BRT: Skip duplicate BRT prefetches

[mirror_zfs.git] / module / zfs / range_tree.c

/*
 * CDDL HEADER START
 *
 * The contents of this file are subject to the terms of the
 * Common Development and Distribution License (the "License").
 * You may not use this file except in compliance with the License.
 *
 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
 * or https://opensource.org/licenses/CDDL-1.0.
 * See the License for the specific language governing permissions
 * and limitations under the License.
 *
 * When distributing Covered Code, include this CDDL HEADER in each
 * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
 * If applicable, add the following below this CDDL HEADER, with the
 * fields enclosed by brackets "[]" replaced with your own identifying
 * information: Portions Copyright [yyyy] [name of copyright owner]
 *
 * CDDL HEADER END
 */
/*
 * Copyright 2009 Sun Microsystems, Inc.  All rights reserved.
 * Use is subject to license terms.
 */
/*
 * Copyright (c) 2013, 2019 by Delphix. All rights reserved.
 * Copyright (c) 2015, Nexenta Systems, Inc. All rights reserved.
 */

#include <sys/zfs_context.h>
#include <sys/spa.h>
#include <sys/dmu.h>
#include <sys/dnode.h>
#include <sys/zio.h>
#include <sys/range_tree.h>

/*
 * Range trees are tree-based data structures that can be used to
 * track free space or generally any space allocation information.
 * A range tree keeps track of individual segments and automatically
 * provides facilities such as adjacent extent merging and extent
 * splitting in response to range add/remove requests.
 *
 * A range tree starts out completely empty, with no segments in it.
 * Adding an allocation via range_tree_add to the range tree can either:
 * 1) create a new extent
 * 2) extend an adjacent extent
 * 3) merge two adjacent extents
 * Conversely, removing an allocation via range_tree_remove can:
 * 1) completely remove an extent
 * 2) shorten an extent (if the allocation was near one of its ends)
 * 3) split an extent into two extents, in effect punching a hole
 *
 * A range tree is also capable of 'bridging' gaps when adding
 * allocations. This is useful for cases when close proximity of
 * allocations is an important detail that needs to be represented
 * in the range tree. See range_tree_set_gap(). The default behavior
 * is not to bridge gaps (i.e. the maximum allowed gap size is 0).
 *
 * In order to traverse a range tree, use either the range_tree_walk()
 * or range_tree_vacate() functions.
 *
 * To obtain more accurate information on individual segment
 * operations that the range tree performs "under the hood", you can
 * specify a set of callbacks by passing a range_tree_ops_t structure
 * to the range_tree_create function. Any callbacks that are non-NULL
 * are then called at the appropriate times.
 *
 * The range tree code also supports a special variant of range trees
 * that can bridge small gaps between segments. This kind of tree is used
 * by the dsl scanning code to group I/Os into mostly sequential chunks to
 * optimize disk performance. The code here attempts to do this with as
 * little memory and computational overhead as possible. One limitation of
 * this implementation is that segments of range trees with gaps can only
 * support removing complete segments.
 */

static inline void
rs_copy(range_seg_t *src, range_seg_t *dest, range_tree_t *rt)
{
        ASSERT3U(rt->rt_type, <, RANGE_SEG_NUM_TYPES);
        size_t size = 0;
        switch (rt->rt_type) {
        case RANGE_SEG32:
                size = sizeof (range_seg32_t);
                break;
        case RANGE_SEG64:
                size = sizeof (range_seg64_t);
                break;
        case RANGE_SEG_GAP:
                size = sizeof (range_seg_gap_t);
                break;
        default:
                __builtin_unreachable();
        }
        memcpy(dest, src, size);
}

void
range_tree_stat_verify(range_tree_t *rt)
{
        range_seg_t *rs;
        zfs_btree_index_t where;
        uint64_t hist[RANGE_TREE_HISTOGRAM_SIZE] = { 0 };
        int i;

        for (rs = zfs_btree_first(&rt->rt_root, &where); rs != NULL;
            rs = zfs_btree_next(&rt->rt_root, &where, &where)) {
                uint64_t size = rs_get_end(rs, rt) - rs_get_start(rs, rt);
                int idx = highbit64(size) - 1;

                hist[idx]++;
                ASSERT3U(hist[idx], !=, 0);
        }

        for (i = 0; i < RANGE_TREE_HISTOGRAM_SIZE; i++) {
                if (hist[i] != rt->rt_histogram[i]) {
                        zfs_dbgmsg("i=%d, hist=%px, hist=%llu, rt_hist=%llu",
                            i, hist, (u_longlong_t)hist[i],
                            (u_longlong_t)rt->rt_histogram[i]);
                }
                VERIFY3U(hist[i], ==, rt->rt_histogram[i]);
        }
}

static void
range_tree_stat_incr(range_tree_t *rt, range_seg_t *rs)
{
        uint64_t size = rs_get_end(rs, rt) - rs_get_start(rs, rt);
        int idx = highbit64(size) - 1;

        ASSERT(size != 0);
        ASSERT3U(idx, <,
            sizeof (rt->rt_histogram) / sizeof (*rt->rt_histogram));

        rt->rt_histogram[idx]++;
        ASSERT3U(rt->rt_histogram[idx], !=, 0);
}

static void
range_tree_stat_decr(range_tree_t *rt, range_seg_t *rs)
{
        uint64_t size = rs_get_end(rs, rt) - rs_get_start(rs, rt);
        int idx = highbit64(size) - 1;

        ASSERT(size != 0);
        ASSERT3U(idx, <,
            sizeof (rt->rt_histogram) / sizeof (*rt->rt_histogram));

        ASSERT3U(rt->rt_histogram[idx], !=, 0);
        rt->rt_histogram[idx]--;
}

__attribute__((always_inline)) inline
static int
range_tree_seg32_compare(const void *x1, const void *x2)
{
        const range_seg32_t *r1 = x1;
        const range_seg32_t *r2 = x2;

        ASSERT3U(r1->rs_start, <=, r1->rs_end);
        ASSERT3U(r2->rs_start, <=, r2->rs_end);

        return ((r1->rs_start >= r2->rs_end) - (r1->rs_end <= r2->rs_start));
}

__attribute__((always_inline)) inline
static int
range_tree_seg64_compare(const void *x1, const void *x2)
{
        const range_seg64_t *r1 = x1;
        const range_seg64_t *r2 = x2;

        ASSERT3U(r1->rs_start, <=, r1->rs_end);
        ASSERT3U(r2->rs_start, <=, r2->rs_end);

        return ((r1->rs_start >= r2->rs_end) - (r1->rs_end <= r2->rs_start));
}

__attribute__((always_inline)) inline
static int
range_tree_seg_gap_compare(const void *x1, const void *x2)
{
        const range_seg_gap_t *r1 = x1;
        const range_seg_gap_t *r2 = x2;

        ASSERT3U(r1->rs_start, <=, r1->rs_end);
        ASSERT3U(r2->rs_start, <=, r2->rs_end);

        return ((r1->rs_start >= r2->rs_end) - (r1->rs_end <= r2->rs_start));
}

ZFS_BTREE_FIND_IN_BUF_FUNC(range_tree_seg32_find_in_buf, range_seg32_t,
    range_tree_seg32_compare)

ZFS_BTREE_FIND_IN_BUF_FUNC(range_tree_seg64_find_in_buf, range_seg64_t,
    range_tree_seg64_compare)

ZFS_BTREE_FIND_IN_BUF_FUNC(range_tree_seg_gap_find_in_buf, range_seg_gap_t,
    range_tree_seg_gap_compare)

range_tree_t *
range_tree_create_gap(const range_tree_ops_t *ops, range_seg_type_t type,
    void *arg, uint64_t start, uint64_t shift, uint64_t gap)
{
        range_tree_t *rt = kmem_zalloc(sizeof (range_tree_t), KM_SLEEP);

        ASSERT3U(shift, <, 64);
        ASSERT3U(type, <=, RANGE_SEG_NUM_TYPES);
        size_t size;
        int (*compare) (const void *, const void *);
        bt_find_in_buf_f bt_find;
        switch (type) {
        case RANGE_SEG32:
                size = sizeof (range_seg32_t);
                compare = range_tree_seg32_compare;
                bt_find = range_tree_seg32_find_in_buf;
                break;
        case RANGE_SEG64:
                size = sizeof (range_seg64_t);
                compare = range_tree_seg64_compare;
                bt_find = range_tree_seg64_find_in_buf;
                break;
        case RANGE_SEG_GAP:
                size = sizeof (range_seg_gap_t);
                compare = range_tree_seg_gap_compare;
                bt_find = range_tree_seg_gap_find_in_buf;
                break;
        default:
                panic("Invalid range seg type %d", type);
        }
        zfs_btree_create(&rt->rt_root, compare, bt_find, size);

        rt->rt_ops = ops;
        rt->rt_gap = gap;
        rt->rt_arg = arg;
        rt->rt_type = type;
        rt->rt_start = start;
        rt->rt_shift = shift;

        if (rt->rt_ops != NULL && rt->rt_ops->rtop_create != NULL)
                rt->rt_ops->rtop_create(rt, rt->rt_arg);

        return (rt);
}

range_tree_t *
range_tree_create(const range_tree_ops_t *ops, range_seg_type_t type,
    void *arg, uint64_t start, uint64_t shift)
{
        return (range_tree_create_gap(ops, type, arg, start, shift, 0));
}

void
range_tree_destroy(range_tree_t *rt)
{
        VERIFY0(rt->rt_space);

        if (rt->rt_ops != NULL && rt->rt_ops->rtop_destroy != NULL)
                rt->rt_ops->rtop_destroy(rt, rt->rt_arg);

        zfs_btree_destroy(&rt->rt_root);
        kmem_free(rt, sizeof (*rt));
}

void
range_tree_adjust_fill(range_tree_t *rt, range_seg_t *rs, int64_t delta)
{
        if (delta < 0 && delta * -1 >= rs_get_fill(rs, rt)) {
                zfs_panic_recover("zfs: attempting to decrease fill to or "
                    "below 0; probable double remove in segment [%llx:%llx]",
                    (longlong_t)rs_get_start(rs, rt),
                    (longlong_t)rs_get_end(rs, rt));
        }
        if (rs_get_fill(rs, rt) + delta > rs_get_end(rs, rt) -
            rs_get_start(rs, rt)) {
                zfs_panic_recover("zfs: attempting to increase fill beyond "
                    "max; probable double add in segment [%llx:%llx]",
                    (longlong_t)rs_get_start(rs, rt),
                    (longlong_t)rs_get_end(rs, rt));
        }

        if (rt->rt_ops != NULL && rt->rt_ops->rtop_remove != NULL)
                rt->rt_ops->rtop_remove(rt, rs, rt->rt_arg);
        rs_set_fill(rs, rt, rs_get_fill(rs, rt) + delta);
        if (rt->rt_ops != NULL && rt->rt_ops->rtop_add != NULL)
                rt->rt_ops->rtop_add(rt, rs, rt->rt_arg);
}

static void
range_tree_add_impl(void *arg, uint64_t start, uint64_t size, uint64_t fill)
{
        range_tree_t *rt = arg;
        zfs_btree_index_t where;
        range_seg_t *rs_before, *rs_after, *rs;
        range_seg_max_t tmp, rsearch;
        uint64_t end = start + size, gap = rt->rt_gap;
        uint64_t bridge_size = 0;
        boolean_t merge_before, merge_after;

        ASSERT3U(size, !=, 0);
        ASSERT3U(fill, <=, size);
        ASSERT3U(start + size, >, start);

        rs_set_start(&rsearch, rt, start);
        rs_set_end(&rsearch, rt, end);
        rs = zfs_btree_find(&rt->rt_root, &rsearch, &where);

        /*
         * If this is a gap-supporting range tree, it is possible that we
         * are inserting into an existing segment. In this case simply
         * bump the fill count and call the remove / add callbacks. If the
         * new range will extend an existing segment, we remove the
         * existing one, apply the new extent to it and re-insert it using
         * the normal code paths.
         */
        if (rs != NULL) {
                if (gap == 0) {
                        zfs_panic_recover("zfs: adding existent segment to "
                            "range tree (offset=%llx size=%llx)",
                            (longlong_t)start, (longlong_t)size);
                        return;
                }
                uint64_t rstart = rs_get_start(rs, rt);
                uint64_t rend = rs_get_end(rs, rt);
                if (rstart <= start && rend >= end) {
                        range_tree_adjust_fill(rt, rs, fill);
                        return;
                }

                if (rt->rt_ops != NULL && rt->rt_ops->rtop_remove != NULL)
                        rt->rt_ops->rtop_remove(rt, rs, rt->rt_arg);

                range_tree_stat_decr(rt, rs);
                rt->rt_space -= rend - rstart;

                fill += rs_get_fill(rs, rt);
                start = MIN(start, rstart);
                end = MAX(end, rend);
                size = end - start;

                zfs_btree_remove(&rt->rt_root, rs);
                range_tree_add_impl(rt, start, size, fill);
                return;
        }

        ASSERT3P(rs, ==, NULL);

        /*
         * Determine whether or not we will have to merge with our neighbors.
         * If gap != 0, we might need to merge with our neighbors even if we
         * aren't directly touching.
         */
        zfs_btree_index_t where_before, where_after;
        rs_before = zfs_btree_prev(&rt->rt_root, &where, &where_before);
        rs_after = zfs_btree_next(&rt->rt_root, &where, &where_after);

        merge_before = (rs_before != NULL && rs_get_end(rs_before, rt) >=
            start - gap);
        merge_after = (rs_after != NULL && rs_get_start(rs_after, rt) <= end +
            gap);

        if (merge_before && gap != 0)
                bridge_size += start - rs_get_end(rs_before, rt);
        if (merge_after && gap != 0)
                bridge_size += rs_get_start(rs_after, rt) - end;

        if (merge_before && merge_after) {
                if (rt->rt_ops != NULL && rt->rt_ops->rtop_remove != NULL) {
                        rt->rt_ops->rtop_remove(rt, rs_before, rt->rt_arg);
                        rt->rt_ops->rtop_remove(rt, rs_after, rt->rt_arg);
                }

                range_tree_stat_decr(rt, rs_before);
                range_tree_stat_decr(rt, rs_after);

                rs_copy(rs_after, &tmp, rt);
                uint64_t before_start = rs_get_start_raw(rs_before, rt);
                uint64_t before_fill = rs_get_fill(rs_before, rt);
                uint64_t after_fill = rs_get_fill(rs_after, rt);
                zfs_btree_remove_idx(&rt->rt_root, &where_before);

                /*
                 * We have to re-find the node because our old reference is
                 * invalid as soon as we do any mutating btree operations.
                 */
                rs_after = zfs_btree_find(&rt->rt_root, &tmp, &where_after);
                ASSERT3P(rs_after, !=, NULL);
                rs_set_start_raw(rs_after, rt, before_start);
                rs_set_fill(rs_after, rt, after_fill + before_fill + fill);
                rs = rs_after;
        } else if (merge_before) {
                if (rt->rt_ops != NULL && rt->rt_ops->rtop_remove != NULL)
                        rt->rt_ops->rtop_remove(rt, rs_before, rt->rt_arg);

                range_tree_stat_decr(rt, rs_before);

                uint64_t before_fill = rs_get_fill(rs_before, rt);
                rs_set_end(rs_before, rt, end);
                rs_set_fill(rs_before, rt, before_fill + fill);
                rs = rs_before;
        } else if (merge_after) {
                if (rt->rt_ops != NULL && rt->rt_ops->rtop_remove != NULL)
                        rt->rt_ops->rtop_remove(rt, rs_after, rt->rt_arg);

                range_tree_stat_decr(rt, rs_after);

                uint64_t after_fill = rs_get_fill(rs_after, rt);
                rs_set_start(rs_after, rt, start);
                rs_set_fill(rs_after, rt, after_fill + fill);
                rs = rs_after;
        } else {
                rs = &tmp;

                rs_set_start(rs, rt, start);
                rs_set_end(rs, rt, end);
                rs_set_fill(rs, rt, fill);
                zfs_btree_add_idx(&rt->rt_root, rs, &where);
        }

        if (gap != 0) {
                ASSERT3U(rs_get_fill(rs, rt), <=, rs_get_end(rs, rt) -
                    rs_get_start(rs, rt));
        } else {
                ASSERT3U(rs_get_fill(rs, rt), ==, rs_get_end(rs, rt) -
                    rs_get_start(rs, rt));
        }

        if (rt->rt_ops != NULL && rt->rt_ops->rtop_add != NULL)
                rt->rt_ops->rtop_add(rt, rs, rt->rt_arg);

        range_tree_stat_incr(rt, rs);
        rt->rt_space += size + bridge_size;
}

void
range_tree_add(void *arg, uint64_t start, uint64_t size)
{
        range_tree_add_impl(arg, start, size, size);
}

static void
range_tree_remove_impl(range_tree_t *rt, uint64_t start, uint64_t size,
    boolean_t do_fill)
{
        zfs_btree_index_t where;
        range_seg_t *rs;
        range_seg_max_t rsearch, rs_tmp;
        uint64_t end = start + size;
        boolean_t left_over, right_over;

        VERIFY3U(size, !=, 0);
        VERIFY3U(size, <=, rt->rt_space);
        if (rt->rt_type == RANGE_SEG64)
                ASSERT3U(start + size, >, start);

        rs_set_start(&rsearch, rt, start);
        rs_set_end(&rsearch, rt, end);
        rs = zfs_btree_find(&rt->rt_root, &rsearch, &where);

        /* Make sure we completely overlap with someone */
        if (rs == NULL) {
                zfs_panic_recover("zfs: removing nonexistent segment from "
                    "range tree (offset=%llx size=%llx)",
                    (longlong_t)start, (longlong_t)size);
                return;
        }

        /*
         * Range trees with gap support must only remove complete segments
         * from the tree. This allows us to maintain accurate fill accounting
         * and to ensure that bridged sections are not leaked. If we need to
         * remove less than the full segment, we can only adjust the fill count.
         */
        if (rt->rt_gap != 0) {
                if (do_fill) {
                        if (rs_get_fill(rs, rt) == size) {
                                start = rs_get_start(rs, rt);
                                end = rs_get_end(rs, rt);
                                size = end - start;
                        } else {
                                range_tree_adjust_fill(rt, rs, -size);
                                return;
                        }
                } else if (rs_get_start(rs, rt) != start ||
                    rs_get_end(rs, rt) != end) {
                        zfs_panic_recover("zfs: freeing partial segment of "
                            "gap tree (offset=%llx size=%llx) of "
                            "(offset=%llx size=%llx)",
                            (longlong_t)start, (longlong_t)size,
                            (longlong_t)rs_get_start(rs, rt),
                            (longlong_t)rs_get_end(rs, rt) - rs_get_start(rs,
                            rt));
                        return;
                }
        }

        VERIFY3U(rs_get_start(rs, rt), <=, start);
        VERIFY3U(rs_get_end(rs, rt), >=, end);

        left_over = (rs_get_start(rs, rt) != start);
        right_over = (rs_get_end(rs, rt) != end);

        range_tree_stat_decr(rt, rs);

        if (rt->rt_ops != NULL && rt->rt_ops->rtop_remove != NULL)
                rt->rt_ops->rtop_remove(rt, rs, rt->rt_arg);

        if (left_over && right_over) {
                range_seg_max_t newseg;
                rs_set_start(&newseg, rt, end);
                rs_set_end_raw(&newseg, rt, rs_get_end_raw(rs, rt));
                rs_set_fill(&newseg, rt, rs_get_end(rs, rt) - end);
                range_tree_stat_incr(rt, &newseg);

                // This modifies the buffer already inside the range tree
                rs_set_end(rs, rt, start);

                rs_copy(rs, &rs_tmp, rt);
                if (zfs_btree_next(&rt->rt_root, &where, &where) != NULL)
                        zfs_btree_add_idx(&rt->rt_root, &newseg, &where);
                else
                        zfs_btree_add(&rt->rt_root, &newseg);

                if (rt->rt_ops != NULL && rt->rt_ops->rtop_add != NULL)
                        rt->rt_ops->rtop_add(rt, &newseg, rt->rt_arg);
        } else if (left_over) {
                // This modifies the buffer already inside the range tree
                rs_set_end(rs, rt, start);
                rs_copy(rs, &rs_tmp, rt);
        } else if (right_over) {
                // This modifies the buffer already inside the range tree
                rs_set_start(rs, rt, end);
                rs_copy(rs, &rs_tmp, rt);
        } else {
                zfs_btree_remove_idx(&rt->rt_root, &where);
                rs = NULL;
        }

        if (rs != NULL) {
                /*
                 * The fill of the leftover segment will always be equal to
                 * the size, since we do not support removing partial segments
                 * of range trees with gaps.
                 */
                rs_set_fill_raw(rs, rt, rs_get_end_raw(rs, rt) -
                    rs_get_start_raw(rs, rt));
                range_tree_stat_incr(rt, &rs_tmp);

                if (rt->rt_ops != NULL && rt->rt_ops->rtop_add != NULL)
                        rt->rt_ops->rtop_add(rt, &rs_tmp, rt->rt_arg);
        }

        rt->rt_space -= size;
}

void
range_tree_remove(void *arg, uint64_t start, uint64_t size)
{
        range_tree_remove_impl(arg, start, size, B_FALSE);
}

void
range_tree_remove_fill(range_tree_t *rt, uint64_t start, uint64_t size)
{
        range_tree_remove_impl(rt, start, size, B_TRUE);
}

void
range_tree_resize_segment(range_tree_t *rt, range_seg_t *rs,
    uint64_t newstart, uint64_t newsize)
{
        int64_t delta = newsize - (rs_get_end(rs, rt) - rs_get_start(rs, rt));

        range_tree_stat_decr(rt, rs);
        if (rt->rt_ops != NULL && rt->rt_ops->rtop_remove != NULL)
                rt->rt_ops->rtop_remove(rt, rs, rt->rt_arg);

        rs_set_start(rs, rt, newstart);
        rs_set_end(rs, rt, newstart + newsize);

        range_tree_stat_incr(rt, rs);
        if (rt->rt_ops != NULL && rt->rt_ops->rtop_add != NULL)
                rt->rt_ops->rtop_add(rt, rs, rt->rt_arg);

        rt->rt_space += delta;
}

static range_seg_t *
range_tree_find_impl(range_tree_t *rt, uint64_t start, uint64_t size)
{
        range_seg_max_t rsearch;
        uint64_t end = start + size;

        VERIFY(size != 0);

        rs_set_start(&rsearch, rt, start);
        rs_set_end(&rsearch, rt, end);
        return (zfs_btree_find(&rt->rt_root, &rsearch, NULL));
}

range_seg_t *
range_tree_find(range_tree_t *rt, uint64_t start, uint64_t size)
{
        if (rt->rt_type == RANGE_SEG64)
                ASSERT3U(start + size, >, start);

        range_seg_t *rs = range_tree_find_impl(rt, start, size);
        if (rs != NULL && rs_get_start(rs, rt) <= start &&
            rs_get_end(rs, rt) >= start + size) {
                return (rs);
        }
        return (NULL);
}

void
range_tree_verify_not_present(range_tree_t *rt, uint64_t off, uint64_t size)
{
        range_seg_t *rs = range_tree_find(rt, off, size);
        if (rs != NULL)
                panic("segment already in tree; rs=%p", (void *)rs);
}

boolean_t
range_tree_contains(range_tree_t *rt, uint64_t start, uint64_t size)
{
        return (range_tree_find(rt, start, size) != NULL);
}

/*
 * Returns the first subset of the given range which overlaps with the range
 * tree. Returns true if there is a segment in the range, and false if there
 * isn't.
 */
boolean_t
range_tree_find_in(range_tree_t *rt, uint64_t start, uint64_t size,
    uint64_t *ostart, uint64_t *osize)
{
        if (rt->rt_type == RANGE_SEG64)
                ASSERT3U(start + size, >, start);

        range_seg_max_t rsearch;
        rs_set_start(&rsearch, rt, start);
        rs_set_end_raw(&rsearch, rt, rs_get_start_raw(&rsearch, rt) + 1);

        zfs_btree_index_t where;
        range_seg_t *rs = zfs_btree_find(&rt->rt_root, &rsearch, &where);
        if (rs != NULL) {
                *ostart = start;
                *osize = MIN(size, rs_get_end(rs, rt) - start);
                return (B_TRUE);
        }

        rs = zfs_btree_next(&rt->rt_root, &where, &where);
        if (rs == NULL || rs_get_start(rs, rt) > start + size)
                return (B_FALSE);

        *ostart = rs_get_start(rs, rt);
        *osize = MIN(start + size, rs_get_end(rs, rt)) -
            rs_get_start(rs, rt);
        return (B_TRUE);
}

/*
 * Ensure that this range is not in the tree, regardless of whether
 * it is currently in the tree.
 */
void
range_tree_clear(range_tree_t *rt, uint64_t start, uint64_t size)
{
        range_seg_t *rs;

        if (size == 0)
                return;

        if (rt->rt_type == RANGE_SEG64)
                ASSERT3U(start + size, >, start);

        while ((rs = range_tree_find_impl(rt, start, size)) != NULL) {
                uint64_t free_start = MAX(rs_get_start(rs, rt), start);
                uint64_t free_end = MIN(rs_get_end(rs, rt), start + size);
                range_tree_remove(rt, free_start, free_end - free_start);
        }
}

void
range_tree_swap(range_tree_t **rtsrc, range_tree_t **rtdst)
{
        range_tree_t *rt;

        ASSERT0(range_tree_space(*rtdst));
        ASSERT0(zfs_btree_numnodes(&(*rtdst)->rt_root));

        rt = *rtsrc;
        *rtsrc = *rtdst;
        *rtdst = rt;
}

void
range_tree_vacate(range_tree_t *rt, range_tree_func_t *func, void *arg)
{
        if (rt->rt_ops != NULL && rt->rt_ops->rtop_vacate != NULL)
                rt->rt_ops->rtop_vacate(rt, rt->rt_arg);

        if (func != NULL) {
                range_seg_t *rs;
                zfs_btree_index_t *cookie = NULL;

                while ((rs = zfs_btree_destroy_nodes(&rt->rt_root, &cookie)) !=
                    NULL) {
                        func(arg, rs_get_start(rs, rt), rs_get_end(rs, rt) -
                            rs_get_start(rs, rt));
                }
        } else {
                zfs_btree_clear(&rt->rt_root);
        }

        memset(rt->rt_histogram, 0, sizeof (rt->rt_histogram));
        rt->rt_space = 0;
}

void
range_tree_walk(range_tree_t *rt, range_tree_func_t *func, void *arg)
{
        zfs_btree_index_t where;
        for (range_seg_t *rs = zfs_btree_first(&rt->rt_root, &where);
            rs != NULL; rs = zfs_btree_next(&rt->rt_root, &where, &where)) {
                func(arg, rs_get_start(rs, rt), rs_get_end(rs, rt) -
                    rs_get_start(rs, rt));
        }
}

range_seg_t *
range_tree_first(range_tree_t *rt)
{
        return (zfs_btree_first(&rt->rt_root, NULL));
}

uint64_t
range_tree_space(range_tree_t *rt)
{
        return (rt->rt_space);
}

uint64_t
range_tree_numsegs(range_tree_t *rt)
{
        return ((rt == NULL) ? 0 : zfs_btree_numnodes(&rt->rt_root));
}

boolean_t
range_tree_is_empty(range_tree_t *rt)
{
        ASSERT(rt != NULL);
        return (range_tree_space(rt) == 0);
}

/*
 * Remove any overlapping ranges between the given segment [start, end)
 * from removefrom. Add non-overlapping leftovers to addto.
 */
void
range_tree_remove_xor_add_segment(uint64_t start, uint64_t end,
    range_tree_t *removefrom, range_tree_t *addto)
{
        zfs_btree_index_t where;
        range_seg_max_t starting_rs;
        rs_set_start(&starting_rs, removefrom, start);
        rs_set_end_raw(&starting_rs, removefrom, rs_get_start_raw(&starting_rs,
            removefrom) + 1);

        range_seg_t *curr = zfs_btree_find(&removefrom->rt_root,
            &starting_rs, &where);

        if (curr == NULL)
                curr = zfs_btree_next(&removefrom->rt_root, &where, &where);

        range_seg_t *next;
        for (; curr != NULL; curr = next) {
                if (start == end)
                        return;
                VERIFY3U(start, <, end);

                /* there is no overlap */
                if (end <= rs_get_start(curr, removefrom)) {
                        range_tree_add(addto, start, end - start);
                        return;
                }

                uint64_t overlap_start = MAX(rs_get_start(curr, removefrom),
                    start);
                uint64_t overlap_end = MIN(rs_get_end(curr, removefrom),
                    end);
                uint64_t overlap_size = overlap_end - overlap_start;
                ASSERT3S(overlap_size, >, 0);
                range_seg_max_t rs;
                rs_copy(curr, &rs, removefrom);

                range_tree_remove(removefrom, overlap_start, overlap_size);

                if (start < overlap_start)
                        range_tree_add(addto, start, overlap_start - start);

                start = overlap_end;
                next = zfs_btree_find(&removefrom->rt_root, &rs, &where);
                /*
                 * If we find something here, we only removed part of the
                 * curr segment. Either there's some left at the end
                 * because we've reached the end of the range we're removing,
                 * or there's some left at the start because we started
                 * partway through the range.  Either way, we continue with
                 * the loop. If it's the former, we'll return at the start of
                 * the loop, and if it's the latter we'll see if there is more
                 * area to process.
                 */
                if (next != NULL) {
                        ASSERT(start == end || start == rs_get_end(&rs,
                            removefrom));
                }

                next = zfs_btree_next(&removefrom->rt_root, &where, &where);
        }
        VERIFY3P(curr, ==, NULL);

        if (start != end) {
                VERIFY3U(start, <, end);
                range_tree_add(addto, start, end - start);
        } else {
                VERIFY3U(start, ==, end);
        }
}

/*
 * For each entry in rt, if it exists in removefrom, remove it
 * from removefrom. Otherwise, add it to addto.
 */
void
range_tree_remove_xor_add(range_tree_t *rt, range_tree_t *removefrom,
    range_tree_t *addto)
{
        zfs_btree_index_t where;
        for (range_seg_t *rs = zfs_btree_first(&rt->rt_root, &where); rs;
            rs = zfs_btree_next(&rt->rt_root, &where, &where)) {
                range_tree_remove_xor_add_segment(rs_get_start(rs, rt),
                    rs_get_end(rs, rt), removefrom, addto);
        }
}

uint64_t
range_tree_min(range_tree_t *rt)
{
        range_seg_t *rs = zfs_btree_first(&rt->rt_root, NULL);
        return (rs != NULL ? rs_get_start(rs, rt) : 0);
}

uint64_t
range_tree_max(range_tree_t *rt)
{
        range_seg_t *rs = zfs_btree_last(&rt->rt_root, NULL);
        return (rs != NULL ? rs_get_end(rs, rt) : 0);
}

uint64_t
range_tree_span(range_tree_t *rt)
{
        return (range_tree_max(rt) - range_tree_min(rt));
}