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Illumos #3642, #3643
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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@4a92375

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.
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grwilson authored and behlendorf committed Nov 1, 2013
1 parent 7ec0928 commit 2696dfa
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Showing 5 changed files with 78 additions and 14 deletions.
3 changes: 2 additions & 1 deletion include/sys/dsl_scan.h
Original file line number Diff line number Diff line change
Expand Up @@ -20,7 +20,7 @@
*/
/*
* 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
Expand Down Expand Up @@ -82,6 +82,7 @@ typedef struct dsl_scan {

/* for freeing blocks */
boolean_t scn_is_bptree;
boolean_t scn_async_destroying;

/* for debugging / information */
uint64_t scn_visited_this_txg;
Expand Down
49 changes: 47 additions & 2 deletions include/sys/txg_impl.h
Original file line number Diff line number Diff line change
Expand Up @@ -23,6 +23,10 @@
* Use is subject to license terms.
*/

/*
* Copyright (c) 2013 by Delphix. All rights reserved.
*/

#ifndef _SYS_TXG_IMPL_H
#define _SYS_TXG_IMPL_H

Expand All @@ -33,14 +37,55 @@
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 */
Expand Down
4 changes: 4 additions & 0 deletions module/zfs/dsl_destroy.c
Original file line number Diff line number Diff line change
Expand Up @@ -761,12 +761,16 @@ dsl_destroy_head_sync_impl(dsl_dataset_t *ds, dmu_tx_t *tx)
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;
Expand Down
18 changes: 13 additions & 5 deletions module/zfs/dsl_scan.c
Original file line number Diff line number Diff line change
Expand Up @@ -91,6 +91,15 @@ dsl_scan_init(dsl_pool_t *dp, uint64_t txg)
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) {
Expand Down Expand Up @@ -1362,13 +1371,10 @@ dsl_scan_active(dsl_scan_t *scn)
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);
Expand Down Expand Up @@ -1424,6 +1430,7 @@ dsl_scan_sync(dsl_pool_t *dp, dmu_tx_t *tx)

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);
Expand All @@ -1444,6 +1451,7 @@ dsl_scan_sync(dsl_pool_t *dp, dmu_tx_t *tx)
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) {
Expand Down
18 changes: 12 additions & 6 deletions module/zfs/txg.c
Original file line number Diff line number Diff line change
Expand Up @@ -127,6 +127,8 @@ txg_init(dsl_pool_t *dp, uint64_t 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);
Expand Down Expand Up @@ -169,6 +171,7 @@ txg_fini(dsl_pool_t *dp)
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]);
Expand Down Expand Up @@ -303,10 +306,12 @@ txg_hold_open(dsl_pool_t *dp, txg_handle_t *th)
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;
Expand All @@ -319,7 +324,8 @@ txg_rele_to_quiesce(txg_handle_t *th)
{
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
Expand Down Expand Up @@ -356,10 +362,10 @@ txg_quiesce(dsl_pool_t *dp, uint64_t txg)
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++;
Expand All @@ -372,7 +378,7 @@ txg_quiesce(dsl_pool_t *dp, uint64_t 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().
Expand Down

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