[PATCH] btrfs-progs: docs: add a note about RW degraded mount

When a new chunk is allocated during an RW degraded mount, btrfs can
allocate new chunks with other profiles, like SINGLE, if the current
devices can no longer support the original profile.

This can cause unexpected chunk profiles, and the end user is
recommended to balance them out if they want to maintain the current
allocation profile.

Signed-off-by: Qu Wenruo <[email protected]>
---
 Documentation/ch-mount-options.rst | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/Documentation/ch-mount-options.rst b/Documentation/ch-mount-options.rst
index 7ce56c7068ee..b3997edda7ff 100644
--- a/Documentation/ch-mount-options.rst
+++ b/Documentation/ch-mount-options.rst
@@ -180,6 +180,14 @@ degraded
         then the constraint of single/data is not satisfied and the filesystem
         cannot be mounted.
 
+	.. note::
+		During a degraded mount, if BTRFS is going to allocate a new chunk,
+		and the existing devices can not meet the requirement for the
+		current profile, BTRFS will fall back to other profiles like SINGLE.
+
+		It is recommended to check and balance chunks with unwanted profiles,
+		after an RW degraded mount.
+
 .. duplabel:: mount-option-device
 
 device=<devicepath>
-- 
2.54.0