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OpenZFS 7606 - dmu_objset_find_dp() takes a long time while importing pool

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When importing a pool with a large number of filesystems within the same
parent filesystem, we see that dmu_objset_find_dp() takes a long time.
It is called from 3 places: spa_check_logs(), spa_ld_claim_log_blocks(),
and spa_load_verify().

There are several ways to improve performance here:

    1. We don't really need to do spa_check_logs() or
       spa_ld_claim_log_blocks() if the pool was closed cleanly.

    2. spa_load_verify() uses dmu_objset_find_dp() to check that no
       datasets have too long of names.

    3. dmu_objset_find_dp() is slow because it's doing
       zap_value_search() (which is O(N sibling datasets)) to determine
       the name of each dsl_dir when it's opened. In this case we
       actually know the name when we are opening it, so we can provide
       it and avoid the lookup.

This change implements fix #3 from the above list; i.e. make
dmu_objset_find_dp() provide the name of the dataset so that we don't
have to search for it.

Authored by: Matthew Ahrens <mahrens@delphix.com>
Reviewed by: Steve Gonczi <steve.gonczi@delphix.com>
Reviewed by: George Wilson <george.wilson@delphix.com>
Reviewed by: Prashanth Sreenivasa <prashksp@gmail.com>
Reviewed-by: David Quigley <david.quigley@intel.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Ported-by: George Melikov <mail@gmelikov.ru>

OpenZFS-issue: https://www.illumos.org/issues/7606
OpenZFS-commit: https://github.com/openzfs/openzfs/commit/cac6bab
Closes #5662
This commit is contained in:
George Melikov 2017-01-26 23:46:02 +03:00 committed by Brian Behlendorf
parent 89d43feb0b
commit 1149ba6478
1 changed files with 24 additions and 4 deletions
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28
module/zfs/dmu_objset.c
View File

@ -1927,6 +1927,7 @@ typedef struct dmu_objset_find_ctx {
taskq_t *dc_tq;
dsl_pool_t *dc_dp;
uint64_t dc_ddobj;
char *dc_ddname; /* last component of ddobj's name */
int (*dc_func)(dsl_pool_t *, dsl_dataset_t *, void *);
void *dc_arg;
int dc_flags;
@ -1950,7 +1951,12 @@ dmu_objset_find_dp_impl(dmu_objset_find_ctx_t *dcp)
if (*dcp->dc_error != 0)
goto out;
err = dsl_dir_hold_obj(dp, dcp->dc_ddobj, NULL, FTAG, &dd);
/*
* Note: passing the name (dc_ddname) here is optional, but it
* improves performance because we don't need to call
* zap_value_search() to determine the name.
*/
err = dsl_dir_hold_obj(dp, dcp->dc_ddobj, dcp->dc_ddname, FTAG, &dd);
if (err != 0)
goto out;
@ -1975,9 +1981,11 @@ dmu_objset_find_dp_impl(dmu_objset_find_ctx_t *dcp)
sizeof (uint64_t));
ASSERT3U(attr->za_num_integers, ==, 1);
child_dcp = kmem_alloc(sizeof (*child_dcp), KM_SLEEP);
child_dcp =
kmem_alloc(sizeof (*child_dcp), KM_SLEEP);
*child_dcp = *dcp;
child_dcp->dc_ddobj = attr->za_first_integer;
child_dcp->dc_ddname = spa_strdup(attr->za_name);
if (dcp->dc_tq != NULL)
(void) taskq_dispatch(dcp->dc_tq,
dmu_objset_find_dp_cb, child_dcp, TQ_SLEEP);
@ -2020,16 +2028,25 @@ dmu_objset_find_dp_impl(dmu_objset_find_ctx_t *dcp)
}
}
dsl_dir_rele(dd, FTAG);
kmem_free(attr, sizeof (zap_attribute_t));
if (err != 0)
if (err != 0) {
dsl_dir_rele(dd, FTAG);
goto out;
}
/*
* Apply to self.
*/
err = dsl_dataset_hold_obj(dp, thisobj, FTAG, &ds);
/*
* Note: we hold the dir while calling dsl_dataset_hold_obj() so
* that the dir will remain cached, and we won't have to re-instantiate
* it (which could be expensive due to finding its name via
* zap_value_search()).
*/
dsl_dir_rele(dd, FTAG);
if (err != 0)
goto out;
err = dcp->dc_func(dp, ds, dcp->dc_arg);
@ -2044,6 +2061,8 @@ dmu_objset_find_dp_impl(dmu_objset_find_ctx_t *dcp)
mutex_exit(dcp->dc_error_lock);
}
if (dcp->dc_ddname != NULL)
spa_strfree(dcp->dc_ddname);
kmem_free(dcp, sizeof (*dcp));
}
@ -2088,6 +2107,7 @@ dmu_objset_find_dp(dsl_pool_t *dp, uint64_t ddobj,
dcp->dc_tq = NULL;
dcp->dc_dp = dp;
dcp->dc_ddobj = ddobj;
dcp->dc_ddname = NULL;
dcp->dc_func = func;
dcp->dc_arg = arg;
dcp->dc_flags = flags;