Illumos #3006

[mirror_zfs.git] / module / zfs / dsl_pool.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 http://www.opensolaris.org/os/licensing.
 * 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) 2005, 2010, Oracle and/or its affiliates. All rights reserved.
 * Copyright (c) 2012 by Delphix. All rights reserved.
 */

#include <sys/dsl_pool.h>
#include <sys/dsl_dataset.h>
#include <sys/dsl_prop.h>
#include <sys/dsl_dir.h>
#include <sys/dsl_synctask.h>
#include <sys/dsl_scan.h>
#include <sys/dnode.h>
#include <sys/dmu_tx.h>
#include <sys/dmu_objset.h>
#include <sys/arc.h>
#include <sys/zap.h>
#include <sys/zio.h>
#include <sys/zfs_context.h>
#include <sys/fs/zfs.h>
#include <sys/zfs_znode.h>
#include <sys/spa_impl.h>
#include <sys/dsl_deadlist.h>
#include <sys/bptree.h>
#include <sys/zfeature.h>
#include <sys/zil_impl.h>

int zfs_no_write_throttle = 0;
int zfs_write_limit_shift = 3;                  /* 1/8th of physical memory */
int zfs_txg_synctime_ms = 1000;         /* target millisecs to sync a txg */
int zfs_txg_history = 60;               /* statistics for the last N txgs */

unsigned long zfs_write_limit_min = 32 << 20;   /* min write limit is 32MB */
unsigned long zfs_write_limit_max = 0;          /* max data payload per txg */
unsigned long zfs_write_limit_inflated = 0;
unsigned long zfs_write_limit_override = 0;

kmutex_t zfs_write_limit_lock;

static pgcnt_t old_physmem = 0;

static int
dsl_pool_txg_history_update(kstat_t *ksp, int rw)
{
        dsl_pool_t *dp = ksp->ks_private;
        txg_history_t *th;
        int i = 0;

        if (rw == KSTAT_WRITE)
                return (EACCES);

        if (ksp->ks_data)
                kmem_free(ksp->ks_data, ksp->ks_data_size);

        mutex_enter(&dp->dp_lock);

        ksp->ks_ndata = dp->dp_txg_history_size;
        ksp->ks_data_size = dp->dp_txg_history_size * sizeof(kstat_txg_t);
        if (ksp->ks_data_size > 0)
                ksp->ks_data = kmem_alloc(ksp->ks_data_size, KM_PUSHPAGE);

        /* Traversed oldest to youngest for the most readable kstat output */
        for (th = list_tail(&dp->dp_txg_history); th != NULL;
             th = list_prev(&dp->dp_txg_history, th)) {
                mutex_enter(&th->th_lock);
                ASSERT3S(i + sizeof(kstat_txg_t), <=, ksp->ks_data_size);
                memcpy(ksp->ks_data + i, &th->th_kstat, sizeof(kstat_txg_t));
                i += sizeof(kstat_txg_t);
                mutex_exit(&th->th_lock);
        }

        mutex_exit(&dp->dp_lock);

        return (0);
}

static void
dsl_pool_txg_history_init(dsl_pool_t *dp, uint64_t txg)
{
        char name[KSTAT_STRLEN];

        list_create(&dp->dp_txg_history, sizeof (txg_history_t),
            offsetof(txg_history_t, th_link));
        dsl_pool_txg_history_add(dp, txg);

        (void) snprintf(name, KSTAT_STRLEN, "txgs-%s", spa_name(dp->dp_spa));
        dp->dp_txg_kstat = kstat_create("zfs", 0, name, "misc",
            KSTAT_TYPE_TXG, 0, KSTAT_FLAG_VIRTUAL);
        if (dp->dp_txg_kstat) {
                dp->dp_txg_kstat->ks_data = NULL;
                dp->dp_txg_kstat->ks_private = dp;
                dp->dp_txg_kstat->ks_update = dsl_pool_txg_history_update;
                kstat_install(dp->dp_txg_kstat);
        }
}

static void
dsl_pool_txg_history_destroy(dsl_pool_t *dp)
{
        txg_history_t *th;

        if (dp->dp_txg_kstat) {
                if (dp->dp_txg_kstat->ks_data)
                        kmem_free(dp->dp_txg_kstat->ks_data,
                            dp->dp_txg_kstat->ks_data_size);

                kstat_delete(dp->dp_txg_kstat);
        }

        mutex_enter(&dp->dp_lock);
        while ((th = list_remove_head(&dp->dp_txg_history))) {
                dp->dp_txg_history_size--;
                mutex_destroy(&th->th_lock);
                kmem_free(th, sizeof(txg_history_t));
        }

        ASSERT3U(dp->dp_txg_history_size, ==, 0);
        list_destroy(&dp->dp_txg_history);
        mutex_exit(&dp->dp_lock);
}

txg_history_t *
dsl_pool_txg_history_add(dsl_pool_t *dp, uint64_t txg)
{
        txg_history_t *th, *rm;

        th = kmem_zalloc(sizeof(txg_history_t), KM_PUSHPAGE);
        mutex_init(&th->th_lock, NULL, MUTEX_DEFAULT, NULL);
        th->th_kstat.txg = txg;
        th->th_kstat.state = TXG_STATE_OPEN;
        th->th_kstat.birth = gethrtime();

        mutex_enter(&dp->dp_lock);

        list_insert_head(&dp->dp_txg_history, th);
        dp->dp_txg_history_size++;

        while (dp->dp_txg_history_size > zfs_txg_history) {
                dp->dp_txg_history_size--;
                rm = list_remove_tail(&dp->dp_txg_history);
                mutex_destroy(&rm->th_lock);
                kmem_free(rm, sizeof(txg_history_t));
        }

        mutex_exit(&dp->dp_lock);

        return (th);
}

/*
 * Traversed youngest to oldest because lookups are only done for open
 * or syncing txgs which are guaranteed to be at the head of the list.
 * The txg_history_t structure will be returned locked.
 */
txg_history_t *
dsl_pool_txg_history_get(dsl_pool_t *dp, uint64_t txg)
{
        txg_history_t *th;

        mutex_enter(&dp->dp_lock);
        for (th = list_head(&dp->dp_txg_history); th != NULL;
             th = list_next(&dp->dp_txg_history, th)) {
                if (th->th_kstat.txg == txg) {
                        mutex_enter(&th->th_lock);
                        break;
                }
        }
        mutex_exit(&dp->dp_lock);

        return (th);
}

void
dsl_pool_txg_history_put(txg_history_t *th)
{
        mutex_exit(&th->th_lock);
}

int
dsl_pool_open_special_dir(dsl_pool_t *dp, const char *name, dsl_dir_t **ddp)
{
        uint64_t obj;
        int err;

        err = zap_lookup(dp->dp_meta_objset,
            dp->dp_root_dir->dd_phys->dd_child_dir_zapobj,
            name, sizeof (obj), 1, &obj);
        if (err)
                return (err);

        return (dsl_dir_open_obj(dp, obj, name, dp, ddp));
}

static dsl_pool_t *
dsl_pool_open_impl(spa_t *spa, uint64_t txg)
{
        dsl_pool_t *dp;
        blkptr_t *bp = spa_get_rootblkptr(spa);

        dp = kmem_zalloc(sizeof (dsl_pool_t), KM_SLEEP);
        dp->dp_spa = spa;
        dp->dp_meta_rootbp = *bp;
        rw_init(&dp->dp_config_rwlock, NULL, RW_DEFAULT, NULL);
        dp->dp_write_limit = zfs_write_limit_min;
        txg_init(dp, txg);

        txg_list_create(&dp->dp_dirty_datasets,
            offsetof(dsl_dataset_t, ds_dirty_link));
        txg_list_create(&dp->dp_dirty_zilogs,
            offsetof(zilog_t, zl_dirty_link));
        txg_list_create(&dp->dp_dirty_dirs,
            offsetof(dsl_dir_t, dd_dirty_link));
        txg_list_create(&dp->dp_sync_tasks,
            offsetof(dsl_sync_task_group_t, dstg_node));

        mutex_init(&dp->dp_lock, NULL, MUTEX_DEFAULT, NULL);

        dp->dp_iput_taskq = taskq_create("zfs_iput_taskq", 1, minclsyspri,
            1, 4, 0);

        dsl_pool_txg_history_init(dp, txg);

        return (dp);
}

int
dsl_pool_init(spa_t *spa, uint64_t txg, dsl_pool_t **dpp)
{
        int err;
        dsl_pool_t *dp = dsl_pool_open_impl(spa, txg);

        err = dmu_objset_open_impl(spa, NULL, &dp->dp_meta_rootbp,
            &dp->dp_meta_objset);
        if (err != 0)
                dsl_pool_close(dp);
        else
                *dpp = dp;

        return (err);
}

int
dsl_pool_open(dsl_pool_t *dp)
{
        int err;
        dsl_dir_t *dd;
        dsl_dataset_t *ds;
        uint64_t obj;

        rw_enter(&dp->dp_config_rwlock, RW_WRITER);
        err = zap_lookup(dp->dp_meta_objset, DMU_POOL_DIRECTORY_OBJECT,
            DMU_POOL_ROOT_DATASET, sizeof (uint64_t), 1,
            &dp->dp_root_dir_obj);
        if (err)
                goto out;

        err = dsl_dir_open_obj(dp, dp->dp_root_dir_obj,
            NULL, dp, &dp->dp_root_dir);
        if (err)
                goto out;

        err = dsl_pool_open_special_dir(dp, MOS_DIR_NAME, &dp->dp_mos_dir);
        if (err)
                goto out;

        if (spa_version(dp->dp_spa) >= SPA_VERSION_ORIGIN) {
                err = dsl_pool_open_special_dir(dp, ORIGIN_DIR_NAME, &dd);
                if (err)
                        goto out;
                err = dsl_dataset_hold_obj(dp, dd->dd_phys->dd_head_dataset_obj,
                    FTAG, &ds);
                if (err == 0) {
                        err = dsl_dataset_hold_obj(dp,
                            ds->ds_phys->ds_prev_snap_obj, dp,
                            &dp->dp_origin_snap);
                        dsl_dataset_rele(ds, FTAG);
                }
                dsl_dir_close(dd, dp);
                if (err)
                        goto out;
        }

        if (spa_version(dp->dp_spa) >= SPA_VERSION_DEADLISTS) {
                err = dsl_pool_open_special_dir(dp, FREE_DIR_NAME,
                    &dp->dp_free_dir);
                if (err)
                        goto out;

                err = zap_lookup(dp->dp_meta_objset, DMU_POOL_DIRECTORY_OBJECT,
                    DMU_POOL_FREE_BPOBJ, sizeof (uint64_t), 1, &obj);
                if (err)
                        goto out;
                VERIFY3U(0, ==, bpobj_open(&dp->dp_free_bpobj,
                    dp->dp_meta_objset, obj));
        }

        if (spa_feature_is_active(dp->dp_spa,
            &spa_feature_table[SPA_FEATURE_ASYNC_DESTROY])) {
                err = zap_lookup(dp->dp_meta_objset, DMU_POOL_DIRECTORY_OBJECT,
                    DMU_POOL_BPTREE_OBJ, sizeof (uint64_t), 1,
                    &dp->dp_bptree_obj);
                if (err != 0)
                        goto out;
        }

        if (spa_feature_is_active(dp->dp_spa,
            &spa_feature_table[SPA_FEATURE_EMPTY_BPOBJ])) {
                err = zap_lookup(dp->dp_meta_objset, DMU_POOL_DIRECTORY_OBJECT,
                    DMU_POOL_EMPTY_BPOBJ, sizeof (uint64_t), 1,
                    &dp->dp_empty_bpobj);
                if (err != 0)
                        goto out;
        }

        err = zap_lookup(dp->dp_meta_objset, DMU_POOL_DIRECTORY_OBJECT,
            DMU_POOL_TMP_USERREFS, sizeof (uint64_t), 1,
            &dp->dp_tmp_userrefs_obj);
        if (err == ENOENT)
                err = 0;
        if (err)
                goto out;

        err = dsl_scan_init(dp, dp->dp_tx.tx_open_txg);

out:
        rw_exit(&dp->dp_config_rwlock);
        return (err);
}

void
dsl_pool_close(dsl_pool_t *dp)
{
        /* drop our references from dsl_pool_open() */

        /*
         * Since we held the origin_snap from "syncing" context (which
         * includes pool-opening context), it actually only got a "ref"
         * and not a hold, so just drop that here.
         */
        if (dp->dp_origin_snap)
                dsl_dataset_drop_ref(dp->dp_origin_snap, dp);
        if (dp->dp_mos_dir)
                dsl_dir_close(dp->dp_mos_dir, dp);
        if (dp->dp_free_dir)
                dsl_dir_close(dp->dp_free_dir, dp);
        if (dp->dp_root_dir)
                dsl_dir_close(dp->dp_root_dir, dp);

        bpobj_close(&dp->dp_free_bpobj);

        /* undo the dmu_objset_open_impl(mos) from dsl_pool_open() */
        if (dp->dp_meta_objset)
                dmu_objset_evict(dp->dp_meta_objset);

        txg_list_destroy(&dp->dp_dirty_datasets);
        txg_list_destroy(&dp->dp_dirty_zilogs);
        txg_list_destroy(&dp->dp_sync_tasks);
        txg_list_destroy(&dp->dp_dirty_dirs);

        arc_flush(dp->dp_spa);
        txg_fini(dp);
        dsl_scan_fini(dp);
        dsl_pool_txg_history_destroy(dp);
        rw_destroy(&dp->dp_config_rwlock);
        mutex_destroy(&dp->dp_lock);
        taskq_destroy(dp->dp_iput_taskq);
        if (dp->dp_blkstats)
                kmem_free(dp->dp_blkstats, sizeof (zfs_all_blkstats_t));
        kmem_free(dp, sizeof (dsl_pool_t));
}

dsl_pool_t *
dsl_pool_create(spa_t *spa, nvlist_t *zplprops, uint64_t txg)
{
        int err;
        dsl_pool_t *dp = dsl_pool_open_impl(spa, txg);
        dmu_tx_t *tx = dmu_tx_create_assigned(dp, txg);
        objset_t *os;
        dsl_dataset_t *ds;
        uint64_t obj;

        /* create and open the MOS (meta-objset) */
        dp->dp_meta_objset = dmu_objset_create_impl(spa,
            NULL, &dp->dp_meta_rootbp, DMU_OST_META, tx);

        /* create the pool directory */
        err = zap_create_claim(dp->dp_meta_objset, DMU_POOL_DIRECTORY_OBJECT,
            DMU_OT_OBJECT_DIRECTORY, DMU_OT_NONE, 0, tx);
        ASSERT0(err);

        /* Initialize scan structures */
        VERIFY3U(0, ==, dsl_scan_init(dp, txg));

        /* create and open the root dir */
        dp->dp_root_dir_obj = dsl_dir_create_sync(dp, NULL, NULL, tx);
        VERIFY(0 == dsl_dir_open_obj(dp, dp->dp_root_dir_obj,
            NULL, dp, &dp->dp_root_dir));

        /* create and open the meta-objset dir */
        (void) dsl_dir_create_sync(dp, dp->dp_root_dir, MOS_DIR_NAME, tx);
        VERIFY(0 == dsl_pool_open_special_dir(dp,
            MOS_DIR_NAME, &dp->dp_mos_dir));

        if (spa_version(spa) >= SPA_VERSION_DEADLISTS) {
                /* create and open the free dir */
                (void) dsl_dir_create_sync(dp, dp->dp_root_dir,
                    FREE_DIR_NAME, tx);
                VERIFY(0 == dsl_pool_open_special_dir(dp,
                    FREE_DIR_NAME, &dp->dp_free_dir));

                /* create and open the free_bplist */
                obj = bpobj_alloc(dp->dp_meta_objset, SPA_MAXBLOCKSIZE, tx);
                VERIFY(zap_add(dp->dp_meta_objset, DMU_POOL_DIRECTORY_OBJECT,
                    DMU_POOL_FREE_BPOBJ, sizeof (uint64_t), 1, &obj, tx) == 0);
                VERIFY3U(0, ==, bpobj_open(&dp->dp_free_bpobj,
                    dp->dp_meta_objset, obj));
        }

        if (spa_version(spa) >= SPA_VERSION_DSL_SCRUB)
                dsl_pool_create_origin(dp, tx);

        /* create the root dataset */
        obj = dsl_dataset_create_sync_dd(dp->dp_root_dir, NULL, 0, tx);

        /* create the root objset */
        VERIFY(0 == dsl_dataset_hold_obj(dp, obj, FTAG, &ds));
        VERIFY(NULL != (os = dmu_objset_create_impl(dp->dp_spa, ds,
            dsl_dataset_get_blkptr(ds), DMU_OST_ZFS, tx)));
#ifdef _KERNEL
        zfs_create_fs(os, kcred, zplprops, tx);
#endif
        dsl_dataset_rele(ds, FTAG);

        dmu_tx_commit(tx);

        return (dp);
}

/*
 * Account for the meta-objset space in its placeholder dsl_dir.
 */
void
dsl_pool_mos_diduse_space(dsl_pool_t *dp,
    int64_t used, int64_t comp, int64_t uncomp)
{
        ASSERT3U(comp, ==, uncomp); /* it's all metadata */
        mutex_enter(&dp->dp_lock);
        dp->dp_mos_used_delta += used;
        dp->dp_mos_compressed_delta += comp;
        dp->dp_mos_uncompressed_delta += uncomp;
        mutex_exit(&dp->dp_lock);
}

static int
deadlist_enqueue_cb(void *arg, const blkptr_t *bp, dmu_tx_t *tx)
{
        dsl_deadlist_t *dl = arg;
        dsl_pool_t *dp = dmu_objset_pool(dl->dl_os);
        rw_enter(&dp->dp_config_rwlock, RW_READER);
        dsl_deadlist_insert(dl, bp, tx);
        rw_exit(&dp->dp_config_rwlock);
        return (0);
}

void
dsl_pool_sync(dsl_pool_t *dp, uint64_t txg)
{
        zio_t *zio;
        dmu_tx_t *tx;
        dsl_dir_t *dd;
        dsl_dataset_t *ds;
        objset_t *mos = dp->dp_meta_objset;
        hrtime_t start, write_time;
        uint64_t data_written;
        int err;
        list_t synced_datasets;

        list_create(&synced_datasets, sizeof (dsl_dataset_t),
            offsetof(dsl_dataset_t, ds_synced_link));

        /*
         * We need to copy dp_space_towrite() before doing
         * dsl_sync_task_group_sync(), because
         * dsl_dataset_snapshot_reserve_space() will increase
         * dp_space_towrite but not actually write anything.
         */
        data_written = dp->dp_space_towrite[txg & TXG_MASK];

        tx = dmu_tx_create_assigned(dp, txg);

        dp->dp_read_overhead = 0;
        start = gethrtime();

        zio = zio_root(dp->dp_spa, NULL, NULL, ZIO_FLAG_MUSTSUCCEED);
        while ((ds = txg_list_remove(&dp->dp_dirty_datasets, txg))) {
                /*
                 * We must not sync any non-MOS datasets twice, because
                 * we may have taken a snapshot of them.  However, we
                 * may sync newly-created datasets on pass 2.
                 */
                ASSERT(!list_link_active(&ds->ds_synced_link));
                list_insert_tail(&synced_datasets, ds);
                dsl_dataset_sync(ds, zio, tx);
        }
        DTRACE_PROBE(pool_sync__1setup);
        err = zio_wait(zio);

        write_time = gethrtime() - start;
        ASSERT(err == 0);
        DTRACE_PROBE(pool_sync__2rootzio);

        /*
         * After the data blocks have been written (ensured by the zio_wait()
         * above), update the user/group space accounting.
         */
        for (ds = list_head(&synced_datasets); ds;
            ds = list_next(&synced_datasets, ds))
                dmu_objset_do_userquota_updates(ds->ds_objset, tx);

        /*
         * Sync the datasets again to push out the changes due to
         * userspace updates.  This must be done before we process the
         * sync tasks, so that any snapshots will have the correct
         * user accounting information (and we won't get confused
         * about which blocks are part of the snapshot).
         */
        zio = zio_root(dp->dp_spa, NULL, NULL, ZIO_FLAG_MUSTSUCCEED);
        while ((ds = txg_list_remove(&dp->dp_dirty_datasets, txg))) {
                ASSERT(list_link_active(&ds->ds_synced_link));
                dmu_buf_rele(ds->ds_dbuf, ds);
                dsl_dataset_sync(ds, zio, tx);
        }
        err = zio_wait(zio);

        /*
         * Now that the datasets have been completely synced, we can
         * clean up our in-memory structures accumulated while syncing:
         *
         *  - move dead blocks from the pending deadlist to the on-disk deadlist
         *  - clean up zil records
         *  - release hold from dsl_dataset_dirty()
         */
        while ((ds = list_remove_head(&synced_datasets))) {
                ASSERTV(objset_t *os = ds->ds_objset);
                bplist_iterate(&ds->ds_pending_deadlist,
                    deadlist_enqueue_cb, &ds->ds_deadlist, tx);
                ASSERT(!dmu_objset_is_dirty(os, txg));
                dmu_buf_rele(ds->ds_dbuf, ds);
        }

        start = gethrtime();
        while ((dd = txg_list_remove(&dp->dp_dirty_dirs, txg)))
                dsl_dir_sync(dd, tx);
        write_time += gethrtime() - start;

        /*
         * The MOS's space is accounted for in the pool/$MOS
         * (dp_mos_dir).  We can't modify the mos while we're syncing
         * it, so we remember the deltas and apply them here.
         */
        if (dp->dp_mos_used_delta != 0 || dp->dp_mos_compressed_delta != 0 ||
            dp->dp_mos_uncompressed_delta != 0) {
                dsl_dir_diduse_space(dp->dp_mos_dir, DD_USED_HEAD,
                    dp->dp_mos_used_delta,
                    dp->dp_mos_compressed_delta,
                    dp->dp_mos_uncompressed_delta, tx);
                dp->dp_mos_used_delta = 0;
                dp->dp_mos_compressed_delta = 0;
                dp->dp_mos_uncompressed_delta = 0;
        }

        start = gethrtime();
        if (list_head(&mos->os_dirty_dnodes[txg & TXG_MASK]) != NULL ||
            list_head(&mos->os_free_dnodes[txg & TXG_MASK]) != NULL) {
                zio = zio_root(dp->dp_spa, NULL, NULL, ZIO_FLAG_MUSTSUCCEED);
                dmu_objset_sync(mos, zio, tx);
                err = zio_wait(zio);
                ASSERT(err == 0);
                dprintf_bp(&dp->dp_meta_rootbp, "meta objset rootbp is %s", "");
                spa_set_rootblkptr(dp->dp_spa, &dp->dp_meta_rootbp);
        }
        write_time += gethrtime() - start;
        DTRACE_PROBE2(pool_sync__4io, hrtime_t, write_time,
            hrtime_t, dp->dp_read_overhead);
        write_time -= dp->dp_read_overhead;

        /*
         * If we modify a dataset in the same txg that we want to destroy it,
         * its dsl_dir's dd_dbuf will be dirty, and thus have a hold on it.
         * dsl_dir_destroy_check() will fail if there are unexpected holds.
         * Therefore, we want to sync the MOS (thus syncing the dd_dbuf
         * and clearing the hold on it) before we process the sync_tasks.
         * The MOS data dirtied by the sync_tasks will be synced on the next
         * pass.
         */
        DTRACE_PROBE(pool_sync__3task);
        if (!txg_list_empty(&dp->dp_sync_tasks, txg)) {
                dsl_sync_task_group_t *dstg;
                /*
                 * No more sync tasks should have been added while we
                 * were syncing.
                 */
                ASSERT(spa_sync_pass(dp->dp_spa) == 1);
                while ((dstg = txg_list_remove(&dp->dp_sync_tasks, txg)))
                        dsl_sync_task_group_sync(dstg, tx);
        }

        dmu_tx_commit(tx);

        dp->dp_space_towrite[txg & TXG_MASK] = 0;
        ASSERT(dp->dp_tempreserved[txg & TXG_MASK] == 0);

        /*
         * If the write limit max has not been explicitly set, set it
         * to a fraction of available physical memory (default 1/8th).
         * Note that we must inflate the limit because the spa
         * inflates write sizes to account for data replication.
         * Check this each sync phase to catch changing memory size.
         */
        if (physmem != old_physmem && zfs_write_limit_shift) {
                mutex_enter(&zfs_write_limit_lock);
                old_physmem = physmem;
                zfs_write_limit_max = ptob(physmem) >> zfs_write_limit_shift;
                zfs_write_limit_inflated = MAX(zfs_write_limit_min,
                    spa_get_asize(dp->dp_spa, zfs_write_limit_max));
                mutex_exit(&zfs_write_limit_lock);
        }

        /*
         * Attempt to keep the sync time consistent by adjusting the
         * amount of write traffic allowed into each transaction group.
         * Weight the throughput calculation towards the current value:
         *      thru = 3/4 old_thru + 1/4 new_thru
         *
         * Note: write_time is in nanosecs, so write_time/MICROSEC
         * yields millisecs
         */
        ASSERT(zfs_write_limit_min > 0);
        if (data_written > zfs_write_limit_min / 8 && write_time > MICROSEC) {
                uint64_t throughput = data_written / (write_time / MICROSEC);

                if (dp->dp_throughput)
                        dp->dp_throughput = throughput / 4 +
                            3 * dp->dp_throughput / 4;
                else
                        dp->dp_throughput = throughput;
                dp->dp_write_limit = MIN(zfs_write_limit_inflated,
                    MAX(zfs_write_limit_min,
                    dp->dp_throughput * zfs_txg_synctime_ms));
        }
}

void
dsl_pool_sync_done(dsl_pool_t *dp, uint64_t txg)
{
        zilog_t *zilog;
        dsl_dataset_t *ds;

        while ((zilog = txg_list_remove(&dp->dp_dirty_zilogs, txg))) {
                ds = dmu_objset_ds(zilog->zl_os);
                zil_clean(zilog, txg);
                ASSERT(!dmu_objset_is_dirty(zilog->zl_os, txg));
                dmu_buf_rele(ds->ds_dbuf, zilog);
        }
        ASSERT(!dmu_objset_is_dirty(dp->dp_meta_objset, txg));
}

/*
 * TRUE if the current thread is the tx_sync_thread or if we
 * are being called from SPA context during pool initialization.
 */
int
dsl_pool_sync_context(dsl_pool_t *dp)
{
        return (curthread == dp->dp_tx.tx_sync_thread ||
            spa_is_initializing(dp->dp_spa));
}

uint64_t
dsl_pool_adjustedsize(dsl_pool_t *dp, boolean_t netfree)
{
        uint64_t space, resv;

        /*
         * Reserve about 1.6% (1/64), or at least 32MB, for allocation
         * efficiency.
         * XXX The intent log is not accounted for, so it must fit
         * within this slop.
         *
         * If we're trying to assess whether it's OK to do a free,
         * cut the reservation in half to allow forward progress
         * (e.g. make it possible to rm(1) files from a full pool).
         */
        space = spa_get_dspace(dp->dp_spa);
        resv = MAX(space >> 6, SPA_MINDEVSIZE >> 1);
        if (netfree)
                resv >>= 1;

        return (space - resv);
}

int
dsl_pool_tempreserve_space(dsl_pool_t *dp, uint64_t space, dmu_tx_t *tx)
{
        uint64_t reserved = 0;
        uint64_t write_limit = (zfs_write_limit_override ?
            zfs_write_limit_override : dp->dp_write_limit);

        if (zfs_no_write_throttle) {
                atomic_add_64(&dp->dp_tempreserved[tx->tx_txg & TXG_MASK],
                    space);
                return (0);
        }

        /*
         * Check to see if we have exceeded the maximum allowed IO for
         * this transaction group.  We can do this without locks since
         * a little slop here is ok.  Note that we do the reserved check
         * with only half the requested reserve: this is because the
         * reserve requests are worst-case, and we really don't want to
         * throttle based off of worst-case estimates.
         */
        if (write_limit > 0) {
                reserved = dp->dp_space_towrite[tx->tx_txg & TXG_MASK]
                    + dp->dp_tempreserved[tx->tx_txg & TXG_MASK] / 2;

                if (reserved && reserved > write_limit) {
                        DMU_TX_STAT_BUMP(dmu_tx_write_limit);
                        return (ERESTART);
                }
        }

        atomic_add_64(&dp->dp_tempreserved[tx->tx_txg & TXG_MASK], space);

        /*
         * If this transaction group is over 7/8ths capacity, delay
         * the caller 1 clock tick.  This will slow down the "fill"
         * rate until the sync process can catch up with us.
         */
        if (reserved && reserved > (write_limit - (write_limit >> 3)))
                txg_delay(dp, tx->tx_txg, 1);

        return (0);
}

void
dsl_pool_tempreserve_clear(dsl_pool_t *dp, int64_t space, dmu_tx_t *tx)
{
        ASSERT(dp->dp_tempreserved[tx->tx_txg & TXG_MASK] >= space);
        atomic_add_64(&dp->dp_tempreserved[tx->tx_txg & TXG_MASK], -space);
}

void
dsl_pool_memory_pressure(dsl_pool_t *dp)
{
        uint64_t space_inuse = 0;
        int i;

        if (dp->dp_write_limit == zfs_write_limit_min)
                return;

        for (i = 0; i < TXG_SIZE; i++) {
                space_inuse += dp->dp_space_towrite[i];
                space_inuse += dp->dp_tempreserved[i];
        }
        dp->dp_write_limit = MAX(zfs_write_limit_min,
            MIN(dp->dp_write_limit, space_inuse / 4));
}

void
dsl_pool_willuse_space(dsl_pool_t *dp, int64_t space, dmu_tx_t *tx)
{
        if (space > 0) {
                mutex_enter(&dp->dp_lock);
                dp->dp_space_towrite[tx->tx_txg & TXG_MASK] += space;
                mutex_exit(&dp->dp_lock);
        }
}

/* ARGSUSED */
static int
upgrade_clones_cb(spa_t *spa, uint64_t dsobj, const char *dsname, void *arg)
{
        dmu_tx_t *tx = arg;
        dsl_dataset_t *ds, *prev = NULL;
        int err;
        dsl_pool_t *dp = spa_get_dsl(spa);

        err = dsl_dataset_hold_obj(dp, dsobj, FTAG, &ds);
        if (err)
                return (err);

        while (ds->ds_phys->ds_prev_snap_obj != 0) {
                err = dsl_dataset_hold_obj(dp, ds->ds_phys->ds_prev_snap_obj,
                    FTAG, &prev);
                if (err) {
                        dsl_dataset_rele(ds, FTAG);
                        return (err);
                }

                if (prev->ds_phys->ds_next_snap_obj != ds->ds_object)
                        break;
                dsl_dataset_rele(ds, FTAG);
                ds = prev;
                prev = NULL;
        }

        if (prev == NULL) {
                prev = dp->dp_origin_snap;

                /*
                 * The $ORIGIN can't have any data, or the accounting
                 * will be wrong.
                 */
                ASSERT(prev->ds_phys->ds_bp.blk_birth == 0);

                /* The origin doesn't get attached to itself */
                if (ds->ds_object == prev->ds_object) {
                        dsl_dataset_rele(ds, FTAG);
                        return (0);
                }

                dmu_buf_will_dirty(ds->ds_dbuf, tx);
                ds->ds_phys->ds_prev_snap_obj = prev->ds_object;
                ds->ds_phys->ds_prev_snap_txg = prev->ds_phys->ds_creation_txg;

                dmu_buf_will_dirty(ds->ds_dir->dd_dbuf, tx);
                ds->ds_dir->dd_phys->dd_origin_obj = prev->ds_object;

                dmu_buf_will_dirty(prev->ds_dbuf, tx);
                prev->ds_phys->ds_num_children++;

                if (ds->ds_phys->ds_next_snap_obj == 0) {
                        ASSERT(ds->ds_prev == NULL);
                        VERIFY(0 == dsl_dataset_hold_obj(dp,
                            ds->ds_phys->ds_prev_snap_obj, ds, &ds->ds_prev));
                }
        }

        ASSERT(ds->ds_dir->dd_phys->dd_origin_obj == prev->ds_object);
        ASSERT(ds->ds_phys->ds_prev_snap_obj == prev->ds_object);

        if (prev->ds_phys->ds_next_clones_obj == 0) {
                dmu_buf_will_dirty(prev->ds_dbuf, tx);
                prev->ds_phys->ds_next_clones_obj =
                    zap_create(dp->dp_meta_objset,
                    DMU_OT_NEXT_CLONES, DMU_OT_NONE, 0, tx);
        }
        VERIFY(0 == zap_add_int(dp->dp_meta_objset,
            prev->ds_phys->ds_next_clones_obj, ds->ds_object, tx));

        dsl_dataset_rele(ds, FTAG);
        if (prev != dp->dp_origin_snap)
                dsl_dataset_rele(prev, FTAG);
        return (0);
}

void
dsl_pool_upgrade_clones(dsl_pool_t *dp, dmu_tx_t *tx)
{
        ASSERT(dmu_tx_is_syncing(tx));
        ASSERT(dp->dp_origin_snap != NULL);

        VERIFY3U(0, ==, dmu_objset_find_spa(dp->dp_spa, NULL, upgrade_clones_cb,
            tx, DS_FIND_CHILDREN));
}

/* ARGSUSED */
static int
upgrade_dir_clones_cb(spa_t *spa, uint64_t dsobj, const char *dsname, void *arg)
{
        dmu_tx_t *tx = arg;
        dsl_dataset_t *ds;
        dsl_pool_t *dp = spa_get_dsl(spa);
        objset_t *mos = dp->dp_meta_objset;

        VERIFY3U(0, ==, dsl_dataset_hold_obj(dp, dsobj, FTAG, &ds));

        if (ds->ds_dir->dd_phys->dd_origin_obj) {
                dsl_dataset_t *origin;

                VERIFY3U(0, ==, dsl_dataset_hold_obj(dp,
                    ds->ds_dir->dd_phys->dd_origin_obj, FTAG, &origin));

                if (origin->ds_dir->dd_phys->dd_clones == 0) {
                        dmu_buf_will_dirty(origin->ds_dir->dd_dbuf, tx);
                        origin->ds_dir->dd_phys->dd_clones = zap_create(mos,
                            DMU_OT_DSL_CLONES, DMU_OT_NONE, 0, tx);
                }

                VERIFY3U(0, ==, zap_add_int(dp->dp_meta_objset,
                    origin->ds_dir->dd_phys->dd_clones, dsobj, tx));

                dsl_dataset_rele(origin, FTAG);
        }

        dsl_dataset_rele(ds, FTAG);
        return (0);
}

void
dsl_pool_upgrade_dir_clones(dsl_pool_t *dp, dmu_tx_t *tx)
{
        uint64_t obj;

        ASSERT(dmu_tx_is_syncing(tx));

        (void) dsl_dir_create_sync(dp, dp->dp_root_dir, FREE_DIR_NAME, tx);
        VERIFY(0 == dsl_pool_open_special_dir(dp,
            FREE_DIR_NAME, &dp->dp_free_dir));

        /*
         * We can't use bpobj_alloc(), because spa_version() still
         * returns the old version, and we need a new-version bpobj with
         * subobj support.  So call dmu_object_alloc() directly.
         */
        obj = dmu_object_alloc(dp->dp_meta_objset, DMU_OT_BPOBJ,
            SPA_MAXBLOCKSIZE, DMU_OT_BPOBJ_HDR, sizeof (bpobj_phys_t), tx);
        VERIFY3U(0, ==, zap_add(dp->dp_meta_objset, DMU_POOL_DIRECTORY_OBJECT,
            DMU_POOL_FREE_BPOBJ, sizeof (uint64_t), 1, &obj, tx));
        VERIFY3U(0, ==, bpobj_open(&dp->dp_free_bpobj,
            dp->dp_meta_objset, obj));

        VERIFY3U(0, ==, dmu_objset_find_spa(dp->dp_spa, NULL,
            upgrade_dir_clones_cb, tx, DS_FIND_CHILDREN));
}

void
dsl_pool_create_origin(dsl_pool_t *dp, dmu_tx_t *tx)
{
        uint64_t dsobj;
        dsl_dataset_t *ds;

        ASSERT(dmu_tx_is_syncing(tx));
        ASSERT(dp->dp_origin_snap == NULL);

        /* create the origin dir, ds, & snap-ds */
        rw_enter(&dp->dp_config_rwlock, RW_WRITER);
        dsobj = dsl_dataset_create_sync(dp->dp_root_dir, ORIGIN_DIR_NAME,
            NULL, 0, kcred, tx);
        VERIFY(0 == dsl_dataset_hold_obj(dp, dsobj, FTAG, &ds));
        dsl_dataset_snapshot_sync(ds, ORIGIN_DIR_NAME, tx);
        VERIFY(0 == dsl_dataset_hold_obj(dp, ds->ds_phys->ds_prev_snap_obj,
            dp, &dp->dp_origin_snap));
        dsl_dataset_rele(ds, FTAG);
        rw_exit(&dp->dp_config_rwlock);
}

taskq_t *
dsl_pool_iput_taskq(dsl_pool_t *dp)
{
        return (dp->dp_iput_taskq);
}

/*
 * Walk through the pool-wide zap object of temporary snapshot user holds
 * and release them.
 */
void
dsl_pool_clean_tmp_userrefs(dsl_pool_t *dp)
{
        zap_attribute_t za;
        zap_cursor_t zc;
        objset_t *mos = dp->dp_meta_objset;
        uint64_t zapobj = dp->dp_tmp_userrefs_obj;

        if (zapobj == 0)
                return;
        ASSERT(spa_version(dp->dp_spa) >= SPA_VERSION_USERREFS);

        for (zap_cursor_init(&zc, mos, zapobj);
            zap_cursor_retrieve(&zc, &za) == 0;
            zap_cursor_advance(&zc)) {
                char *htag;
                uint64_t dsobj;

                htag = strchr(za.za_name, '-');
                *htag = '\0';
                ++htag;
                dsobj = strtonum(za.za_name, NULL);
                (void) dsl_dataset_user_release_tmp(dp, dsobj, htag, B_FALSE);
        }
        zap_cursor_fini(&zc);
}

/*
 * Create the pool-wide zap object for storing temporary snapshot holds.
 */
void
dsl_pool_user_hold_create_obj(dsl_pool_t *dp, dmu_tx_t *tx)
{
        objset_t *mos = dp->dp_meta_objset;

        ASSERT(dp->dp_tmp_userrefs_obj == 0);
        ASSERT(dmu_tx_is_syncing(tx));

        dp->dp_tmp_userrefs_obj = zap_create_link(mos, DMU_OT_USERREFS,
            DMU_POOL_DIRECTORY_OBJECT, DMU_POOL_TMP_USERREFS, tx);
}

static int
dsl_pool_user_hold_rele_impl(dsl_pool_t *dp, uint64_t dsobj,
    const char *tag, uint64_t *now, dmu_tx_t *tx, boolean_t holding)
{
        objset_t *mos = dp->dp_meta_objset;
        uint64_t zapobj = dp->dp_tmp_userrefs_obj;
        char *name;
        int error;

        ASSERT(spa_version(dp->dp_spa) >= SPA_VERSION_USERREFS);
        ASSERT(dmu_tx_is_syncing(tx));

        /*
         * If the pool was created prior to SPA_VERSION_USERREFS, the
         * zap object for temporary holds might not exist yet.
         */
        if (zapobj == 0) {
                if (holding) {
                        dsl_pool_user_hold_create_obj(dp, tx);
                        zapobj = dp->dp_tmp_userrefs_obj;
                } else {
                        return (ENOENT);
                }
        }

        name = kmem_asprintf("%llx-%s", (u_longlong_t)dsobj, tag);
        if (holding)
                error = zap_add(mos, zapobj, name, 8, 1, now, tx);
        else
                error = zap_remove(mos, zapobj, name, tx);
        strfree(name);

        return (error);
}

/*
 * Add a temporary hold for the given dataset object and tag.
 */
int
dsl_pool_user_hold(dsl_pool_t *dp, uint64_t dsobj, const char *tag,
    uint64_t *now, dmu_tx_t *tx)
{
        return (dsl_pool_user_hold_rele_impl(dp, dsobj, tag, now, tx, B_TRUE));
}

/*
 * Release a temporary hold for the given dataset object and tag.
 */
int
dsl_pool_user_release(dsl_pool_t *dp, uint64_t dsobj, const char *tag,
    dmu_tx_t *tx)
{
        return (dsl_pool_user_hold_rele_impl(dp, dsobj, tag, NULL,
            tx, B_FALSE));
}

#if defined(_KERNEL) && defined(HAVE_SPL)
module_param(zfs_no_write_throttle, int, 0644);
MODULE_PARM_DESC(zfs_no_write_throttle, "Disable write throttling");

module_param(zfs_write_limit_shift, int, 0444);
MODULE_PARM_DESC(zfs_write_limit_shift, "log2(fraction of memory) per txg");

module_param(zfs_txg_synctime_ms, int, 0644);
MODULE_PARM_DESC(zfs_txg_synctime_ms, "Target milliseconds between txg sync");

module_param(zfs_txg_history, int, 0644);
MODULE_PARM_DESC(zfs_txg_history, "Historic statistics for the last N txgs");

module_param(zfs_write_limit_min, ulong, 0444);
MODULE_PARM_DESC(zfs_write_limit_min, "Min txg write limit");

module_param(zfs_write_limit_max, ulong, 0444);
MODULE_PARM_DESC(zfs_write_limit_max, "Max txg write limit");

module_param(zfs_write_limit_inflated, ulong, 0444);
MODULE_PARM_DESC(zfs_write_limit_inflated, "Inflated txg write limit");

module_param(zfs_write_limit_override, ulong, 0444);
MODULE_PARM_DESC(zfs_write_limit_override, "Override txg write limit");
#endif