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Remove parent ZIO from dbuf_prefetch()

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I am not sure why it was added there 10 years ago, but it seems not
needed now.  According to my tests removing it improves sequential
read performance with recordsize=4K by 5-10% by reducing the CPU
overhead in prefetcher.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Rob Norris <robn@despairlabs.com>
Reviewed-by: Ameer Hamza <ahamza@ixsystems.com>
Reviewed-by: Akash B <akash-b@hpe.com>
Signed-off-by: Alexander Motin <alexander.motin@TrueNAS.com>
Closes #18214
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Alexander Motin 2026-02-18 21:12:13 -05:00 committed by GitHub
parent d489677280
commit 370570890f
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1 changed files with 3 additions and 14 deletions
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17
module/zfs/dbuf.c
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@ -3553,7 +3553,6 @@ typedef struct dbuf_prefetch_arg {
int dpa_curlevel; /* The current level that we're reading */
dnode_t *dpa_dnode; /* The dnode associated with the prefetch */
zio_priority_t dpa_prio; /* The priority I/Os should be issued at. */
zio_t *dpa_zio; /* The parent zio_t for all prefetches. */
arc_flags_t dpa_aflags; /* Flags to pass to the final prefetch. */
dbuf_prefetch_fn dpa_cb; /* prefetch completion callback */
void *dpa_arg; /* prefetch completion arg */
@ -3605,8 +3604,7 @@ dbuf_issue_final_prefetch(dbuf_prefetch_arg_t *dpa, blkptr_t *bp)
ASSERT3U(dpa->dpa_curlevel, ==, BP_GET_LEVEL(bp));
ASSERT3U(dpa->dpa_curlevel, ==, dpa->dpa_zb.zb_level);
ASSERT(dpa->dpa_zio != NULL);
(void) arc_read(dpa->dpa_zio, dpa->dpa_spa, bp,
(void) arc_read(NULL, dpa->dpa_spa, bp,
dbuf_issue_final_prefetch_done, dpa,
dpa->dpa_prio, zio_flags, &aflags, &dpa->dpa_zb);
}
@ -3706,7 +3704,7 @@ dbuf_prefetch_indirect_done(zio_t *zio, const zbookmark_phys_t *zb,
SET_BOOKMARK(&zb, dpa->dpa_zb.zb_objset,
dpa->dpa_zb.zb_object, dpa->dpa_curlevel, nextblkid);
(void) arc_read(dpa->dpa_zio, dpa->dpa_spa,
(void) arc_read(NULL, dpa->dpa_spa,
bp, dbuf_prefetch_indirect_done, dpa,
ZIO_PRIORITY_SYNC_READ,
ZIO_FLAG_CANFAIL | ZIO_FLAG_SPECULATIVE,
@ -3801,9 +3799,6 @@ dbuf_prefetch_impl(dnode_t *dn, int64_t level, uint64_t blkid,
ASSERT3U(curlevel, ==, BP_GET_LEVEL(&bp));
zio_t *pio = zio_root(dmu_objset_spa(dn->dn_objset), NULL, NULL,
ZIO_FLAG_CANFAIL);
dbuf_prefetch_arg_t *dpa = kmem_zalloc(sizeof (*dpa), KM_SLEEP);
dsl_dataset_t *ds = dn->dn_objset->os_dsl_dataset;
SET_BOOKMARK(&dpa->dpa_zb, ds != NULL ? ds->ds_object : DMU_META_OBJSET,
@ -3814,7 +3809,6 @@ dbuf_prefetch_impl(dnode_t *dn, int64_t level, uint64_t blkid,
dpa->dpa_spa = dn->dn_objset->os_spa;
dpa->dpa_dnode = dn;
dpa->dpa_epbs = epbs;
dpa->dpa_zio = pio;
dpa->dpa_cb = cb;
dpa->dpa_arg = arg;
@ -3843,17 +3837,12 @@ dbuf_prefetch_impl(dnode_t *dn, int64_t level, uint64_t blkid,
SET_BOOKMARK(&zb, ds != NULL ? ds->ds_object : DMU_META_OBJSET,
dn->dn_object, curlevel, curblkid);
(void) arc_read(dpa->dpa_zio, dpa->dpa_spa,
(void) arc_read(NULL, dpa->dpa_spa,
&bp, dbuf_prefetch_indirect_done, dpa,
ZIO_PRIORITY_SYNC_READ,
ZIO_FLAG_CANFAIL | ZIO_FLAG_SPECULATIVE,
&iter_aflags, &zb);
}
/*
* We use pio here instead of dpa_zio since it's possible that
* dpa may have already been freed.
*/
zio_nowait(pio);
return (1);
no_issue:
if (cb != NULL)