/*
 *  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/rbtree.h>
#include "ext4.h"
#include "extents_status.h"
#include "ext4_extents.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_try_to_reclaim_extents(struct ext4_inode_info *ei,
                                       int nr_to_scan);

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 %llx",
                       es->es_lblk, es->es_len,
                       ext4_es_pblock(es), ext4_es_status(es));
                node = rb_next(node);
        }
        printk(KERN_DEBUG "\n");
}
#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 %llx\n",
                                 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);

        ext4_es_lru_add(inode);
        trace_ext4_es_find_delayed_extent_range_exit(inode, es);
}

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)) {
                EXT4_I(inode)->i_es_lru_nr++;
                percpu_counter_inc(&EXT4_SB(inode->i_sb)->s_extent_cache_cnt);
        }

        return es;
}

static void ext4_es_free_extent(struct inode *inode, struct extent_status *es)
{
        /* Decrease the lru counter when this es is not delayed */
        if (!ext4_es_is_delayed(es)) {
                BUG_ON(EXT4_I(inode)->i_es_lru_nr == 0);
                EXT4_I(inode)->i_es_lru_nr--;
                percpu_counter_dec(&EXT4_SB(inode->i_sb)->s_extent_cache_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_status(es1) != ext4_es_status(es2))
                return 0;

        if (((__u64) es1->es_len) + es2->es_len > 0xFFFFFFFFULL)
                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;
                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;
                rb_erase(node, &tree->root);
                ext4_es_free_extent(inode, es1);
        }

        return es;
}

#ifdef ES_AGGRESSIVE_TEST
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_ext_find_extent(inode, es->es_lblk, NULL);
        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_uninitialized(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 assertation failed for "
                                        "inode: %lu we can find an extent "
                                        "at block [%d/%d/%llu/%c], but we "
                                        "want to add an delayed/hole extent "
                                        "[%d/%d/%llu/%llx]\n",
                                        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 assertation failed for inode: %lu "
                                "ex_status [%d/%d/%llu/%c] != "
                                "es_status [%d/%d/%llu/%c]\n", 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 assertation failed for inode: %lu "
                                "ex_status [%d/%d/%llu/%c] != "
                                "es_status [%d/%d/%llu/%c]\n", 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 assertation failed for inode: %lu "
                                "can't find an extent at block %d but we want "
                                "to add an written/unwritten extent "
                                "[%d/%d/%llu/%llx]\n", inode->i_ino,
                                es->es_lblk, es->es_lblk, es->es_len,
                                ext4_es_pblock(es), ext4_es_status(es));
                }
        }
out:
        if (path) {
                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 assertation failed for inode: %lu "
                                "We can find blocks but we want to add a "
                                "delayed/hole extent [%d/%d/%llu/%llx]\n",
                                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 assertation failed for "
                                        "inode: %lu retval %d != es_len %d\n",
                                        inode->i_ino, retval, es->es_len);
                                return;
                        }
                        if (map.m_pblk != ext4_es_pblock(es)) {
                                pr_warn("ES insert assertation failed for "
                                        "inode: %lu m_pblk %llu != "
                                        "es_pblk %llu\n",
                                        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 assertation failed for inode: %lu "
                                "We can't find the block but we want to add "
                                "an written extent [%d/%d/%llu/%llx]\n",
                                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 a space to a extent status tree.
 *
 * ext4_es_insert_extent is called by ext4_da_write_begin and
 * ext4_es_remove_extent.
 *
 * 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 long long status)
{
        struct extent_status newes;
        ext4_lblk_t end = lblk + len - 1;
        int err = 0;

        es_debug("add [%u/%u) %llu %llx to extent status tree of inode %lu\n",
                 lblk, len, pblk, status, inode->i_ino);

        if (!len)
                return 0;

        BUG_ON(end < lblk);

        newes.es_lblk = lblk;
        newes.es_len = len;
        ext4_es_store_pblock(&newes, pblk);
        ext4_es_store_status(&newes, 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;
        err = __es_insert_extent(inode, &newes);

error:
        write_unlock(&EXT4_I(inode)->i_es_lock);

        ext4_es_lru_add(inode);
        ext4_es_print_tree(inode);

        return err;
}

/*
 * 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 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\n", 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)\n",
                                 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:
        if (found) {
                BUG_ON(!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);

        ext4_es_lru_add(inode);
        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 = 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;
                        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(&newes, block);
                        }
                        ext4_es_store_status(&newes, 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;
                                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\n",
                 lblk, len, inode->i_ino);

        if (!len)
                return err;

        end = lblk + len - 1;
        BUG_ON(end < lblk);

        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;
}

int ext4_es_zeroout(struct inode *inode, struct ext4_extent *ex)
{
        ext4_lblk_t  ee_block;
        ext4_fsblk_t ee_pblock;
        unsigned int ee_len;

        ee_block  = le32_to_cpu(ex->ee_block);
        ee_len    = ext4_ext_get_actual_len(ex);
        ee_pblock = ext4_ext_pblock(ex);

        if (ee_len == 0)
                return 0;

        return ext4_es_insert_extent(inode, ee_block, ee_len, ee_pblock,
                                     EXTENT_STATUS_WRITTEN);
}

static int ext4_es_shrink(struct shrinker *shrink, struct shrink_control *sc)
{
        struct ext4_sb_info *sbi = container_of(shrink,
                                        struct ext4_sb_info, s_es_shrinker);
        struct ext4_inode_info *ei;
        struct list_head *cur, *tmp, scanned;
        int nr_to_scan = sc->nr_to_scan;
        int ret, nr_shrunk = 0;

        ret = percpu_counter_read_positive(&sbi->s_extent_cache_cnt);
        trace_ext4_es_shrink_enter(sbi->s_sb, nr_to_scan, ret);

        if (!nr_to_scan)
                return ret;

        INIT_LIST_HEAD(&scanned);

        spin_lock(&sbi->s_es_lru_lock);
        list_for_each_safe(cur, tmp, &sbi->s_es_lru) {
                list_move_tail(cur, &scanned);

                ei = list_entry(cur, struct ext4_inode_info, i_es_lru);

                read_lock(&ei->i_es_lock);
                if (ei->i_es_lru_nr == 0) {
                        read_unlock(&ei->i_es_lock);
                        continue;
                }
                read_unlock(&ei->i_es_lock);

                write_lock(&ei->i_es_lock);
                ret = __es_try_to_reclaim_extents(ei, nr_to_scan);
                write_unlock(&ei->i_es_lock);

                nr_shrunk += ret;
                nr_to_scan -= ret;
                if (nr_to_scan == 0)
                        break;
        }
        list_splice_tail(&scanned, &sbi->s_es_lru);
        spin_unlock(&sbi->s_es_lru_lock);

        ret = percpu_counter_read_positive(&sbi->s_extent_cache_cnt);
        trace_ext4_es_shrink_exit(sbi->s_sb, nr_shrunk, ret);
        return ret;
}

void ext4_es_register_shrinker(struct super_block *sb)
{
        struct ext4_sb_info *sbi;

        sbi = EXT4_SB(sb);
        INIT_LIST_HEAD(&sbi->s_es_lru);
        spin_lock_init(&sbi->s_es_lru_lock);
        sbi->s_es_shrinker.shrink = ext4_es_shrink;
        sbi->s_es_shrinker.seeks = DEFAULT_SEEKS;
        register_shrinker(&sbi->s_es_shrinker);
}

void ext4_es_unregister_shrinker(struct super_block *sb)
{
        unregister_shrinker(&EXT4_SB(sb)->s_es_shrinker);
}

void ext4_es_lru_add(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_lru_lock);
        if (list_empty(&ei->i_es_lru))
                list_add_tail(&ei->i_es_lru, &sbi->s_es_lru);
        else
                list_move_tail(&ei->i_es_lru, &sbi->s_es_lru);
        spin_unlock(&sbi->s_es_lru_lock);
}

void ext4_es_lru_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_lru_lock);
        if (!list_empty(&ei->i_es_lru))
                list_del_init(&ei->i_es_lru);
        spin_unlock(&sbi->s_es_lru_lock);
}

static int __es_try_to_reclaim_extents(struct ext4_inode_info *ei,
                                       int nr_to_scan)
{
        struct inode *inode = &ei->vfs_inode;
        struct ext4_es_tree *tree = &ei->i_es_tree;
        struct rb_node *node;
        struct extent_status *es;
        int nr_shrunk = 0;

        if (ei->i_es_lru_nr == 0)
                return 0;

        node = rb_first(&tree->root);
        while (node != NULL) {
                es = rb_entry(node, struct extent_status, rb_node);
                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)) {
                        rb_erase(&es->rb_node, &tree->root);
                        ext4_es_free_extent(inode, es);
                        nr_shrunk++;
                        if (--nr_to_scan == 0)
                                break;
                }
        }
        tree->cache_es = NULL;
        return nr_shrunk;
}