ddt_zap: standardise temp buffer allocations

[mirror_zfs.git] / module / zfs / ddt.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 (c) 2009, 2010, Oracle and/or its affiliates. All rights reserved.
 * Copyright (c) 2012, 2016 by Delphix. All rights reserved.
 * Copyright (c) 2022 by Pawel Jakub Dawidek
 */

#include <sys/zfs_context.h>
#include <sys/spa.h>
#include <sys/spa_impl.h>
#include <sys/zio.h>
#include <sys/ddt.h>
#include <sys/zap.h>
#include <sys/dmu_tx.h>
#include <sys/arc.h>
#include <sys/dsl_pool.h>
#include <sys/zio_checksum.h>
#include <sys/dsl_scan.h>
#include <sys/abd.h>

static kmem_cache_t *ddt_cache;
static kmem_cache_t *ddt_entry_cache;

/*
 * Enable/disable prefetching of dedup-ed blocks which are going to be freed.
 */
int zfs_dedup_prefetch = 0;

static const ddt_ops_t *const ddt_ops[DDT_TYPES] = {
        &ddt_zap_ops,
};

static const char *const ddt_class_name[DDT_CLASSES] = {
        "ditto",
        "duplicate",
        "unique",
};

static void
ddt_object_create(ddt_t *ddt, enum ddt_type type, enum ddt_class class,
    dmu_tx_t *tx)
{
        spa_t *spa = ddt->ddt_spa;
        objset_t *os = ddt->ddt_os;
        uint64_t *objectp = &ddt->ddt_object[type][class];
        boolean_t prehash = zio_checksum_table[ddt->ddt_checksum].ci_flags &
            ZCHECKSUM_FLAG_DEDUP;
        char name[DDT_NAMELEN];

        ddt_object_name(ddt, type, class, name);

        ASSERT3U(*objectp, ==, 0);
        VERIFY0(ddt_ops[type]->ddt_op_create(os, objectp, tx, prehash));
        ASSERT3U(*objectp, !=, 0);

        VERIFY0(zap_add(os, DMU_POOL_DIRECTORY_OBJECT, name,
            sizeof (uint64_t), 1, objectp, tx));

        VERIFY0(zap_add(os, spa->spa_ddt_stat_object, name,
            sizeof (uint64_t), sizeof (ddt_histogram_t) / sizeof (uint64_t),
            &ddt->ddt_histogram[type][class], tx));
}

static void
ddt_object_destroy(ddt_t *ddt, enum ddt_type type, enum ddt_class class,
    dmu_tx_t *tx)
{
        spa_t *spa = ddt->ddt_spa;
        objset_t *os = ddt->ddt_os;
        uint64_t *objectp = &ddt->ddt_object[type][class];
        uint64_t count;
        char name[DDT_NAMELEN];

        ddt_object_name(ddt, type, class, name);

        ASSERT3U(*objectp, !=, 0);
        ASSERT(ddt_histogram_empty(&ddt->ddt_histogram[type][class]));
        VERIFY0(ddt_object_count(ddt, type, class, &count));
        VERIFY0(count);
        VERIFY0(zap_remove(os, DMU_POOL_DIRECTORY_OBJECT, name, tx));
        VERIFY0(zap_remove(os, spa->spa_ddt_stat_object, name, tx));
        VERIFY0(ddt_ops[type]->ddt_op_destroy(os, *objectp, tx));
        memset(&ddt->ddt_object_stats[type][class], 0, sizeof (ddt_object_t));

        *objectp = 0;
}

static int
ddt_object_load(ddt_t *ddt, enum ddt_type type, enum ddt_class class)
{
        ddt_object_t *ddo = &ddt->ddt_object_stats[type][class];
        dmu_object_info_t doi;
        uint64_t count;
        char name[DDT_NAMELEN];
        int error;

        ddt_object_name(ddt, type, class, name);

        error = zap_lookup(ddt->ddt_os, DMU_POOL_DIRECTORY_OBJECT, name,
            sizeof (uint64_t), 1, &ddt->ddt_object[type][class]);
        if (error != 0)
                return (error);

        error = zap_lookup(ddt->ddt_os, ddt->ddt_spa->spa_ddt_stat_object, name,
            sizeof (uint64_t), sizeof (ddt_histogram_t) / sizeof (uint64_t),
            &ddt->ddt_histogram[type][class]);
        if (error != 0)
                return (error);

        /*
         * Seed the cached statistics.
         */
        error = ddt_object_info(ddt, type, class, &doi);
        if (error)
                return (error);

        error = ddt_object_count(ddt, type, class, &count);
        if (error)
                return (error);

        ddo->ddo_count = count;
        ddo->ddo_dspace = doi.doi_physical_blocks_512 << 9;
        ddo->ddo_mspace = doi.doi_fill_count * doi.doi_data_block_size;

        return (0);
}

static void
ddt_object_sync(ddt_t *ddt, enum ddt_type type, enum ddt_class class,
    dmu_tx_t *tx)
{
        ddt_object_t *ddo = &ddt->ddt_object_stats[type][class];
        dmu_object_info_t doi;
        uint64_t count;
        char name[DDT_NAMELEN];

        ddt_object_name(ddt, type, class, name);

        VERIFY0(zap_update(ddt->ddt_os, ddt->ddt_spa->spa_ddt_stat_object, name,
            sizeof (uint64_t), sizeof (ddt_histogram_t) / sizeof (uint64_t),
            &ddt->ddt_histogram[type][class], tx));

        /*
         * Cache DDT statistics; this is the only time they'll change.
         */
        VERIFY0(ddt_object_info(ddt, type, class, &doi));
        VERIFY0(ddt_object_count(ddt, type, class, &count));

        ddo->ddo_count = count;
        ddo->ddo_dspace = doi.doi_physical_blocks_512 << 9;
        ddo->ddo_mspace = doi.doi_fill_count * doi.doi_data_block_size;
}

static int
ddt_object_lookup(ddt_t *ddt, enum ddt_type type, enum ddt_class class,
    ddt_entry_t *dde)
{
        if (!ddt_object_exists(ddt, type, class))
                return (SET_ERROR(ENOENT));

        return (ddt_ops[type]->ddt_op_lookup(ddt->ddt_os,
            ddt->ddt_object[type][class], dde));
}

static void
ddt_object_prefetch(ddt_t *ddt, enum ddt_type type, enum ddt_class class,
    ddt_entry_t *dde)
{
        if (!ddt_object_exists(ddt, type, class))
                return;

        ddt_ops[type]->ddt_op_prefetch(ddt->ddt_os,
            ddt->ddt_object[type][class], dde);
}

int
ddt_object_update(ddt_t *ddt, enum ddt_type type, enum ddt_class class,
    ddt_entry_t *dde, dmu_tx_t *tx)
{
        ASSERT(ddt_object_exists(ddt, type, class));

        return (ddt_ops[type]->ddt_op_update(ddt->ddt_os,
            ddt->ddt_object[type][class], dde, tx));
}

static int
ddt_object_remove(ddt_t *ddt, enum ddt_type type, enum ddt_class class,
    ddt_entry_t *dde, dmu_tx_t *tx)
{
        ASSERT(ddt_object_exists(ddt, type, class));

        return (ddt_ops[type]->ddt_op_remove(ddt->ddt_os,
            ddt->ddt_object[type][class], dde, tx));
}

int
ddt_object_walk(ddt_t *ddt, enum ddt_type type, enum ddt_class class,
    uint64_t *walk, ddt_entry_t *dde)
{
        ASSERT(ddt_object_exists(ddt, type, class));

        return (ddt_ops[type]->ddt_op_walk(ddt->ddt_os,
            ddt->ddt_object[type][class], dde, walk));
}

int
ddt_object_count(ddt_t *ddt, enum ddt_type type, enum ddt_class class,
    uint64_t *count)
{
        ASSERT(ddt_object_exists(ddt, type, class));

        return (ddt_ops[type]->ddt_op_count(ddt->ddt_os,
            ddt->ddt_object[type][class], count));
}

int
ddt_object_info(ddt_t *ddt, enum ddt_type type, enum ddt_class class,
    dmu_object_info_t *doi)
{
        if (!ddt_object_exists(ddt, type, class))
                return (SET_ERROR(ENOENT));

        return (dmu_object_info(ddt->ddt_os, ddt->ddt_object[type][class],
            doi));
}

boolean_t
ddt_object_exists(ddt_t *ddt, enum ddt_type type, enum ddt_class class)
{
        return (!!ddt->ddt_object[type][class]);
}

void
ddt_object_name(ddt_t *ddt, enum ddt_type type, enum ddt_class class,
    char *name)
{
        (void) snprintf(name, DDT_NAMELEN, DMU_POOL_DDT,
            zio_checksum_table[ddt->ddt_checksum].ci_name,
            ddt_ops[type]->ddt_op_name, ddt_class_name[class]);
}

void
ddt_bp_fill(const ddt_phys_t *ddp, blkptr_t *bp, uint64_t txg)
{
        ASSERT3U(txg, !=, 0);

        for (int d = 0; d < SPA_DVAS_PER_BP; d++)
                bp->blk_dva[d] = ddp->ddp_dva[d];
        BP_SET_BIRTH(bp, txg, ddp->ddp_phys_birth);
}

/*
 * The bp created via this function may be used for repairs and scrub, but it
 * will be missing the salt / IV required to do a full decrypting read.
 */
void
ddt_bp_create(enum zio_checksum checksum,
    const ddt_key_t *ddk, const ddt_phys_t *ddp, blkptr_t *bp)
{
        BP_ZERO(bp);

        if (ddp != NULL)
                ddt_bp_fill(ddp, bp, ddp->ddp_phys_birth);

        bp->blk_cksum = ddk->ddk_cksum;

        BP_SET_LSIZE(bp, DDK_GET_LSIZE(ddk));
        BP_SET_PSIZE(bp, DDK_GET_PSIZE(ddk));
        BP_SET_COMPRESS(bp, DDK_GET_COMPRESS(ddk));
        BP_SET_CRYPT(bp, DDK_GET_CRYPT(ddk));
        BP_SET_FILL(bp, 1);
        BP_SET_CHECKSUM(bp, checksum);
        BP_SET_TYPE(bp, DMU_OT_DEDUP);
        BP_SET_LEVEL(bp, 0);
        BP_SET_DEDUP(bp, 1);
        BP_SET_BYTEORDER(bp, ZFS_HOST_BYTEORDER);
}

void
ddt_key_fill(ddt_key_t *ddk, const blkptr_t *bp)
{
        ddk->ddk_cksum = bp->blk_cksum;
        ddk->ddk_prop = 0;

        ASSERT(BP_IS_ENCRYPTED(bp) || !BP_USES_CRYPT(bp));

        DDK_SET_LSIZE(ddk, BP_GET_LSIZE(bp));
        DDK_SET_PSIZE(ddk, BP_GET_PSIZE(bp));
        DDK_SET_COMPRESS(ddk, BP_GET_COMPRESS(bp));
        DDK_SET_CRYPT(ddk, BP_USES_CRYPT(bp));
}

void
ddt_phys_fill(ddt_phys_t *ddp, const blkptr_t *bp)
{
        ASSERT0(ddp->ddp_phys_birth);

        for (int d = 0; d < SPA_DVAS_PER_BP; d++)
                ddp->ddp_dva[d] = bp->blk_dva[d];
        ddp->ddp_phys_birth = BP_PHYSICAL_BIRTH(bp);
}

void
ddt_phys_clear(ddt_phys_t *ddp)
{
        memset(ddp, 0, sizeof (*ddp));
}

void
ddt_phys_addref(ddt_phys_t *ddp)
{
        ddp->ddp_refcnt++;
}

void
ddt_phys_decref(ddt_phys_t *ddp)
{
        if (ddp) {
                ASSERT3U(ddp->ddp_refcnt, >, 0);
                ddp->ddp_refcnt--;
        }
}

void
ddt_phys_free(ddt_t *ddt, ddt_key_t *ddk, ddt_phys_t *ddp, uint64_t txg)
{
        blkptr_t blk;

        ddt_bp_create(ddt->ddt_checksum, ddk, ddp, &blk);

        /*
         * We clear the dedup bit so that zio_free() will actually free the
         * space, rather than just decrementing the refcount in the DDT.
         */
        BP_SET_DEDUP(&blk, 0);

        ddt_phys_clear(ddp);
        zio_free(ddt->ddt_spa, txg, &blk);
}

ddt_phys_t *
ddt_phys_select(const ddt_entry_t *dde, const blkptr_t *bp)
{
        ddt_phys_t *ddp = (ddt_phys_t *)dde->dde_phys;

        for (int p = 0; p < DDT_PHYS_TYPES; p++, ddp++) {
                if (DVA_EQUAL(BP_IDENTITY(bp), &ddp->ddp_dva[0]) &&
                    BP_PHYSICAL_BIRTH(bp) == ddp->ddp_phys_birth)
                        return (ddp);
        }
        return (NULL);
}

uint64_t
ddt_phys_total_refcnt(const ddt_entry_t *dde)
{
        uint64_t refcnt = 0;

        for (int p = DDT_PHYS_SINGLE; p <= DDT_PHYS_TRIPLE; p++)
                refcnt += dde->dde_phys[p].ddp_refcnt;

        return (refcnt);
}

static void
ddt_stat_generate(ddt_t *ddt, ddt_entry_t *dde, ddt_stat_t *dds)
{
        spa_t *spa = ddt->ddt_spa;
        ddt_phys_t *ddp = dde->dde_phys;
        ddt_key_t *ddk = &dde->dde_key;
        uint64_t lsize = DDK_GET_LSIZE(ddk);
        uint64_t psize = DDK_GET_PSIZE(ddk);

        memset(dds, 0, sizeof (*dds));

        for (int p = 0; p < DDT_PHYS_TYPES; p++, ddp++) {
                uint64_t dsize = 0;
                uint64_t refcnt = ddp->ddp_refcnt;

                if (ddp->ddp_phys_birth == 0)
                        continue;

                for (int d = 0; d < DDE_GET_NDVAS(dde); d++)
                        dsize += dva_get_dsize_sync(spa, &ddp->ddp_dva[d]);

                dds->dds_blocks += 1;
                dds->dds_lsize += lsize;
                dds->dds_psize += psize;
                dds->dds_dsize += dsize;

                dds->dds_ref_blocks += refcnt;
                dds->dds_ref_lsize += lsize * refcnt;
                dds->dds_ref_psize += psize * refcnt;
                dds->dds_ref_dsize += dsize * refcnt;
        }
}

void
ddt_stat_add(ddt_stat_t *dst, const ddt_stat_t *src, uint64_t neg)
{
        const uint64_t *s = (const uint64_t *)src;
        uint64_t *d = (uint64_t *)dst;
        uint64_t *d_end = (uint64_t *)(dst + 1);

        ASSERT(neg == 0 || neg == -1ULL);       /* add or subtract */

        for (int i = 0; i < d_end - d; i++)
                d[i] += (s[i] ^ neg) - neg;
}

static void
ddt_stat_update(ddt_t *ddt, ddt_entry_t *dde, uint64_t neg)
{
        ddt_stat_t dds;
        ddt_histogram_t *ddh;
        int bucket;

        ddt_stat_generate(ddt, dde, &dds);

        bucket = highbit64(dds.dds_ref_blocks) - 1;
        ASSERT3U(bucket, >=, 0);

        ddh = &ddt->ddt_histogram[dde->dde_type][dde->dde_class];

        ddt_stat_add(&ddh->ddh_stat[bucket], &dds, neg);
}

void
ddt_histogram_add(ddt_histogram_t *dst, const ddt_histogram_t *src)
{
        for (int h = 0; h < 64; h++)
                ddt_stat_add(&dst->ddh_stat[h], &src->ddh_stat[h], 0);
}

void
ddt_histogram_stat(ddt_stat_t *dds, const ddt_histogram_t *ddh)
{
        memset(dds, 0, sizeof (*dds));

        for (int h = 0; h < 64; h++)
                ddt_stat_add(dds, &ddh->ddh_stat[h], 0);
}

boolean_t
ddt_histogram_empty(const ddt_histogram_t *ddh)
{
        const uint64_t *s = (const uint64_t *)ddh;
        const uint64_t *s_end = (const uint64_t *)(ddh + 1);

        while (s < s_end)
                if (*s++ != 0)
                        return (B_FALSE);

        return (B_TRUE);
}

void
ddt_get_dedup_object_stats(spa_t *spa, ddt_object_t *ddo_total)
{
        /* Sum the statistics we cached in ddt_object_sync(). */
        for (enum zio_checksum c = 0; c < ZIO_CHECKSUM_FUNCTIONS; c++) {
                ddt_t *ddt = spa->spa_ddt[c];
                for (enum ddt_type type = 0; type < DDT_TYPES; type++) {
                        for (enum ddt_class class = 0; class < DDT_CLASSES;
                            class++) {
                                ddt_object_t *ddo =
                                    &ddt->ddt_object_stats[type][class];
                                ddo_total->ddo_count += ddo->ddo_count;
                                ddo_total->ddo_dspace += ddo->ddo_dspace;
                                ddo_total->ddo_mspace += ddo->ddo_mspace;
                        }
                }
        }

        /* ... and compute the averages. */
        if (ddo_total->ddo_count != 0) {
                ddo_total->ddo_dspace /= ddo_total->ddo_count;
                ddo_total->ddo_mspace /= ddo_total->ddo_count;
        }
}

void
ddt_get_dedup_histogram(spa_t *spa, ddt_histogram_t *ddh)
{
        for (enum zio_checksum c = 0; c < ZIO_CHECKSUM_FUNCTIONS; c++) {
                ddt_t *ddt = spa->spa_ddt[c];
                for (enum ddt_type type = 0; type < DDT_TYPES && ddt; type++) {
                        for (enum ddt_class class = 0; class < DDT_CLASSES;
                            class++) {
                                ddt_histogram_add(ddh,
                                    &ddt->ddt_histogram_cache[type][class]);
                        }
                }
        }
}

void
ddt_get_dedup_stats(spa_t *spa, ddt_stat_t *dds_total)
{
        ddt_histogram_t *ddh_total;

        ddh_total = kmem_zalloc(sizeof (ddt_histogram_t), KM_SLEEP);
        ddt_get_dedup_histogram(spa, ddh_total);
        ddt_histogram_stat(dds_total, ddh_total);
        kmem_free(ddh_total, sizeof (ddt_histogram_t));
}

uint64_t
ddt_get_dedup_dspace(spa_t *spa)
{
        ddt_stat_t dds_total;

        if (spa->spa_dedup_dspace != ~0ULL)
                return (spa->spa_dedup_dspace);

        memset(&dds_total, 0, sizeof (ddt_stat_t));

        /* Calculate and cache the stats */
        ddt_get_dedup_stats(spa, &dds_total);
        spa->spa_dedup_dspace = dds_total.dds_ref_dsize - dds_total.dds_dsize;
        return (spa->spa_dedup_dspace);
}

uint64_t
ddt_get_pool_dedup_ratio(spa_t *spa)
{
        ddt_stat_t dds_total = { 0 };

        ddt_get_dedup_stats(spa, &dds_total);
        if (dds_total.dds_dsize == 0)
                return (100);

        return (dds_total.dds_ref_dsize * 100 / dds_total.dds_dsize);
}

ddt_t *
ddt_select(spa_t *spa, const blkptr_t *bp)
{
        return (spa->spa_ddt[BP_GET_CHECKSUM(bp)]);
}

void
ddt_enter(ddt_t *ddt)
{
        mutex_enter(&ddt->ddt_lock);
}

void
ddt_exit(ddt_t *ddt)
{
        mutex_exit(&ddt->ddt_lock);
}

void
ddt_init(void)
{
        ddt_cache = kmem_cache_create("ddt_cache",
            sizeof (ddt_t), 0, NULL, NULL, NULL, NULL, NULL, 0);
        ddt_entry_cache = kmem_cache_create("ddt_entry_cache",
            sizeof (ddt_entry_t), 0, NULL, NULL, NULL, NULL, NULL, 0);
}

void
ddt_fini(void)
{
        kmem_cache_destroy(ddt_entry_cache);
        kmem_cache_destroy(ddt_cache);
}

static ddt_entry_t *
ddt_alloc(const ddt_key_t *ddk)
{
        ddt_entry_t *dde;

        dde = kmem_cache_alloc(ddt_entry_cache, KM_SLEEP);
        memset(dde, 0, sizeof (ddt_entry_t));
        cv_init(&dde->dde_cv, NULL, CV_DEFAULT, NULL);

        dde->dde_key = *ddk;

        return (dde);
}

static void
ddt_free(ddt_entry_t *dde)
{
        ASSERT(!dde->dde_loading);

        for (int p = 0; p < DDT_PHYS_TYPES; p++)
                ASSERT3P(dde->dde_lead_zio[p], ==, NULL);

        if (dde->dde_repair_abd != NULL)
                abd_free(dde->dde_repair_abd);

        cv_destroy(&dde->dde_cv);
        kmem_cache_free(ddt_entry_cache, dde);
}

void
ddt_remove(ddt_t *ddt, ddt_entry_t *dde)
{
        ASSERT(MUTEX_HELD(&ddt->ddt_lock));

        avl_remove(&ddt->ddt_tree, dde);
        ddt_free(dde);
}

ddt_entry_t *
ddt_lookup(ddt_t *ddt, const blkptr_t *bp, boolean_t add)
{
        ddt_entry_t *dde, dde_search;
        enum ddt_type type;
        enum ddt_class class;
        avl_index_t where;
        int error;

        ASSERT(MUTEX_HELD(&ddt->ddt_lock));

        ddt_key_fill(&dde_search.dde_key, bp);

        dde = avl_find(&ddt->ddt_tree, &dde_search, &where);
        if (dde == NULL) {
                if (!add)
                        return (NULL);
                dde = ddt_alloc(&dde_search.dde_key);
                avl_insert(&ddt->ddt_tree, dde, where);
        }

        while (dde->dde_loading)
                cv_wait(&dde->dde_cv, &ddt->ddt_lock);

        if (dde->dde_loaded)
                return (dde);

        dde->dde_loading = B_TRUE;

        ddt_exit(ddt);

        error = ENOENT;

        for (type = 0; type < DDT_TYPES; type++) {
                for (class = 0; class < DDT_CLASSES; class++) {
                        error = ddt_object_lookup(ddt, type, class, dde);
                        if (error != ENOENT) {
                                ASSERT0(error);
                                break;
                        }
                }
                if (error != ENOENT)
                        break;
        }

        ddt_enter(ddt);

        ASSERT(!dde->dde_loaded);
        ASSERT(dde->dde_loading);

        dde->dde_type = type;   /* will be DDT_TYPES if no entry found */
        dde->dde_class = class; /* will be DDT_CLASSES if no entry found */
        dde->dde_loaded = B_TRUE;
        dde->dde_loading = B_FALSE;

        if (error == 0)
                ddt_stat_update(ddt, dde, -1ULL);

        cv_broadcast(&dde->dde_cv);

        return (dde);
}

void
ddt_prefetch(spa_t *spa, const blkptr_t *bp)
{
        ddt_t *ddt;
        ddt_entry_t dde;

        if (!zfs_dedup_prefetch || bp == NULL || !BP_GET_DEDUP(bp))
                return;

        /*
         * We only remove the DDT once all tables are empty and only
         * prefetch dedup blocks when there are entries in the DDT.
         * Thus no locking is required as the DDT can't disappear on us.
         */
        ddt = ddt_select(spa, bp);
        ddt_key_fill(&dde.dde_key, bp);

        for (enum ddt_type type = 0; type < DDT_TYPES; type++) {
                for (enum ddt_class class = 0; class < DDT_CLASSES; class++) {
                        ddt_object_prefetch(ddt, type, class, &dde);
                }
        }
}

/*
 * Opaque struct used for ddt_key comparison
 */
#define DDT_KEY_CMP_LEN (sizeof (ddt_key_t) / sizeof (uint16_t))

typedef struct ddt_key_cmp {
        uint16_t        u16[DDT_KEY_CMP_LEN];
} ddt_key_cmp_t;

int
ddt_entry_compare(const void *x1, const void *x2)
{
        const ddt_entry_t *dde1 = x1;
        const ddt_entry_t *dde2 = x2;
        const ddt_key_cmp_t *k1 = (const ddt_key_cmp_t *)&dde1->dde_key;
        const ddt_key_cmp_t *k2 = (const ddt_key_cmp_t *)&dde2->dde_key;
        int32_t cmp = 0;

        for (int i = 0; i < DDT_KEY_CMP_LEN; i++) {
                cmp = (int32_t)k1->u16[i] - (int32_t)k2->u16[i];
                if (likely(cmp))
                        break;
        }

        return (TREE_ISIGN(cmp));
}

static ddt_t *
ddt_table_alloc(spa_t *spa, enum zio_checksum c)
{
        ddt_t *ddt;

        ddt = kmem_cache_alloc(ddt_cache, KM_SLEEP);
        memset(ddt, 0, sizeof (ddt_t));

        mutex_init(&ddt->ddt_lock, NULL, MUTEX_DEFAULT, NULL);
        avl_create(&ddt->ddt_tree, ddt_entry_compare,
            sizeof (ddt_entry_t), offsetof(ddt_entry_t, dde_node));
        avl_create(&ddt->ddt_repair_tree, ddt_entry_compare,
            sizeof (ddt_entry_t), offsetof(ddt_entry_t, dde_node));
        ddt->ddt_checksum = c;
        ddt->ddt_spa = spa;
        ddt->ddt_os = spa->spa_meta_objset;

        return (ddt);
}

static void
ddt_table_free(ddt_t *ddt)
{
        ASSERT0(avl_numnodes(&ddt->ddt_tree));
        ASSERT0(avl_numnodes(&ddt->ddt_repair_tree));
        avl_destroy(&ddt->ddt_tree);
        avl_destroy(&ddt->ddt_repair_tree);
        mutex_destroy(&ddt->ddt_lock);
        kmem_cache_free(ddt_cache, ddt);
}

void
ddt_create(spa_t *spa)
{
        spa->spa_dedup_checksum = ZIO_DEDUPCHECKSUM;

        for (enum zio_checksum c = 0; c < ZIO_CHECKSUM_FUNCTIONS; c++)
                spa->spa_ddt[c] = ddt_table_alloc(spa, c);
}

int
ddt_load(spa_t *spa)
{
        int error;

        ddt_create(spa);

        error = zap_lookup(spa->spa_meta_objset, DMU_POOL_DIRECTORY_OBJECT,
            DMU_POOL_DDT_STATS, sizeof (uint64_t), 1,
            &spa->spa_ddt_stat_object);

        if (error)
                return (error == ENOENT ? 0 : error);

        for (enum zio_checksum c = 0; c < ZIO_CHECKSUM_FUNCTIONS; c++) {
                ddt_t *ddt = spa->spa_ddt[c];
                for (enum ddt_type type = 0; type < DDT_TYPES; type++) {
                        for (enum ddt_class class = 0; class < DDT_CLASSES;
                            class++) {
                                error = ddt_object_load(ddt, type, class);
                                if (error != 0 && error != ENOENT)
                                        return (error);
                        }
                }

                /*
                 * Seed the cached histograms.
                 */
                memcpy(&ddt->ddt_histogram_cache, ddt->ddt_histogram,
                    sizeof (ddt->ddt_histogram));
                spa->spa_dedup_dspace = ~0ULL;
        }

        return (0);
}

void
ddt_unload(spa_t *spa)
{
        for (enum zio_checksum c = 0; c < ZIO_CHECKSUM_FUNCTIONS; c++) {
                if (spa->spa_ddt[c]) {
                        ddt_table_free(spa->spa_ddt[c]);
                        spa->spa_ddt[c] = NULL;
                }
        }
}

boolean_t
ddt_class_contains(spa_t *spa, enum ddt_class max_class, const blkptr_t *bp)
{
        ddt_t *ddt;
        ddt_entry_t *dde;

        if (!BP_GET_DEDUP(bp))
                return (B_FALSE);

        if (max_class == DDT_CLASS_UNIQUE)
                return (B_TRUE);

        ddt = spa->spa_ddt[BP_GET_CHECKSUM(bp)];
        dde = kmem_cache_alloc(ddt_entry_cache, KM_SLEEP);

        ddt_key_fill(&(dde->dde_key), bp);

        for (enum ddt_type type = 0; type < DDT_TYPES; type++) {
                for (enum ddt_class class = 0; class <= max_class; class++) {
                        if (ddt_object_lookup(ddt, type, class, dde) == 0) {
                                kmem_cache_free(ddt_entry_cache, dde);
                                return (B_TRUE);
                        }
                }
        }

        kmem_cache_free(ddt_entry_cache, dde);
        return (B_FALSE);
}

ddt_entry_t *
ddt_repair_start(ddt_t *ddt, const blkptr_t *bp)
{
        ddt_key_t ddk;
        ddt_entry_t *dde;

        ddt_key_fill(&ddk, bp);

        dde = ddt_alloc(&ddk);

        for (enum ddt_type type = 0; type < DDT_TYPES; type++) {
                for (enum ddt_class class = 0; class < DDT_CLASSES; class++) {
                        /*
                         * We can only do repair if there are multiple copies
                         * of the block.  For anything in the UNIQUE class,
                         * there's definitely only one copy, so don't even try.
                         */
                        if (class != DDT_CLASS_UNIQUE &&
                            ddt_object_lookup(ddt, type, class, dde) == 0)
                                return (dde);
                }
        }

        memset(dde->dde_phys, 0, sizeof (dde->dde_phys));

        return (dde);
}

void
ddt_repair_done(ddt_t *ddt, ddt_entry_t *dde)
{
        avl_index_t where;

        ddt_enter(ddt);

        if (dde->dde_repair_abd != NULL && spa_writeable(ddt->ddt_spa) &&
            avl_find(&ddt->ddt_repair_tree, dde, &where) == NULL)
                avl_insert(&ddt->ddt_repair_tree, dde, where);
        else
                ddt_free(dde);

        ddt_exit(ddt);
}

static void
ddt_repair_entry_done(zio_t *zio)
{
        ddt_entry_t *rdde = zio->io_private;

        ddt_free(rdde);
}

static void
ddt_repair_entry(ddt_t *ddt, ddt_entry_t *dde, ddt_entry_t *rdde, zio_t *rio)
{
        ddt_phys_t *ddp = dde->dde_phys;
        ddt_phys_t *rddp = rdde->dde_phys;
        ddt_key_t *ddk = &dde->dde_key;
        ddt_key_t *rddk = &rdde->dde_key;
        zio_t *zio;
        blkptr_t blk;

        zio = zio_null(rio, rio->io_spa, NULL,
            ddt_repair_entry_done, rdde, rio->io_flags);

        for (int p = 0; p < DDT_PHYS_TYPES; p++, ddp++, rddp++) {
                if (ddp->ddp_phys_birth == 0 ||
                    ddp->ddp_phys_birth != rddp->ddp_phys_birth ||
                    memcmp(ddp->ddp_dva, rddp->ddp_dva, sizeof (ddp->ddp_dva)))
                        continue;
                ddt_bp_create(ddt->ddt_checksum, ddk, ddp, &blk);
                zio_nowait(zio_rewrite(zio, zio->io_spa, 0, &blk,
                    rdde->dde_repair_abd, DDK_GET_PSIZE(rddk), NULL, NULL,
                    ZIO_PRIORITY_SYNC_WRITE, ZIO_DDT_CHILD_FLAGS(zio), NULL));
        }

        zio_nowait(zio);
}

static void
ddt_repair_table(ddt_t *ddt, zio_t *rio)
{
        spa_t *spa = ddt->ddt_spa;
        ddt_entry_t *dde, *rdde_next, *rdde;
        avl_tree_t *t = &ddt->ddt_repair_tree;
        blkptr_t blk;

        if (spa_sync_pass(spa) > 1)
                return;

        ddt_enter(ddt);
        for (rdde = avl_first(t); rdde != NULL; rdde = rdde_next) {
                rdde_next = AVL_NEXT(t, rdde);
                avl_remove(&ddt->ddt_repair_tree, rdde);
                ddt_exit(ddt);
                ddt_bp_create(ddt->ddt_checksum, &rdde->dde_key, NULL, &blk);
                dde = ddt_repair_start(ddt, &blk);
                ddt_repair_entry(ddt, dde, rdde, rio);
                ddt_repair_done(ddt, dde);
                ddt_enter(ddt);
        }
        ddt_exit(ddt);
}

static void
ddt_sync_entry(ddt_t *ddt, ddt_entry_t *dde, dmu_tx_t *tx, uint64_t txg)
{
        dsl_pool_t *dp = ddt->ddt_spa->spa_dsl_pool;
        ddt_phys_t *ddp = dde->dde_phys;
        ddt_key_t *ddk = &dde->dde_key;
        enum ddt_type otype = dde->dde_type;
        enum ddt_type ntype = DDT_TYPE_CURRENT;
        enum ddt_class oclass = dde->dde_class;
        enum ddt_class nclass;
        uint64_t total_refcnt = 0;

        ASSERT(dde->dde_loaded);
        ASSERT(!dde->dde_loading);

        for (int p = 0; p < DDT_PHYS_TYPES; p++, ddp++) {
                ASSERT3P(dde->dde_lead_zio[p], ==, NULL);
                if (ddp->ddp_phys_birth == 0) {
                        ASSERT0(ddp->ddp_refcnt);
                        continue;
                }
                if (p == DDT_PHYS_DITTO) {
                        /*
                         * Note, we no longer create DDT-DITTO blocks, but we
                         * don't want to leak any written by older software.
                         */
                        ddt_phys_free(ddt, ddk, ddp, txg);
                        continue;
                }
                if (ddp->ddp_refcnt == 0)
                        ddt_phys_free(ddt, ddk, ddp, txg);
                total_refcnt += ddp->ddp_refcnt;
        }

        /* We do not create new DDT-DITTO blocks. */
        ASSERT0(dde->dde_phys[DDT_PHYS_DITTO].ddp_phys_birth);
        if (total_refcnt > 1)
                nclass = DDT_CLASS_DUPLICATE;
        else
                nclass = DDT_CLASS_UNIQUE;

        if (otype != DDT_TYPES &&
            (otype != ntype || oclass != nclass || total_refcnt == 0)) {
                VERIFY0(ddt_object_remove(ddt, otype, oclass, dde, tx));
                ASSERT3U(
                    ddt_object_lookup(ddt, otype, oclass, dde), ==, ENOENT);
        }

        if (total_refcnt != 0) {
                dde->dde_type = ntype;
                dde->dde_class = nclass;
                ddt_stat_update(ddt, dde, 0);
                if (!ddt_object_exists(ddt, ntype, nclass))
                        ddt_object_create(ddt, ntype, nclass, tx);
                VERIFY0(ddt_object_update(ddt, ntype, nclass, dde, tx));

                /*
                 * If the class changes, the order that we scan this bp
                 * changes.  If it decreases, we could miss it, so
                 * scan it right now.  (This covers both class changing
                 * while we are doing ddt_walk(), and when we are
                 * traversing.)
                 */
                if (nclass < oclass) {
                        dsl_scan_ddt_entry(dp->dp_scan,
                            ddt->ddt_checksum, dde, tx);
                }
        }
}

static void
ddt_sync_table(ddt_t *ddt, dmu_tx_t *tx, uint64_t txg)
{
        spa_t *spa = ddt->ddt_spa;
        ddt_entry_t *dde;
        void *cookie = NULL;

        if (avl_numnodes(&ddt->ddt_tree) == 0)
                return;

        ASSERT3U(spa->spa_uberblock.ub_version, >=, SPA_VERSION_DEDUP);

        if (spa->spa_ddt_stat_object == 0) {
                spa->spa_ddt_stat_object = zap_create_link(ddt->ddt_os,
                    DMU_OT_DDT_STATS, DMU_POOL_DIRECTORY_OBJECT,
                    DMU_POOL_DDT_STATS, tx);
        }

        while ((dde = avl_destroy_nodes(&ddt->ddt_tree, &cookie)) != NULL) {
                ddt_sync_entry(ddt, dde, tx, txg);
                ddt_free(dde);
        }

        for (enum ddt_type type = 0; type < DDT_TYPES; type++) {
                uint64_t add, count = 0;
                for (enum ddt_class class = 0; class < DDT_CLASSES; class++) {
                        if (ddt_object_exists(ddt, type, class)) {
                                ddt_object_sync(ddt, type, class, tx);
                                VERIFY0(ddt_object_count(ddt, type, class,
                                    &add));
                                count += add;
                        }
                }
                for (enum ddt_class class = 0; class < DDT_CLASSES; class++) {
                        if (count == 0 && ddt_object_exists(ddt, type, class))
                                ddt_object_destroy(ddt, type, class, tx);
                }
        }

        memcpy(&ddt->ddt_histogram_cache, ddt->ddt_histogram,
            sizeof (ddt->ddt_histogram));
        spa->spa_dedup_dspace = ~0ULL;
}

void
ddt_sync(spa_t *spa, uint64_t txg)
{
        dsl_scan_t *scn = spa->spa_dsl_pool->dp_scan;
        dmu_tx_t *tx;
        zio_t *rio;

        ASSERT3U(spa_syncing_txg(spa), ==, txg);

        tx = dmu_tx_create_assigned(spa->spa_dsl_pool, txg);

        rio = zio_root(spa, NULL, NULL,
            ZIO_FLAG_CANFAIL | ZIO_FLAG_SPECULATIVE | ZIO_FLAG_SELF_HEAL);

        /*
         * This function may cause an immediate scan of ddt blocks (see
         * the comment above dsl_scan_ddt() for details). We set the
         * scan's root zio here so that we can wait for any scan IOs in
         * addition to the regular ddt IOs.
         */
        ASSERT3P(scn->scn_zio_root, ==, NULL);
        scn->scn_zio_root = rio;

        for (enum zio_checksum c = 0; c < ZIO_CHECKSUM_FUNCTIONS; c++) {
                ddt_t *ddt = spa->spa_ddt[c];
                if (ddt == NULL)
                        continue;
                ddt_sync_table(ddt, tx, txg);
                ddt_repair_table(ddt, rio);
        }

        (void) zio_wait(rio);
        scn->scn_zio_root = NULL;

        dmu_tx_commit(tx);
}

int
ddt_walk(spa_t *spa, ddt_bookmark_t *ddb, ddt_entry_t *dde)
{
        do {
                do {
                        do {
                                ddt_t *ddt = spa->spa_ddt[ddb->ddb_checksum];
                                int error = ENOENT;
                                if (ddt_object_exists(ddt, ddb->ddb_type,
                                    ddb->ddb_class)) {
                                        error = ddt_object_walk(ddt,
                                            ddb->ddb_type, ddb->ddb_class,
                                            &ddb->ddb_cursor, dde);
                                }
                                dde->dde_type = ddb->ddb_type;
                                dde->dde_class = ddb->ddb_class;
                                if (error == 0)
                                        return (0);
                                if (error != ENOENT)
                                        return (error);
                                ddb->ddb_cursor = 0;
                        } while (++ddb->ddb_checksum < ZIO_CHECKSUM_FUNCTIONS);
                        ddb->ddb_checksum = 0;
                } while (++ddb->ddb_type < DDT_TYPES);
                ddb->ddb_type = 0;
        } while (++ddb->ddb_class < DDT_CLASSES);

        return (SET_ERROR(ENOENT));
}

/*
 * This function is used by Block Cloning (brt.c) to increase reference
 * counter for the DDT entry if the block is already in DDT.
 *
 * Return false if the block, despite having the D bit set, is not present
 * in the DDT. Currently this is not possible but might be in the future.
 * See the comment below.
 */
boolean_t
ddt_addref(spa_t *spa, const blkptr_t *bp)
{
        ddt_t *ddt;
        ddt_entry_t *dde;
        boolean_t result;

        spa_config_enter(spa, SCL_ZIO, FTAG, RW_READER);
        ddt = ddt_select(spa, bp);
        ddt_enter(ddt);

        dde = ddt_lookup(ddt, bp, B_TRUE);
        ASSERT3P(dde, !=, NULL);

        if (dde->dde_type < DDT_TYPES) {
                ddt_phys_t *ddp;

                ASSERT3S(dde->dde_class, <, DDT_CLASSES);

                ddp = &dde->dde_phys[BP_GET_NDVAS(bp)];

                /*
                 * This entry already existed (dde_type is real), so it must
                 * have refcnt >0 at the start of this txg. We are called from
                 * brt_pending_apply(), before frees are issued, so the refcnt
                 * can't be lowered yet. Therefore, it must be >0. We assert
                 * this because if the order of BRT and DDT interactions were
                 * ever to change and the refcnt was ever zero here, then
                 * likely further action is required to fill out the DDT entry,
                 * and this is a place that is likely to be missed in testing.
                 */
                ASSERT3U(ddp->ddp_refcnt, >, 0);

                ddt_phys_addref(ddp);
                result = B_TRUE;
        } else {
                /*
                 * At the time of implementating this if the block has the
                 * DEDUP flag set it must exist in the DEDUP table, but
                 * there are many advocates that want ability to remove
                 * entries from DDT with refcnt=1. If this will happen,
                 * we may have a block with the DEDUP set, but which doesn't
                 * have a corresponding entry in the DDT. Be ready.
                 */
                ASSERT3S(dde->dde_class, ==, DDT_CLASSES);
                ddt_remove(ddt, dde);
                result = B_FALSE;
        }

        ddt_exit(ddt);
        spa_config_exit(spa, SCL_ZIO, FTAG);

        return (result);
}

ZFS_MODULE_PARAM(zfs_dedup, zfs_dedup_, prefetch, INT, ZMOD_RW,
        "Enable prefetching dedup-ed blks");