[PATCH] permit to online CPUs before local memory comes online

[minskey <chaohong_guo@linux.intel.com>]

This patch enables users to online CPUs even if the CPUs belongs to
a numa node which doesn't have onlined local memory.

The zonlists(pg_data_t.node_zonelists[]) of a numa node are created
either in system boot/init period, or at the time of local memory
online.  For a numa node without onlined local memory, its zonelists
are not initialized at present. As a result, any memory allocation
operations executed by CPUs within this node will fail. In fact, an
out-of-memory error is triggered when attempt to online CPUs before
memory comes to online.

This patch tries to create zonelists for such numa nodes, so that
the memory allocation for this node can be fallback'ed to other
nodes.

Signed-off-by: minskey guo<chaohong.guo@intel.com>
---
 include/linux/memory_hotplug.h |    1 +
 kernel/cpu.c                   |   26 ++++++++++++++++++++++++++
 mm/memory_hotplug.c            |   25 +++++++++++++++++++++++++
 3 files changed, 52 insertions(+), 0 deletions(-)

diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h
index 35b07b7..864035f 100644
--- a/include/linux/memory_hotplug.h
+++ b/include/linux/memory_hotplug.h
@@ -202,6 +202,7 @@ static inline int is_mem_section_removable(unsigned long pfn,
 }
 #endif /* CONFIG_MEMORY_HOTREMOVE */
 
+extern int mem_online_node(int nid);
 extern int add_memory(int nid, u64 start, u64 size);
 extern int arch_add_memory(int nid, u64 start, u64 size);
 extern int remove_memory(u64 start, u64 size);
diff --git a/kernel/cpu.c b/kernel/cpu.c
index f8cced2..c31b9cb 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -335,6 +335,12 @@ out_notify:
 int __cpuinit cpu_up(unsigned int cpu)
 {
 	int err = 0;
+
+#ifdef	CONFIG_MEMORY_HOTPLUG
+	int nid;
+	pg_data_t	*pgdat;
+#endif
+
 	if (!cpu_possible(cpu)) {
 		printk(KERN_ERR "can't online cpu %d because it is not "
 			"configured as may-hotadd at boot time\n", cpu);
@@ -345,6 +351,26 @@ int __cpuinit cpu_up(unsigned int cpu)
 		return -EINVAL;
 	}
 
+#ifdef	CONFIG_MEMORY_HOTPLUG
+	nid = cpu_to_node(cpu);
+	if (!node_online(nid)) {
+		err = mem_online_node(nid);
+		if (err)
+			return err;
+	}
+
+	pgdat = NODE_DATA(nid);
+	if (!pgdat) {
+		printk(KERN_ERR
+			"Can't online cpu %d due to NULL pgdat\n", cpu);
+		return -ENOMEM;
+	}
+
+	if (pgdat->node_zonelists->_zonerefs->zone == NULL) {
+		build_all_zonelists();
+	} 
+#endif
+
 	cpu_maps_update_begin();
 
 	if (cpu_hotplug_disabled) {
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index be211a5..2d24bef 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -482,6 +482,31 @@ static void rollback_node_hotadd(int nid, pg_data_t *pgdat)
 }
 
 
+/*
+ * called by cpu_up() to online a node without onlined memory.
+ */
+int mem_online_node(int nid)
+{
+	pg_data_t	*pgdat;
+	int	ret;
+
+	lock_system_sleep();
+	pgdat = hotadd_new_pgdat(nid, 0);
+	if (pgdat) {
+		ret = -ENOMEM;
+		goto out;
+	}
+	node_set_online(nid);
+	ret = register_one_node(nid);
+	BUG_ON(ret);
+
+out:
+	unlock_system_sleep();
+	return ret;
+}
+EXPORT_SYMBOL_GPL(mem_online_node);
+
+
 /* we are OK calling __meminit stuff here - we have CONFIG_MEMORY_HOTPLUG */
 int __ref add_memory(int nid, u64 start, u64 size)
 {
-- 
1.6.3.3