Function zil_commit_writer

freebsd/contrib/openzfs/module/zfs/zil.c:2453–2489

* This function is responsible for ensuring the passed in commit waiter * (and associated commit itx) is committed to an lwb. If the waiter is * not already committed to an lwb, all itxs in the zilog's queue of * itxs will be processed. The assumption is the passed in waiter's * commit itx will found in the queue just like the other non-commit * itxs, such that when the entire queue is proces

 * the lwb, or the timeout mechanism found in zil_commit_waiter().
 */
static void
zil_commit_writer(zilog_t *zilog, zil_commit_waiter_t *zcw)
{
	ASSERT(!MUTEX_HELD(&zilog->zl_lock));
	ASSERT(spa_writeable(zilog->zl_spa));

	mutex_enter(&zilog->zl_issuer_lock);

	if (zcw->zcw_lwb != NULL || zcw->zcw_done) {
		/*
		 * It's possible that, while we were waiting to acquire
		 * the "zl_issuer_lock", another thread committed this
		 * waiter to an lwb. If that occurs, we bail out early,
		 * without processing any of the zilog's queue of itxs.
		 *
		 * On certain workloads and system configurations, the
		 * "zl_issuer_lock" can become highly contended. In an
		 * attempt to reduce this contention, we immediately drop
		 * the lock if the waiter has already been processed.
		 *
		 * We've measured this optimization to reduce CPU spent
		 * contending on this lock by up to 5%, using a system
		 * with 32 CPUs, low latency storage (~50 usec writes),
		 * and 1024 threads performing sync writes.
		 */
		goto out;
	}

	ZIL_STAT_BUMP(zil_commit_writer_count);

	zil_get_commit_list(zilog);
	zil_prune_commit_list(zilog);
	zil_process_commit_list(zilog);

out:
	mutex_exit(&zilog->zl_issuer_lock);
}

static void
zil_commit_waiter_timeout(zilog_t *zilog, zil_commit_waiter_t *zcw)