+5. All the page table references to the page are converted
+ to migration entries or dropped (nonlinear vmas).
+ This decrease the mapcount of a page. If the resulting
+ mapcount is not zero then we do not migrate the page.
+ All user space processes that attempt to access the page
+ will now wait on the page lock.
+
+6. The radix tree lock is taken. This will cause all processes trying
+ to access the page via the mapping to block on the radix tree spinlock.