extent_status, rb_node);
  	}
  
  	if (es && es->es_lblk < end + 1) {
  		ext4_lblk_t orig_len = es->es_len;
  
  		len1 = ext4_es_end(es) - end;
  		es->es_lblk = end + 1;
  		es->es_len = len1;
  		if (ext4_es_is_written(es) || ext4_es_is_unwritten(es)) {
  			block = es->es_pblk + orig_len - len1;
  			ext4_es_store_pblock(es, block);
  		}
  	}
  
  out:
  	return err;
  }
  
  /*
   * ext4_es_remove_extent() removes a space from a extent status tree.
   *
   * Return 0 on success, error code on failure.
   */
  int ext4_es_remove_extent(struct inode *inode, ext4_lblk_t lblk,
  			  ext4_lblk_t len)
  {
  	ext4_lblk_t end;
  	int err = 0;
  
  	trace_ext4_es_remove_extent(inode, lblk, len);
  	es_debug("remove [%u/%u) from extent status tree of inode %lu
  ",
  		 lblk, len, inode->i_ino);
  
  	if (!len)
  		return err;
  
  	end = lblk + len - 1;
  	BUG_ON(end < lblk);
  
  	/*
  	 * ext4_clear_inode() depends on us taking i_es_lock unconditionally
  	 * so that we are sure __es_shrink() is done with the inode before it
  	 * is reclaimed.
  	 */
  	write_lock(&EXT4_I(inode)->i_es_lock);
  	err = __es_remove_extent(inode, lblk, end);
  	write_unlock(&EXT4_I(inode)->i_es_lock);
  	ext4_es_print_tree(inode);
  	return err;
  }
  
  static int __es_shrink(struct ext4_sb_info *sbi, int nr_to_scan,
  		       struct ext4_inode_info *locked_ei)
  {
  	struct ext4_inode_info *ei;
  	struct ext4_es_stats *es_stats;
  	ktime_t start_time;
  	u64 scan_time;
  	int nr_to_walk;
  	int nr_shrunk = 0;
  	int retried = 0, nr_skipped = 0;
  
  	es_stats = &sbi->s_es_stats;
  	start_time = ktime_get();
  
  retry:
  	spin_lock(&sbi->s_es_lock);
  	nr_to_walk = sbi->s_es_nr_inode;
  	while (nr_to_walk-- > 0) {
  		if (list_empty(&sbi->s_es_list)) {
  			spin_unlock(&sbi->s_es_lock);
  			goto out;
  		}
  		ei = list_first_entry(&sbi->s_es_list, struct ext4_inode_info,
  				      i_es_list);
  		/* Move the inode to the tail */
  		list_move_tail(&ei->i_es_list, &sbi->s_es_list);
  
  		/*
  		 * Normally we try hard to avoid shrinking precached inodes,
  		 * but we will as a last resort.
  		 */
  		if (!retried && ext4_test_inode_state(&ei->vfs_inode,
  						EXT4_STATE_EXT_PRECACHED)) {
  			nr_skipped++;
  			continue;
  		}
  
  		if (ei == locked_ei || !write_trylock(&ei->i_es_lock)) {
  			nr_skipped++;
  			continue;
  		}
  		/*
  		 * Now we hold i_es_lock which protects us from inode reclaim
  		 * freeing inode under us
  		 */
  		spin_unlock(&sbi->s_es_lock);
  
  		nr_shrunk += es_reclaim_extents(ei, &nr_to_scan);
  		write_unlock(&ei->i_es_lock);
  
  		if (nr_to_scan <= 0)
  			goto out;
  		spin_lock(&sbi->s_es_lock);
  	}
  	spin_unlock(&sbi->s_es_lock);
  
  	/*
  	 * If we skipped any inodes, and we weren't able to make any
  	 * forward progress, try again to scan precached inodes.
  	 */
  	if ((nr_shrunk == 0) && nr_skipped && !retried) {
  		retried++;
  		goto retry;
  	}
  
  	if (locked_ei && nr_shrunk == 0)
  		nr_shrunk = es_reclaim_extents(locked_ei, &nr_to_scan);
  
  out:
  	scan_time = ktime_to_ns(ktime_sub(ktime_get(), start_time));
  	if (likely(es_stats->es_stats_scan_time))
  		es_stats->es_stats_scan_time = (scan_time +
  				es_stats->es_stats_scan_time*3) / 4;
  	else
  		es_stats->es_stats_scan_time = scan_time;
  	if (scan_time > es_stats->es_stats_max_scan_time)
  		es_stats->es_stats_max_scan_time = scan_time;
  	if (likely(es_stats->es_stats_shrunk))
  		es_stats->es_stats_shrunk = (nr_shrunk +
  				es_stats->es_stats_shrunk*3) / 4;
  	else
  		es_stats->es_stats_shrunk = nr_shrunk;
  
  	trace_ext4_es_shrink(sbi->s_sb, nr_shrunk, scan_time,
  			     nr_skipped, retried);
  	return nr_shrunk;
  }
  
  static unsigned long ext4_es_count(struct shrinker *shrink,
  				   struct shrink_control *sc)
  {
  	unsigned long nr;
  	struct ext4_sb_info *sbi;
  
  	sbi = container_of(shrink, struct ext4_sb_info, s_es_shrinker);
  	nr = percpu_counter_read_positive(&sbi->s_es_stats.es_stats_shk_cnt);
  	trace_ext4_es_shrink_count(sbi->s_sb, sc->nr_to_scan, nr);
  	return nr;
  }
  
  static unsigned long ext4_es_scan(struct shrinker *shrink,
  				  struct shrink_control *sc)
  {
  	struct ext4_sb_info *sbi = container_of(shrink,
  					struct ext4_sb_info, s_es_shrinker);
  	int nr_to_scan = sc->nr_to_scan;
  	int ret, nr_shrunk;
  
  	ret = percpu_counter_read_positive(&sbi->s_es_stats.es_stats_shk_cnt);
  	trace_ext4_es_shrink_scan_enter(sbi->s_sb, nr_to_scan, ret);
  
  	if (!nr_to_scan)
  		return ret;
  
  	nr_shrunk = __es_shrink(sbi, nr_to_scan, NULL);
  
  	trace_ext4_es_shrink_scan_exit(sbi->s_sb, nr_shrunk, ret);
  	return nr_shrunk;
  }
  
  int ext4_seq_es_shrinker_info_show(struct seq_file *seq, void *v)
  {
  	struct ext4_sb_info *sbi = EXT4_SB((struct super_block *) seq->private);
  	struct ext4_es_stats *es_stats = &sbi->s_es_stats;
  	struct ext4_inode_info *ei, *max = NULL;
  	unsigned int inode_cnt = 0;
  
  	if (v != SEQ_START_TOKEN)
  		return 0;
  
  	/* here we just find an inode that has the max nr. of objects */
  	spin_lock(&sbi->s_es_lock);
  	list_for_each_entry(ei, &sbi->s_es_list, i_es_list) {
  		inode_cnt++;
  		if (max && max->i_es_all_nr < ei->i_es_all_nr)
  			max = ei;
  		else if (!max)
  			max = ei;
  	}
  	spin_unlock(&sbi->s_es_lock);
  
  	seq_printf(seq, "stats:
    %lld objects
    %lld reclaimable objects
  ",
  		   percpu_counter_sum_positive(&es_stats->es_stats_all_cnt),
  		   percpu_counter_sum_positive(&es_stats->es_stats_shk_cnt));
  	seq_printf(seq, "  %lu/%lu cache hits/misses
  ",
  		   es_stats->es_stats_cache_hits,
  		   es_stats->es_stats_cache_misses);
  	if (inode_cnt)
  		seq_printf(seq, "  %d inodes on list
  ", inode_cnt);
  
  	seq_printf(seq, "average:
    %llu us scan time
  ",
  	    div_u64(es_stats->es_stats_scan_time, 1000));
  	seq_printf(seq, "  %lu shrunk objects
  ", es_stats->es_stats_shrunk);
  	if (inode_cnt)
  		seq_printf(seq,
  		    "maximum:
    %lu inode (%u objects, %u reclaimable)
  "
  		    "  %llu us max scan time
  ",
  		    max->vfs_inode.i_ino, max->i_es_all_nr, max->i_es_shk_nr,
  		    div_u64(es_stats->es_stats_max_scan_time, 1000));
  
  	return 0;
  }
  
  int ext4_es_register_shrinker(struct ext4_sb_info *sbi)
  {
  	int err;
  
  	/* Make sure we have enough bits for physical block number */
  	BUILD_BUG_ON(ES_SHIFT < 48);
  	INIT_LIST_HEAD(&sbi->s_es_list);
  	sbi->s_es_nr_inode = 0;
  	spin_lock_init(&sbi->s_es_lock);
  	sbi->s_es_stats.es_stats_shrunk = 0;
  	sbi->s_es_stats.es_stats_cache_hits = 0;
  	sbi->s_es_stats.es_stats_cache_misses = 0;
  	sbi->s_es_stats.es_stats_scan_time = 0;
  	sbi->s_es_stats.es_stats_max_scan_time = 0;
  	err = percpu_counter_init(&sbi->s_es_stats.es_stats_all_cnt, 0, GFP_KERNEL);
  	if (err)
  		return err;
  	err = percpu_counter_init(&sbi->s_es_stats.es_stats_shk_cnt, 0, GFP_KERNEL);
  	if (err)
  		goto err1;
  
  	sbi->s_es_shrinker.scan_objects = ext4_es_scan;
  	sbi->s_es_shrinker.count_objects = ext4_es_count;
  	sbi->s_es_shrinker.seeks = DEFAULT_SEEKS;
  	err = register_shrinker(&sbi->s_es_shrinker);
  	if (err)
  		goto err2;
  
  	return 0;
  
  err2:
  	percpu_counter_destroy(&sbi->s_es_stats.es_stats_shk_cnt);
  err1:
  	percpu_counter_destroy(&sbi->s_es_stats.es_stats_all_cnt);
  	return err;
  }
  
  void ext4_es_unregister_shrinker(struct ext4_sb_info *sbi)
  {
  	percpu_counter_destroy(&sbi->s_es_stats.es_stats_all_cnt);
  	percpu_counter_destroy(&sbi->s_es_stats.es_stats_shk_cnt);
  	unregister_shrinker(&sbi->s_es_shrinker);
  }
  
  /*
   * Shrink extents in given inode from ei->i_es_shrink_lblk till end. Scan at
   * most *nr_to_scan extents, update *nr_to_scan accordingly.
   *
   * Return 0 if we hit end of tree / interval, 1 if we exhausted nr_to_scan.
   * Increment *nr_shrunk by the number of reclaimed extents. Also update
   * ei->i_es_shrink_lblk to where we should continue scanning.
   */
  static int es_do_reclaim_extents(struct ext4_inode_info *ei, ext4_lblk_t end,
  				 int *nr_to_scan, int *nr_shrunk)
  {
  	struct inode *inode = &ei->vfs_inode;
  	struct ext4_es_tree *tree = &ei->i_es_tree;
  	struct extent_status *es;
  	struct rb_node *node;
  
  	es = __es_tree_search(&tree->root, ei->i_es_shrink_lblk);
  	if (!es)
  		goto out_wrap;
  	node = &es->rb_node;
  	while (*nr_to_scan > 0) {
  		if (es->es_lblk > end) {
  			ei->i_es_shrink_lblk = end + 1;
  			return 0;
  		}
  
  		(*nr_to_scan)--;
  		node = rb_next(&es->rb_node);
  		/*
  		 * We can't reclaim delayed extent from status tree because
  		 * fiemap, bigallic, and seek_data/hole need to use it.
  		 */
  		if (ext4_es_is_delayed(es))
  			goto next;
  		if (ext4_es_is_referenced(es)) {
  			ext4_es_clear_referenced(es);
  			goto next;
  		}
  
  		rb_erase(&es->rb_node, &tree->root);
  		ext4_es_free_extent(inode, es);
  		(*nr_shrunk)++;
  next:
  		if (!node)
  			goto out_wrap;
  		es = rb_entry(node, struct extent_status, rb_node);
  	}
  	ei->i_es_shrink_lblk = es->es_lblk;
  	return 1;
  out_wrap:
  	ei->i_es_shrink_lblk = 0;
  	return 0;
  }
  
  static int es_reclaim_extents(struct ext4_inode_info *ei, int *nr_to_scan)
  {
  	struct inode *inode = &ei->vfs_inode;
  	int nr_shrunk = 0;
  	ext4_lblk_t start = ei->i_es_shrink_lblk;
  	static DEFINE_RATELIMIT_STATE(_rs, DEFAULT_RATELIMIT_INTERVAL,
  				      DEFAULT_RATELIMIT_BURST);
  
  	if (ei->i_es_shk_nr == 0)
  		return 0;
  
  	if (ext4_test_inode_state(inode, EXT4_STATE_EXT_PRECACHED) &&
  	    __ratelimit(&_rs))
  		ext4_warning(inode->i_sb, "forced shrink of precached extents");
  
  	if (!es_do_reclaim_extents(ei, EXT_MAX_BLOCKS, nr_to_scan, &nr_shrunk) &&
  	    start != 0)
  		es_do_reclaim_extents(ei, start - 1, nr_to_scan, &nr_shrunk);
  
  	ei->i_es_tree.cache_es = NULL;
  	return nr_shrunk;
  }