[PATCH] f2fs: document: add description about compressed space handling

[Chao Yu]

User or developer may still be confused about why f2fs doesn't expose
compressed space to userspace, add description about compressed space
handling policy into f2fs documentation.

Signed-off-by: Chao Yu <yuchao0@xxxxxxxxxx>
---
 Documentation/filesystems/f2fs.rst | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/Documentation/filesystems/f2fs.rst b/Documentation/filesystems/f2fs.rst
index 63c0c49b726d..992bf91eeec8 100644
--- a/Documentation/filesystems/f2fs.rst
+++ b/Documentation/filesystems/f2fs.rst
@@ -819,6 +819,14 @@ Compression implementation
   * chattr +c file
   * chattr +c dir; touch dir/file
   * mount w/ -o compress_extension=ext; touch file.ext
+  * mount w/ -o compress_extension=*; touch any_file
+
+- At this point, compression feature doesn't expose compressed space to user
+  directly in order to guarantee potential data updates later to the space.
+  Instead, the main goal is to reduce data writes to flash disk as much as
+  possible, resulting in extending disk life time as well as relaxing IO
+  congestion. Alternatively, we've added ioctl interface to reclaim compressed
+  space and show it to user after putting the immutable bit.
 
 Compress metadata layout::
 
-- 
2.29.2