3642 dsl_scan_active() should not issue I/O to determine if async
destroying is active
3643 txg_delay should not hold the tc_lock
Reviewed by: Matthew Ahrens <mahrens@delphix.com>
Reviewed by: Adam Leventhal <ahl@delphix.com>
Approved by: Gordon Ross <gwr@nexenta.com>
References:
https://www.illumos.org/issues/3642
https://www.illumos.org/issues/3643
illumos/illumos-gate@
4a92375985c37d61406d66cd2b10ee642eb1f5e7
Ported-by: Richard Yao <ryao@gentoo.org>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Issue #1775
Porting Notes:
1. The alignment assumptions for the tx_cpu structure assume that
a kmutex_t is 8 bytes. This isn't true under Linux but tc_pad[]
was adjusted anyway for consistency since this structure was
never carefully aligned in ZoL. If careful alignment does impact
performance significantly this should be reworked to be portable.
*/
/*
* Copyright (c) 2010, Oracle and/or its affiliates. All rights reserved.
- * Copyright (c) 2012 by Delphix. All rights reserved.
+ * Copyright (c) 2013 by Delphix. All rights reserved.
*/
#ifndef _SYS_DSL_SCAN_H
/* for freeing blocks */
boolean_t scn_is_bptree;
+ boolean_t scn_async_destroying;
/* for debugging / information */
uint64_t scn_visited_this_txg;
* Use is subject to license terms.
*/
+/*
+ * Copyright (c) 2013 by Delphix. All rights reserved.
+ */
+
#ifndef _SYS_TXG_IMPL_H
#define _SYS_TXG_IMPL_H
extern "C" {
#endif
+/*
+ * The tx_cpu structure is a per-cpu structure that is used to track
+ * the number of active transaction holds (tc_count). As transactions
+ * are assigned into a transaction group the appropriate tc_count is
+ * incremented to indicate that there are pending changes that have yet
+ * to quiesce. Consumers evenutally call txg_rele_to_sync() to decrement
+ * the tc_count. A transaction group is not considered quiesced until all
+ * tx_cpu structures have reached a tc_count of zero.
+ *
+ * This structure is a per-cpu structure by design. Updates to this structure
+ * are frequent and concurrent. Having a single structure would result in
+ * heavy lock contention so a per-cpu design was implemented. With the fanned
+ * out mutex design, consumers only need to lock the mutex associated with
+ * thread's cpu.
+ *
+ * The tx_cpu contains two locks, the tc_lock and tc_open_lock.
+ * The tc_lock is used to protect all members of the tx_cpu structure with
+ * the exception of the tc_open_lock. This lock should only be held for a
+ * short period of time, typically when updating the value of tc_count.
+ *
+ * The tc_open_lock protects the tx_open_txg member of the tx_state structure.
+ * This lock is used to ensure that transactions are only assigned into
+ * the current open transaction group. In order to move the current open
+ * transaction group to the quiesce phase, the txg_quiesce thread must
+ * grab all tc_open_locks, increment the tx_open_txg, and drop the locks.
+ * The tc_open_lock is held until the transaction is assigned into the
+ * transaction group. Typically, this is a short operation but if throttling
+ * is occuring it may be held for longer periods of time.
+ */
struct tx_cpu {
- kmutex_t tc_lock;
+ kmutex_t tc_open_lock; /* protects tx_open_txg */
+ kmutex_t tc_lock; /* protects the rest of this struct */
kcondvar_t tc_cv[TXG_SIZE];
uint64_t tc_count[TXG_SIZE];
list_t tc_callbacks[TXG_SIZE]; /* commit cb list */
- char tc_pad[16];
+ char tc_pad[8]; /* pad to fill 3 cache lines */
};
+/*
+ * The tx_state structure maintains the state information about the different
+ * stages of the pool's transcation groups. A per pool tx_state structure
+ * is used to track this information. The tx_state structure also points to
+ * an array of tx_cpu structures (described above). Although the tx_sync_lock
+ * is used to protect the members of this structure, it is not used to
+ * protect the tx_open_txg. Instead a special lock in the tx_cpu structure
+ * is used. Readers of tx_open_txg must grab the per-cpu tc_open_lock.
+ * Any thread wishing to update tx_open_txg must grab the tc_open_lock on
+ * every cpu (see txg_quiesce()).
+ */
typedef struct tx_state {
tx_cpu_t *tx_cpu; /* protects right to enter txg */
kmutex_t tx_sync_lock; /* protects tx_state_t */
zil_destroy_sync(dmu_objset_zil(os), tx);
if (!spa_feature_is_active(dp->dp_spa, async_destroy)) {
+ dsl_scan_t *scn = dp->dp_scan;
+
spa_feature_incr(dp->dp_spa, async_destroy, tx);
dp->dp_bptree_obj = bptree_alloc(mos, tx);
VERIFY0(zap_add(mos,
DMU_POOL_DIRECTORY_OBJECT,
DMU_POOL_BPTREE_OBJ, sizeof (uint64_t), 1,
&dp->dp_bptree_obj, tx));
+ ASSERT(!scn->scn_async_destroying);
+ scn->scn_async_destroying = B_TRUE;
}
used = ds->ds_dir->dd_phys->dd_used_bytes;
scn = dp->dp_scan = kmem_zalloc(sizeof (dsl_scan_t), KM_SLEEP);
scn->scn_dp = dp;
+ /*
+ * It's possible that we're resuming a scan after a reboot so
+ * make sure that the scan_async_destroying flag is initialized
+ * appropriately.
+ */
+ ASSERT(!scn->scn_async_destroying);
+ scn->scn_async_destroying = spa_feature_is_active(dp->dp_spa,
+ &spa_feature_table[SPA_FEATURE_ASYNC_DESTROY]);
+
err = zap_lookup(dp->dp_meta_objset, DMU_POOL_DIRECTORY_OBJECT,
"scrub_func", sizeof (uint64_t), 1, &f);
if (err == 0) {
if (spa_shutting_down(spa))
return (B_FALSE);
- if (scn->scn_phys.scn_state == DSS_SCANNING)
+ if (scn->scn_phys.scn_state == DSS_SCANNING ||
+ scn->scn_async_destroying)
return (B_TRUE);
- if (spa_feature_is_active(spa,
- &spa_feature_table[SPA_FEATURE_ASYNC_DESTROY])) {
- return (B_TRUE);
- }
if (spa_version(scn->scn_dp->dp_spa) >= SPA_VERSION_DEADLISTS) {
(void) bpobj_space(&scn->scn_dp->dp_free_bpobj,
&used, &comp, &uncomp);
if (err == 0 && spa_feature_is_active(spa,
&spa_feature_table[SPA_FEATURE_ASYNC_DESTROY])) {
+ ASSERT(scn->scn_async_destroying);
scn->scn_is_bptree = B_TRUE;
scn->scn_zio_root = zio_root(dp->dp_spa, NULL,
NULL, ZIO_FLAG_MUSTSUCCEED);
VERIFY0(bptree_free(dp->dp_meta_objset,
dp->dp_bptree_obj, tx));
dp->dp_bptree_obj = 0;
+ scn->scn_async_destroying = B_FALSE;
}
}
if (scn->scn_visited_this_txg) {
int i;
mutex_init(&tx->tx_cpu[c].tc_lock, NULL, MUTEX_DEFAULT, NULL);
+ mutex_init(&tx->tx_cpu[c].tc_open_lock, NULL, MUTEX_DEFAULT,
+ NULL);
for (i = 0; i < TXG_SIZE; i++) {
cv_init(&tx->tx_cpu[c].tc_cv[i], NULL, CV_DEFAULT,
NULL);
for (c = 0; c < max_ncpus; c++) {
int i;
+ mutex_destroy(&tx->tx_cpu[c].tc_open_lock);
mutex_destroy(&tx->tx_cpu[c].tc_lock);
for (i = 0; i < TXG_SIZE; i++) {
cv_destroy(&tx->tx_cpu[c].tc_cv[i]);
tc = &tx->tx_cpu[CPU_SEQID];
kpreempt_enable();
- mutex_enter(&tc->tc_lock);
-
+ mutex_enter(&tc->tc_open_lock);
txg = tx->tx_open_txg;
+
+ mutex_enter(&tc->tc_lock);
tc->tc_count[txg & TXG_MASK]++;
+ mutex_exit(&tc->tc_lock);
th->th_cpu = tc;
th->th_txg = txg;
{
tx_cpu_t *tc = th->th_cpu;
- mutex_exit(&tc->tc_lock);
+ ASSERT(!MUTEX_HELD(&tc->tc_lock));
+ mutex_exit(&tc->tc_open_lock);
}
void
int c;
/*
- * Grab all tx_cpu locks so nobody else can get into this txg.
+ * Grab all tc_open_locks so nobody else can get into this txg.
*/
for (c = 0; c < max_ncpus; c++)
- mutex_enter(&tx->tx_cpu[c].tc_lock);
+ mutex_enter(&tx->tx_cpu[c].tc_open_lock);
ASSERT(txg == tx->tx_open_txg);
tx->tx_open_txg++;
* enter the next transaction group.
*/
for (c = 0; c < max_ncpus; c++)
- mutex_exit(&tx->tx_cpu[c].tc_lock);
+ mutex_exit(&tx->tx_cpu[c].tc_open_lock);
/*
* Quiesce the transaction group by waiting for everyone to txg_exit().
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