dm writecache: add "cleaner" and "max_age" to Documentation

Backfill missing Documentation.

Fixes: 93de44eb3fc8 ("dm writecache: implement the "cleaner" policy")
Fixes: 3923d4854e18 ("dm writecache: implement gradual cleanup")
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

diff --git a/Documentation/admin-guide/device-mapper/writecache.rst b/Documentation/admin-guide/device-mapper/writecache.rst
index dce0184..c181f26 100644 (file)
--- a/Documentation/admin-guide/device-mapper/writecache.rst
+++ b/Documentation/admin-guide/device-mapper/writecache.rst
@@ -53,6 +53,21 @@ Constructor parameters:
 
                - some underlying devices perform better with fua, some
                  with nofua. The user should test it
+       cleaner
+               when this option is activated (either in the constructor
+               arguments or by a message), the cache will not promote
+               new writes (however, writes to already cached blocks are
+               promoted, to avoid data corruption due to misordered
+               writes) and it will gradually writeback any cached
+               data. The userspace can then monitor the cleaning
+               process with "dmsetup status". When the number of cached
+               blocks drops to zero, userspace can unload the
+               dm-writecache target and replace it with dm-linear or
+               other targets.
+       max_age n
+               specifies the maximum age of a block in milliseconds. If
+               a block is stored in the cache for too long, it will be
+               written to the underlying device and cleaned up.
 
 Status:
 1. error indicator - 0 if there was no error, otherwise error number
@@ -77,3 +92,5 @@ Messages:
                5. resume the device, so that it will use the linear
                   target
                6. the cache device is now inactive and it can be deleted
+       cleaner
+               See above "cleaner" constructor documentation.