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Improved dnode allocation and dmu_hold_impl() (#6611)

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Refactor dmu_object_alloc_dnsize() and dnode_hold_impl() to simplify the
code, fix errors introduced by commit dbeb879 (PR #6117) interacting
badly with large dnodes, and improve performance.

* When allocating a new dnode in dmu_object_alloc_dnsize(), update the
percpu object ID for the core's metadnode chunk immediately.  This
eliminates most lock contention when taking the hold and creating the
dnode.

* Correct detection of the chunk boundary to work properly with large
dnodes.

* Separate the dmu_hold_impl() code for the FREE case from the code for
the ALLOCATED case to make it easier to read.

* Fully populate the dnode handle array immediately after reading a
block of the metadnode from disk.  Subsequently the dnode handle array
provides enough information to determine which dnode slots are in use
and which are free.

* Add several kstats to allow the behavior of the code to be examined.

* Verify dnode packing in large_dnode_008_pos.ksh.  Since the test is
purely creates, it should leave very few holes in the metadnode.

* Add test large_dnode_009_pos.ksh, which performs concurrent creates
and deletes, to complement existing test which does only creates.

With the above fixes, there is very little contention in a test of about
200,000 racing dnode allocations produced by tests 'large_dnode_008_pos'
and 'large_dnode_009_pos'.

name                            type data
dnode_hold_dbuf_hold            4    0
dnode_hold_dbuf_read            4    0
dnode_hold_alloc_hits           4    3804690
dnode_hold_alloc_misses         4    216
dnode_hold_alloc_interior       4    3
dnode_hold_alloc_lock_retry     4    0
dnode_hold_alloc_lock_misses    4    0
dnode_hold_alloc_type_none      4    0
dnode_hold_free_hits            4    203105
dnode_hold_free_misses          4    4
dnode_hold_free_lock_misses     4    0
dnode_hold_free_lock_retry      4    0
dnode_hold_free_overflow        4    0
dnode_hold_free_refcount        4    57
dnode_hold_free_txg             4    0
dnode_allocate                  4    203154
dnode_reallocate                4    0
dnode_buf_evict                 4    23918
dnode_alloc_next_chunk          4    4887
dnode_alloc_race                4    0
dnode_alloc_next_block          4    18

The performance is slightly improved for concurrent creates with
16+ threads, and unchanged for low thread counts.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Olaf Faaland <faaland1@llnl.gov>
This commit is contained in:
Giuseppe Di Natale
2017-09-13 15:46:15 -07:00
committed by Tony Hutter
parent 89950722c6
commit 45d1abc74d
9 changed files with 616 additions and 258 deletions
Download Patch File Download Diff File Expand all files Collapse all files
cmd/zdb/zdb.c
+29 -7
View File
@@ -1933,7 +1933,8 @@ static object_viewer_t *object_viewer[DMU_OT_NUMTYPES + 1] = {
};
static void
dump_object(objset_t *os, uint64_t object, int verbosity, int *print_header)
dump_object(objset_t *os, uint64_t object, int verbosity, int *print_header,
uint64_t *dnode_slots_used)
{
dmu_buf_t *db = NULL;
dmu_object_info_t doi;
@@ -1965,6 +1966,9 @@ dump_object(objset_t *os, uint64_t object, int verbosity, int *print_header)
}
dmu_object_info_from_dnode(dn, &doi);
if (dnode_slots_used)
*dnode_slots_used = doi.doi_dnodesize / DNODE_MIN_SIZE;
zdb_nicenum(doi.doi_metadata_block_size, iblk);
zdb_nicenum(doi.doi_data_block_size, dblk);
zdb_nicenum(doi.doi_max_offset, lsize);
@@ -2072,6 +2076,9 @@ dump_dir(objset_t *os)
int verbosity = dump_opt['d'];
int print_header = 1;
int i, error;
uint64_t total_slots_used = 0;
uint64_t max_slot_used = 0;
uint64_t dnode_slots;
dsl_pool_config_enter(dmu_objset_pool(os), FTAG);
dmu_objset_fast_stat(os, &dds);
@@ -2112,7 +2119,7 @@ dump_dir(objset_t *os)
if (zopt_objects != 0) {
for (i = 0; i < zopt_objects; i++)
dump_object(os, zopt_object[i], verbosity,
&print_header);
&print_header, NULL);
(void) printf("\n");
return;
}
@@ -2129,24 +2136,39 @@ dump_dir(objset_t *os)
if (BP_IS_HOLE(os->os_rootbp))
return;
dump_object(os, 0, verbosity, &print_header);
dump_object(os, 0, verbosity, &print_header, NULL);
object_count = 0;
if (DMU_USERUSED_DNODE(os) != NULL &&
DMU_USERUSED_DNODE(os)->dn_type != 0) {
dump_object(os, DMU_USERUSED_OBJECT, verbosity, &print_header);
dump_object(os, DMU_GROUPUSED_OBJECT, verbosity, &print_header);
dump_object(os, DMU_USERUSED_OBJECT, verbosity, &print_header,
NULL);
dump_object(os, DMU_GROUPUSED_OBJECT, verbosity, &print_header,
NULL);
}
object = 0;
while ((error = dmu_object_next(os, &object, B_FALSE, 0)) == 0) {
dump_object(os, object, verbosity, &print_header);
dump_object(os, object, verbosity, &print_header, &dnode_slots);
object_count++;
total_slots_used += dnode_slots;
max_slot_used = object + dnode_slots - 1;
}
ASSERT3U(object_count, ==, usedobjs);
(void) printf("\n");
(void) printf(" Dnode slots:\n");
(void) printf("\tTotal used: %10llu\n",
(u_longlong_t)total_slots_used);
(void) printf("\tMax used: %10llu\n",
(u_longlong_t)max_slot_used);
(void) printf("\tPercent empty: %10lf\n",
(double)(max_slot_used - total_slots_used)*100 /
(double)max_slot_used);
(void) printf("\n");
if (error != ESRCH) {
(void) fprintf(stderr, "dmu_object_next() = %d\n", error);
abort();
@@ -2610,7 +2632,7 @@ dump_path_impl(objset_t *os, uint64_t obj, char *name)
return (dump_path_impl(os, child_obj, s + 1));
/*FALLTHROUGH*/
case DMU_OT_PLAIN_FILE_CONTENTS:
dump_object(os, child_obj, dump_opt['v'], &header);
dump_object(os, child_obj, dump_opt['v'], &header, NULL);
return (0);
default:
(void) fprintf(stderr, "object %llu has non-file/directory "