Linux 6.13-rc4

[linux.git] / fs / btrfs / extent_map.c

// SPDX-License-Identifier: GPL-2.0

#include <linux/err.h>
#include <linux/slab.h>
#include <linux/spinlock.h>
#include "messages.h"
#include "ctree.h"
#include "extent_map.h"
#include "compression.h"
#include "btrfs_inode.h"
#include "disk-io.h"


static struct kmem_cache *extent_map_cache;

int __init extent_map_init(void)
{
        extent_map_cache = kmem_cache_create("btrfs_extent_map",
                                             sizeof(struct extent_map), 0, 0, NULL);
        if (!extent_map_cache)
                return -ENOMEM;
        return 0;
}

void __cold extent_map_exit(void)
{
        kmem_cache_destroy(extent_map_cache);
}

/*
 * Initialize the extent tree @tree.  Should be called for each new inode or
 * other user of the extent_map interface.
 */
void extent_map_tree_init(struct extent_map_tree *tree)
{
        tree->root = RB_ROOT;
        INIT_LIST_HEAD(&tree->modified_extents);
        rwlock_init(&tree->lock);
}

/*
 * Allocate a new extent_map structure.  The new structure is returned with a
 * reference count of one and needs to be freed using free_extent_map()
 */
struct extent_map *alloc_extent_map(void)
{
        struct extent_map *em;
        em = kmem_cache_zalloc(extent_map_cache, GFP_NOFS);
        if (!em)
                return NULL;
        RB_CLEAR_NODE(&em->rb_node);
        refcount_set(&em->refs, 1);
        INIT_LIST_HEAD(&em->list);
        return em;
}

/*
 * Drop the reference out on @em by one and free the structure if the reference
 * count hits zero.
 */
void free_extent_map(struct extent_map *em)
{
        if (!em)
                return;
        if (refcount_dec_and_test(&em->refs)) {
                WARN_ON(extent_map_in_tree(em));
                WARN_ON(!list_empty(&em->list));
                kmem_cache_free(extent_map_cache, em);
        }
}

/* Do the math around the end of an extent, handling wrapping. */
static u64 range_end(u64 start, u64 len)
{
        if (start + len < start)
                return (u64)-1;
        return start + len;
}

static void remove_em(struct btrfs_inode *inode, struct extent_map *em)
{
        struct btrfs_fs_info *fs_info = inode->root->fs_info;

        rb_erase(&em->rb_node, &inode->extent_tree.root);
        RB_CLEAR_NODE(&em->rb_node);

        if (!btrfs_is_testing(fs_info) && is_fstree(btrfs_root_id(inode->root)))
                percpu_counter_dec(&fs_info->evictable_extent_maps);
}

static int tree_insert(struct rb_root *root, struct extent_map *em)
{
        struct rb_node **p = &root->rb_node;
        struct rb_node *parent = NULL;
        struct extent_map *entry = NULL;
        struct rb_node *orig_parent = NULL;
        u64 end = range_end(em->start, em->len);

        while (*p) {
                parent = *p;
                entry = rb_entry(parent, struct extent_map, rb_node);

                if (em->start < entry->start)
                        p = &(*p)->rb_left;
                else if (em->start >= extent_map_end(entry))
                        p = &(*p)->rb_right;
                else
                        return -EEXIST;
        }

        orig_parent = parent;
        while (parent && em->start >= extent_map_end(entry)) {
                parent = rb_next(parent);
                entry = rb_entry(parent, struct extent_map, rb_node);
        }
        if (parent)
                if (end > entry->start && em->start < extent_map_end(entry))
                        return -EEXIST;

        parent = orig_parent;
        entry = rb_entry(parent, struct extent_map, rb_node);
        while (parent && em->start < entry->start) {
                parent = rb_prev(parent);
                entry = rb_entry(parent, struct extent_map, rb_node);
        }
        if (parent)
                if (end > entry->start && em->start < extent_map_end(entry))
                        return -EEXIST;

        rb_link_node(&em->rb_node, orig_parent, p);
        rb_insert_color(&em->rb_node, root);
        return 0;
}

/*
 * Search through the tree for an extent_map with a given offset.  If it can't
 * be found, try to find some neighboring extents
 */
static struct rb_node *__tree_search(struct rb_root *root, u64 offset,
                                     struct rb_node **prev_or_next_ret)
{
        struct rb_node *n = root->rb_node;
        struct rb_node *prev = NULL;
        struct rb_node *orig_prev = NULL;
        struct extent_map *entry;
        struct extent_map *prev_entry = NULL;

        ASSERT(prev_or_next_ret);

        while (n) {
                entry = rb_entry(n, struct extent_map, rb_node);
                prev = n;
                prev_entry = entry;

                if (offset < entry->start)
                        n = n->rb_left;
                else if (offset >= extent_map_end(entry))
                        n = n->rb_right;
                else
                        return n;
        }

        orig_prev = prev;
        while (prev && offset >= extent_map_end(prev_entry)) {
                prev = rb_next(prev);
                prev_entry = rb_entry(prev, struct extent_map, rb_node);
        }

        /*
         * Previous extent map found, return as in this case the caller does not
         * care about the next one.
         */
        if (prev) {
                *prev_or_next_ret = prev;
                return NULL;
        }

        prev = orig_prev;
        prev_entry = rb_entry(prev, struct extent_map, rb_node);
        while (prev && offset < prev_entry->start) {
                prev = rb_prev(prev);
                prev_entry = rb_entry(prev, struct extent_map, rb_node);
        }
        *prev_or_next_ret = prev;

        return NULL;
}

static inline u64 extent_map_block_len(const struct extent_map *em)
{
        if (extent_map_is_compressed(em))
                return em->disk_num_bytes;
        return em->len;
}

static inline u64 extent_map_block_end(const struct extent_map *em)
{
        const u64 block_start = extent_map_block_start(em);
        const u64 block_end = block_start + extent_map_block_len(em);

        if (block_end < block_start)
                return (u64)-1;

        return block_end;
}

static bool can_merge_extent_map(const struct extent_map *em)
{
        if (em->flags & EXTENT_FLAG_PINNED)
                return false;

        /* Don't merge compressed extents, we need to know their actual size. */
        if (extent_map_is_compressed(em))
                return false;

        if (em->flags & EXTENT_FLAG_LOGGING)
                return false;

        /*
         * We don't want to merge stuff that hasn't been written to the log yet
         * since it may not reflect exactly what is on disk, and that would be
         * bad.
         */
        if (!list_empty(&em->list))
                return false;

        return true;
}

/* Check to see if two extent_map structs are adjacent and safe to merge. */
static bool mergeable_maps(const struct extent_map *prev, const struct extent_map *next)
{
        if (extent_map_end(prev) != next->start)
                return false;

        /*
         * The merged flag is not an on-disk flag, it just indicates we had the
         * extent maps of 2 (or more) adjacent extents merged, so factor it out.
         */
        if ((prev->flags & ~EXTENT_FLAG_MERGED) !=
            (next->flags & ~EXTENT_FLAG_MERGED))
                return false;

        if (next->disk_bytenr < EXTENT_MAP_LAST_BYTE - 1)
                return extent_map_block_start(next) == extent_map_block_end(prev);

        /* HOLES and INLINE extents. */
        return next->disk_bytenr == prev->disk_bytenr;
}

/*
 * Handle the on-disk data extents merge for @prev and @next.
 *
 * @prev:    left extent to merge
 * @next:    right extent to merge
 * @merged:  the extent we will not discard after the merge; updated with new values
 *
 * After this, one of the two extents is the new merged extent and the other is
 * removed from the tree and likely freed. Note that @merged is one of @prev/@next
 * so there is const/non-const aliasing occurring here.
 *
 * Only touches disk_bytenr/disk_num_bytes/offset/ram_bytes.
 * For now only uncompressed regular extent can be merged.
 */
static void merge_ondisk_extents(const struct extent_map *prev, const struct extent_map *next,
                                 struct extent_map *merged)
{
        u64 new_disk_bytenr;
        u64 new_disk_num_bytes;
        u64 new_offset;

        /* @prev and @next should not be compressed. */
        ASSERT(!extent_map_is_compressed(prev));
        ASSERT(!extent_map_is_compressed(next));

        /*
         * There are two different cases where @prev and @next can be merged.
         *
         * 1) They are referring to the same data extent:
         *
         * |<----- data extent A ----->|
         *    |<- prev ->|<- next ->|
         *
         * 2) They are referring to different data extents but still adjacent:
         *
         * |<-- data extent A -->|<-- data extent B -->|
         *            |<- prev ->|<- next ->|
         *
         * The calculation here always merges the data extents first, then updates
         * @offset using the new data extents.
         *
         * For case 1), the merged data extent would be the same.
         * For case 2), we just merge the two data extents into one.
         */
        new_disk_bytenr = min(prev->disk_bytenr, next->disk_bytenr);
        new_disk_num_bytes = max(prev->disk_bytenr + prev->disk_num_bytes,
                                 next->disk_bytenr + next->disk_num_bytes) -
                             new_disk_bytenr;
        new_offset = prev->disk_bytenr + prev->offset - new_disk_bytenr;

        merged->disk_bytenr = new_disk_bytenr;
        merged->disk_num_bytes = new_disk_num_bytes;
        merged->ram_bytes = new_disk_num_bytes;
        merged->offset = new_offset;
}

static void dump_extent_map(struct btrfs_fs_info *fs_info, const char *prefix,
                            struct extent_map *em)
{
        if (!IS_ENABLED(CONFIG_BTRFS_DEBUG))
                return;
        btrfs_crit(fs_info,
"%s, start=%llu len=%llu disk_bytenr=%llu disk_num_bytes=%llu ram_bytes=%llu offset=%llu flags=0x%x",
                prefix, em->start, em->len, em->disk_bytenr, em->disk_num_bytes,
                em->ram_bytes, em->offset, em->flags);
        ASSERT(0);
}

/* Internal sanity checks for btrfs debug builds. */
static void validate_extent_map(struct btrfs_fs_info *fs_info, struct extent_map *em)
{
        if (!IS_ENABLED(CONFIG_BTRFS_DEBUG))
                return;
        if (em->disk_bytenr < EXTENT_MAP_LAST_BYTE) {
                if (em->disk_num_bytes == 0)
                        dump_extent_map(fs_info, "zero disk_num_bytes", em);
                if (em->offset + em->len > em->ram_bytes)
                        dump_extent_map(fs_info, "ram_bytes too small", em);
                if (em->offset + em->len > em->disk_num_bytes &&
                    !extent_map_is_compressed(em))
                        dump_extent_map(fs_info, "disk_num_bytes too small", em);
                if (!extent_map_is_compressed(em) &&
                    em->ram_bytes != em->disk_num_bytes)
                        dump_extent_map(fs_info,
                "ram_bytes mismatch with disk_num_bytes for non-compressed em",
                                        em);
        } else if (em->offset) {
                dump_extent_map(fs_info, "non-zero offset for hole/inline", em);
        }
}

static void try_merge_map(struct btrfs_inode *inode, struct extent_map *em)
{
        struct btrfs_fs_info *fs_info = inode->root->fs_info;
        struct extent_map *merge = NULL;
        struct rb_node *rb;

        /*
         * We can't modify an extent map that is in the tree and that is being
         * used by another task, as it can cause that other task to see it in
         * inconsistent state during the merging. We always have 1 reference for
         * the tree and 1 for this task (which is unpinning the extent map or
         * clearing the logging flag), so anything > 2 means it's being used by
         * other tasks too.
         */
        if (refcount_read(&em->refs) > 2)
                return;

        if (!can_merge_extent_map(em))
                return;

        if (em->start != 0) {
                rb = rb_prev(&em->rb_node);
                if (rb)
                        merge = rb_entry(rb, struct extent_map, rb_node);
                if (rb && can_merge_extent_map(merge) && mergeable_maps(merge, em)) {
                        em->start = merge->start;
                        em->len += merge->len;
                        em->generation = max(em->generation, merge->generation);

                        if (em->disk_bytenr < EXTENT_MAP_LAST_BYTE)
                                merge_ondisk_extents(merge, em, em);
                        em->flags |= EXTENT_FLAG_MERGED;

                        validate_extent_map(fs_info, em);
                        remove_em(inode, merge);
                        free_extent_map(merge);
                }
        }

        rb = rb_next(&em->rb_node);
        if (rb)
                merge = rb_entry(rb, struct extent_map, rb_node);
        if (rb && can_merge_extent_map(merge) && mergeable_maps(em, merge)) {
                em->len += merge->len;
                if (em->disk_bytenr < EXTENT_MAP_LAST_BYTE)
                        merge_ondisk_extents(em, merge, em);
                validate_extent_map(fs_info, em);
                em->generation = max(em->generation, merge->generation);
                em->flags |= EXTENT_FLAG_MERGED;
                remove_em(inode, merge);
                free_extent_map(merge);
        }
}

/*
 * Unpin an extent from the cache.
 *
 * @inode:      the inode from which we are unpinning an extent range
 * @start:      logical offset in the file
 * @len:        length of the extent
 * @gen:        generation that this extent has been modified in
 *
 * Called after an extent has been written to disk properly.  Set the generation
 * to the generation that actually added the file item to the inode so we know
 * we need to sync this extent when we call fsync().
 *
 * Returns: 0        on success
 *          -ENOENT  when the extent is not found in the tree
 *          -EUCLEAN if the found extent does not match the expected start
 */
int unpin_extent_cache(struct btrfs_inode *inode, u64 start, u64 len, u64 gen)
{
        struct btrfs_fs_info *fs_info = inode->root->fs_info;
        struct extent_map_tree *tree = &inode->extent_tree;
        int ret = 0;
        struct extent_map *em;

        write_lock(&tree->lock);
        em = lookup_extent_mapping(tree, start, len);

        if (WARN_ON(!em)) {
                btrfs_warn(fs_info,
"no extent map found for inode %llu (root %lld) when unpinning extent range [%llu, %llu), generation %llu",
                           btrfs_ino(inode), btrfs_root_id(inode->root),
                           start, start + len, gen);
                ret = -ENOENT;
                goto out;
        }

        if (WARN_ON(em->start != start)) {
                btrfs_warn(fs_info,
"found extent map for inode %llu (root %lld) with unexpected start offset %llu when unpinning extent range [%llu, %llu), generation %llu",
                           btrfs_ino(inode), btrfs_root_id(inode->root),
                           em->start, start, start + len, gen);
                ret = -EUCLEAN;
                goto out;
        }

        em->generation = gen;
        em->flags &= ~EXTENT_FLAG_PINNED;

        try_merge_map(inode, em);

out:
        write_unlock(&tree->lock);
        free_extent_map(em);
        return ret;

}

void clear_em_logging(struct btrfs_inode *inode, struct extent_map *em)
{
        lockdep_assert_held_write(&inode->extent_tree.lock);

        em->flags &= ~EXTENT_FLAG_LOGGING;
        if (extent_map_in_tree(em))
                try_merge_map(inode, em);
}

static inline void setup_extent_mapping(struct btrfs_inode *inode,
                                        struct extent_map *em,
                                        int modified)
{
        refcount_inc(&em->refs);

        ASSERT(list_empty(&em->list));

        if (modified)
                list_add(&em->list, &inode->extent_tree.modified_extents);
        else
                try_merge_map(inode, em);
}

/*
 * Add a new extent map to an inode's extent map tree.
 *
 * @inode:      the target inode
 * @em:         map to insert
 * @modified:   indicate whether the given @em should be added to the
 *              modified list, which indicates the extent needs to be logged
 *
 * Insert @em into the @inode's extent map tree or perform a simple
 * forward/backward merge with existing mappings.  The extent_map struct passed
 * in will be inserted into the tree directly, with an additional reference
 * taken, or a reference dropped if the merge attempt was successful.
 */
static int add_extent_mapping(struct btrfs_inode *inode,
                              struct extent_map *em, int modified)
{
        struct extent_map_tree *tree = &inode->extent_tree;
        struct btrfs_root *root = inode->root;
        struct btrfs_fs_info *fs_info = root->fs_info;
        int ret;

        lockdep_assert_held_write(&tree->lock);

        validate_extent_map(fs_info, em);
        ret = tree_insert(&tree->root, em);
        if (ret)
                return ret;

        setup_extent_mapping(inode, em, modified);

        if (!btrfs_is_testing(fs_info) && is_fstree(btrfs_root_id(root)))
                percpu_counter_inc(&fs_info->evictable_extent_maps);

        return 0;
}

static struct extent_map *
__lookup_extent_mapping(struct extent_map_tree *tree,
                        u64 start, u64 len, int strict)
{
        struct extent_map *em;
        struct rb_node *rb_node;
        struct rb_node *prev_or_next = NULL;
        u64 end = range_end(start, len);

        rb_node = __tree_search(&tree->root, start, &prev_or_next);
        if (!rb_node) {
                if (prev_or_next)
                        rb_node = prev_or_next;
                else
                        return NULL;
        }

        em = rb_entry(rb_node, struct extent_map, rb_node);

        if (strict && !(end > em->start && start < extent_map_end(em)))
                return NULL;

        refcount_inc(&em->refs);
        return em;
}

/*
 * Lookup extent_map that intersects @start + @len range.
 *
 * @tree:       tree to lookup in
 * @start:      byte offset to start the search
 * @len:        length of the lookup range
 *
 * Find and return the first extent_map struct in @tree that intersects the
 * [start, len] range.  There may be additional objects in the tree that
 * intersect, so check the object returned carefully to make sure that no
 * additional lookups are needed.
 */
struct extent_map *lookup_extent_mapping(struct extent_map_tree *tree,
                                         u64 start, u64 len)
{
        return __lookup_extent_mapping(tree, start, len, 1);
}

/*
 * Find a nearby extent map intersecting @start + @len (not an exact search).
 *
 * @tree:       tree to lookup in
 * @start:      byte offset to start the search
 * @len:        length of the lookup range
 *
 * Find and return the first extent_map struct in @tree that intersects the
 * [start, len] range.
 *
 * If one can't be found, any nearby extent may be returned
 */
struct extent_map *search_extent_mapping(struct extent_map_tree *tree,
                                         u64 start, u64 len)
{
        return __lookup_extent_mapping(tree, start, len, 0);
}

/*
 * Remove an extent_map from its inode's extent tree.
 *
 * @inode:      the inode the extent map belongs to
 * @em:         extent map being removed
 *
 * Remove @em from the extent tree of @inode.  No reference counts are dropped,
 * and no checks are done to see if the range is in use.
 */
void remove_extent_mapping(struct btrfs_inode *inode, struct extent_map *em)
{
        struct extent_map_tree *tree = &inode->extent_tree;

        lockdep_assert_held_write(&tree->lock);

        WARN_ON(em->flags & EXTENT_FLAG_PINNED);
        if (!(em->flags & EXTENT_FLAG_LOGGING))
                list_del_init(&em->list);

        remove_em(inode, em);
}

static void replace_extent_mapping(struct btrfs_inode *inode,
                                   struct extent_map *cur,
                                   struct extent_map *new,
                                   int modified)
{
        struct btrfs_fs_info *fs_info = inode->root->fs_info;
        struct extent_map_tree *tree = &inode->extent_tree;

        lockdep_assert_held_write(&tree->lock);

        validate_extent_map(fs_info, new);

        WARN_ON(cur->flags & EXTENT_FLAG_PINNED);
        ASSERT(extent_map_in_tree(cur));
        if (!(cur->flags & EXTENT_FLAG_LOGGING))
                list_del_init(&cur->list);
        rb_replace_node(&cur->rb_node, &new->rb_node, &tree->root);
        RB_CLEAR_NODE(&cur->rb_node);

        setup_extent_mapping(inode, new, modified);
}

static struct extent_map *next_extent_map(const struct extent_map *em)
{
        struct rb_node *next;

        next = rb_next(&em->rb_node);
        if (!next)
                return NULL;
        return container_of(next, struct extent_map, rb_node);
}

static struct extent_map *prev_extent_map(struct extent_map *em)
{
        struct rb_node *prev;

        prev = rb_prev(&em->rb_node);
        if (!prev)
                return NULL;
        return container_of(prev, struct extent_map, rb_node);
}

/*
 * Helper for btrfs_get_extent.  Given an existing extent in the tree,
 * the existing extent is the nearest extent to map_start,
 * and an extent that you want to insert, deal with overlap and insert
 * the best fitted new extent into the tree.
 */
static noinline int merge_extent_mapping(struct btrfs_inode *inode,
                                         struct extent_map *existing,
                                         struct extent_map *em,
                                         u64 map_start)
{
        struct extent_map *prev;
        struct extent_map *next;
        u64 start;
        u64 end;
        u64 start_diff;

        if (map_start < em->start || map_start >= extent_map_end(em))
                return -EINVAL;

        if (existing->start > map_start) {
                next = existing;
                prev = prev_extent_map(next);
        } else {
                prev = existing;
                next = next_extent_map(prev);
        }

        start = prev ? extent_map_end(prev) : em->start;
        start = max_t(u64, start, em->start);
        end = next ? next->start : extent_map_end(em);
        end = min_t(u64, end, extent_map_end(em));
        start_diff = start - em->start;
        em->start = start;
        em->len = end - start;
        if (em->disk_bytenr < EXTENT_MAP_LAST_BYTE)
                em->offset += start_diff;
        return add_extent_mapping(inode, em, 0);
}

/*
 * Add extent mapping into an inode's extent map tree.
 *
 * @inode:    target inode
 * @em_in:    extent we are inserting
 * @start:    start of the logical range btrfs_get_extent() is requesting
 * @len:      length of the logical range btrfs_get_extent() is requesting
 *
 * Note that @em_in's range may be different from [start, start+len),
 * but they must be overlapped.
 *
 * Insert @em_in into the inode's extent map tree. In case there is an
 * overlapping range, handle the -EEXIST by either:
 * a) Returning the existing extent in @em_in if @start is within the
 *    existing em.
 * b) Merge the existing extent with @em_in passed in.
 *
 * Return 0 on success, otherwise -EEXIST.
 *
 */
int btrfs_add_extent_mapping(struct btrfs_inode *inode,
                             struct extent_map **em_in, u64 start, u64 len)
{
        int ret;
        struct extent_map *em = *em_in;
        struct btrfs_fs_info *fs_info = inode->root->fs_info;

        /*
         * Tree-checker should have rejected any inline extent with non-zero
         * file offset. Here just do a sanity check.
         */
        if (em->disk_bytenr == EXTENT_MAP_INLINE)
                ASSERT(em->start == 0);

        ret = add_extent_mapping(inode, em, 0);
        /* it is possible that someone inserted the extent into the tree
         * while we had the lock dropped.  It is also possible that
         * an overlapping map exists in the tree
         */
        if (ret == -EEXIST) {
                struct extent_map *existing;

                existing = search_extent_mapping(&inode->extent_tree, start, len);

                trace_btrfs_handle_em_exist(fs_info, existing, em, start, len);

                /*
                 * existing will always be non-NULL, since there must be
                 * extent causing the -EEXIST.
                 */
                if (start >= existing->start &&
                    start < extent_map_end(existing)) {
                        free_extent_map(em);
                        *em_in = existing;
                        ret = 0;
                } else {
                        u64 orig_start = em->start;
                        u64 orig_len = em->len;

                        /*
                         * The existing extent map is the one nearest to
                         * the [start, start + len) range which overlaps
                         */
                        ret = merge_extent_mapping(inode, existing, em, start);
                        if (WARN_ON(ret)) {
                                free_extent_map(em);
                                *em_in = NULL;
                                btrfs_warn(fs_info,
"extent map merge error existing [%llu, %llu) with em [%llu, %llu) start %llu",
                                           existing->start, extent_map_end(existing),
                                           orig_start, orig_start + orig_len, start);
                        }
                        free_extent_map(existing);
                }
        }

        ASSERT(ret == 0 || ret == -EEXIST);
        return ret;
}

/*
 * Drop all extent maps from a tree in the fastest possible way, rescheduling
 * if needed. This avoids searching the tree, from the root down to the first
 * extent map, before each deletion.
 */
static void drop_all_extent_maps_fast(struct btrfs_inode *inode)
{
        struct extent_map_tree *tree = &inode->extent_tree;
        struct rb_node *node;

        write_lock(&tree->lock);
        node = rb_first(&tree->root);
        while (node) {
                struct extent_map *em;
                struct rb_node *next = rb_next(node);

                em = rb_entry(node, struct extent_map, rb_node);
                em->flags &= ~(EXTENT_FLAG_PINNED | EXTENT_FLAG_LOGGING);
                remove_extent_mapping(inode, em);
                free_extent_map(em);

                if (cond_resched_rwlock_write(&tree->lock))
                        node = rb_first(&tree->root);
                else
                        node = next;
        }
        write_unlock(&tree->lock);
}

/*
 * Drop all extent maps in a given range.
 *
 * @inode:       The target inode.
 * @start:       Start offset of the range.
 * @end:         End offset of the range (inclusive value).
 * @skip_pinned: Indicate if pinned extent maps should be ignored or not.
 *
 * This drops all the extent maps that intersect the given range [@start, @end].
 * Extent maps that partially overlap the range and extend behind or beyond it,
 * are split.
 * The caller should have locked an appropriate file range in the inode's io
 * tree before calling this function.
 */
void btrfs_drop_extent_map_range(struct btrfs_inode *inode, u64 start, u64 end,
                                 bool skip_pinned)
{
        struct extent_map *split;
        struct extent_map *split2;
        struct extent_map *em;
        struct extent_map_tree *em_tree = &inode->extent_tree;
        u64 len = end - start + 1;

        WARN_ON(end < start);
        if (end == (u64)-1) {
                if (start == 0 && !skip_pinned) {
                        drop_all_extent_maps_fast(inode);
                        return;
                }
                len = (u64)-1;
        } else {
                /* Make end offset exclusive for use in the loop below. */
                end++;
        }

        /*
         * It's ok if we fail to allocate the extent maps, see the comment near
         * the bottom of the loop below. We only need two spare extent maps in
         * the worst case, where the first extent map that intersects our range
         * starts before the range and the last extent map that intersects our
         * range ends after our range (and they might be the same extent map),
         * because we need to split those two extent maps at the boundaries.
         */
        split = alloc_extent_map();
        split2 = alloc_extent_map();

        write_lock(&em_tree->lock);
        em = lookup_extent_mapping(em_tree, start, len);

        while (em) {
                /* extent_map_end() returns exclusive value (last byte + 1). */
                const u64 em_end = extent_map_end(em);
                struct extent_map *next_em = NULL;
                u64 gen;
                unsigned long flags;
                bool modified;

                if (em_end < end) {
                        next_em = next_extent_map(em);
                        if (next_em) {
                                if (next_em->start < end)
                                        refcount_inc(&next_em->refs);
                                else
                                        next_em = NULL;
                        }
                }

                if (skip_pinned && (em->flags & EXTENT_FLAG_PINNED)) {
                        start = em_end;
                        goto next;
                }

                flags = em->flags;
                /*
                 * In case we split the extent map, we want to preserve the
                 * EXTENT_FLAG_LOGGING flag on our extent map, but we don't want
                 * it on the new extent maps.
                 */
                em->flags &= ~(EXTENT_FLAG_PINNED | EXTENT_FLAG_LOGGING);
                modified = !list_empty(&em->list);

                /*
                 * The extent map does not cross our target range, so no need to
                 * split it, we can remove it directly.
                 */
                if (em->start >= start && em_end <= end)
                        goto remove_em;

                gen = em->generation;

                if (em->start < start) {
                        if (!split) {
                                split = split2;
                                split2 = NULL;
                                if (!split)
                                        goto remove_em;
                        }
                        split->start = em->start;
                        split->len = start - em->start;

                        if (em->disk_bytenr < EXTENT_MAP_LAST_BYTE) {
                                split->disk_bytenr = em->disk_bytenr;
                                split->disk_num_bytes = em->disk_num_bytes;
                                split->offset = em->offset;
                                split->ram_bytes = em->ram_bytes;
                        } else {
                                split->disk_bytenr = em->disk_bytenr;
                                split->disk_num_bytes = 0;
                                split->offset = 0;
                                split->ram_bytes = split->len;
                        }

                        split->generation = gen;
                        split->flags = flags;
                        replace_extent_mapping(inode, em, split, modified);
                        free_extent_map(split);
                        split = split2;
                        split2 = NULL;
                }
                if (em_end > end) {
                        if (!split) {
                                split = split2;
                                split2 = NULL;
                                if (!split)
                                        goto remove_em;
                        }
                        split->start = end;
                        split->len = em_end - end;
                        split->disk_bytenr = em->disk_bytenr;
                        split->flags = flags;
                        split->generation = gen;

                        if (em->disk_bytenr < EXTENT_MAP_LAST_BYTE) {
                                split->disk_num_bytes = em->disk_num_bytes;
                                split->offset = em->offset + end - em->start;
                                split->ram_bytes = em->ram_bytes;
                        } else {
                                split->disk_num_bytes = 0;
                                split->offset = 0;
                                split->ram_bytes = split->len;
                        }

                        if (extent_map_in_tree(em)) {
                                replace_extent_mapping(inode, em, split, modified);
                        } else {
                                int ret;

                                ret = add_extent_mapping(inode, split, modified);
                                /* Logic error, shouldn't happen. */
                                ASSERT(ret == 0);
                                if (WARN_ON(ret != 0) && modified)
                                        btrfs_set_inode_full_sync(inode);
                        }
                        free_extent_map(split);
                        split = NULL;
                }
remove_em:
                if (extent_map_in_tree(em)) {
                        /*
                         * If the extent map is still in the tree it means that
                         * either of the following is true:
                         *
                         * 1) It fits entirely in our range (doesn't end beyond
                         *    it or starts before it);
                         *
                         * 2) It starts before our range and/or ends after our
                         *    range, and we were not able to allocate the extent
                         *    maps for split operations, @split and @split2.
                         *
                         * If we are at case 2) then we just remove the entire
                         * extent map - this is fine since if anyone needs it to
                         * access the subranges outside our range, will just
                         * load it again from the subvolume tree's file extent
                         * item. However if the extent map was in the list of
                         * modified extents, then we must mark the inode for a
                         * full fsync, otherwise a fast fsync will miss this
                         * extent if it's new and needs to be logged.
                         */
                        if ((em->start < start || em_end > end) && modified) {
                                ASSERT(!split);
                                btrfs_set_inode_full_sync(inode);
                        }
                        remove_extent_mapping(inode, em);
                }

                /*
                 * Once for the tree reference (we replaced or removed the
                 * extent map from the tree).
                 */
                free_extent_map(em);
next:
                /* Once for us (for our lookup reference). */
                free_extent_map(em);

                em = next_em;
        }

        write_unlock(&em_tree->lock);

        free_extent_map(split);
        free_extent_map(split2);
}

/*
 * Replace a range in the inode's extent map tree with a new extent map.
 *
 * @inode:      The target inode.
 * @new_em:     The new extent map to add to the inode's extent map tree.
 * @modified:   Indicate if the new extent map should be added to the list of
 *              modified extents (for fast fsync tracking).
 *
 * Drops all the extent maps in the inode's extent map tree that intersect the
 * range of the new extent map and adds the new extent map to the tree.
 * The caller should have locked an appropriate file range in the inode's io
 * tree before calling this function.
 */
int btrfs_replace_extent_map_range(struct btrfs_inode *inode,
                                   struct extent_map *new_em,
                                   bool modified)
{
        const u64 end = new_em->start + new_em->len - 1;
        struct extent_map_tree *tree = &inode->extent_tree;
        int ret;

        ASSERT(!extent_map_in_tree(new_em));

        /*
         * The caller has locked an appropriate file range in the inode's io
         * tree, but getting -EEXIST when adding the new extent map can still
         * happen in case there are extents that partially cover the range, and
         * this is due to two tasks operating on different parts of the extent.
         * See commit 18e83ac75bfe67 ("Btrfs: fix unexpected EEXIST from
         * btrfs_get_extent") for an example and details.
         */
        do {
                btrfs_drop_extent_map_range(inode, new_em->start, end, false);
                write_lock(&tree->lock);
                ret = add_extent_mapping(inode, new_em, modified);
                write_unlock(&tree->lock);
        } while (ret == -EEXIST);

        return ret;
}

/*
 * Split off the first pre bytes from the extent_map at [start, start + len],
 * and set the block_start for it to new_logical.
 *
 * This function is used when an ordered_extent needs to be split.
 */
int split_extent_map(struct btrfs_inode *inode, u64 start, u64 len, u64 pre,
                     u64 new_logical)
{
        struct extent_map_tree *em_tree = &inode->extent_tree;
        struct extent_map *em;
        struct extent_map *split_pre = NULL;
        struct extent_map *split_mid = NULL;
        int ret = 0;
        unsigned long flags;

        ASSERT(pre != 0);
        ASSERT(pre < len);

        split_pre = alloc_extent_map();
        if (!split_pre)
                return -ENOMEM;
        split_mid = alloc_extent_map();
        if (!split_mid) {
                ret = -ENOMEM;
                goto out_free_pre;
        }

        lock_extent(&inode->io_tree, start, start + len - 1, NULL);
        write_lock(&em_tree->lock);
        em = lookup_extent_mapping(em_tree, start, len);
        if (!em) {
                ret = -EIO;
                goto out_unlock;
        }

        ASSERT(em->len == len);
        ASSERT(!extent_map_is_compressed(em));
        ASSERT(em->disk_bytenr < EXTENT_MAP_LAST_BYTE);
        ASSERT(em->flags & EXTENT_FLAG_PINNED);
        ASSERT(!(em->flags & EXTENT_FLAG_LOGGING));
        ASSERT(!list_empty(&em->list));

        flags = em->flags;
        em->flags &= ~EXTENT_FLAG_PINNED;

        /* First, replace the em with a new extent_map starting from * em->start */
        split_pre->start = em->start;
        split_pre->len = pre;
        split_pre->disk_bytenr = new_logical;
        split_pre->disk_num_bytes = split_pre->len;
        split_pre->offset = 0;
        split_pre->ram_bytes = split_pre->len;
        split_pre->flags = flags;
        split_pre->generation = em->generation;

        replace_extent_mapping(inode, em, split_pre, 1);

        /*
         * Now we only have an extent_map at:
         *     [em->start, em->start + pre]
         */

        /* Insert the middle extent_map. */
        split_mid->start = em->start + pre;
        split_mid->len = em->len - pre;
        split_mid->disk_bytenr = extent_map_block_start(em) + pre;
        split_mid->disk_num_bytes = split_mid->len;
        split_mid->offset = 0;
        split_mid->ram_bytes = split_mid->len;
        split_mid->flags = flags;
        split_mid->generation = em->generation;
        add_extent_mapping(inode, split_mid, 1);

        /* Once for us */
        free_extent_map(em);
        /* Once for the tree */
        free_extent_map(em);

out_unlock:
        write_unlock(&em_tree->lock);
        unlock_extent(&inode->io_tree, start, start + len - 1, NULL);
        free_extent_map(split_mid);
out_free_pre:
        free_extent_map(split_pre);
        return ret;
}

struct btrfs_em_shrink_ctx {
        long nr_to_scan;
        long scanned;
};

static long btrfs_scan_inode(struct btrfs_inode *inode, struct btrfs_em_shrink_ctx *ctx)
{
        struct btrfs_fs_info *fs_info = inode->root->fs_info;
        const u64 cur_fs_gen = btrfs_get_fs_generation(fs_info);
        struct extent_map_tree *tree = &inode->extent_tree;
        long nr_dropped = 0;
        struct rb_node *node;

        /*
         * Take the mmap lock so that we serialize with the inode logging phase
         * of fsync because we may need to set the full sync flag on the inode,
         * in case we have to remove extent maps in the tree's list of modified
         * extents. If we set the full sync flag in the inode while an fsync is
         * in progress, we may risk missing new extents because before the flag
         * is set, fsync decides to only wait for writeback to complete and then
         * during inode logging it sees the flag set and uses the subvolume tree
         * to find new extents, which may not be there yet because ordered
         * extents haven't completed yet.
         *
         * We also do a try lock because otherwise we could deadlock. This is
         * because the shrinker for this filesystem may be invoked while we are
         * in a path that is holding the mmap lock in write mode. For example in
         * a reflink operation while COWing an extent buffer, when allocating
         * pages for a new extent buffer and under memory pressure, the shrinker
         * may be invoked, and therefore we would deadlock by attempting to read
         * lock the mmap lock while we are holding already a write lock on it.
         */
        if (!down_read_trylock(&inode->i_mmap_lock))
                return 0;

        /*
         * We want to be fast so if the lock is busy we don't want to spend time
         * waiting for it - either some task is about to do IO for the inode or
         * we may have another task shrinking extent maps, here in this code, so
         * skip this inode.
         */
        if (!write_trylock(&tree->lock)) {
                up_read(&inode->i_mmap_lock);
                return 0;
        }

        node = rb_first(&tree->root);
        while (node) {
                struct rb_node *next = rb_next(node);
                struct extent_map *em;

                em = rb_entry(node, struct extent_map, rb_node);
                ctx->scanned++;

                if (em->flags & EXTENT_FLAG_PINNED)
                        goto next;

                /*
                 * If the inode is in the list of modified extents (new) and its
                 * generation is the same (or is greater than) the current fs
                 * generation, it means it was not yet persisted so we have to
                 * set the full sync flag so that the next fsync will not miss
                 * it.
                 */
                if (!list_empty(&em->list) && em->generation >= cur_fs_gen)
                        btrfs_set_inode_full_sync(inode);

                remove_extent_mapping(inode, em);
                trace_btrfs_extent_map_shrinker_remove_em(inode, em);
                /* Drop the reference for the tree. */
                free_extent_map(em);
                nr_dropped++;
next:
                if (ctx->scanned >= ctx->nr_to_scan)
                        break;

                /*
                 * Stop if we need to reschedule or there's contention on the
                 * lock. This is to avoid slowing other tasks trying to take the
                 * lock.
                 */
                if (need_resched() || rwlock_needbreak(&tree->lock) ||
                    btrfs_fs_closing(fs_info))
                        break;
                node = next;
        }
        write_unlock(&tree->lock);
        up_read(&inode->i_mmap_lock);

        return nr_dropped;
}

static long btrfs_scan_root(struct btrfs_root *root, struct btrfs_em_shrink_ctx *ctx)
{
        struct btrfs_fs_info *fs_info = root->fs_info;
        struct btrfs_inode *inode;
        long nr_dropped = 0;
        u64 min_ino = fs_info->em_shrinker_last_ino + 1;

        inode = btrfs_find_first_inode(root, min_ino);
        while (inode) {
                nr_dropped += btrfs_scan_inode(inode, ctx);

                min_ino = btrfs_ino(inode) + 1;
                fs_info->em_shrinker_last_ino = btrfs_ino(inode);
                btrfs_add_delayed_iput(inode);

                if (ctx->scanned >= ctx->nr_to_scan ||
                    btrfs_fs_closing(inode->root->fs_info))
                        break;

                cond_resched();

                inode = btrfs_find_first_inode(root, min_ino);
        }

        if (inode) {
                /*
                 * There are still inodes in this root or we happened to process
                 * the last one and reached the scan limit. In either case set
                 * the current root to this one, so we'll resume from the next
                 * inode if there is one or we will find out this was the last
                 * one and move to the next root.
                 */
                fs_info->em_shrinker_last_root = btrfs_root_id(root);
        } else {
                /*
                 * No more inodes in this root, set extent_map_shrinker_last_ino to 0 so
                 * that when processing the next root we start from its first inode.
                 */
                fs_info->em_shrinker_last_ino = 0;
                fs_info->em_shrinker_last_root = btrfs_root_id(root) + 1;
        }

        return nr_dropped;
}

static void btrfs_extent_map_shrinker_worker(struct work_struct *work)
{
        struct btrfs_fs_info *fs_info;
        struct btrfs_em_shrink_ctx ctx;
        u64 start_root_id;
        u64 next_root_id;
        bool cycled = false;
        long nr_dropped = 0;

        fs_info = container_of(work, struct btrfs_fs_info, em_shrinker_work);

        ctx.scanned = 0;
        ctx.nr_to_scan = atomic64_read(&fs_info->em_shrinker_nr_to_scan);

        start_root_id = fs_info->em_shrinker_last_root;
        next_root_id = fs_info->em_shrinker_last_root;

        if (trace_btrfs_extent_map_shrinker_scan_enter_enabled()) {
                s64 nr = percpu_counter_sum_positive(&fs_info->evictable_extent_maps);

                trace_btrfs_extent_map_shrinker_scan_enter(fs_info, nr);
        }

        while (ctx.scanned < ctx.nr_to_scan && !btrfs_fs_closing(fs_info)) {
                struct btrfs_root *root;
                unsigned long count;

                cond_resched();

                spin_lock(&fs_info->fs_roots_radix_lock);
                count = radix_tree_gang_lookup(&fs_info->fs_roots_radix,
                                               (void **)&root,
                                               (unsigned long)next_root_id, 1);
                if (count == 0) {
                        spin_unlock(&fs_info->fs_roots_radix_lock);
                        if (start_root_id > 0 && !cycled) {
                                next_root_id = 0;
                                fs_info->em_shrinker_last_root = 0;
                                fs_info->em_shrinker_last_ino = 0;
                                cycled = true;
                                continue;
                        }
                        break;
                }
                next_root_id = btrfs_root_id(root) + 1;
                root = btrfs_grab_root(root);
                spin_unlock(&fs_info->fs_roots_radix_lock);

                if (!root)
                        continue;

                if (is_fstree(btrfs_root_id(root)))
                        nr_dropped += btrfs_scan_root(root, &ctx);

                btrfs_put_root(root);
        }

        if (trace_btrfs_extent_map_shrinker_scan_exit_enabled()) {
                s64 nr = percpu_counter_sum_positive(&fs_info->evictable_extent_maps);

                trace_btrfs_extent_map_shrinker_scan_exit(fs_info, nr_dropped, nr);
        }

        atomic64_set(&fs_info->em_shrinker_nr_to_scan, 0);
}

void btrfs_free_extent_maps(struct btrfs_fs_info *fs_info, long nr_to_scan)
{
        /*
         * Do nothing if the shrinker is already running. In case of high memory
         * pressure we can have a lot of tasks calling us and all passing the
         * same nr_to_scan value, but in reality we may need only to free
         * nr_to_scan extent maps (or less). In case we need to free more than
         * that, we will be called again by the fs shrinker, so no worries about
         * not doing enough work to reclaim memory from extent maps.
         * We can also be repeatedly called with the same nr_to_scan value
         * simply because the shrinker runs asynchronously and multiple calls
         * to this function are made before the shrinker does enough progress.
         *
         * That's why we set the atomic counter to nr_to_scan only if its
         * current value is zero, instead of incrementing the counter by
         * nr_to_scan.
         */
        if (atomic64_cmpxchg(&fs_info->em_shrinker_nr_to_scan, 0, nr_to_scan) != 0)
                return;

        queue_work(system_unbound_wq, &fs_info->em_shrinker_work);
}

void btrfs_init_extent_map_shrinker_work(struct btrfs_fs_info *fs_info)
{
        atomic64_set(&fs_info->em_shrinker_nr_to_scan, 0);
        INIT_WORK(&fs_info->em_shrinker_work, btrfs_extent_map_shrinker_worker);
}