[RFC PATCH v3 1/4] topology: add support for node_to_mem_node() to determine the fallback node

[Nishanth Aravamudan]

From: Joonsoo Kim <iamjoonsoo.kim at lge.com>

We need to determine the fallback node in slub allocator if the
allocation target node is memoryless node. Without it, the SLUB wrongly
select the node which has no memory and can't use a partial slab,
because of node mismatch. Introduced function, node_to_mem_node(X), will
return a node Y with memory that has the nearest distance. If X is
memoryless node, it will return nearest distance node, but, if X is
normal node, it will return itself.

We will use this function in following patch to determine the fallback
node.

Signed-off-by: Joonsoo Kim <iamjoonsoo.kim at lge.com>
Signed-off-by: Nishanth Aravamudan <nacc at linux.vnet.ibm.com>
Cc: David Rientjes <rientjes at google.com>
Cc: Han Pingtian <hanpt at linux.vnet.ibm.com>
Cc: Pekka Enberg <penberg at kernel.org>
Cc: Paul Mackerras <paulus at samba.org>
Cc: Anton Blanchard <anton at samba.org>
Cc: Matt Mackall <mpm at selenic.com>
Cc: Christoph Lameter <cl at linux.com>
Cc: Wanpeng Li <liwanp at linux.vnet.ibm.com>
Cc: Tejun Heo <tj at kernel.org>
Cc: Benjamin Herrenschmidt <benh at kernel.crashing.org>
Cc: Michael Ellerman <mpe at ellerman.id.au>
Cc: Linux Memory Management List <linux-mm at kvack.org>
Cc: linuxppc-dev at lists.ozlabs.org

---
v2 -> v3 (Nishanth):
  Fix declaration and definition of _node_numa_mem_.
  s/node_numa_mem/node_to_mem_node/ as suggested by David Rientjes.

diff --git a/include/linux/topology.h b/include/linux/topology.h
index dda6ee521e74..909b6e43b694 100644
--- a/include/linux/topology.h
+++ b/include/linux/topology.h
@@ -119,11 +119,20 @@ static inline int numa_node_id(void)
  * Use the accessor functions set_numa_mem(), numa_mem_id() and cpu_to_mem().
  */
 DECLARE_PER_CPU(int, _numa_mem_);
+extern int _node_numa_mem_[MAX_NUMNODES];
 
 #ifndef set_numa_mem
 static inline void set_numa_mem(int node)
 {
 	this_cpu_write(_numa_mem_, node);
+	_node_numa_mem_[numa_node_id()] = node;
+}
+#endif
+
+#ifndef node_to_mem_node
+static inline int node_to_mem_node(int node)
+{
+	return _node_numa_mem_[node];
 }
 #endif
 
@@ -146,6 +155,7 @@ static inline int cpu_to_mem(int cpu)
 static inline void set_cpu_numa_mem(int cpu, int node)
 {
 	per_cpu(_numa_mem_, cpu) = node;
+	_node_numa_mem_[cpu_to_node(cpu)] = node;
 }
 #endif
 
@@ -159,6 +169,13 @@ static inline int numa_mem_id(void)
 }
 #endif
 
+#ifndef node_to_mem_node
+static inline int node_to_mem_node(int node)
+{
+	return node;
+}
+#endif
+
 #ifndef cpu_to_mem
 static inline int cpu_to_mem(int cpu)
 {
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 18cee0d4c8a2..0883c42936d4 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -85,6 +85,7 @@ EXPORT_PER_CPU_SYMBOL(numa_node);
  */
 DEFINE_PER_CPU(int, _numa_mem_);		/* Kernel "local memory" node */
 EXPORT_PER_CPU_SYMBOL(_numa_mem_);
+int _node_numa_mem_[MAX_NUMNODES];
 #endif
 
 /*