mempolicy: mPOL_PREFERRED cleanups for "local allocation"

Here are a couple of "cleanups" for MPOL_PREFERRED behavior when
v.preferred_node < 0 -- i.e., "local allocation":

1)  [do_]get_mempolicy() calls the now renamed get_policy_nodemask()
    to fetch the nodemask associated with a policy.  Currently,
    get_policy_nodemask() returns the set of nodes with memory, when
    the policy 'mode' is 'PREFERRED, and the preferred_node is < 0.
    Change to return an empty nodemask, as this is what was specified
    to achieve "local allocation".

2)  When a task is moved into a [new] cpuset, mpol_rebind_policy() is
    called to adjust any task and vma policy nodes to be valid in the
    new cpuset.  However, when the policy is MPOL_PREFERRED, and the
    preferred_node is <0, no rebind is necessary.  The "local allocation"
    indication is valid in any cpuset.  Existing code will "do the right
    thing" because node_remap() will just return the argument node when
    it is outside of the valid range of node ids.  However, I think it is
    clearer and cleaner to skip the remap explicitly in this case.

3)  mpol_to_str() produces a printable, "human readable" string from a
    struct mempolicy.  For MPOL_PREFERRED with preferred_node <0,  show
    "local", as this indicates local allocation, as the task migrates
    among nodes.  Note that this matches the usage of "local allocation"
    in libnuma() and numactl.  Without this change, I believe that node_set()
    [via set_bit()] will set bit 31, resulting in a misleading display.
Signed-off-by: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Christoph Lameter <clameter@sgi.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Mel Gorman <mel@csn.ul.ie>
Cc: Andi Kleen <ak@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/mempolicy.c

@@ -645,11 +645,9 @@ static void get_policy_nodemask(struct mempolicy *p, nodemask_t *nodes)
 		*nodes = p->v.nodes;
 		break;
 	case MPOL_PREFERRED:
-		/* or use current node instead of memory_map? */
-		if (p->v.preferred_node < 0)
-			*nodes = node_states[N_HIGH_MEMORY];
-		else
+		if (p->v.preferred_node >= 0)
 			node_set(p->v.preferred_node, *nodes);
+		/* else return empty node mask for local allocation */
 		break;
 	default:
 		BUG();
@@ -1948,10 +1946,12 @@ void numa_default_policy(void)
 }
 
 /*
- * Display pages allocated per node and memory policy via /proc.
+ * "local" is pseudo-policy:  MPOL_PREFERRED with preferred_node == -1
+ * Used only for mpol_to_str()
  */
+#define MPOL_LOCAL (MPOL_INTERLEAVE + 1)
 static const char * const policy_types[] =
-	{ "default", "prefer", "bind", "interleave" };
+	{ "default", "prefer", "bind", "interleave", "local" };
 
 /*
  * Convert a mempolicy into a string.
@@ -1962,6 +1962,7 @@ static inline int mpol_to_str(char *buffer, int maxlen, struct mempolicy *pol)
 {
 	char *p = buffer;
 	int l;
+	int nid;
 	nodemask_t nodes;
 	unsigned short mode;
 	unsigned short flags = pol ? pol->flags : 0;
@@ -1978,7 +1979,11 @@ static inline int mpol_to_str(char *buffer, int maxlen, struct mempolicy *pol)
 
 	case MPOL_PREFERRED:
 		nodes_clear(nodes);
-		node_set(pol->v.preferred_node, nodes);
+		nid = pol->v.preferred_node;
+		if (nid < 0)
+			mode = MPOL_LOCAL;	/* pseudo-policy */
+		else
+			node_set(nid, nodes);
 		break;
 
 	case MPOL_BIND:
@@ -2093,6 +2098,9 @@ static inline void check_huge_range(struct vm_area_struct *vma,
 }
 #endif
 
+/*
+ * Display pages allocated per node and memory policy via /proc.
+ */
 int show_numa_map(struct seq_file *m, void *v)
 {
 	struct proc_maps_private *priv = m->private;