Function txg_sync_thread

freebsd/contrib/openzfs/module/zfs/txg.c:503–588

}

static void
txg_sync_thread(void *arg)
{
	dsl_pool_t *dp = arg;
	spa_t *spa = dp->dp_spa;
	tx_state_t *tx = &dp->dp_tx;
	callb_cpr_t cpr;
	clock_t start, delta;

	(void) spl_fstrans_mark();
	txg_thread_enter(tx, &cpr);

	start = delta = 0;
	for (;;) {
		clock_t timeout = zfs_txg_timeout * hz;
		clock_t timer;
		uint64_t txg;
		uint64_t dirty_min_bytes =
		    zfs_dirty_data_max * zfs_dirty_data_sync_percent / 100;

		/*
		 * We sync when we're scanning, there's someone waiting
		 * on us, or the quiesce thread has handed off a txg to
		 * us, or we have reached our timeout.
		 */
		timer = (delta >= timeout ? 0 : timeout - delta);
		while (!dsl_scan_active(dp->dp_scan) &&
		    !tx->tx_exiting && timer > 0 &&
		    tx->tx_synced_txg >= tx->tx_sync_txg_waiting &&
		    !txg_has_quiesced_to_sync(dp) &&
		    dp->dp_dirty_total < dirty_min_bytes) {
			dprintf("waiting; tx_synced=%llu waiting=%llu dp=%p\n",
			    tx->tx_synced_txg, tx->tx_sync_txg_waiting, dp);
			txg_thread_wait(tx, &cpr, &tx->tx_sync_more_cv, timer);
			delta = ddi_get_lbolt() - start;
			timer = (delta > timeout ? 0 : timeout - delta);
		}

		/*
		 * Wait until the quiesce thread hands off a txg to us,
		 * prompting it to do so if necessary.
		 */
		while (!tx->tx_exiting && !txg_has_quiesced_to_sync(dp)) {
			if (tx->tx_quiesce_txg_waiting < tx->tx_open_txg+1)
				tx->tx_quiesce_txg_waiting = tx->tx_open_txg+1;
			cv_broadcast(&tx->tx_quiesce_more_cv);
			txg_thread_wait(tx, &cpr, &tx->tx_quiesce_done_cv, 0);
		}

		if (tx->tx_exiting)
			txg_thread_exit(tx, &cpr, &tx->tx_sync_thread);

		/*
		 * Consume the quiesced txg which has been handed off to
		 * us.  This may cause the quiescing thread to now be
		 * able to quiesce another txg, so we must signal it.
		 */
		ASSERT(tx->tx_quiesced_txg != 0);