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Fix inflated quiesce time caused by lwb_tx during zil_commit() 

In current zil_commit() process, transaction lwb_tx is assigned in
zil_lwb_write_issue(), and is committed in zil_lwb_flush_vdevs_done().
Thus, during lwb write out process, the txg is held in open or quiesing
state, until zil_lwb_flush_vdevs_done() is called. If the zil's zio
latency is high, it will cause txg_sync_thread() to starve.

The goal here is to defer waiting for zil_lwb_flush_vdevs_done to the
'syncing' txg state. That is, in zil_sync().

In this patch, it achieves the goal without holding transaction.
A new function zil_lwb_flush_wait_all() is introduced. It waits for
the completion of all the zil_lwb_flush_vdevs_done() by given txg.

Reviewed-by: Alexander Motin <mav@FreeBSD.org>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Prakash Surya <prakash.surya@delphix.com>
Signed-off-by: jxdking <lostking2008@hotmail.com>
Closes #12321
This commit is contained in:
Kevin Jin 2022-05-26 12:36:14 -04:00 committed by GitHub
parent d98a67a53a
commit 152d6fda54
No known key found for this signature in database
GPG Key ID: 4AEE18F83AFDEB23
2 changed files with 76 additions and 21 deletions
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8
include/sys/zil_impl.h
View File

@ -99,7 +99,7 @@ typedef struct lwb {
char *lwb_buf; /* log write buffer */
zio_t *lwb_write_zio; /* zio for the lwb buffer */
zio_t *lwb_root_zio; /* root zio for lwb write and flushes */
dmu_tx_t *lwb_tx; /* tx for log block allocation */
uint64_t lwb_issued_txg; /* the txg when the write is issued */
uint64_t lwb_max_txg; /* highest txg in this lwb */
list_node_t lwb_node; /* zilog->zl_lwb_list linkage */
list_t lwb_itxs; /* list of itx's */
@ -209,6 +209,12 @@ struct zilog {
uint_t zl_prev_rotor; /* rotor for zl_prev[] */
txg_node_t zl_dirty_link; /* protected by dp_dirty_zilogs list */
uint64_t zl_dirty_max_txg; /* highest txg used to dirty zilog */
kmutex_t zl_lwb_io_lock; /* protect following members */
uint64_t zl_lwb_inflight[TXG_SIZE]; /* io issued, but not done */
kcondvar_t zl_lwb_io_cv; /* signal when the flush is done */
uint64_t zl_lwb_max_issued_txg; /* max txg when lwb io issued */
/*
* Max block size for this ZIL. Note that this can not be changed
* while the ZIL is in use because consumers (ZPL/zvol) need to take

87
module/zfs/zil.c
View File

@ -559,8 +559,8 @@ zil_alloc_lwb(zilog_t *zilog, blkptr_t *bp, boolean_t slog, uint64_t txg,
lwb->lwb_max_txg = txg;
lwb->lwb_write_zio = NULL;
lwb->lwb_root_zio = NULL;
lwb->lwb_tx = NULL;
lwb->lwb_issued_timestamp = 0;
lwb->lwb_issued_txg = 0;
if (BP_GET_CHECKSUM(bp) == ZIO_CHECKSUM_ZILOG2) {
lwb->lwb_nused = sizeof (zil_chain_t);
lwb->lwb_sz = BP_GET_LSIZE(bp);
@ -1183,9 +1183,9 @@ zil_lwb_flush_vdevs_done(zio_t *zio)
{
lwb_t *lwb = zio->io_private;
zilog_t *zilog = lwb->lwb_zilog;
dmu_tx_t *tx = lwb->lwb_tx;
zil_commit_waiter_t *zcw;
itx_t *itx;
uint64_t txg;
spa_config_exit(zilog->zl_spa, SCL_STATE, lwb);
@ -1194,15 +1194,13 @@ zil_lwb_flush_vdevs_done(zio_t *zio)
mutex_enter(&zilog->zl_lock);
/*
* Ensure the lwb buffer pointer is cleared before releasing the
* txg. If we have had an allocation failure and the txg is
* If we have had an allocation failure and the txg is
* waiting to sync then we want zil_sync() to remove the lwb so
* that it's not picked up as the next new one in
* zil_process_commit_list(). zil_sync() will only remove the
* lwb if lwb_buf is null.
*/
lwb->lwb_buf = NULL;
lwb->lwb_tx = NULL;
ASSERT3U(lwb->lwb_issued_timestamp, >, 0);
zilog->zl_last_lwb_latency = gethrtime() - lwb->lwb_issued_timestamp;
@ -1261,12 +1259,47 @@ zil_lwb_flush_vdevs_done(zio_t *zio)
mutex_exit(&zilog->zl_lock);
/*
* Now that we've written this log block, we have a stable pointer
* to the next block in the chain, so it's OK to let the txg in
* which we allocated the next block sync.
mutex_enter(&zilog->zl_lwb_io_lock);
txg = lwb->lwb_issued_txg;
ASSERT3U(zilog->zl_lwb_inflight[txg & TXG_MASK], >, 0);
zilog->zl_lwb_inflight[txg & TXG_MASK]--;
if (zilog->zl_lwb_inflight[txg & TXG_MASK] == 0)
cv_broadcast(&zilog->zl_lwb_io_cv);
mutex_exit(&zilog->zl_lwb_io_lock);
}
/*
* Wait for the completion of all issued write/flush of that txg provided.
* It guarantees zil_lwb_flush_vdevs_done() is called and returned.
*/
dmu_tx_commit(tx);
static void
zil_lwb_flush_wait_all(zilog_t *zilog, uint64_t txg)
{
ASSERT3U(txg, ==, spa_syncing_txg(zilog->zl_spa));
mutex_enter(&zilog->zl_lwb_io_lock);
while (zilog->zl_lwb_inflight[txg & TXG_MASK] > 0)
cv_wait(&zilog->zl_lwb_io_cv, &zilog->zl_lwb_io_lock);
mutex_exit(&zilog->zl_lwb_io_lock);
#ifdef ZFS_DEBUG
mutex_enter(&zilog->zl_lock);
mutex_enter(&zilog->zl_lwb_io_lock);
lwb_t *lwb = list_head(&zilog->zl_lwb_list);
while (lwb != NULL && lwb->lwb_max_txg <= txg) {
if (lwb->lwb_issued_txg <= txg) {
ASSERT(lwb->lwb_state != LWB_STATE_ISSUED);
ASSERT(lwb->lwb_state != LWB_STATE_WRITE_DONE);
IMPLY(lwb->lwb_issued_txg > 0,
lwb->lwb_state == LWB_STATE_FLUSH_DONE);
}
IMPLY(lwb->lwb_state == LWB_STATE_FLUSH_DONE,
lwb->lwb_buf == NULL);
lwb = list_next(&zilog->zl_lwb_list, lwb);
}
mutex_exit(&zilog->zl_lwb_io_lock);
mutex_exit(&zilog->zl_lock);
#endif
}
/*
@ -1562,11 +1595,6 @@ zil_lwb_write_issue(zilog_t *zilog, lwb_t *lwb)
/*
* Allocate the next block and save its address in this block
* before writing it in order to establish the log chain.
* Note that if the allocation of nlwb synced before we wrote
* the block that points at it (lwb), we'd leak it if we crashed.
* Therefore, we don't do dmu_tx_commit() until zil_lwb_write_done().
* We dirty the dataset to ensure that zil_sync() will be called
* to clean up in the event of allocation failure or I/O failure.
*/
tx = dmu_tx_create(zilog->zl_os);
@ -1582,7 +1610,11 @@ zil_lwb_write_issue(zilog_t *zilog, lwb_t *lwb)
dsl_dataset_dirty(dmu_objset_ds(zilog->zl_os), tx);
txg = dmu_tx_get_txg(tx);
lwb->lwb_tx = tx;
mutex_enter(&zilog->zl_lwb_io_lock);
lwb->lwb_issued_txg = txg;
zilog->zl_lwb_inflight[txg & TXG_MASK]++;
zilog->zl_lwb_max_issued_txg = MAX(txg, zilog->zl_lwb_max_issued_txg);
mutex_exit(&zilog->zl_lwb_io_lock);
/*
* Log blocks are pre-allocated. Here we select the size of the next
@ -1657,6 +1689,8 @@ zil_lwb_write_issue(zilog_t *zilog, lwb_t *lwb)
zio_nowait(lwb->lwb_root_zio);
zio_nowait(lwb->lwb_write_zio);
dmu_tx_commit(tx);
/*
* If there was an allocation failure then nlwb will be null which
* forces a txg_wait_synced().
@ -3124,6 +3158,8 @@ zil_sync(zilog_t *zilog, dmu_tx_t *tx)
if (spa_sync_pass(spa) != 1)
return;
zil_lwb_flush_wait_all(zilog, txg);
mutex_enter(&zilog->zl_lock);
ASSERT(zilog->zl_stop_sync == 0);
@ -3290,6 +3326,7 @@ zil_alloc(objset_t *os, zil_header_t *zh_phys)
mutex_init(&zilog->zl_lock, NULL, MUTEX_DEFAULT, NULL);
mutex_init(&zilog->zl_issuer_lock, NULL, MUTEX_DEFAULT, NULL);
mutex_init(&zilog->zl_lwb_io_lock, NULL, MUTEX_DEFAULT, NULL);
for (int i = 0; i < TXG_SIZE; i++) {
mutex_init(&zilog->zl_itxg[i].itxg_lock, NULL,
@ -3303,6 +3340,7 @@ zil_alloc(objset_t *os, zil_header_t *zh_phys)
offsetof(itx_t, itx_node));
cv_init(&zilog->zl_cv_suspend, NULL, CV_DEFAULT, NULL);
cv_init(&zilog->zl_lwb_io_cv, NULL, CV_DEFAULT, NULL);
return (zilog);
}
@ -3338,8 +3376,10 @@ zil_free(zilog_t *zilog)
mutex_destroy(&zilog->zl_issuer_lock);
mutex_destroy(&zilog->zl_lock);
mutex_destroy(&zilog->zl_lwb_io_lock);
cv_destroy(&zilog->zl_cv_suspend);
cv_destroy(&zilog->zl_lwb_io_cv);
kmem_free(zilog, sizeof (zilog_t));
}
@ -3387,9 +3427,18 @@ zil_close(zilog_t *zilog)
mutex_exit(&zilog->zl_lock);
/*
* We need to use txg_wait_synced() to wait long enough for the
* ZIL to be clean, and to wait for all pending lwbs to be
* written out.
* zl_lwb_max_issued_txg may be larger than lwb_max_txg. It depends
* on the time when the dmu_tx transaction is assigned in
* zil_lwb_write_issue().
*/
mutex_enter(&zilog->zl_lwb_io_lock);
txg = MAX(zilog->zl_lwb_max_issued_txg, txg);
mutex_exit(&zilog->zl_lwb_io_lock);
/*
* We need to use txg_wait_synced() to wait until that txg is synced.
* zil_sync() will guarantee all lwbs up to that txg have been
* written out, flushed, and cleaned.
*/
if (txg != 0)
txg_wait_synced(zilog->zl_dmu_pool, txg);