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Improve ZFS objset sync parallelism

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As part of transaction group commit, dsl_pool_sync() sequentially calls
dsl_dataset_sync() for each dirty dataset, which subsequently calls
dmu_objset_sync().  dmu_objset_sync() in turn uses up to 75% of CPU
cores to run sync_dnodes_task() in taskq threads to sync the dirty
dnodes (files).

There are two problems:

1. Each ZVOL in a pool is a separate dataset/objset having a single
   dnode.  This means the objsets are synchronized serially, which
   leads to a bottleneck of ~330K blocks written per second per pool.

2. In the case of multiple dirty dnodes/files on a dataset/objset on a
   big system they will be sync'd in parallel taskq threads. However,
   it is inefficient to to use 75% of CPU cores of a big system to do
   that, because of (a) bottlenecks on a single write issue taskq, and
   (b) allocation throttling.  In addition, if not for the allocation
   throttling sorting write requests by bookmarks (logical address),
   writes for different files may reach space allocators interleaved,
   leading to unwanted fragmentation.

The solution to both problems is to always sync no more and (if
possible) no fewer dnodes at the same time than there are allocators
the pool.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Alexander Motin <mav@FreeBSD.org>
Signed-off-by: Edmund Nadolski <edmund.nadolski@ixsystems.com>
Closes #15197
This commit is contained in:
ednadolski-ix
2023-11-06 11:38:42 -07:00
committed by GitHub
parent 0527774066
commit 3bd4df3841
18 changed files with 513 additions and 118 deletions
Download Patch File Download Diff File Expand all files Collapse all files
module/zfs/dmu_objset.c
+104 -34
View File
@@ -1639,28 +1639,90 @@ dmu_objset_write_done(zio_t *zio, arc_buf_t *abuf, void *arg)
kmem_free(bp, sizeof (*bp));
}
typedef struct sync_objset_arg {
zio_t *soa_zio;
objset_t *soa_os;
dmu_tx_t *soa_tx;
kmutex_t soa_mutex;
int soa_count;
taskq_ent_t soa_tq_ent;
} sync_objset_arg_t;
typedef struct sync_dnodes_arg {
multilist_t *sda_list;
int sda_sublist_idx;
multilist_t *sda_newlist;
dmu_tx_t *sda_tx;
multilist_t *sda_list;
int sda_sublist_idx;
multilist_t *sda_newlist;
sync_objset_arg_t *sda_soa;
} sync_dnodes_arg_t;
static void sync_meta_dnode_task(void *arg);
static void
sync_dnodes_task(void *arg)
{
sync_dnodes_arg_t *sda = arg;
sync_objset_arg_t *soa = sda->sda_soa;
objset_t *os = soa->soa_os;
multilist_sublist_t *ms =
multilist_sublist_lock(sda->sda_list, sda->sda_sublist_idx);
dmu_objset_sync_dnodes(ms, sda->sda_tx);
dmu_objset_sync_dnodes(ms, soa->soa_tx);
multilist_sublist_unlock(ms);
kmem_free(sda, sizeof (*sda));
mutex_enter(&soa->soa_mutex);
ASSERT(soa->soa_count != 0);
if (--soa->soa_count != 0) {
mutex_exit(&soa->soa_mutex);
return;
}
mutex_exit(&soa->soa_mutex);
taskq_dispatch_ent(dmu_objset_pool(os)->dp_sync_taskq,
sync_meta_dnode_task, soa, TQ_FRONT, &soa->soa_tq_ent);
}
/*
* Issue the zio_nowait() for all dirty record zios on the meta dnode,
* then trigger the callback for the zil_sync. This runs once for each
* objset, only after any/all sublists in the objset have been synced.
*/
static void
sync_meta_dnode_task(void *arg)
{
sync_objset_arg_t *soa = arg;
objset_t *os = soa->soa_os;
dmu_tx_t *tx = soa->soa_tx;
int txgoff = tx->tx_txg & TXG_MASK;
dbuf_dirty_record_t *dr;
ASSERT0(soa->soa_count);
list_t *list = &DMU_META_DNODE(os)->dn_dirty_records[txgoff];
while ((dr = list_remove_head(list)) != NULL) {
ASSERT0(dr->dr_dbuf->db_level);
zio_nowait(dr->dr_zio);
}
/* Enable dnode backfill if enough objects have been freed. */
if (os->os_freed_dnodes >= dmu_rescan_dnode_threshold) {
os->os_rescan_dnodes = B_TRUE;
os->os_freed_dnodes = 0;
}
/*
* Free intent log blocks up to this tx.
*/
zil_sync(os->os_zil, tx);
os->os_phys->os_zil_header = os->os_zil_header;
zio_nowait(soa->soa_zio);
mutex_destroy(&soa->soa_mutex);
kmem_free(soa, sizeof (*soa));
}
/* called from dsl */
void
@@ -1670,8 +1732,6 @@ dmu_objset_sync(objset_t *os, zio_t *pio, dmu_tx_t *tx)
zbookmark_phys_t zb;
zio_prop_t zp;
zio_t *zio;
list_t *list;
dbuf_dirty_record_t *dr;
int num_sublists;
multilist_t *ml;
blkptr_t *blkptr_copy = kmem_alloc(sizeof (*os->os_rootbp), KM_SLEEP);
@@ -1758,39 +1818,49 @@ dmu_objset_sync(objset_t *os, zio_t *pio, dmu_tx_t *tx)
offsetof(dnode_t, dn_dirty_link[txgoff]));
}
/*
* zio_nowait(zio) is done after any/all sublist and meta dnode
* zios have been nowaited, and the zil_sync() has been performed.
* The soa is freed at the end of sync_meta_dnode_task.
*/
sync_objset_arg_t *soa = kmem_alloc(sizeof (*soa), KM_SLEEP);
soa->soa_zio = zio;
soa->soa_os = os;
soa->soa_tx = tx;
taskq_init_ent(&soa->soa_tq_ent);
mutex_init(&soa->soa_mutex, NULL, MUTEX_DEFAULT, NULL);
ml = &os->os_dirty_dnodes[txgoff];
num_sublists = multilist_get_num_sublists(ml);
soa->soa_count = num_sublists = multilist_get_num_sublists(ml);
for (int i = 0; i < num_sublists; i++) {
if (multilist_sublist_is_empty_idx(ml, i))
continue;
sync_dnodes_arg_t *sda = kmem_alloc(sizeof (*sda), KM_SLEEP);
sda->sda_list = ml;
sda->sda_sublist_idx = i;
sda->sda_tx = tx;
(void) taskq_dispatch(dmu_objset_pool(os)->dp_sync_taskq,
sync_dnodes_task, sda, 0);
/* callback frees sda */
}
taskq_wait(dmu_objset_pool(os)->dp_sync_taskq);
list = &DMU_META_DNODE(os)->dn_dirty_records[txgoff];
while ((dr = list_remove_head(list)) != NULL) {
ASSERT0(dr->dr_dbuf->db_level);
zio_nowait(dr->dr_zio);
soa->soa_count--;
}
/* Enable dnode backfill if enough objects have been freed. */
if (os->os_freed_dnodes >= dmu_rescan_dnode_threshold) {
os->os_rescan_dnodes = B_TRUE;
os->os_freed_dnodes = 0;
if (soa->soa_count == 0) {
taskq_dispatch_ent(dmu_objset_pool(os)->dp_sync_taskq,
sync_meta_dnode_task, soa, TQ_FRONT, &soa->soa_tq_ent);
} else {
/*
* Sync sublists in parallel. The last to finish
* (i.e., when soa->soa_count reaches zero) must
* dispatch sync_meta_dnode_task.
*/
for (int i = 0; i < num_sublists; i++) {
if (multilist_sublist_is_empty_idx(ml, i))
continue;
sync_dnodes_arg_t *sda =
kmem_alloc(sizeof (*sda), KM_SLEEP);
sda->sda_list = ml;
sda->sda_sublist_idx = i;
sda->sda_soa = soa;
(void) taskq_dispatch(
dmu_objset_pool(os)->dp_sync_taskq,
sync_dnodes_task, sda, 0);
/* sync_dnodes_task frees sda */
}
}
/*
* Free intent log blocks up to this tx.
*/
zil_sync(os->os_zil, tx);
os->os_phys->os_zil_header = os->os_zil_header;
zio_nowait(zio);
}
boolean_t