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From 2b266bd36980caefe353411bd56b2487c44aeb6e Mon Sep 17 00:00:00 2001
From: Sam James <sam@gentoo.org>
Date: Fri, 24 Nov 2023 21:38:06 +0000
Subject: [PATCH] Disable zfs_dmu_offset_next_sync tunable by default
As a mitigation until more is understood and fixes are tested & reviewed, change
the default of zfs_dmu_offset_next_sync from 1 to 0, as it was before
05b3eb6d232009db247882a39d518e7282630753.
There are no reported cases of The Bug being hit with zfs_dmu_offset_next_sync=1:
that does not mean this is a cure or a real fix, but it _appears_ to be at least
effective in reducing the chances of it happening. By itself, it's a safe change
anyway, so it feels worth us doing while we wait.
Bug: https://github.com/openzfs/zfs/issues/11900
Bug: https://github.com/openzfs/zfs/issues/15526
Bug: https://bugs.gentoo.org/917224
Signed-off-by: Sam James <sam@gentoo.org>
--- a/man/man4/zfs.4
+++ b/man/man4/zfs.4
@@ -1646,7 +1646,7 @@ Allow no-operation writes.
The occurrence of nopwrites will further depend on other pool properties
.Pq i.a. the checksumming and compression algorithms .
.
-.It Sy zfs_dmu_offset_next_sync Ns = Ns Sy 1 Ns | Ns 0 Pq int
+.It Sy zfs_dmu_offset_next_sync Ns = Ns Sy 0 Ns | Ns 1 Pq int
Enable forcing TXG sync to find holes.
When enabled forces ZFS to sync data when
.Sy SEEK_HOLE No or Sy SEEK_DATA
--- a/module/zfs/dmu.c
+++ b/module/zfs/dmu.c
@@ -80,7 +80,7 @@ unsigned long zfs_per_txg_dirty_frees_percent = 30;
* Disabling this option will result in holes never being reported in dirty
* files which is always safe.
*/
-int zfs_dmu_offset_next_sync = 1;
+int zfs_dmu_offset_next_sync = 0;
/*
* Limit the amount we can prefetch with one call to this amount. This
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