docs/admin-guide/mm: start moving here files from Documentation/vm

Several documents in Documentation/vm fit quite well into the "admin/user
guide" category. The documents that don't overload the reader with lots of
implementation details and provide coherent description of certain feature
can be moved to Documentation/admin-guide/mm.

Signed-off-by: Mike Rapoport <rppt@linux.vnet.ibm.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/admin-guide/mm/index.rst

@@ -17,3 +17,12 @@ are described in Documentation/sysctl/vm.txt and in `man 5 proc`_.
 
 Here we document in detail how to interact with various mechanisms in
 the Linux memory management.
+
+.. toctree::
+   :maxdepth: 1
+
+   hugetlbpage
+   idle_page_tracking
+   pagemap
+   soft-dirty
+   userfaultfd