[mirror_zfs.git] / module / zfs / dmu_zfetch.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, 2017 by Delphix. All rights reserved.
 */

#include <sys/zfs_context.h>
#include <sys/arc_impl.h>
#include <sys/dnode.h>
#include <sys/dmu_objset.h>
#include <sys/dmu_zfetch.h>
#include <sys/dmu.h>
#include <sys/dbuf.h>
#include <sys/kstat.h>
#include <sys/wmsum.h>

/*
 * This tunable disables predictive prefetch.  Note that it leaves "prescient"
 * prefetch (e.g. prefetch for zfs send) intact.  Unlike predictive prefetch,
 * prescient prefetch never issues i/os that end up not being needed,
 * so it can't hurt performance.
 */

static int zfs_prefetch_disable = B_FALSE;

/* max # of streams per zfetch */
static unsigned int     zfetch_max_streams = 8;
/* min time before stream reclaim */
static unsigned int     zfetch_min_sec_reap = 1;
/* max time before stream delete */
static unsigned int     zfetch_max_sec_reap = 2;
#ifdef _ILP32
/* min bytes to prefetch per stream (default 2MB) */
static unsigned int     zfetch_min_distance = 2 * 1024 * 1024;
/* max bytes to prefetch per stream (default 8MB) */
unsigned int    zfetch_max_distance = 8 * 1024 * 1024;
#else
/* min bytes to prefetch per stream (default 4MB) */
static unsigned int     zfetch_min_distance = 4 * 1024 * 1024;
/* max bytes to prefetch per stream (default 64MB) */
unsigned int    zfetch_max_distance = 64 * 1024 * 1024;
#endif
/* max bytes to prefetch indirects for per stream (default 64MB) */
unsigned int    zfetch_max_idistance = 64 * 1024 * 1024;

typedef struct zfetch_stats {
        kstat_named_t zfetchstat_hits;
        kstat_named_t zfetchstat_misses;
        kstat_named_t zfetchstat_max_streams;
        kstat_named_t zfetchstat_io_issued;
        kstat_named_t zfetchstat_io_active;
} zfetch_stats_t;

static zfetch_stats_t zfetch_stats = {
        { "hits",                       KSTAT_DATA_UINT64 },
        { "misses",                     KSTAT_DATA_UINT64 },
        { "max_streams",                KSTAT_DATA_UINT64 },
        { "io_issued",                  KSTAT_DATA_UINT64 },
        { "io_active",                  KSTAT_DATA_UINT64 },
};

struct {
        wmsum_t zfetchstat_hits;
        wmsum_t zfetchstat_misses;
        wmsum_t zfetchstat_max_streams;
        wmsum_t zfetchstat_io_issued;
        aggsum_t zfetchstat_io_active;
} zfetch_sums;

#define ZFETCHSTAT_BUMP(stat)                                   \
        wmsum_add(&zfetch_sums.stat, 1)
#define ZFETCHSTAT_ADD(stat, val)                               \
        wmsum_add(&zfetch_sums.stat, val)


static kstat_t          *zfetch_ksp;

static int
zfetch_kstats_update(kstat_t *ksp, int rw)
{
        zfetch_stats_t *zs = ksp->ks_data;

        if (rw == KSTAT_WRITE)
                return (EACCES);
        zs->zfetchstat_hits.value.ui64 =
            wmsum_value(&zfetch_sums.zfetchstat_hits);
        zs->zfetchstat_misses.value.ui64 =
            wmsum_value(&zfetch_sums.zfetchstat_misses);
        zs->zfetchstat_max_streams.value.ui64 =
            wmsum_value(&zfetch_sums.zfetchstat_max_streams);
        zs->zfetchstat_io_issued.value.ui64 =
            wmsum_value(&zfetch_sums.zfetchstat_io_issued);
        zs->zfetchstat_io_active.value.ui64 =
            aggsum_value(&zfetch_sums.zfetchstat_io_active);
        return (0);
}

void
zfetch_init(void)
{
        wmsum_init(&zfetch_sums.zfetchstat_hits, 0);
        wmsum_init(&zfetch_sums.zfetchstat_misses, 0);
        wmsum_init(&zfetch_sums.zfetchstat_max_streams, 0);
        wmsum_init(&zfetch_sums.zfetchstat_io_issued, 0);
        aggsum_init(&zfetch_sums.zfetchstat_io_active, 0);

        zfetch_ksp = kstat_create("zfs", 0, "zfetchstats", "misc",
            KSTAT_TYPE_NAMED, sizeof (zfetch_stats) / sizeof (kstat_named_t),
            KSTAT_FLAG_VIRTUAL);

        if (zfetch_ksp != NULL) {
                zfetch_ksp->ks_data = &zfetch_stats;
                zfetch_ksp->ks_update = zfetch_kstats_update;
                kstat_install(zfetch_ksp);
        }
}

void
zfetch_fini(void)
{
        if (zfetch_ksp != NULL) {
                kstat_delete(zfetch_ksp);
                zfetch_ksp = NULL;
        }

        wmsum_fini(&zfetch_sums.zfetchstat_hits);
        wmsum_fini(&zfetch_sums.zfetchstat_misses);
        wmsum_fini(&zfetch_sums.zfetchstat_max_streams);
        wmsum_fini(&zfetch_sums.zfetchstat_io_issued);
        ASSERT0(aggsum_value(&zfetch_sums.zfetchstat_io_active));
        aggsum_fini(&zfetch_sums.zfetchstat_io_active);
}

/*
 * This takes a pointer to a zfetch structure and a dnode.  It performs the
 * necessary setup for the zfetch structure, grokking data from the
 * associated dnode.
 */
void
dmu_zfetch_init(zfetch_t *zf, dnode_t *dno)
{
        if (zf == NULL)
                return;
        zf->zf_dnode = dno;
        zf->zf_numstreams = 0;

        list_create(&zf->zf_stream, sizeof (zstream_t),
            offsetof(zstream_t, zs_node));

        mutex_init(&zf->zf_lock, NULL, MUTEX_DEFAULT, NULL);
}

static void
dmu_zfetch_stream_fini(zstream_t *zs)
{
        ASSERT(!list_link_active(&zs->zs_node));
        zfs_refcount_destroy(&zs->zs_callers);
        zfs_refcount_destroy(&zs->zs_refs);
        kmem_free(zs, sizeof (*zs));
}

static void
dmu_zfetch_stream_remove(zfetch_t *zf, zstream_t *zs)
{
        ASSERT(MUTEX_HELD(&zf->zf_lock));
        list_remove(&zf->zf_stream, zs);
        zf->zf_numstreams--;
        membar_producer();
        if (zfs_refcount_remove(&zs->zs_refs, NULL) == 0)
                dmu_zfetch_stream_fini(zs);
}

/*
 * Clean-up state associated with a zfetch structure (e.g. destroy the
 * streams).  This doesn't free the zfetch_t itself, that's left to the caller.
 */
void
dmu_zfetch_fini(zfetch_t *zf)
{
        zstream_t *zs;

        mutex_enter(&zf->zf_lock);
        while ((zs = list_head(&zf->zf_stream)) != NULL)
                dmu_zfetch_stream_remove(zf, zs);
        mutex_exit(&zf->zf_lock);
        list_destroy(&zf->zf_stream);
        mutex_destroy(&zf->zf_lock);

        zf->zf_dnode = NULL;
}

/*
 * If there aren't too many active streams already, create one more.
 * In process delete/reuse all streams without hits for zfetch_max_sec_reap.
 * If needed, reuse oldest stream without hits for zfetch_min_sec_reap or ever.
 * The "blkid" argument is the next block that we expect this stream to access.
 */
static void
dmu_zfetch_stream_create(zfetch_t *zf, uint64_t blkid)
{
        zstream_t *zs, *zs_next, *zs_old = NULL;
        hrtime_t now = gethrtime(), t;

        ASSERT(MUTEX_HELD(&zf->zf_lock));

        /*
         * Delete too old streams, reusing the first found one.
         */
        t = now - SEC2NSEC(zfetch_max_sec_reap);
        for (zs = list_head(&zf->zf_stream); zs != NULL; zs = zs_next) {
                zs_next = list_next(&zf->zf_stream, zs);
                /*
                 * Skip if still active.  1 -- zf_stream reference.
                 */
                if (zfs_refcount_count(&zs->zs_refs) != 1)
                        continue;
                if (zs->zs_atime > t)
                        continue;
                if (zs_old)
                        dmu_zfetch_stream_remove(zf, zs);
                else
                        zs_old = zs;
        }
        if (zs_old) {
                zs = zs_old;
                goto reuse;
        }

        /*
         * The maximum number of streams is normally zfetch_max_streams,
         * but for small files we lower it such that it's at least possible
         * for all the streams to be non-overlapping.
         */
        uint32_t max_streams = MAX(1, MIN(zfetch_max_streams,
            zf->zf_dnode->dn_maxblkid * zf->zf_dnode->dn_datablksz /
            zfetch_max_distance));
        if (zf->zf_numstreams >= max_streams) {
                t = now - SEC2NSEC(zfetch_min_sec_reap);
                for (zs = list_head(&zf->zf_stream); zs != NULL;
                    zs = list_next(&zf->zf_stream, zs)) {
                        if (zfs_refcount_count(&zs->zs_refs) != 1)
                                continue;
                        if (zs->zs_atime > t)
                                continue;
                        if (zs_old == NULL || zs->zs_atime < zs_old->zs_atime)
                                zs_old = zs;
                }
                if (zs_old) {
                        zs = zs_old;
                        goto reuse;
                }
                ZFETCHSTAT_BUMP(zfetchstat_max_streams);
                return;
        }

        zs = kmem_zalloc(sizeof (*zs), KM_SLEEP);
        zs->zs_fetch = zf;
        zfs_refcount_create(&zs->zs_callers);
        zfs_refcount_create(&zs->zs_refs);
        /* One reference for zf_stream. */
        zfs_refcount_add(&zs->zs_refs, NULL);
        zf->zf_numstreams++;
        list_insert_head(&zf->zf_stream, zs);

reuse:
        zs->zs_blkid = blkid;
        zs->zs_pf_dist = 0;
        zs->zs_pf_start = blkid;
        zs->zs_pf_end = blkid;
        zs->zs_ipf_dist = 0;
        zs->zs_ipf_start = blkid;
        zs->zs_ipf_end = blkid;
        /* Allow immediate stream reuse until first hit. */
        zs->zs_atime = now - SEC2NSEC(zfetch_min_sec_reap);
        zs->zs_missed = B_FALSE;
        zs->zs_more = B_FALSE;
}

static void
dmu_zfetch_done(void *arg, uint64_t level, uint64_t blkid, boolean_t io_issued)
{
        zstream_t *zs = arg;

        if (io_issued && level == 0 && blkid < zs->zs_blkid)
                zs->zs_more = B_TRUE;
        if (zfs_refcount_remove(&zs->zs_refs, NULL) == 0)
                dmu_zfetch_stream_fini(zs);
        aggsum_add(&zfetch_sums.zfetchstat_io_active, -1);
}

/*
 * This is the predictive prefetch entry point.  dmu_zfetch_prepare()
 * associates dnode access specified with blkid and nblks arguments with
 * prefetch stream, predicts further accesses based on that stats and returns
 * the stream pointer on success.  That pointer must later be passed to
 * dmu_zfetch_run() to initiate the speculative prefetch for the stream and
 * release it.  dmu_zfetch() is a wrapper for simple cases when window between
 * prediction and prefetch initiation is not needed.
 * fetch_data argument specifies whether actual data blocks should be fetched:
 *   FALSE -- prefetch only indirect blocks for predicted data blocks;
 *   TRUE -- prefetch predicted data blocks plus following indirect blocks.
 */
zstream_t *
dmu_zfetch_prepare(zfetch_t *zf, uint64_t blkid, uint64_t nblks,
    boolean_t fetch_data, boolean_t have_lock)
{
        zstream_t *zs;
        spa_t *spa = zf->zf_dnode->dn_objset->os_spa;
        zfs_prefetch_type_t os_prefetch = zf->zf_dnode->dn_objset->os_prefetch;

        if (zfs_prefetch_disable || os_prefetch == ZFS_PREFETCH_NONE)
                return (NULL);

        if (os_prefetch == ZFS_PREFETCH_METADATA)
                fetch_data = B_FALSE;

        /*
         * If we haven't yet loaded the indirect vdevs' mappings, we
         * can only read from blocks that we carefully ensure are on
         * concrete vdevs (or previously-loaded indirect vdevs).  So we
         * can't allow the predictive prefetcher to attempt reads of other
         * blocks (e.g. of the MOS's dnode object).
         */
        if (!spa_indirect_vdevs_loaded(spa))
                return (NULL);

        /*
         * As a fast path for small (single-block) files, ignore access
         * to the first block.
         */
        if (!have_lock && blkid == 0)
                return (NULL);

        if (!have_lock)
                rw_enter(&zf->zf_dnode->dn_struct_rwlock, RW_READER);

        /*
         * A fast path for small files for which no prefetch will
         * happen.
         */
        uint64_t maxblkid = zf->zf_dnode->dn_maxblkid;
        if (maxblkid < 2) {
                if (!have_lock)
                        rw_exit(&zf->zf_dnode->dn_struct_rwlock);
                return (NULL);
        }
        mutex_enter(&zf->zf_lock);

        /*
         * Find matching prefetch stream.  Depending on whether the accesses
         * are block-aligned, first block of the new access may either follow
         * the last block of the previous access, or be equal to it.
         */
        for (zs = list_head(&zf->zf_stream); zs != NULL;
            zs = list_next(&zf->zf_stream, zs)) {
                if (blkid == zs->zs_blkid) {
                        break;
                } else if (blkid + 1 == zs->zs_blkid) {
                        blkid++;
                        nblks--;
                        break;
                }
        }

        /*
         * If the file is ending, remove the matching stream if found.
         * If not found then it is too late to create a new one now.
         */
        uint64_t end_of_access_blkid = blkid + nblks;
        if (end_of_access_blkid >= maxblkid) {
                if (zs != NULL)
                        dmu_zfetch_stream_remove(zf, zs);
                mutex_exit(&zf->zf_lock);
                if (!have_lock)
                        rw_exit(&zf->zf_dnode->dn_struct_rwlock);
                return (NULL);
        }

        /* Exit if we already prefetched this block before. */
        if (nblks == 0) {
                mutex_exit(&zf->zf_lock);
                if (!have_lock)
                        rw_exit(&zf->zf_dnode->dn_struct_rwlock);
                return (NULL);
        }

        if (zs == NULL) {
                /*
                 * This access is not part of any existing stream.  Create
                 * a new stream for it.
                 */
                dmu_zfetch_stream_create(zf, end_of_access_blkid);
                mutex_exit(&zf->zf_lock);
                if (!have_lock)
                        rw_exit(&zf->zf_dnode->dn_struct_rwlock);
                ZFETCHSTAT_BUMP(zfetchstat_misses);
                return (NULL);
        }

        /*
         * This access was to a block that we issued a prefetch for on
         * behalf of this stream.  Calculate further prefetch distances.
         *
         * Start prefetch from the demand access size (nblks).  Double the
         * distance every access up to zfetch_min_distance.  After that only
         * if needed increase the distance by 1/8 up to zfetch_max_distance.
         *
         * Don't double the distance beyond single block if we have more
         * than ~6% of ARC held by active prefetches.  It should help with
         * getting out of RAM on some badly mispredicted read patterns.
         */
        unsigned int dbs = zf->zf_dnode->dn_datablkshift;
        unsigned int nbytes = nblks << dbs;
        unsigned int pf_nblks;
        if (fetch_data) {
                if (unlikely(zs->zs_pf_dist < nbytes))
                        zs->zs_pf_dist = nbytes;
                else if (zs->zs_pf_dist < zfetch_min_distance &&
                    (zs->zs_pf_dist < (1 << dbs) ||
                    aggsum_compare(&zfetch_sums.zfetchstat_io_active,
                    arc_c_max >> (4 + dbs)) < 0))
                        zs->zs_pf_dist *= 2;
                else if (zs->zs_more)
                        zs->zs_pf_dist += zs->zs_pf_dist / 8;
                zs->zs_more = B_FALSE;
                if (zs->zs_pf_dist > zfetch_max_distance)
                        zs->zs_pf_dist = zfetch_max_distance;
                pf_nblks = zs->zs_pf_dist >> dbs;
        } else {
                pf_nblks = 0;
        }
        if (zs->zs_pf_start < end_of_access_blkid)
                zs->zs_pf_start = end_of_access_blkid;
        if (zs->zs_pf_end < end_of_access_blkid + pf_nblks)
                zs->zs_pf_end = end_of_access_blkid + pf_nblks;

        /*
         * Do the same for indirects, starting where we will stop reading
         * data blocks (and the indirects that point to them).
         */
        if (unlikely(zs->zs_ipf_dist < nbytes))
                zs->zs_ipf_dist = nbytes;
        else
                zs->zs_ipf_dist *= 2;
        if (zs->zs_ipf_dist > zfetch_max_idistance)
                zs->zs_ipf_dist = zfetch_max_idistance;
        pf_nblks = zs->zs_ipf_dist >> dbs;
        if (zs->zs_ipf_start < zs->zs_pf_end)
                zs->zs_ipf_start = zs->zs_pf_end;
        if (zs->zs_ipf_end < zs->zs_pf_end + pf_nblks)
                zs->zs_ipf_end = zs->zs_pf_end + pf_nblks;

        zs->zs_blkid = end_of_access_blkid;
        /* Protect the stream from reclamation. */
        zs->zs_atime = gethrtime();
        zfs_refcount_add(&zs->zs_refs, NULL);
        /* Count concurrent callers. */
        zfs_refcount_add(&zs->zs_callers, NULL);
        mutex_exit(&zf->zf_lock);

        if (!have_lock)
                rw_exit(&zf->zf_dnode->dn_struct_rwlock);

        ZFETCHSTAT_BUMP(zfetchstat_hits);
        return (zs);
}

void
dmu_zfetch_run(zstream_t *zs, boolean_t missed, boolean_t have_lock)
{
        zfetch_t *zf = zs->zs_fetch;
        int64_t pf_start, pf_end, ipf_start, ipf_end;
        int epbs, issued;

        if (missed)
                zs->zs_missed = missed;

        /*
         * Postpone the prefetch if there are more concurrent callers.
         * It happens when multiple requests are waiting for the same
         * indirect block.  The last one will run the prefetch for all.
         */
        if (zfs_refcount_remove(&zs->zs_callers, NULL) != 0) {
                /* Drop reference taken in dmu_zfetch_prepare(). */
                if (zfs_refcount_remove(&zs->zs_refs, NULL) == 0)
                        dmu_zfetch_stream_fini(zs);
                return;
        }

        mutex_enter(&zf->zf_lock);
        if (zs->zs_missed) {
                pf_start = zs->zs_pf_start;
                pf_end = zs->zs_pf_start = zs->zs_pf_end;
        } else {
                pf_start = pf_end = 0;
        }
        ipf_start = zs->zs_ipf_start;
        ipf_end = zs->zs_ipf_start = zs->zs_ipf_end;
        mutex_exit(&zf->zf_lock);
        ASSERT3S(pf_start, <=, pf_end);
        ASSERT3S(ipf_start, <=, ipf_end);

        epbs = zf->zf_dnode->dn_indblkshift - SPA_BLKPTRSHIFT;
        ipf_start = P2ROUNDUP(ipf_start, 1 << epbs) >> epbs;
        ipf_end = P2ROUNDUP(ipf_end, 1 << epbs) >> epbs;
        ASSERT3S(ipf_start, <=, ipf_end);
        issued = pf_end - pf_start + ipf_end - ipf_start;
        if (issued > 1) {
                /* More references on top of taken in dmu_zfetch_prepare(). */
                zfs_refcount_add_few(&zs->zs_refs, issued - 1, NULL);
        } else if (issued == 0) {
                /* Some other thread has done our work, so drop the ref. */
                if (zfs_refcount_remove(&zs->zs_refs, NULL) == 0)
                        dmu_zfetch_stream_fini(zs);
                return;
        }
        aggsum_add(&zfetch_sums.zfetchstat_io_active, issued);

        if (!have_lock)
                rw_enter(&zf->zf_dnode->dn_struct_rwlock, RW_READER);

        issued = 0;
        for (int64_t blk = pf_start; blk < pf_end; blk++) {
                issued += dbuf_prefetch_impl(zf->zf_dnode, 0, blk,
                    ZIO_PRIORITY_ASYNC_READ, 0, dmu_zfetch_done, zs);
        }
        for (int64_t iblk = ipf_start; iblk < ipf_end; iblk++) {
                issued += dbuf_prefetch_impl(zf->zf_dnode, 1, iblk,
                    ZIO_PRIORITY_ASYNC_READ, 0, dmu_zfetch_done, zs);
        }

        if (!have_lock)
                rw_exit(&zf->zf_dnode->dn_struct_rwlock);

        if (issued)
                ZFETCHSTAT_ADD(zfetchstat_io_issued, issued);
}

void
dmu_zfetch(zfetch_t *zf, uint64_t blkid, uint64_t nblks, boolean_t fetch_data,
    boolean_t missed, boolean_t have_lock)
{
        zstream_t *zs;

        zs = dmu_zfetch_prepare(zf, blkid, nblks, fetch_data, have_lock);
        if (zs)
                dmu_zfetch_run(zs, missed, have_lock);
}

ZFS_MODULE_PARAM(zfs_prefetch, zfs_prefetch_, disable, INT, ZMOD_RW,
        "Disable all ZFS prefetching");

ZFS_MODULE_PARAM(zfs_prefetch, zfetch_, max_streams, UINT, ZMOD_RW,
        "Max number of streams per zfetch");

ZFS_MODULE_PARAM(zfs_prefetch, zfetch_, min_sec_reap, UINT, ZMOD_RW,
        "Min time before stream reclaim");

ZFS_MODULE_PARAM(zfs_prefetch, zfetch_, max_sec_reap, UINT, ZMOD_RW,
        "Max time before stream delete");

ZFS_MODULE_PARAM(zfs_prefetch, zfetch_, min_distance, UINT, ZMOD_RW,
        "Min bytes to prefetch per stream");

ZFS_MODULE_PARAM(zfs_prefetch, zfetch_, max_distance, UINT, ZMOD_RW,
        "Max bytes to prefetch per stream");

ZFS_MODULE_PARAM(zfs_prefetch, zfetch_, max_idistance, UINT, ZMOD_RW,
        "Max bytes to prefetch indirects for per stream");