mm/mempolicy.c: fix mempolicy printing in numa_maps

As a result of commit 5606e38 ("mm: numa: Migrate on reference
policy"), /proc/<pid>/numa_maps prints the mempolicy for any <pid> as
"prefer:N" for the local node, N, of the process reading the file.

This should only be printed when the mempolicy of <pid> is
MPOL_PREFERRED for node N.

If the process is actually only using the default mempolicy for local
node allocation, make sure "default" is printed as expected.

Signed-off-by: David Rientjes <[email protected]>
Reported-by: Robert Lippert <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Acked-by: Mel Gorman <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: <[email protected]>	[3.7+]
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

mm/mempolicy.c

@@ -2930,7 +2930,7 @@ void mpol_to_str(char *buffer, int maxlen, struct mempolicy *pol)
 	unsigned short mode = MPOL_DEFAULT;
 	unsigned short flags = 0;
 
-	if (pol && pol != &default_policy) {
+	if (pol && pol != &default_policy && !(pol->flags & MPOL_F_MORON)) {
 		mode = pol->mode;
 		flags = pol->flags;
 	}