[PATCH][RFC] Fix INTERLEAVE with memoryless nodes

[Nishanth Aravamudan <nacc@us.ibm.com>]

Applies to 2.6.22-rc4-mm2 with
add-populated_map-to-account-for-memoryless-nodes
applied.

Based on ideas from Christoph Lameter, add checks in the INTERLEAVE
paths for memoryless nodes. We do not want to try interleaving onto
those nodes.

Christoph said:
"This does not work for the address based interleaving for anonymous
vmas.  I am not sure what to do there. We could change the calculation
of the node to be based only on nodes with memory and then skip the
memoryless ones. I have only added a comment to describe its brokennes
for now."

I have copied his draft comment.

Change alloc_pages_node() to fail __GFP_THISNODE allocations if the node
is not populated.

Again, Christoph said:
"This will fix the alloc_pages_node case but not the alloc_pages() case.
In the alloc_pages() case we do not specify a node. Implicitly it is
understood that we (in the case of no memory policy / cpuset options)
allocate from the nearest node. So it may be argued there that the
GFP_THISNODE behavior of taking the first node from the zonelist is
okay."

Christoph was also worried about the performance impact on these paths,
so, as he suggested, uninline alloc_pages_node() and move it to
mempolicy.c.

Signed-off-by: Nishanth Aravamudan <nacc@us.ibm.com>

diff --git a/include/linux/gfp.h b/include/linux/gfp.h
index 49dcc2f..c83e56a 100644
--- a/include/linux/gfp.h
+++ b/include/linux/gfp.h
@@ -165,19 +165,7 @@ static inline void arch_alloc_page(struct page *page, int order) { }
 extern struct page *
 FASTCALL(__alloc_pages(gfp_t, unsigned int, struct zonelist *));
 
-static inline struct page *alloc_pages_node(int nid, gfp_t gfp_mask,
-						unsigned int order)
-{
-	if (unlikely(order >= MAX_ORDER))
-		return NULL;
-
-	/* Unknown node is current node */
-	if (nid < 0)
-		nid = numa_node_id();
-
-	return __alloc_pages(gfp_mask, order,
-		NODE_DATA(nid)->node_zonelists + gfp_zone(gfp_mask));
-}
+extern struct page *alloc_pages_node(int, gfp_t, unsigned int);
 
 #ifdef CONFIG_NUMA
 extern struct page *alloc_pages_current(gfp_t gfp_mask, unsigned order);
diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 144805c..4e7c48c 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -174,6 +174,7 @@ static struct zonelist *bind_zonelist(nodemask_t *nodes)
 static struct mempolicy *mpol_new(int mode, nodemask_t *nodes)
 {
 	struct mempolicy *policy;
+	unsigned nid;
 
 	PDprintk("setting mode %d nodes[0] %lx\n", mode, nodes_addr(*nodes)[0]);
 	if (mode == MPOL_DEFAULT)
@@ -184,6 +185,16 @@ static struct mempolicy *mpol_new(int mode, nodemask_t *nodes)
 	atomic_set(&policy->refcnt, 1);
 	switch (mode) {
 	case MPOL_INTERLEAVE:
+		/*
+		 * Clear any memoryless nodes here so that v.nodes can be used
+		 * without extra checks
+		 */
+		nid = first_node(*nodes);
+		while (nid < MAX_NUMNODES) {
+			if (!node_populated(nid))
+				node_clear(nid, *nodes);
+			nid = next_node(nid, *nodes);
+		}
 		policy->v.nodes = *nodes;
 		if (nodes_weight(*nodes) == 0) {
 			kmem_cache_free(policy_cache, policy);
@@ -578,6 +589,22 @@ long do_get_mempolicy(int *policy, nodemask_t *nmask,
 	return err;
 }
 
+struct page *alloc_pages_node(int nid, gfp_t gfp_mask, unsigned int order)
+{
+	if (unlikely(order >= MAX_ORDER))
+		return NULL;
+
+	/* Unknown node is current node */
+	if (nid < 0)
+		nid = numa_node_id();
+
+	if ((gfp_mask & __GFP_THISNODE) && !node_populated(nid))
+		return NULL;
+
+	return __alloc_pages(gfp_mask, order,
+		NODE_DATA(nid)->node_zonelists + gfp_zone(gfp_mask));
+}
+
 #ifdef CONFIG_MIGRATION
 /*
  * page migration
@@ -1126,9 +1153,11 @@ static unsigned interleave_nodes(struct mempolicy *policy)
 	struct task_struct *me = current;
 
 	nid = me->il_next;
-	next = next_node(nid, policy->v.nodes);
-	if (next >= MAX_NUMNODES)
-		next = first_node(policy->v.nodes);
+	do {
+		next = next_node(nid, policy->v.nodes);
+		if (next >= MAX_NUMNODES)
+			next = first_node(policy->v.nodes);
+	} while (!node_populated(next));
 	me->il_next = next;
 	return nid;
 }
@@ -1192,6 +1221,11 @@ static inline unsigned interleave_nid(struct mempolicy *pol,
 		 * for huge pages, since vm_pgoff is in units of small
 		 * pages, we need to shift off the always 0 bits to get
 		 * a useful offset.
+		 *
+		 * NOTE: For configurations with memoryless nodes this
+		 * is broken since the allocation attempts on that node
+		 * will fall back to other nodes and thus one
+		 * neighboring node will be overallocated from.
 		 */
 		BUG_ON(shift < PAGE_SHIFT);
 		off = vma->vm_pgoff >> (shift - PAGE_SHIFT);

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