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MFV r318927: 8025 dbuf_read() creates unnecessary zio_root() for bonus buf

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illumos/illumos-gate@def4fac588
def4fac588

https://www.illumos.org/issues/8025
  dbuf_read() creates a zio_root() to track and wait for all the zio's
  that may happen as part of this call. However, if the blkptr_t for
  this buffer is NULL or a hole, we will not create any more zio's, so
  this zio_root() is unnecessary. This is always the case when calling
  dbuf_read() on a bonus buffer, because it has no blkptr (it's part of
  the containing dnode). For workloads that read a lot of bonus buffers
  (e.g. file creation and removal), creating and destroying these
  unnecessary zio's can decrease performance by around 3%.

Reviewed by: Dan Kimmel <dan.kimmel@delphix.com>
Reviewed by: Pavel Zakharov <pavel.zakharov@delphix.com>
Reviewed by: Prashanth Sreenivasa <pks@delphix.com>
Approved by: Robert Mustacchi <rm@joyent.com>
Author: Matthew Ahrens <mahrens@delphix.com>
This commit is contained in:
avg 2017-05-26 11:30:55 +00:00
parent 9e3a16fd34
commit e306ed52e7
1 changed files with 6 additions and 4 deletions
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10
sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dbuf.c
View File

@ -1088,7 +1088,6 @@ int
dbuf_read(dmu_buf_impl_t *db, zio_t *zio, uint32_t flags)
{
int err = 0;
boolean_t havepzio = (zio != NULL);
boolean_t prefetch;
dnode_t *dn;
@ -1132,9 +1131,13 @@ dbuf_read(dmu_buf_impl_t *db, zio_t *zio, uint32_t flags)
DB_DNODE_EXIT(db);
} else if (db->db_state == DB_UNCACHED) {
spa_t *spa = dn->dn_objset->os_spa;
boolean_t need_wait = B_FALSE;
if (zio == NULL)
if (zio == NULL &&
db->db_blkptr != NULL && !BP_IS_HOLE(db->db_blkptr)) {
zio = zio_root(spa, NULL, NULL, ZIO_FLAG_CANFAIL);
need_wait = B_TRUE;
}
dbuf_read_impl(db, zio, flags);
/* dbuf_read_impl has dropped db_mtx for us */
@ -1146,7 +1149,7 @@ dbuf_read(dmu_buf_impl_t *db, zio_t *zio, uint32_t flags)
rw_exit(&dn->dn_struct_rwlock);
DB_DNODE_EXIT(db);
if (!havepzio)
if (need_wait)
err = zio_wait(zio);
} else {
/*
@ -1181,7 +1184,6 @@ dbuf_read(dmu_buf_impl_t *db, zio_t *zio, uint32_t flags)
mutex_exit(&db->db_mtx);
}
ASSERT(err || havepzio || db->db_state == DB_CACHED);
return (err);
}