+18. If swap pte's were generated for the page then replace them with real
+ ptes. This will reenable access for processes not blocked by the page lock.
+
+19. The page locks are dropped from the old and new page.
+ Processes waiting on the page lock can continue.
+
+20. The new page is moved to the LRU and can be scanned by the swapper
+ etc again.
+
+TODO list
+---------
+
+- Page migration requires the use of swap handles to preserve the
+ information of the anonymous page table entries. This means that swap
+ space is reserved but never used. The maximum number of swap handles used
+ is determined by CHUNK_SIZE (see mm/mempolicy.c) per ongoing migration.
+ Reservation of pages could be avoided by having a special type of swap
+ handle that does not require swap space and that would only track the page
+ references. Something like that was proposed by Marcelo Tosatti in the
+ past (search for migration cache on lkml or linux-mm@kvack.org).