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ZFS send should use spill block prefetched from send_reader_thread
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Currently, even though send_reader_thread prefetches spill block,
do_dump() will not use it and issues its own blocking arc_read. This
causes significant performance degradation when sending datasets with
lots of spill blocks.

For unmodified spill blocks, we also create send_range struct for them
in send_reader_thread and issue prefetches for them. We piggyback them
on the dnode send_range instead of enqueueing them so we don't break
send_range_after check.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Alexander Motin <mav@FreeBSD.org>
Signed-off-by: Chunwei Chen <david.chen@nutanix.com>
Co-authored-by: david.chen <david.chen@nutanix.com>
Closes #16701
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@tuxoko
tuxoko authored Nov 6, 2024
1 parent 7b6e967 commit 5945676
Showing 1 changed file with 64 additions and 62 deletions.
126 changes: 64 additions & 62 deletions module/zfs/dmu_send.c
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Original file line number Diff line number Diff line change
Expand Up @@ -180,6 +180,8 @@ struct send_range {
*/
dnode_phys_t *dnp;
blkptr_t bp;
/* Piggyback unmodified spill block */
struct send_range *spill_range;
} object;
struct srr {
uint32_t datablksz;
Expand Down Expand Up @@ -231,6 +233,8 @@ range_free(struct send_range *range)
size_t size = sizeof (dnode_phys_t) *
(range->sru.object.dnp->dn_extra_slots + 1);
kmem_free(range->sru.object.dnp, size);
if (range->sru.object.spill_range)
range_free(range->sru.object.spill_range);
} else if (range->type == DATA) {
mutex_enter(&range->sru.data.lock);
while (range->sru.data.io_outstanding)
Expand Down Expand Up @@ -617,7 +621,7 @@ dump_spill(dmu_send_cookie_t *dscp, const blkptr_t *bp, uint64_t object,
drrs->drr_length = blksz;
drrs->drr_toguid = dscp->dsc_toguid;

/* See comment in dump_dnode() for full details */
/* See comment in piggyback_unmodified_spill() for full details */
if (zfs_send_unmodified_spill_blocks &&
(BP_GET_LOGICAL_BIRTH(bp) <= dscp->dsc_fromtxg)) {
drrs->drr_flags |= DRR_SPILL_UNMODIFIED;
Expand Down Expand Up @@ -793,35 +797,6 @@ dump_dnode(dmu_send_cookie_t *dscp, const blkptr_t *bp, uint64_t object,
(dnp->dn_datablkszsec << SPA_MINBLOCKSHIFT), DMU_OBJECT_END) != 0)
return (SET_ERROR(EINTR));

/*
* Send DRR_SPILL records for unmodified spill blocks. This is useful
* because changing certain attributes of the object (e.g. blocksize)
* can cause old versions of ZFS to incorrectly remove a spill block.
* Including these records in the stream forces an up to date version
* to always be written ensuring they're never lost. Current versions
* of the code which understand the DRR_FLAG_SPILL_BLOCK feature can
* ignore these unmodified spill blocks.
*/
if (zfs_send_unmodified_spill_blocks &&
(dnp->dn_flags & DNODE_FLAG_SPILL_BLKPTR) &&
(BP_GET_LOGICAL_BIRTH(DN_SPILL_BLKPTR(dnp)) <= dscp->dsc_fromtxg)) {
struct send_range record;
blkptr_t *bp = DN_SPILL_BLKPTR(dnp);

memset(&record, 0, sizeof (struct send_range));
record.type = DATA;
record.object = object;
record.eos_marker = B_FALSE;
record.start_blkid = DMU_SPILL_BLKID;
record.end_blkid = record.start_blkid + 1;
record.sru.data.bp = *bp;
record.sru.data.obj_type = dnp->dn_type;
record.sru.data.datablksz = BP_GET_LSIZE(bp);

if (do_dump(dscp, &record) != 0)
return (SET_ERROR(EINTR));
}

if (dscp->dsc_err != 0)
return (SET_ERROR(EINTR));

Expand Down Expand Up @@ -911,6 +886,9 @@ do_dump(dmu_send_cookie_t *dscp, struct send_range *range)
case OBJECT:
err = dump_dnode(dscp, &range->sru.object.bp, range->object,
range->sru.object.dnp);
/* Dump piggybacked unmodified spill block */
if (!err && range->sru.object.spill_range)
err = do_dump(dscp, range->sru.object.spill_range);
return (err);
case OBJECT_RANGE: {
ASSERT3U(range->start_blkid + 1, ==, range->end_blkid);
Expand Down Expand Up @@ -939,34 +917,7 @@ do_dump(dmu_send_cookie_t *dscp, struct send_range *range)

ASSERT3U(srdp->datablksz, ==, BP_GET_LSIZE(bp));
ASSERT3U(range->start_blkid + 1, ==, range->end_blkid);
if (BP_GET_TYPE(bp) == DMU_OT_SA) {
arc_flags_t aflags = ARC_FLAG_WAIT;
zio_flag_t zioflags = ZIO_FLAG_CANFAIL;

if (dscp->dsc_featureflags & DMU_BACKUP_FEATURE_RAW) {
ASSERT(BP_IS_PROTECTED(bp));
zioflags |= ZIO_FLAG_RAW;
}

zbookmark_phys_t zb;
ASSERT3U(range->start_blkid, ==, DMU_SPILL_BLKID);
zb.zb_objset = dmu_objset_id(dscp->dsc_os);
zb.zb_object = range->object;
zb.zb_level = 0;
zb.zb_blkid = range->start_blkid;

arc_buf_t *abuf = NULL;
if (!dscp->dsc_dso->dso_dryrun && arc_read(NULL, spa,
bp, arc_getbuf_func, &abuf, ZIO_PRIORITY_ASYNC_READ,
zioflags, &aflags, &zb) != 0)
return (SET_ERROR(EIO));

err = dump_spill(dscp, bp, zb.zb_object,
(abuf == NULL ? NULL : abuf->b_data));
if (abuf != NULL)
arc_buf_destroy(abuf, &abuf);
return (err);
}
if (send_do_embed(bp, dscp->dsc_featureflags)) {
err = dump_write_embedded(dscp, range->object,
range->start_blkid * srdp->datablksz,
Expand All @@ -975,8 +926,9 @@ do_dump(dmu_send_cookie_t *dscp, struct send_range *range)
}
ASSERT(range->object > dscp->dsc_resume_object ||
(range->object == dscp->dsc_resume_object &&
(range->start_blkid == DMU_SPILL_BLKID ||
range->start_blkid * srdp->datablksz >=
dscp->dsc_resume_offset));
dscp->dsc_resume_offset)));
/* it's a level-0 block of a regular object */

mutex_enter(&srdp->lock);
Expand Down Expand Up @@ -1006,8 +958,6 @@ do_dump(dmu_send_cookie_t *dscp, struct send_range *range)
ASSERT(dscp->dsc_dso->dso_dryrun ||
srdp->abuf != NULL || srdp->abd != NULL);

uint64_t offset = range->start_blkid * srdp->datablksz;

char *data = NULL;
if (srdp->abd != NULL) {
data = abd_to_buf(srdp->abd);
Expand All @@ -1016,6 +966,14 @@ do_dump(dmu_send_cookie_t *dscp, struct send_range *range)
data = srdp->abuf->b_data;
}

if (BP_GET_TYPE(bp) == DMU_OT_SA) {
ASSERT3U(range->start_blkid, ==, DMU_SPILL_BLKID);
err = dump_spill(dscp, bp, range->object, data);
return (err);
}

uint64_t offset = range->start_blkid * srdp->datablksz;

/*
* If we have large blocks stored on disk but the send flags
* don't allow us to send large blocks, we split the data from
Expand Down Expand Up @@ -1098,6 +1056,8 @@ range_alloc(enum type type, uint64_t object, uint64_t start_blkid,
range->sru.data.io_outstanding = 0;
range->sru.data.io_err = 0;
range->sru.data.io_compressed = B_FALSE;
} else if (type == OBJECT) {
range->sru.object.spill_range = NULL;
}
return (range);
}
Expand Down Expand Up @@ -1742,6 +1702,45 @@ enqueue_range(struct send_reader_thread_arg *srta, bqueue_t *q, dnode_t *dn,
bqueue_enqueue(q, range, datablksz);
}

/*
* Send DRR_SPILL records for unmodified spill blocks. This is useful
* because changing certain attributes of the object (e.g. blocksize)
* can cause old versions of ZFS to incorrectly remove a spill block.
* Including these records in the stream forces an up to date version
* to always be written ensuring they're never lost. Current versions
* of the code which understand the DRR_FLAG_SPILL_BLOCK feature can
* ignore these unmodified spill blocks.
*
* We piggyback the spill_range to dnode range instead of enqueueing it
* so send_range_after won't complain.
*/
static uint64_t
piggyback_unmodified_spill(struct send_reader_thread_arg *srta,
struct send_range *range)
{
ASSERT3U(range->type, ==, OBJECT);

dnode_phys_t *dnp = range->sru.object.dnp;
uint64_t fromtxg = srta->smta->to_arg->fromtxg;

if (!zfs_send_unmodified_spill_blocks ||
!(dnp->dn_flags & DNODE_FLAG_SPILL_BLKPTR) ||
!(BP_GET_LOGICAL_BIRTH(DN_SPILL_BLKPTR(dnp)) <= fromtxg))
return (0);

blkptr_t *bp = DN_SPILL_BLKPTR(dnp);
struct send_range *spill_range = range_alloc(DATA, range->object,
DMU_SPILL_BLKID, DMU_SPILL_BLKID+1, B_FALSE);
spill_range->sru.data.bp = *bp;
spill_range->sru.data.obj_type = dnp->dn_type;
spill_range->sru.data.datablksz = BP_GET_LSIZE(bp);

issue_data_read(srta, spill_range);
range->sru.object.spill_range = spill_range;

return (BP_GET_LSIZE(bp));
}

/*
* This thread is responsible for two things: First, it retrieves the correct
* blkptr in the to ds if we need to send the data because of something from
Expand Down Expand Up @@ -1773,17 +1772,20 @@ send_reader_thread(void *arg)
uint64_t last_obj_exists = B_TRUE;
while (!range->eos_marker && !srta->cancel && smta->error == 0 &&
err == 0) {
uint64_t spill = 0;
switch (range->type) {
case DATA:
issue_data_read(srta, range);
bqueue_enqueue(outq, range, range->sru.data.datablksz);
range = get_next_range_nofree(inq, range);
break;
case HOLE:
case OBJECT:
spill = piggyback_unmodified_spill(srta, range);
zfs_fallthrough;
case HOLE:
case OBJECT_RANGE:
case REDACT: // Redacted blocks must exist
bqueue_enqueue(outq, range, sizeof (*range));
bqueue_enqueue(outq, range, sizeof (*range) + spill);
range = get_next_range_nofree(inq, range);
break;
case PREVIOUSLY_REDACTED: {
Expand Down

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