From 02ce9030e6ecdb6491096e1d35902da8bcc80fce Mon Sep 17 00:00:00 2001
From: Alexander Motin <mav@FreeBSD.org>
Date: Thu, 27 Jul 2023 12:07:09 -0400
Subject: [PATCH] Avoid waiting in dmu_sync_late_arrival().
The transaction there does not produce any dirty data or log blocks,
so it should not be throttled. All other cases wait for TXG sync, by
which time the log block we are writing will be obsolete, so we can
skip waiting and just return error here instead.
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Alexander Motin <mav@FreeBSD.org>
Sponsored by: iXsystems, Inc.
Closes #15096
---
module/zfs/dmu.c | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)
diff --git a/module/zfs/dmu.c b/module/zfs/dmu.c
index 3a4560cec2..078811dbf4 100644
--- a/module/zfs/dmu.c
+++ b/module/zfs/dmu.c
@@ -1656,7 +1656,13 @@ dmu_sync_late_arrival(zio_t *pio, objset_t *os, dmu_sync_cb_t *done, zgd_t *zgd,
tx = dmu_tx_create(os);
dmu_tx_hold_space(tx, zgd->zgd_db->db_size);
- if (dmu_tx_assign(tx, TXG_WAIT) != 0) {
+ /*
+ * This transaction does not produce any dirty data or log blocks, so
+ * it should not be throttled. All other cases wait for TXG sync, by
+ * which time the log block we are writing will be obsolete, so we can
+ * skip waiting and just return error here instead.
+ */
+ if (dmu_tx_assign(tx, TXG_NOWAIT | TXG_NOTHROTTLE) != 0) {
dmu_tx_abort(tx);
/* Make zl_get_data do txg_waited_synced() */
return (SET_ERROR(EIO));