// SPDX-License-Identifier: GPL-2.0

#include "misc.h"
#include "ctree.h"
#include "space-info.h"
#include "sysfs.h"
#include "volumes.h"
#include "free-space-cache.h"
#include "ordered-data.h"
#include "transaction.h"
#include "block-group.h"

/*
 * HOW DOES SPACE RESERVATION WORK
 *
 * If you want to know about delalloc specifically, there is a separate comment
 * for that with the delalloc code.  This comment is about how the whole system
 * works generally.
 *
 * BASIC CONCEPTS
 *
 *   1) space_info.  This is the ultimate arbiter of how much space we can use.
 *   There's a description of the bytes_ fields with the struct declaration,
 *   refer to that for specifics on each field.  Suffice it to say that for
 *   reservations we care about total_bytes - SUM(space_info->bytes_) when
 *   determining if there is space to make an allocation.  There is a space_info
 *   for METADATA, SYSTEM, and DATA areas.
 *
 *   2) block_rsv's.  These are basically buckets for every different type of
 *   metadata reservation we have.  You can see the comment in the block_rsv
 *   code on the rules for each type, but generally block_rsv->reserved is how
 *   much space is accounted for in space_info->bytes_may_use.
 *
 *   3) btrfs_calc*_size.  These are the worst case calculations we used based
 *   on the number of items we will want to modify.  We have one for changing
 *   items, and one for inserting new items.  Generally we use these helpers to
 *   determine the size of the block reserves, and then use the actual bytes
 *   values to adjust the space_info counters.
 *
 * MAKING RESERVATIONS, THE NORMAL CASE
 *
 *   We call into either btrfs_reserve_data_bytes() or
 *   btrfs_reserve_metadata_bytes(), depending on which we're looking for, with
 *   num_bytes we want to reserve.
 *
 *   ->reserve
 *     space_info->bytes_may_reserve += num_bytes
 *
 *   ->extent allocation
 *     Call btrfs_add_reserved_bytes() which does
 *     space_info->bytes_may_reserve -= num_bytes
 *     space_info->bytes_reserved += extent_bytes
 *
 *   ->insert reference
 *     Call btrfs_update_block_group() which does
 *     space_info->bytes_reserved -= extent_bytes
 *     space_info->bytes_used += extent_bytes
 *
 * MAKING RESERVATIONS, FLUSHING NORMALLY (non-priority)
 *
 *   Assume we are unable to simply make the reservation because we do not have
 *   enough space
 *
 *   -> __reserve_bytes
 *     create a reserve_ticket with ->bytes set to our reservation, add it to
 *     the tail of space_info->tickets, kick async flush thread
 *
 *   ->handle_reserve_ticket
 *     wait on ticket->wait for ->bytes to be reduced to 0, or ->error to be set
 *     on the ticket.
 *
 *   -> btrfs_async_reclaim_metadata_space/btrfs_async_reclaim_data_space
 *     Flushes various things attempting to free up space.
 *
 *   -> btrfs_try_granting_tickets()
 *     This is called by anything that either subtracts space from
 *     space_info->bytes_may_use, ->bytes_pinned, etc, or adds to the
 *     space_info->total_bytes.  This loops through the ->priority_tickets and
 *     then the ->tickets list checking to see if the reservation can be
 *     completed.  If it can the space is added to space_info->bytes_may_use and
 *     the ticket is woken up.
 *
 *   -> ticket wakeup
 *     Check if ->bytes == 0, if it does we got our reservation and we can carry
 *     on, if not return the appropriate error (ENOSPC, but can be EINTR if we
 *     were interrupted.)
 *
 * MAKING RESERVATIONS, FLUSHING HIGH PRIORITY
 *
 *   Same as the above, except we add ourselves to the
 *   space_info->priority_tickets, and we do not use ticket->wait, we simply
 *   call flush_space() ourselves for the states that are safe for us to call
 *   without deadlocking and hope for the best.
 *
 * THE FLUSHING STATES
 *
 *   Generally speaking we will have two cases for each state, a "nice" state
 *   and a "ALL THE THINGS" state.  In btrfs we delay a lot of work in order to
 *   reduce the locking over head on the various trees, and even to keep from
 *   doing any work at all in the case of delayed refs.  Each of these delayed
 *   things however hold reservations, and so letting them run allows us to
 *   reclaim space so we can make new reservations.
 *
 *   FLUSH_DELAYED_ITEMS
 *     Every inode has a delayed item to update the inode.  Take a simple write
 *     for example, we would update the inode item at write time to update the
 *     mtime, and then again at finish_ordered_io() time in order to update the
 *     isize or bytes.  We keep these delayed items to coalesce these operations
 *     into a single operation done on demand.  These are an easy way to reclaim
 *     metadata space.
 *
 *   FLUSH_DELALLOC
 *     Look at the delalloc comment to get an idea of how much space is reserved
 *     for delayed allocation.  We can reclaim some of this space simply by
 *     running delalloc, but usually we need to wait for ordered extents to
 *     reclaim the bulk of this space.
 *
 *   FLUSH_DELAYED_REFS
 *     We have a block reserve for the outstanding delayed refs space, and every
 *     delayed ref operation holds a reservation.  Running these is a quick way
 *     to reclaim space, but we want to hold this until the end because COW can
 *     churn a lot and we can avoid making some extent tree modifications if we
 *     are able to delay for as long as possible.
 *
 *   ALLOC_CHUNK
 *     We will skip this the first time through space reservation, because of
 *     overcommit and we don't want to have a lot of useless metadata space when
 *     our worst case reservations will likely never come true.
 *
 *   RUN_DELAYED_IPUTS
 *     If we're freeing inodes we're likely freeing checksums, file extent
 *     items, and extent tree items.  Loads of space could be freed up by these
 *     operations, however they won't be usable until the transaction commits.
 *
 *   COMMIT_TRANS
 *     This will commit the transaction.  Historically we had a lot of logic
 *     surrounding whether or not we'd commit the transaction, but this waits born
 *     out of a pre-tickets era where we could end up committing the transaction
 *     thousands of times in a row without making progress.  Now thanks to our
 *     ticketing system we know if we're not making progress and can error
 *     everybody out after a few commits rather than burning the disk hoping for
 *     a different answer.
 *
 * OVERCOMMIT
 *
 *   Because we hold so many reservations for metadata we will allow you to
 *   reserve more space than is currently free in the currently allocate
 *   metadata space.  This only happens with metadata, data does not allow
 *   overcommitting.
 *
 *   You can see the current logic for when we allow overcommit in
 *   btrfs_can_overcommit(), but it only applies to unallocated space.  If there
 *   is no unallocated space to be had, all reservations are kept within the
 *   free space in the allocated metadata chunks.
 *
 *   Because of overcommitting, you generally want to use the
 *   btrfs_can_overcommit() logic for metadata allocations, as it does the right
 *   thing with or without extra unallocated space.
 */

u64 __pure btrfs_space_info_used(struct btrfs_space_info *s_info,
                          bool may_use_included)
{
        ASSERT(s_info);
        return s_info->bytes_used + s_info->bytes_reserved +
                s_info->bytes_pinned + s_info->bytes_readonly +
                s_info->bytes_zone_unusable +
                (may_use_included ? s_info->bytes_may_use : 0);
}

/*
 * after adding space to the filesystem, we need to clear the full flags
 * on all the space infos.
 */
void btrfs_clear_space_info_full(struct btrfs_fs_info *info)
{
        struct list_head *head = &info->space_info;
        struct btrfs_space_info *found;

        list_for_each_entry(found, head, list)
                found->full = 0;
}

/*
 * Block groups with more than this value (percents) of unusable space will be
 * scheduled for background reclaim.
 */
#define BTRFS_DEFAULT_ZONED_RECLAIM_THRESH                      (75)

static int create_space_info(struct btrfs_fs_info *info, u64 flags)
{

        struct btrfs_space_info *space_info;
        int i;
        int ret;

        space_info = kzalloc(sizeof(*space_info), GFP_NOFS);
        if (!space_info)
                return -ENOMEM;

        for (i = 0; i < BTRFS_NR_RAID_TYPES; i++)
                INIT_LIST_HEAD(&space_info->block_groups[i]);
        init_rwsem(&space_info->groups_sem);
        spin_lock_init(&space_info->lock);
        space_info->flags = flags & BTRFS_BLOCK_GROUP_TYPE_MASK;
        space_info->force_alloc = CHUNK_ALLOC_NO_FORCE;
        INIT_LIST_HEAD(&space_info->ro_bgs);
        INIT_LIST_HEAD(&space_info->tickets);
        INIT_LIST_HEAD(&space_info->priority_tickets);
        space_info->clamp = 1;

        if (btrfs_is_zoned(info))
                space_info->bg_reclaim_threshold = BTRFS_DEFAULT_ZONED_RECLAIM_THRESH;

        ret = btrfs_sysfs_add_space_info_type(info, space_info);
        if (ret)
                return ret;

        list_add(&space_info->list, &info->space_info);
        if (flags & BTRFS_BLOCK_GROUP_DATA)
                info->data_sinfo = space_info;

        return ret;
}

int btrfs_init_space_info(struct btrfs_fs_info *fs_info)
{
        struct btrfs_super_block *disk_super;
        u64 features;
        u64 flags;
        int mixed = 0;
        int ret;

        disk_super = fs_info->super_copy;
        if (!btrfs_super_root(disk_super))
                return -EINVAL;

        features = btrfs_super_incompat_flags(disk_super);
        if (features & BTRFS_FEATURE_INCOMPAT_MIXED_GROUPS)
                mixed = 1;

        flags = BTRFS_BLOCK_GROUP_SYSTEM;
        ret = create_space_info(fs_info, flags);
        if (ret)
                goto out;

        if (mixed) {
                flags = BTRFS_BLOCK_GROUP_METADATA | BTRFS_BLOCK_GROUP_DATA;
                ret = create_space_info(fs_info, flags);
        } else {
                flags = BTRFS_BLOCK_GROUP_METADATA;
                ret = create_space_info(fs_info, flags);
                if (ret)
                        goto out;

                flags = BTRFS_BLOCK_GROUP_DATA;
                ret = create_space_info(fs_info, flags);
        }
out:
        return ret;
}

void btrfs_update_space_info(struct btrfs_fs_info *info, u64 flags,
                             u64 total_bytes, u64 bytes_used,
                             u64 bytes_readonly, u64 bytes_zone_unusable,
                             struct btrfs_space_info **space_info)
{
        struct btrfs_space_info *found;
        int factor;

        factor = btrfs_bg_type_to_factor(flags);

        found = btrfs_find_space_info(info, flags);
        ASSERT(found);
        spin_lock(&found->lock);
        found->total_bytes += total_bytes;
        found->disk_total += total_bytes * factor;
        found->bytes_used += bytes_used;
        found->disk_used += bytes_used * factor;
        found->bytes_readonly += bytes_readonly;
        found->bytes_zone_unusable += bytes_zone_unusable;
        if (total_bytes > 0)
                found->full = 0;
        btrfs_try_granting_tickets(info, found);
        spin_unlock(&found->lock);
        *space_info = found;
}

struct btrfs_space_info *btrfs_find_space_info(struct btrfs_fs_info *info,
                                               u64 flags)
{
        struct list_head *head = &info->space_info;
        struct btrfs_space_info *found;

        flags &= BTRFS_BLOCK_GROUP_TYPE_MASK;

        list_for_each_entry(found, head, list) {
                if (found->flags & flags)
                        return found;
        }
        return NULL;
}

static u64 calc_available_free_space(struct btrfs_fs_info *fs_info,
                          struct btrfs_space_info *space_info,
                          enum btrfs_reserve_flush_enum flush)
{
        u64 profile;
        u64 avail;
        int factor;

        if (space_info->flags & BTRFS_BLOCK_GROUP_SYSTEM)
                profile = btrfs_system_alloc_profile(fs_info);
        else
                profile = btrfs_metadata_alloc_profile(fs_info);

        avail = atomic64_read(&fs_info->free_chunk_space);

        /*
         * If we have dup, raid1 or raid10 then only half of the free
         * space is actually usable.  For raid56, the space info used
         * doesn't include the parity drive, so we don't have to
         * change the math
         */
        factor = btrfs_bg_type_to_factor(profile);
        avail = div_u64(avail, factor);

        /*
         * If we aren't flushing all things, let us overcommit up to
         * 1/2th of the space. If we can flush, don't let us overcommit
         * too much, let it overcommit up to 1/8 of the space.
         */
        if (flush == BTRFS_RESERVE_FLUSH_ALL)
                avail >>= 3;
        else
                avail >>= 1;
        return avail;
}

int btrfs_can_overcommit(struct btrfs_fs_info *fs_info,
                         struct btrfs_space_info *space_info, u64 bytes,
                         enum btrfs_reserve_flush_enum flush)
{
        u64 avail;
        u64 used;

        /* Don't overcommit when in mixed mode */
        if (space_info->flags & BTRFS_BLOCK_GROUP_DATA)
                return 0;

        used = btrfs_space_info_used(space_info, true);
        avail = calc_available_free_space(fs_info, space_info, flush);

        if (used + bytes < space_info->total_bytes + avail)
                return 1;
        return 0;
}

static void remove_ticket(struct btrfs_space_info *space_info,
                          struct reserve_ticket *ticket)
{
        if (!list_empty(&ticket->list)) {
                list_del_init(&ticket->list);
                ASSERT(space_info->reclaim_size >= ticket->bytes);
                space_info->reclaim_size -= ticket->bytes;
        }
}

/*
 * This is for space we already have accounted in space_info->bytes_may_use, so
 * basically when we're returning space from block_rsv's.
 */
void btrfs_try_granting_tickets(struct btrfs_fs_info *fs_info,
                                struct btrfs_space_info *space_info)
{
        struct list_head *head;
        enum btrfs_reserve_flush_enum flush = BTRFS_RESERVE_NO_FLUSH;

        lockdep_assert_held(&space_info->lock);

        head = &space_info->priority_tickets;
again:
        while (!list_empty(head)) {
                struct reserve_ticket *ticket;
                u64 used = btrfs_space_info_used(space_info, true);

                ticket = list_first_entry(head, struct reserve_ticket, list);

                /* Check and see if our ticket can be satisfied now. */
                if ((used + ticket->bytes <= space_info->total_bytes) ||
                    btrfs_can_overcommit(fs_info, space_info, ticket->bytes,
                                         flush)) {
                        btrfs_space_info_update_bytes_may_use(fs_info,
                                                              space_info,
                                                              ticket->bytes);
                        remove_ticket(space_info, ticket);
                        ticket->bytes = 0;
                        space_info->tickets_id++;
                        wake_up(&ticket->wait);
                } else {
                        break;
                }
        }

        if (head == &space_info->priority_tickets) {
                head = &space_info->tickets;
                flush = BTRFS_RESERVE_FLUSH_ALL;
                goto again;
        }
}

#define DUMP_BLOCK_RSV(fs_info, rsv_name)                               \
do {                                                                    \
        struct btrfs_block_rsv *__rsv = &(fs_info)->rsv_name;           \
        spin_lock(&__rsv->lock);                                        \
        btrfs_info(fs_info, #rsv_name ": size %llu reserved %llu",      \
                   __rsv->size, __rsv->reserved);                       \
        spin_unlock(&__rsv->lock);                                      \
} while (0)

static void __btrfs_dump_space_info(struct btrfs_fs_info *fs_info,
                                    struct btrfs_space_info *info)
{
        lockdep_assert_held(&info->lock);

        /* The free space could be negative in case of overcommit */
        btrfs_info(fs_info, "space_info %llu has %lld free, is %sfull",
                   info->flags,
                   (s64)(info->total_bytes - btrfs_space_info_used(info, true)),
                   info->full ? "" : "not ");
        btrfs_info(fs_info,
                "space_info total=%llu, used=%llu, pinned=%llu, reserved=%llu, may_use=%llu, readonly=%llu zone_unusable=%llu",
                info->total_bytes, info->bytes_used, info->bytes_pinned,
                info->bytes_reserved, info->bytes_may_use,
                info->bytes_readonly, info->bytes_zone_unusable);

        DUMP_BLOCK_RSV(fs_info, global_block_rsv);
        DUMP_BLOCK_RSV(fs_info, trans_block_rsv);
        DUMP_BLOCK_RSV(fs_info, chunk_block_rsv);
        DUMP_BLOCK_RSV(fs_info, delayed_block_rsv);
        DUMP_BLOCK_RSV(fs_info, delayed_refs_rsv);

}

void btrfs_dump_space_info(struct btrfs_fs_info *fs_info,
                           struct btrfs_space_info *info, u64 bytes,
                           int dump_block_groups)
{
        struct btrfs_block_group *cache;
        int index = 0;

        spin_lock(&info->lock);
        __btrfs_dump_space_info(fs_info, info);
        spin_unlock(&info->lock);

        if (!dump_block_groups)
                return;

        down_read(&info->groups_sem);
again:
        list_for_each_entry(cache, &info->block_groups[index], list) {
                spin_lock(&cache->lock);
                btrfs_info(fs_info,
                        "block group %llu has %llu bytes, %llu used %llu pinned %llu reserved %llu zone_unusable %s",
                        cache->start, cache->length, cache->used, cache->pinned,
                        cache->reserved, cache->zone_unusable,
                        cache->ro ? "[readonly]" : "");
                spin_unlock(&cache->lock);
                btrfs_dump_free_space(cache, bytes);
        }
        if (++index < BTRFS_NR_RAID_TYPES)
                goto again;
        up_read(&info->groups_sem);
}

static inline u64 calc_reclaim_items_nr(struct btrfs_fs_info *fs_info,
                                        u64 to_reclaim)
{
        u64 bytes;
        u64 nr;

        bytes = btrfs_calc_insert_metadata_size(fs_info, 1);
        nr = div64_u64(to_reclaim, bytes);
        if (!nr)
                nr = 1;
        return nr;
}

#define EXTENT_SIZE_PER_ITEM    SZ_256K

/*
 * shrink metadata reservation for delalloc
 */
static void shrink_delalloc(struct btrfs_fs_info *fs_info,
                            struct btrfs_space_info *space_info,
                            u64 to_reclaim, bool wait_ordered,
                            bool for_preempt)
{
        struct btrfs_trans_handle *trans;
        u64 delalloc_bytes;
        u64 ordered_bytes;
        u64 items;
        long time_left;
        int loops;

        delalloc_bytes = percpu_counter_sum_positive(&fs_info->delalloc_bytes);
        ordered_bytes = percpu_counter_sum_positive(&fs_info->ordered_bytes);
        if (delalloc_bytes == 0 && ordered_bytes == 0)
                return;

        /* Calc the number of the pages we need flush for space reservation */
        if (to_reclaim == U64_MAX) {
                items = U64_MAX;
        } else {
                /*
                 * to_reclaim is set to however much metadata we need to
                 * reclaim, but reclaiming that much data doesn't really track
                 * exactly.  What we really want to do is reclaim full inode's
                 * worth of reservations, however that's not available to us
                 * here.  We will take a fraction of the delalloc bytes for our
                 * flushing loops and hope for the best.  Delalloc will expand
                 * the amount we write to cover an entire dirty extent, which
                 * will reclaim the metadata reservation for that range.  If
                 * it's not enough subsequent flush stages will be more
                 * aggressive.
                 */
                to_reclaim = max(to_reclaim, delalloc_bytes >> 3);
                items = calc_reclaim_items_nr(fs_info, to_reclaim) * 2;
        }

        trans = current->journal_info;

        /*
         * If we are doing more ordered than delalloc we need to just wait on
         * ordered extents, otherwise we'll waste time trying to flush delalloc
         * that likely won't give us the space back we need.
         */
        if (ordered_bytes > delalloc_bytes && !for_preempt)
                wait_ordered = true;

        loops = 0;
        while ((delalloc_bytes || ordered_bytes) && loops < 3) {
                u64 temp = min(delalloc_bytes, to_reclaim) >> PAGE_SHIFT;
                long nr_pages = min_t(u64, temp, LONG_MAX);
                int async_pages;

                btrfs_start_delalloc_roots(fs_info, nr_pages, true);

                /*
                 * We need to make sure any outstanding async pages are now
                 * processed before we continue.  This is because things like
                 * sync_inode() try to be smart and skip writing if the inode is
                 * marked clean.  We don't use filemap_fwrite for flushing
                 * because we want to control how many pages we write out at a
                 * time, thus this is the only safe way to make sure we've
                 * waited for outstanding compressed workers to have started
                 * their jobs and thus have ordered extents set up properly.
                 *
                 * This exists because we do not want to wait for each
                 * individual inode to finish its async work, we simply want to
                 * start the IO on everybody, and then come back here and wait
                 * for all of the async work to catch up.  Once we're done with
                 * that we know we'll have ordered extents for everything and we
                 * can decide if we wait for that or not.
                 *
                 * If we choose to replace this in the future, make absolutely
                 * sure that the proper waiting is being done in the async case,
                 * as there have been bugs in that area before.
                 */
                async_pages = atomic_read(&fs_info->async_delalloc_pages);
                if (!async_pages)
                        goto skip_async;

                /*
                 * We don't want to wait forever, if we wrote less pages in this
                 * loop than we have outstanding, only wait for that number of
                 * pages, otherwise we can wait for all async pages to finish
                 * before continuing.
                 */
                if (async_pages > nr_pages)
                        async_pages -= nr_pages;
                else
                        async_pages = 0;
                wait_event(fs_info->async_submit_wait,
                           atomic_read(&fs_info->async_delalloc_pages) <=
                           async_pages);
skip_async:
                loops++;
                if (wait_ordered && !trans) {
                        btrfs_wait_ordered_roots(fs_info, items, 0, (u64)-1);
                } else {
                        time_left = schedule_timeout_killable(1);
                        if (time_left)
                                break;
                }

                /*
                 * If we are for preemption we just want a one-shot of delalloc
                 * flushing so we can stop flushing if we decide we don't need
                 * to anymore.
                 */
                if (for_preempt)
                        break;

                spin_lock(&space_info->lock);
                if (list_empty(&space_info->tickets) &&
                    list_empty(&space_info->priority_tickets)) {
                        spin_unlock(&space_info->lock);
                        break;
                }
                spin_unlock(&space_info->lock);

                delalloc_bytes = percpu_counter_sum_positive(
                                                &fs_info->delalloc_bytes);
                ordered_bytes = percpu_counter_sum_positive(
                                                &fs_info->ordered_bytes);
        }
}

/*
 * Try to flush some data based on policy set by @state. This is only advisory
 * and may fail for various reasons. The caller is supposed to examine the
 * state of @space_info to detect the outcome.
 */
static void flush_space(struct btrfs_fs_info *fs_info,
                       struct btrfs_space_info *space_info, u64 num_bytes,
                       enum btrfs_flush_state state, bool for_preempt)
{
        struct btrfs_root *root = fs_info->tree_root;
        struct btrfs_trans_handle *trans;
        int nr;
        int ret = 0;

        switch (state) {
        case FLUSH_DELAYED_ITEMS_NR:
        case FLUSH_DELAYED_ITEMS:
                if (state == FLUSH_DELAYED_ITEMS_NR)
                        nr = calc_reclaim_items_nr(fs_info, num_bytes) * 2;
                else
                        nr = -1;

                trans = btrfs_join_transaction(root);
                if (IS_ERR(trans)) {
                        ret = PTR_ERR(trans);
                        break;
                }
                ret = btrfs_run_delayed_items_nr(trans, nr);
                btrfs_end_transaction(trans);
                break;
        case FLUSH_DELALLOC:
        case FLUSH_DELALLOC_WAIT:
        case FLUSH_DELALLOC_FULL:
                if (state == FLUSH_DELALLOC_FULL)
                        num_bytes = U64_MAX;
                shrink_delalloc(fs_info, space_info, num_bytes,
                                state != FLUSH_DELALLOC, for_preempt);
                break;
        case FLUSH_DELAYED_REFS_NR:
        case FLUSH_DELAYED_REFS:
                trans = btrfs_join_transaction(root);
                if (IS_ERR(trans)) {
                        ret = PTR_ERR(trans);
                        break;
                }
                if (state == FLUSH_DELAYED_REFS_NR)
                        nr = calc_reclaim_items_nr(fs_info, num_bytes);
                else
                        nr = 0;
                btrfs_run_delayed_refs(trans, nr);
                btrfs_end_transaction(trans);
                break;
        case ALLOC_CHUNK:
        case ALLOC_CHUNK_FORCE:
                trans = btrfs_join_transaction(root);
                if (IS_ERR(trans)) {
                        ret = PTR_ERR(trans);
                        break;
                }
                ret = btrfs_chunk_alloc(trans,
                                btrfs_get_alloc_profile(fs_info, space_info->flags),
                                (state == ALLOC_CHUNK) ? CHUNK_ALLOC_NO_FORCE :
                                        CHUNK_ALLOC_FORCE);
                btrfs_end_transaction(trans);
                if (ret > 0 || ret == -ENOSPC)
                        ret = 0;
                break;
        case RUN_DELAYED_IPUTS:
                /*
                 * If we have pending delayed iputs then we could free up a
                 * bunch of pinned space, so make sure we run the iputs before
                 * we do our pinned bytes check below.
                 */
                btrfs_run_delayed_iputs(fs_info);
                btrfs_wait_on_delayed_iputs(fs_info);
                break;
        case COMMIT_TRANS:
                ASSERT(current->journal_info == NULL);
                trans = btrfs_join_transaction(root);
                if (IS_ERR(trans)) {
                        ret = PTR_ERR(trans);
                        break;
                }
                ret = btrfs_commit_transaction(trans);
                break;
        default:
                ret = -ENOSPC;
                break;
        }

        trace_btrfs_flush_space(fs_info, space_info->flags, num_bytes, state,
                                ret, for_preempt);
        return;
}

static inline u64
btrfs_calc_reclaim_metadata_size(struct btrfs_fs_info *fs_info,
                                 struct btrfs_space_info *space_info)
{
        u64 used;
        u64 avail;
        u64 to_reclaim = space_info->reclaim_size;

        lockdep_assert_held(&space_info->lock);

        avail = calc_available_free_space(fs_info, space_info,
                                          BTRFS_RESERVE_FLUSH_ALL);
        used = btrfs_space_info_used(space_info, true);

        /*
         * We may be flushing because suddenly we have less space than we had
         * before, and now we're well over-committed based on our current free
         * space.  If that's the case add in our overage so we make sure to put
         * appropriate pressure on the flushing state machine.
         */
        if (space_info->total_bytes + avail < used)
                to_reclaim += used - (space_info->total_bytes + avail);

        return to_reclaim;
}

static bool need_preemptive_reclaim(struct btrfs_fs_info *fs_info,
                                    struct btrfs_space_info *space_info)
{
        u64 global_rsv_size = fs_info->global_block_rsv.reserved;
        u64 ordered, delalloc;
        u64 thresh = div_factor_fine(space_info->total_bytes, 90);
        u64 used;

        lockdep_assert_held(&space_info->lock);

        /* If we're just plain full then async reclaim just slows us down. */
        if ((space_info->bytes_used + space_info->bytes_reserved +
             global_rsv_size) >= thresh)
                return false;

        used = space_info->bytes_may_use + space_info->bytes_pinned;

        /* The total flushable belongs to the global rsv, don't flush. */
        if (global_rsv_size >= used)
                return false;

        /*
         * 128MiB is 1/4 of the maximum global rsv size.  If we have less than
         * that devoted to other reservations then there's no sense in flushing,
         * we don't have a lot of things that need flushing.
         */
        if (used - global_rsv_size <= SZ_128M)
                return false;

        /*
         * We have tickets queued, bail so we don't compete with the async
         * flushers.
         */
        if (space_info->reclaim_size)
                return false;

        /*
         * If we have over half of the free space occupied by reservations or
         * pinned then we want to start flushing.
         *
         * We do not do the traditional thing here, which is to say
         *
         *   if (used >= ((total_bytes + avail) / 2))
         *     return 1;
         *
         * because this doesn't quite work how we want.  If we had more than 50%
         * of the space_info used by bytes_used and we had 0 available we'd just
         * constantly run the background flusher.  Instead we want it to kick in
         * if our reclaimable space exceeds our clamped free space.
         *
         * Our clamping range is 2^1 -> 2^8.  Practically speaking that means
         * the following:
         *
         * Amount of RAM        Minimum threshold       Maximum threshold
         *
         *        256GiB                     1GiB                  128GiB
         *        128GiB                   512MiB                   64GiB
         *         64GiB                   256MiB                   32GiB
         *         32GiB                   128MiB                   16GiB
         *         16GiB                    64MiB                    8GiB
         *
         * These are the range our thresholds will fall in, corresponding to how
         * much delalloc we need for the background flusher to kick in.
         */

        thresh = calc_available_free_space(fs_info, space_info,
                                           BTRFS_RESERVE_FLUSH_ALL);
        used = space_info->bytes_used + space_info->bytes_reserved +
               space_info->bytes_readonly + global_rsv_size;
        if (used < space_info->total_bytes)
                thresh += space_info->total_bytes - used;
        thresh >>= space_info->clamp;

        used = space_info->bytes_pinned;

        /*
         * If we have more ordered bytes than delalloc bytes then we're either
         * doing a lot of DIO, or we simply don't have a lot of delalloc waiting
         * around.  Preemptive flushing is only useful in that it can free up
         * space before tickets need to wait for things to finish.  In the case
         * of ordered extents, preemptively waiting on ordered extents gets us
         * nothing, if our reservations are tied up in ordered extents we'll
         * simply have to slow down writers by forcing them to wait on ordered
         * extents.
         *
         * In the case that ordered is larger than delalloc, only include the
         * block reserves that we would actually be able to directly reclaim
         * from.  In this case if we're heavy on metadata operations this will
         * clearly be heavy enough to warrant preemptive flushing.  In the case
         * of heavy DIO or ordered reservations, preemptive flushing will just
         * waste time and cause us to slow down.
         *
         * We want to make sure we truly are maxed out on ordered however, so
         * cut ordered in half, and if it's still higher than delalloc then we
         * can keep flushing.  This is to avoid the case where we start
         * flushing, and now delalloc == ordered and we stop preemptively
         * flushing when we could still have several gigs of delalloc to flush.
         */
        ordered = percpu_counter_read_positive(&fs_info->ordered_bytes) >> 1;
        delalloc = percpu_counter_read_positive(&fs_info->delalloc_bytes);
        if (ordered >= delalloc)
                used += fs_info->delayed_refs_rsv.reserved +
                        fs_info->delayed_block_rsv.reserved;
        else
                used += space_info->bytes_may_use - global_rsv_size;

        return (used >= thresh && !btrfs_fs_closing(fs_info) &&
                !test_bit(BTRFS_FS_STATE_REMOUNTING, &fs_info->fs_state));
}

static bool steal_from_global_rsv(struct btrfs_fs_info *fs_info,
                                  struct btrfs_space_info *space_info,
                                  struct reserve_ticket *ticket)
{
        struct btrfs_block_rsv *global_rsv = &fs_info->global_block_rsv;
        u64 min_bytes;

        if (!ticket->steal)
                return false;

        if (global_rsv->space_info != space_info)
                return false;

        spin_lock(&global_rsv->lock);
        min_bytes = div_factor(global_rsv->size, 1);
        if (global_rsv->reserved < min_bytes + ticket->bytes) {
                spin_unlock(&global_rsv->lock);
                return false;
        }
        global_rsv->reserved -= ticket->bytes;
        remove_ticket(space_info, ticket);
        ticket->bytes = 0;
        wake_up(&ticket->wait);
        space_info->tickets_id++;
        if (global_rsv->reserved < global_rsv->size)
                global_rsv->full = 0;
        spin_unlock(&global_rsv->lock);

        return true;
}

/*
 * maybe_fail_all_tickets - we've exhausted our flushing, start failing tickets
 * @fs_info - fs_info for this fs
 * @space_info - the space info we were flushing
 *
 * We call this when we've exhausted our flushing ability and haven't made
 * progress in satisfying tickets.  The reservation code handles tickets in
 * order, so if there is a large ticket first and then smaller ones we could
 * very well satisfy the smaller tickets.  This will attempt to wake up any
 * tickets in the list to catch this case.
 *
 * This function returns true if it was able to make progress by clearing out
 * other tickets, or if it stumbles across a ticket that was smaller than the
 * first ticket.
 */
static bool maybe_fail_all_tickets(struct btrfs_fs_info *fs_info,
                                   struct btrfs_space_info *space_info)
{
        struct reserve_ticket *ticket;
        u64 tickets_id = space_info->tickets_id;
        const bool aborted = BTRFS_FS_ERROR(fs_info);

        trace_btrfs_fail_all_tickets(fs_info, space_info);

        if (btrfs_test_opt(fs_info, ENOSPC_DEBUG)) {
                btrfs_info(fs_info, "cannot satisfy tickets, dumping space info");
                __btrfs_dump_space_info(fs_info, space_info);
        }

        while (!list_empty(&space_info->tickets) &&
               tickets_id == space_info->tickets_id) {
                ticket = list_first_entry(&space_info->tickets,
                                          struct reserve_ticket, list);

                if (!aborted && steal_from_global_rsv(fs_info, space_info, ticket))
                        return true;

                if (!aborted && btrfs_test_opt(fs_info, ENOSPC_DEBUG))
                        btrfs_info(fs_info, "failing ticket with %llu bytes",
                                   ticket->bytes);

                remove_ticket(space_info, ticket);
                if (aborted)
                        ticket->error = -EIO;
                else
                        ticket->error = -ENOSPC;
                wake_up(&ticket->wait);

                /*
                 * We're just throwing tickets away, so more flushing may not
                 * trip over btrfs_try_granting_tickets, so we need to call it
                 * here to see if we can make progress with the next ticket in
                 * the list.
                 */
                if (!aborted)
                        btrfs_try_granting_tickets(fs_info, space_info);
        }
        return (tickets_id != space_info->tickets_id);
}

/*
 * This is for normal flushers, we can wait all goddamned day if we want to.  We
 * will loop and continuously try to flush as long as we are making progress.
 * We count progress as clearing off tickets each time we have to loop.
 */
static void btrfs_async_reclaim_metadata_space(struct work_struct *work)
{
        struct btrfs_fs_info *fs_info;
        struct btrfs_space_info *space_info;
        u64 to_reclaim;
        enum btrfs_flush_state flush_state;
        int commit_cycles = 0;
        u64 last_tickets_id;

        fs_info = container_of(work, struct btrfs_fs_info, async_reclaim_work);
        space_info = btrfs_find_space_info(fs_info, BTRFS_BLOCK_GROUP_METADATA);

        spin_lock(&space_info->lock);
        to_reclaim = btrfs_calc_reclaim_metadata_size(fs_info, space_info);
        if (!to_reclaim) {
                space_info->flush = 0;
                spin_unlock(&space_info->lock);
                return;
        }
        last_tickets_id = space_info->tickets_id;
        spin_unlock(&space_info->lock);

        flush_state = FLUSH_DELAYED_ITEMS_NR;
        do {
                flush_space(fs_info, space_info, to_reclaim, flush_state, false);
                spin_lock(&space_info->lock);
                if (list_empty(&space_info->tickets)) {
                        space_info->flush = 0;
                        spin_unlock(&space_info->lock);
                        return;
                }
                to_reclaim = btrfs_calc_reclaim_metadata_size(fs_info,
                                                              space_info);
                if (last_tickets_id == space_info->tickets_id) {
                        flush_state++;
                } else {
                        last_tickets_id = space_info->tickets_id;
                        flush_state = FLUSH_DELAYED_ITEMS_NR;
                        if (commit_cycles)
                                commit_cycles--;
                }

                /*
                 * We do not want to empty the system of delalloc unless we're
                 * under heavy pressure, so allow one trip through the flushing
                 * logic before we start doing a FLUSH_DELALLOC_FULL.
                 */
                if (flush_state == FLUSH_DELALLOC_FULL && !commit_cycles)
                        flush_state++;

                /*
                 * We don't want to force a chunk allocation until we've tried
                 * pretty hard to reclaim space.  Think of the case where we
                 * freed up a bunch of space and so have a lot of pinned space

                 * to reclaim.  We would rather use that than possibly create a
                 * underutilized metadata chunk.  So if this is our first run
                 * through the flushing state machine skip ALLOC_CHUNK_FORCE and
                 * commit the transaction.  If nothing has changed the next go
                 * around then we can force a chunk allocation.
                 */
                if (flush_state == ALLOC_CHUNK_FORCE && !commit_cycles)
                        flush_state++;

                if (flush_state > COMMIT_TRANS) {
                        commit_cycles++;
                        if (commit_cycles > 2) {
                                if (maybe_fail_all_tickets(fs_info, space_info)) {
                                        flush_state = FLUSH_DELAYED_ITEMS_NR;
                                        commit_cycles--;
                                } else {
                                        space_info->flush = 0;
                                }
                        } else {
                                flush_state = FLUSH_DELAYED_ITEMS_NR;
                        }
                }
                spin_unlock(&space_info->lock);
        } while (flush_state <= COMMIT_TRANS);
}

/*
 * This handles pre-flushing of metadata space before we get to the point that
 * we need to start blocking threads on tickets.  The logic here is different
 * from the other flush paths because it doesn't rely on tickets to tell us how
 * much we need to flush, instead it attempts to keep us below the 80% full
 * watermark of space by flushing whichever reservation pool is currently the
 * largest.
 */
static void btrfs_preempt_reclaim_metadata_space(struct work_struct *work)
{
        struct btrfs_fs_info *fs_info;
        struct btrfs_space_info *space_info;
        struct btrfs_block_rsv *delayed_block_rsv;
        struct btrfs_block_rsv *delayed_refs_rsv;
        struct btrfs_block_rsv *global_rsv;
        struct btrfs_block_rsv *trans_rsv;
        int loops = 0;

        fs_info = container_of(work, struct btrfs_fs_info,
                               preempt_reclaim_work);
        space_info = btrfs_find_space_info(fs_info, BTRFS_BLOCK_GROUP_METADATA);
        delayed_block_rsv = &fs_info->delayed_block_rsv;
        delayed_refs_rsv = &fs_info->delayed_refs_rsv;
        global_rsv = &fs_info->global_block_rsv;
        trans_rsv = &fs_info->trans_block_rsv;

        spin_lock(&space_info->lock);
        while (need_preemptive_reclaim(fs_info, space_info)) {
                enum btrfs_flush_state flush;
                u64 delalloc_size = 0;
                u64 to_reclaim, block_rsv_size;
                u64 global_rsv_size = global_rsv->reserved;

                loops++;

                /*
                 * We don't have a precise counter for the metadata being
                 * reserved for delalloc, so we'll approximate it by subtracting
                 * out the block rsv's space from the bytes_may_use.  If that
                 * amount is higher than the individual reserves, then we can
                 * assume it's tied up in delalloc reservations.
                 */
                block_rsv_size = global_rsv_size +
                        delayed_block_rsv->reserved +
                        delayed_refs_rsv->reserved +
                        trans_rsv->reserved;
                if (block_rsv_size < space_info->bytes_may_use)
                        delalloc_size = space_info->bytes_may_use - block_rsv_size;

                /*
                 * We don't want to include the global_rsv in our calculation,
                 * because that's space we can't touch.  Subtract it from the
                 * block_rsv_size for the next checks.
                 */
                block_rsv_size -= global_rsv_size;

                /*
                 * We really want to avoid flushing delalloc too much, as it
                 * could result in poor allocation patterns, so only flush it if
                 * it's larger than the rest of the pools combined.
                 */
                if (delalloc_size > block_rsv_size) {
                        to_reclaim = delalloc_size;
                        flush = FLUSH_DELALLOC;
                } else if (space_info->bytes_pinned >
                           (delayed_block_rsv->reserved +
                            delayed_refs_rsv->reserved)) {
                        to_reclaim = space_info->bytes_pinned;
                        flush = COMMIT_TRANS;
                } else if (delayed_block_rsv->reserved >
                           delayed_refs_rsv->reserved) {
                        to_reclaim = delayed_block_rsv->reserved;
                        flush = FLUSH_DELAYED_ITEMS_NR;
                } else {
                        to_reclaim = delayed_refs_rsv->reserved;
                        flush = FLUSH_DELAYED_REFS_NR;
                }

                spin_unlock(&space_info->lock);

                /*
                 * We don't want to reclaim everything, just a portion, so scale
                 * down the to_reclaim by 1/4.  If it takes us down to 0,
                 * reclaim 1 items worth.
                 */
                to_reclaim >>= 2;
                if (!to_reclaim)
                        to_reclaim = btrfs_calc_insert_metadata_size(fs_info, 1);
                flush_space(fs_info, space_info, to_reclaim, flush, true);
                cond_resched();
                spin_lock(&space_info->lock);
        }

        /* We only went through once, back off our clamping. */
        if (loops == 1 && !space_info->reclaim_size)
                space_info->clamp = max(1, space_info->clamp - 1);
        trace_btrfs_done_preemptive_reclaim(fs_info, space_info);
        spin_unlock(&space_info->lock);
}

/*
 * FLUSH_DELALLOC_WAIT:
 *   Space is freed from flushing delalloc in one of two ways.
 *
 *   1) compression is on and we allocate less space than we reserved
 *   2) we are overwriting existing space
 *
 *   For #1 that extra space is reclaimed as soon as the delalloc pages are
 *   COWed, by way of btrfs_add_reserved_bytes() which adds the actual extent
 *   length to ->bytes_reserved, and subtracts the reserved space from
 *   ->bytes_may_use.
 *
 *   For #2 this is trickier.  Once the ordered extent runs we will drop the
 *   extent in the range we are overwriting, which creates a delayed ref for
 *   that freed extent.  This however is not reclaimed until the transaction
 *   commits, thus the next stages.
 *
 * RUN_DELAYED_IPUTS
 *   If we are freeing inodes, we want to make sure all delayed iputs have
 *   completed, because they could have been on an inode with i_nlink == 0, and
 *   thus have been truncated and freed up space.  But again this space is not
 *   immediately re-usable, it comes in the form of a delayed ref, which must be
 *   run and then the transaction must be committed.
 *
 * COMMIT_TRANS
 *   This is where we reclaim all of the pinned space generated by running the
 *   iputs
 *
 * ALLOC_CHUNK_FORCE
 *   For data we start with alloc chunk force, however we could have been full
 *   before, and then the transaction commit could have freed new block groups,
 *   so if we now have space to allocate do the force chunk allocation.
 */
static const enum btrfs_flush_state data_flush_states[] = {
        FLUSH_DELALLOC_FULL,
        RUN_DELAYED_IPUTS,
        COMMIT_TRANS,
        ALLOC_CHUNK_FORCE,
};

static void btrfs_async_reclaim_data_space(struct work_struct *work)
{
        struct btrfs_fs_info *fs_info;
        struct btrfs_space_info *space_info;
        u64 last_tickets_id;
        enum btrfs_flush_state flush_state = 0;

        fs_info = container_of(work, struct btrfs_fs_info, async_data_reclaim_work);
        space_info = fs_info->data_sinfo;

        spin_lock(&space_info->lock);
        if (list_empty(&space_info->tickets)) {
                space_info->flush = 0;
                spin_unlock(&space_info->lock);
                return;
        }
        last_tickets_id = space_info->tickets_id;
        spin_unlock(&space_info->lock);

        while (!space_info->full) {
                flush_space(fs_info, space_info, U64_MAX, ALLOC_CHUNK_FORCE, false);
                spin_lock(&space_info->lock);
                if (list_empty(&space_info->tickets)) {
                        space_info->flush = 0;
                        spin_unlock(&space_info->lock);
                        return;
                }

                /* Something happened, fail everything and bail. */
                if (BTRFS_FS_ERROR(fs_info))
                        goto aborted_fs;
                last_tickets_id = space_info->tickets_id;
                spin_unlock(&space_info->lock);
        }

        while (flush_state < ARRAY_SIZE(data_flush_states)) {
                flush_space(fs_info, space_info, U64_MAX,
                            data_flush_states[flush_state], false);
                spin_lock(&space_info->lock);
                if (list_empty(&space_info->tickets)) {
                        space_info->flush = 0;
                        spin_unlock(&space_info->lock);
                        return;
                }

                if (last_tickets_id == space_info->tickets_id) {
                        flush_state++;
                } else {
                        last_tickets_id = space_info->tickets_id;
                        flush_state = 0;
                }

                if (flush_state >= ARRAY_SIZE(data_flush_states)) {
                        if (space_info->full) {
                                if (maybe_fail_all_tickets(fs_info, space_info))
                                        flush_state = 0;
                                else
                                        space_info->flush = 0;
                        } else {
                                flush_state = 0;
                        }

                        /* Something happened, fail everything and bail. */
                        if (BTRFS_FS_ERROR(fs_info))
                                goto aborted_fs;

                }
                spin_unlock(&space_info->lock);
        }
        return;

aborted_fs:
        maybe_fail_all_tickets(fs_info, space_info);
        space_info->flush = 0;
        spin_unlock(&space_info->lock);
}

void btrfs_init_async_reclaim_work(struct btrfs_fs_info *fs_info)
{
        INIT_WORK(&fs_info->async_reclaim_work, btrfs_async_reclaim_metadata_space);
        INIT_WORK(&fs_info->async_data_reclaim_work, btrfs_async_reclaim_data_space);
        INIT_WORK(&fs_info->preempt_reclaim_work,
                  btrfs_preempt_reclaim_metadata_space);
}

static const enum btrfs_flush_state priority_flush_states[] = {
        FLUSH_DELAYED_ITEMS_NR,
        FLUSH_DELAYED_ITEMS,
        ALLOC_CHUNK,
};

static const enum btrfs_flush_state evict_flush_states[] = {
        FLUSH_DELAYED_ITEMS_NR,
        FLUSH_DELAYED_ITEMS,
        FLUSH_DELAYED_REFS_NR,
        FLUSH_DELAYED_REFS,
        FLUSH_DELALLOC,
        FLUSH_DELALLOC_WAIT,
        FLUSH_DELALLOC_FULL,
        ALLOC_CHUNK,
        COMMIT_TRANS,
};

static void priority_reclaim_metadata_space(struct btrfs_fs_info *fs_info,
                                struct btrfs_space_info *space_info,
                                struct reserve_ticket *ticket,
                                const enum btrfs_flush_state *states,
                                int states_nr)
{
        u64 to_reclaim;
        int flush_state = 0;

        spin_lock(&space_info->lock);
        to_reclaim = btrfs_calc_reclaim_metadata_size(fs_info, space_info);
        /*
         * This is the priority reclaim path, so to_reclaim could be >0 still
         * because we may have only satisified the priority tickets and still
         * left non priority tickets on the list.  We would then have
         * to_reclaim but ->bytes == 0.
         */
        if (ticket->bytes == 0) {
                spin_unlock(&space_info->lock);
                return;
        }

        while (flush_state < states_nr) {
                spin_unlock(&space_info->lock);
                flush_space(fs_info, space_info, to_reclaim, states[flush_state],
                            false);
                flush_state++;
                spin_lock(&space_info->lock);
                if (ticket->bytes == 0) {
                        spin_unlock(&space_info->lock);
                        return;
                }
        }

        /* Attempt to steal from the global rsv if we can. */
        if (!steal_from_global_rsv(fs_info, space_info, ticket)) {
                ticket->error = -ENOSPC;
                remove_ticket(space_info, ticket);
        }

        /*
         * We must run try_granting_tickets here because we could be a large
         * ticket in front of a smaller ticket that can now be satisfied with
         * the available space.
         */
        btrfs_try_granting_tickets(fs_info, space_info);
        spin_unlock(&space_info->lock);
}

static void priority_reclaim_data_space(struct btrfs_fs_info *fs_info,
                                        struct btrfs_space_info *space_info,
                                        struct reserve_ticket *ticket)
{
        spin_lock(&space_info->lock);

        /* We could have been granted before we got here. */
        if (ticket->bytes == 0) {
                spin_unlock(&space_info->lock);
                return;
        }

        while (!space_info->full) {
                spin_unlock(&space_info->lock);
                flush_space(fs_info, space_info, U64_MAX, ALLOC_CHUNK_FORCE, false);
                spin_lock(&space_info->lock);
                if (ticket->bytes == 0) {
                        spin_unlock(&space_info->lock);
                        return;
                }
        }

        ticket->error = -ENOSPC;
        remove_ticket(space_info, ticket);
        btrfs_try_granting_tickets(fs_info, space_info);
        spin_unlock(&space_info->lock);
}

static void wait_reserve_ticket(struct btrfs_fs_info *fs_info,
                                struct btrfs_space_info *space_info,
                                struct reserve_ticket *ticket)

{
        DEFINE_WAIT(wait);
        int ret = 0;

        spin_lock(&space_info->lock);
        while (ticket->bytes > 0 && ticket->error == 0) {
                ret = prepare_to_wait_event(&ticket->wait, &wait, TASK_KILLABLE);
                if (ret) {
                        /*
                         * Delete us from the list. After we unlock the space
                         * info, we don't want the async reclaim job to reserve
                         * space for this ticket. If that would happen, then the
                         * ticket's task would not known that space was reserved
                         * despite getting an error, resulting in a space leak
                         * (bytes_may_use counter of our space_info).
                         */
                        remove_ticket(space_info, ticket);
                        ticket->error = -EINTR;
                        break;
                }
                spin_unlock(&space_info->lock);

                schedule();

                finish_wait(&ticket->wait, &wait);
                spin_lock(&space_info->lock);
        }
        spin_unlock(&space_info->lock);
}

/**
 * Do the appropriate flushing and waiting for a ticket
 *
 * @fs_info:    the filesystem
 * @space_info: space info for the reservation
 * @ticket:     ticket for the reservation
 * @start_ns:   timestamp when the reservation started
 * @orig_bytes: amount of bytes originally reserved
 * @flush:      how much we can flush
 *
 * This does the work of figuring out how to flush for the ticket, waiting for
 * the reservation, and returning the appropriate error if there is one.
 */
static int handle_reserve_ticket(struct btrfs_fs_info *fs_info,
                                 struct btrfs_space_info *space_info,
                                 struct reserve_ticket *ticket,
                                 u64 start_ns, u64 orig_bytes,
                                 enum btrfs_reserve_flush_enum flush)
{
        int ret;

        switch (flush) {
        case BTRFS_RESERVE_FLUSH_DATA:
        case BTRFS_RESERVE_FLUSH_ALL:
        case BTRFS_RESERVE_FLUSH_ALL_STEAL:
                wait_reserve_ticket(fs_info, space_info, ticket);
                break;
        case BTRFS_RESERVE_FLUSH_LIMIT:
                priority_reclaim_metadata_space(fs_info, space_info, ticket,
                                                priority_flush_states,
                                                ARRAY_SIZE(priority_flush_states));
                break;
        case BTRFS_RESERVE_FLUSH_EVICT:
                priority_reclaim_metadata_space(fs_info, space_info, ticket,
                                                evict_flush_states,
                                                ARRAY_SIZE(evict_flush_states));
                break;
        case BTRFS_RESERVE_FLUSH_FREE_SPACE_INODE:
                priority_reclaim_data_space(fs_info, space_info, ticket);
                break;
        default:
                ASSERT(0);
                break;
        }

        ret = ticket->error;
        ASSERT(list_empty(&ticket->list));
        /*
         * Check that we can't have an error set if the reservation succeeded,
         * as that would confuse tasks and lead them to error out without
         * releasing reserved space (if an error happens the expectation is that
         * space wasn't reserved at all).
         */
        ASSERT(!(ticket->bytes == 0 && ticket->error));
        trace_btrfs_reserve_ticket(fs_info, space_info->flags, orig_bytes,
                                   start_ns, flush, ticket->error);
        return ret;
}

/*
 * This returns true if this flush state will go through the ordinary flushing
 * code.
 */
static inline bool is_normal_flushing(enum btrfs_reserve_flush_enum flush)
{
        return  (flush == BTRFS_RESERVE_FLUSH_ALL) ||
                (flush == BTRFS_RESERVE_FLUSH_ALL_STEAL);
}

static inline void maybe_clamp_preempt(struct btrfs_fs_info *fs_info,
                                       struct btrfs_space_info *space_info)
{
        u64 ordered = percpu_counter_sum_positive(&fs_info->ordered_bytes);
        u64 delalloc = percpu_counter_sum_positive(&fs_info->delalloc_bytes);

        /*
         * If we're heavy on ordered operations then clamping won't help us.  We
         * need to clamp specifically to keep up with dirty'ing buffered
         * writers, because there's not a 1:1 correlation of writing delalloc
         * and freeing space, like there is with flushing delayed refs or
         * delayed nodes.  If we're already more ordered than delalloc then
         * we're keeping up, otherwise we aren't and should probably clamp.
         */
        if (ordered < delalloc)
                space_info->clamp = min(space_info->clamp + 1, 8);
}

static inline bool can_steal(enum btrfs_reserve_flush_enum flush)
{
        return (flush == BTRFS_RESERVE_FLUSH_ALL_STEAL ||
                flush == BTRFS_RESERVE_FLUSH_EVICT);
}

/**
 * Try to reserve bytes from the block_rsv's space
 *
 * @fs_info:    the filesystem
 * @space_info: space info we want to allocate from
 * @orig_bytes: number of bytes we want
 * @flush:      whether or not we can flush to make our reservation
 *
 * This will reserve orig_bytes number of bytes from the space info associated
 * with the block_rsv.  If there is not enough space it will make an attempt to
 * flush out space to make room.  It will do this by flushing delalloc if
 * possible or committing the transaction.  If flush is 0 then no attempts to
 * regain reservations will be made and this will fail if there is not enough
 * space already.
 */
static int __reserve_bytes(struct btrfs_fs_info *fs_info,
                           struct btrfs_space_info *space_info, u64 orig_bytes,
                           enum btrfs_reserve_flush_enum flush)
{
        struct work_struct *async_work;
        struct reserve_ticket ticket;
        u64 start_ns = 0;
        u64 used;
        int ret = 0;
        bool pending_tickets;

        ASSERT(orig_bytes);
        ASSERT(!current->journal_info || flush != BTRFS_RESERVE_FLUSH_ALL);

        if (flush == BTRFS_RESERVE_FLUSH_DATA)
                async_work = &fs_info->async_data_reclaim_work;
        else
                async_work = &fs_info->async_reclaim_work;

        spin_lock(&space_info->lock);
        ret = -ENOSPC;
        used = btrfs_space_info_used(space_info, true);

        /*
         * We don't want NO_FLUSH allocations to jump everybody, they can
         * generally handle ENOSPC in a different way, so treat them the same as
         * normal flushers when it comes to skipping pending tickets.
         */
        if (is_normal_flushing(flush) || (flush == BTRFS_RESERVE_NO_FLUSH))
                pending_tickets = !list_empty(&space_info->tickets) ||
                        !list_empty(&space_info->priority_tickets);
        else
                pending_tickets = !list_empty(&space_info->priority_tickets);

        /*
         * Carry on if we have enough space (short-circuit) OR call
         * can_overcommit() to ensure we can overcommit to continue.
         */
        if (!pending_tickets &&
            ((used + orig_bytes <= space_info->total_bytes) ||
             btrfs_can_overcommit(fs_info, space_info, orig_bytes, flush))) {
                btrfs_space_info_update_bytes_may_use(fs_info, space_info,
                                                      orig_bytes);
                ret = 0;
        }

        /*
         * If we couldn't make a reservation then setup our reservation ticket
         * and kick the async worker if it's not already running.
         *
         * If we are a priority flusher then we just need to add our ticket to
         * the list and we will do our own flushing further down.
         */
        if (ret && flush != BTRFS_RESERVE_NO_FLUSH) {
                ticket.bytes = orig_bytes;
                ticket.error = 0;
                space_info->reclaim_size += ticket.bytes;
                init_waitqueue_head(&ticket.wait);
                ticket.steal = can_steal(flush);
                if (trace_btrfs_reserve_ticket_enabled())
                        start_ns = ktime_get_ns();

                if (flush == BTRFS_RESERVE_FLUSH_ALL ||
                    flush == BTRFS_RESERVE_FLUSH_ALL_STEAL ||
                    flush == BTRFS_RESERVE_FLUSH_DATA) {
                        list_add_tail(&ticket.list, &space_info->tickets);
                        if (!space_info->flush) {
                                /*
                                 * We were forced to add a reserve ticket, so
                                 * our preemptive flushing is unable to keep
                                 * up.  Clamp down on the threshold for the
                                 * preemptive flushing in order to keep up with
                                 * the workload.
                                 */
                                maybe_clamp_preempt(fs_info, space_info);

                                space_info->flush = 1;
                                trace_btrfs_trigger_flush(fs_info,
                                                          space_info->flags,
                                                          orig_bytes, flush,
                                                          "enospc");
                                queue_work(system_unbound_wq, async_work);
                        }
                } else {
                        list_add_tail(&ticket.list,
                                      &space_info->priority_tickets);
                }
        } else if (!ret && space_info->flags & BTRFS_BLOCK_GROUP_METADATA) {
                used += orig_bytes;
                /*
                 * We will do the space reservation dance during log replay,
                 * which means we won't have fs_info->fs_root set, so don't do
                 * the async reclaim as we will panic.
                 */
                if (!test_bit(BTRFS_FS_LOG_RECOVERING, &fs_info->flags) &&
                    !work_busy(&fs_info->preempt_reclaim_work) &&
                    need_preemptive_reclaim(fs_info, space_info)) {
                        trace_btrfs_trigger_flush(fs_info, space_info->flags,
                                                  orig_bytes, flush, "preempt");
                        queue_work(system_unbound_wq,
                                   &fs_info->preempt_reclaim_work);
                }
        }
        spin_unlock(&space_info->lock);
        if (!ret || flush == BTRFS_RESERVE_NO_FLUSH)
                return ret;

        return handle_reserve_ticket(fs_info, space_info, &ticket, start_ns,
                                     orig_bytes, flush);
}

/**
 * Trye to reserve metadata bytes from the block_rsv's space
 *
 * @fs_info:    the filesystem
 * @block_rsv:  block_rsv we're allocating for
 * @orig_bytes: number of bytes we want
 * @flush:      whether or not we can flush to make our reservation
 *
 * This will reserve orig_bytes number of bytes from the space info associated
 * with the block_rsv.  If there is not enough space it will make an attempt to
 * flush out space to make room.  It will do this by flushing delalloc if
 * possible or committing the transaction.  If flush is 0 then no attempts to
 * regain reservations will be made and this will fail if there is not enough
 * space already.
 */
int btrfs_reserve_metadata_bytes(struct btrfs_fs_info *fs_info,
                                 struct btrfs_block_rsv *block_rsv,
                                 u64 orig_bytes,
                                 enum btrfs_reserve_flush_enum flush)
{
        int ret;

        ret = __reserve_bytes(fs_info, block_rsv->space_info, orig_bytes, flush);
        if (ret == -ENOSPC) {
                trace_btrfs_space_reservation(fs_info, "space_info:enospc",
                                              block_rsv->space_info->flags,
                                              orig_bytes, 1);

                if (btrfs_test_opt(fs_info, ENOSPC_DEBUG))
                        btrfs_dump_space_info(fs_info, block_rsv->space_info,
                                              orig_bytes, 0);
        }
        return ret;
}

/**
 * Try to reserve data bytes for an allocation
 *
 * @fs_info: the filesystem
 * @bytes:   number of bytes we need
 * @flush:   how we are allowed to flush
 *
 * This will reserve bytes from the data space info.  If there is not enough
 * space then we will attempt to flush space as specified by flush.
 */
int btrfs_reserve_data_bytes(struct btrfs_fs_info *fs_info, u64 bytes,
                             enum btrfs_reserve_flush_enum flush)
{
        struct btrfs_space_info *data_sinfo = fs_info->data_sinfo;
        int ret;

        ASSERT(flush == BTRFS_RESERVE_FLUSH_DATA ||
               flush == BTRFS_RESERVE_FLUSH_FREE_SPACE_INODE);
        ASSERT(!current->journal_info || flush != BTRFS_RESERVE_FLUSH_DATA);

        ret = __reserve_bytes(fs_info, data_sinfo, bytes, flush);
        if (ret == -ENOSPC) {
                trace_btrfs_space_reservation(fs_info, "space_info:enospc",
                                              data_sinfo->flags, bytes, 1);
                if (btrfs_test_opt(fs_info, ENOSPC_DEBUG))
                        btrfs_dump_space_info(fs_info, data_sinfo, bytes, 0);
        }
        return ret;
}