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Flush RRD only when TXGs contain data

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This change modifies the behavior of spa_sync_time_logger when
flushing the RRD database.

Previously, once the sync interval elapsed, a flush would always
be generated. On solid-state devices, especially when the pool was
otherwise idle, this caused disks to wake up solely to write RRD
data. Since RRD is best-effort telemetry, this behavior is
unnecessary and wasteful.

With this change, spa_sync_time_logger delays flushing until a TXG
that already contains data is being synced. The RRD update is
appended to that TXG instead of forcing the creation of
a new write-only TXG.

During pool export, flushing is forced regardless of whether
the TXG contains user data. At that stage, data durability takes
precedence and a write must be issued.

Sponsored by: [Wasabi Technology, Inc.; Klara, Inc.]
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Mariusz Zaborski <mariusz.zaborski@klarasystems.com>
Closes #18082
Closes #18138
This commit is contained in:
Mariusz Zaborski 2026-02-11 20:35:45 +01:00 committed by GitHub
parent cc184fe98b
commit cdf89f413c
No known key found for this signature in database
GPG Key ID: B5690EEEBB952194
1 changed files with 20 additions and 12 deletions
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32
module/zfs/spa.c
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@ -2142,20 +2142,21 @@ spa_destroy_aux_threads(spa_t *spa)
} }
static void static void
spa_sync_time_logger(spa_t *spa, uint64_t txg) spa_sync_time_logger(spa_t *spa, uint64_t txg, boolean_t force)
{ {
uint64_t curtime; uint64_t curtime, dirty;
dmu_tx_t *tx; dmu_tx_t *tx;
dsl_pool_t *dp = spa->spa_dsl_pool;
uint64_t idx = txg & TXG_MASK;
if (!spa_writeable(spa)) { if (!spa_writeable(spa)) {
return; return;
} }
curtime = gethrestime_sec();
if (curtime < spa->spa_last_noted_txg_time + spa_note_txg_time) {
return;
}
if (txg > spa->spa_last_noted_txg) { curtime = gethrestime_sec();
if (txg > spa->spa_last_noted_txg &&
(force ||
curtime >= spa->spa_last_noted_txg_time + spa_note_txg_time)) {
spa->spa_last_noted_txg_time = curtime; spa->spa_last_noted_txg_time = curtime;
spa->spa_last_noted_txg = txg; spa->spa_last_noted_txg = txg;
@ -2164,7 +2165,8 @@ spa_sync_time_logger(spa_t *spa, uint64_t txg)
mutex_exit(&spa->spa_txg_log_time_lock); mutex_exit(&spa->spa_txg_log_time_lock);
} }
if (curtime < spa->spa_last_flush_txg_time + spa_flush_txg_time) { if (!force &&
curtime < spa->spa_last_flush_txg_time + spa_flush_txg_time) {
return; return;
} }
if (txg > spa_final_dirty_txg(spa)) { if (txg > spa_final_dirty_txg(spa)) {
@ -2172,6 +2174,14 @@ spa_sync_time_logger(spa_t *spa, uint64_t txg)
} }
spa->spa_last_flush_txg_time = curtime; spa->spa_last_flush_txg_time = curtime;
mutex_enter(&dp->dp_lock);
dirty = dp->dp_dirty_pertxg[idx];
mutex_exit(&dp->dp_lock);
if (!force && dirty == 0) {
return;
}
spa->spa_last_flush_txg_time = curtime;
tx = dmu_tx_create_assigned(spa_get_dsl(spa), txg); tx = dmu_tx_create_assigned(spa_get_dsl(spa), txg);
VERIFY0(zap_update(spa_meta_objset(spa), DMU_POOL_DIRECTORY_OBJECT, VERIFY0(zap_update(spa_meta_objset(spa), DMU_POOL_DIRECTORY_OBJECT,
@ -2194,9 +2204,7 @@ spa_unload_sync_time_logger(spa_t *spa)
VERIFY0(dmu_tx_assign(tx, DMU_TX_WAIT)); VERIFY0(dmu_tx_assign(tx, DMU_TX_WAIT));
txg = dmu_tx_get_txg(tx); txg = dmu_tx_get_txg(tx);
spa->spa_last_noted_txg_time = 0; spa_sync_time_logger(spa, txg, B_TRUE);
spa->spa_last_flush_txg_time = 0;
spa_sync_time_logger(spa, txg);
dmu_tx_commit(tx); dmu_tx_commit(tx);
} }
@ -10809,7 +10817,7 @@ spa_sync(spa_t *spa, uint64_t txg)
*/ */
brt_pending_apply(spa, txg); brt_pending_apply(spa, txg);
spa_sync_time_logger(spa, txg); spa_sync_time_logger(spa, txg, B_FALSE);
/* /*
* Lock out configuration changes. * Lock out configuration changes.