PendingReleaseNotes: add rbd_diff_iterate2 note

Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
(cherry picked from commit 40e8813e9c705838eee42c98de717b20851aed72)

Conflicts:
	PendingReleaseNotes [ moved to >=16.2.15 section ]

diff --git a/PendingReleaseNotes b/PendingReleaseNotes
index 0cb10ea998121b4577be25f1b5ddded294320958..c02bdf04a74ceebecc095c3f8af090b6eb7eee8e 100644 (file)
--- a/PendingReleaseNotes
+++ b/PendingReleaseNotes
@@ -49,6 +49,12 @@
   due to being prone to false negative results.  It's safer replacement is
   `pool_is_in_selfmanaged_snaps_mode`.
 
+* RBD: When diffing against the beginning of time (`fromsnapname == NULL`) in
+  fast-diff mode (`whole_object == true` with `fast-diff` image feature enabled
+  and valid), diff-iterate is now guaranteed to execute locally if exclusive
+  lock is available.  This brings a dramatic performance improvement for QEMU
+  live disk synchronization and backup use cases.
+
 >= 16.2.14
 ----------