/*

   * Basic Node interface support

   */

  #include <linux/module.h>
  #include <linux/init.h>
  #include <linux/mm.h>

  #include <linux/memory.h>

  #include <linux/vmstat.h>

  #include <linux/notifier.h>

  #include <linux/node.h>
  #include <linux/hugetlb.h>

  #include <linux/compaction.h>

  #include <linux/cpumask.h>
  #include <linux/topology.h>
  #include <linux/nodemask.h>

  #include <linux/cpu.h>

  #include <linux/device.h>

  #include <linux/swap.h>

  #include <linux/slab.h>

  static struct bus_type node_subsys = {

  	.name = "node",

  	.dev_name = "node",

  };

  static ssize_t node_read_cpumap(struct device *dev, bool list, char *buf)

  {
  	struct node *node_dev = to_node(dev);

  	const struct cpumask *mask = cpumask_of_node(node_dev->dev.id);

  	/* 2008/04/07: buf currently PAGE_SIZE, need 9 chars per 32 bits. */
  	BUILD_BUG_ON((NR_CPUS/32 * 9) > (PAGE_SIZE-1));

  	return cpumap_print_to_pagebuf(list, buf, mask);

  }

  static inline ssize_t node_read_cpumask(struct device *dev,
  				struct device_attribute *attr, char *buf)

  {

  	return node_read_cpumap(dev, false, buf);

  }

  static inline ssize_t node_read_cpulist(struct device *dev,
  				struct device_attribute *attr, char *buf)

  {

  	return node_read_cpumap(dev, true, buf);

  }

  static DEVICE_ATTR(cpumap,  S_IRUGO, node_read_cpumask, NULL);
  static DEVICE_ATTR(cpulist, S_IRUGO, node_read_cpulist, NULL);

  
  #define K(x) ((x) << (PAGE_SHIFT - 10))

  static ssize_t node_read_meminfo(struct device *dev,
  			struct device_attribute *attr, char *buf)

  {
  	int n;
  	int nid = dev->id;

  	struct pglist_data *pgdat = NODE_DATA(nid);

  	struct sysinfo i;

  
  	si_meminfo_node(&i, nid);

  	n = sprintf(buf,

  		       "Node %d MemTotal:       %8lu kB
  "
  		       "Node %d MemFree:        %8lu kB
  "
  		       "Node %d MemUsed:        %8lu kB
  "
  		       "Node %d Active:         %8lu kB
  "
  		       "Node %d Inactive:       %8lu kB
  "
  		       "Node %d Active(anon):   %8lu kB
  "
  		       "Node %d Inactive(anon): %8lu kB
  "
  		       "Node %d Active(file):   %8lu kB
  "
  		       "Node %d Inactive(file): %8lu kB
  "

  		       "Node %d Unevictable:    %8lu kB
  "

  		       "Node %d Mlocked:        %8lu kB
  ",
  		       nid, K(i.totalram),
  		       nid, K(i.freeram),
  		       nid, K(i.totalram - i.freeram),

  		       nid, K(node_page_state(pgdat, NR_ACTIVE_ANON) +
  				node_page_state(pgdat, NR_ACTIVE_FILE)),
  		       nid, K(node_page_state(pgdat, NR_INACTIVE_ANON) +
  				node_page_state(pgdat, NR_INACTIVE_FILE)),
  		       nid, K(node_page_state(pgdat, NR_ACTIVE_ANON)),
  		       nid, K(node_page_state(pgdat, NR_INACTIVE_ANON)),
  		       nid, K(node_page_state(pgdat, NR_ACTIVE_FILE)),
  		       nid, K(node_page_state(pgdat, NR_INACTIVE_FILE)),
  		       nid, K(node_page_state(pgdat, NR_UNEVICTABLE)),

  		       nid, K(sum_zone_node_page_state(nid, NR_MLOCK)));

  #ifdef CONFIG_HIGHMEM

  	n += sprintf(buf + n,

  		       "Node %d HighTotal:      %8lu kB
  "
  		       "Node %d HighFree:       %8lu kB
  "
  		       "Node %d LowTotal:       %8lu kB
  "

  		       "Node %d LowFree:        %8lu kB
  ",
  		       nid, K(i.totalhigh),
  		       nid, K(i.freehigh),
  		       nid, K(i.totalram - i.totalhigh),
  		       nid, K(i.freeram - i.freehigh));

  #endif

  	n += sprintf(buf + n,

  		       "Node %d Dirty:          %8lu kB
  "
  		       "Node %d Writeback:      %8lu kB
  "
  		       "Node %d FilePages:      %8lu kB
  "
  		       "Node %d Mapped:         %8lu kB
  "
  		       "Node %d AnonPages:      %8lu kB
  "

  		       "Node %d Shmem:          %8lu kB
  "

  		       "Node %d KernelStack:    %8lu kB
  "

  		       "Node %d PageTables:     %8lu kB
  "
  		       "Node %d NFS_Unstable:   %8lu kB
  "
  		       "Node %d Bounce:         %8lu kB
  "
  		       "Node %d WritebackTmp:   %8lu kB
  "
  		       "Node %d Slab:           %8lu kB
  "
  		       "Node %d SReclaimable:   %8lu kB
  "

  		       "Node %d SUnreclaim:     %8lu kB
  "
  #ifdef CONFIG_TRANSPARENT_HUGEPAGE
  		       "Node %d AnonHugePages:  %8lu kB
  "

  		       "Node %d ShmemHugePages: %8lu kB
  "
  		       "Node %d ShmemPmdMapped: %8lu kB
  "

  #endif
  			,

  		       nid, K(node_page_state(pgdat, NR_FILE_DIRTY)),
  		       nid, K(node_page_state(pgdat, NR_WRITEBACK)),
  		       nid, K(node_page_state(pgdat, NR_FILE_PAGES)),

  		       nid, K(node_page_state(pgdat, NR_FILE_MAPPED)),

  		       nid, K(node_page_state(pgdat, NR_ANON_MAPPED)),

  		       nid, K(i.sharedram),

  		       nid, sum_zone_node_page_state(nid, NR_KERNEL_STACK_KB),

  		       nid, K(sum_zone_node_page_state(nid, NR_PAGETABLE)),

  		       nid, K(node_page_state(pgdat, NR_UNSTABLE_NFS)),

  		       nid, K(sum_zone_node_page_state(nid, NR_BOUNCE)),

  		       nid, K(node_page_state(pgdat, NR_WRITEBACK_TEMP)),

  		       nid, K(sum_zone_node_page_state(nid, NR_SLAB_RECLAIMABLE) +
  				sum_zone_node_page_state(nid, NR_SLAB_UNRECLAIMABLE)),
  		       nid, K(sum_zone_node_page_state(nid, NR_SLAB_RECLAIMABLE)),

  #ifdef CONFIG_TRANSPARENT_HUGEPAGE

  		       nid, K(sum_zone_node_page_state(nid, NR_SLAB_UNRECLAIMABLE)),

  		       nid, K(node_page_state(pgdat, NR_ANON_THPS) *

  				       HPAGE_PMD_NR),

  		       nid, K(node_page_state(pgdat, NR_SHMEM_THPS) *

  				       HPAGE_PMD_NR),

  		       nid, K(node_page_state(pgdat, NR_SHMEM_PMDMAPPED) *

  				       HPAGE_PMD_NR));

  #else

  		       nid, K(sum_zone_node_page_state(nid, NR_SLAB_UNRECLAIMABLE)));

  #endif

  	n += hugetlb_report_node_meminfo(nid, buf + n);
  	return n;
  }
  
  #undef K

  static DEVICE_ATTR(meminfo, S_IRUGO, node_read_meminfo, NULL);

  static ssize_t node_read_numastat(struct device *dev,
  				struct device_attribute *attr, char *buf)

  {

  	return sprintf(buf,
  		       "numa_hit %lu
  "
  		       "numa_miss %lu
  "
  		       "numa_foreign %lu
  "
  		       "interleave_hit %lu
  "
  		       "local_node %lu
  "
  		       "other_node %lu
  ",

  		       sum_zone_node_page_state(dev->id, NUMA_HIT),
  		       sum_zone_node_page_state(dev->id, NUMA_MISS),
  		       sum_zone_node_page_state(dev->id, NUMA_FOREIGN),
  		       sum_zone_node_page_state(dev->id, NUMA_INTERLEAVE_HIT),
  		       sum_zone_node_page_state(dev->id, NUMA_LOCAL),
  		       sum_zone_node_page_state(dev->id, NUMA_OTHER));

  }

  static DEVICE_ATTR(numastat, S_IRUGO, node_read_numastat, NULL);

  static ssize_t node_read_vmstat(struct device *dev,
  				struct device_attribute *attr, char *buf)

  {
  	int nid = dev->id;

  	struct pglist_data *pgdat = NODE_DATA(nid);

  	int i;
  	int n = 0;
  
  	for (i = 0; i < NR_VM_ZONE_STAT_ITEMS; i++)
  		n += sprintf(buf+n, "%s %lu
  ", vmstat_text[i],

  			     sum_zone_node_page_state(nid, i));
  
  	for (i = 0; i < NR_VM_NODE_STAT_ITEMS; i++)
  		n += sprintf(buf+n, "%s %lu
  ",
  			     vmstat_text[i + NR_VM_ZONE_STAT_ITEMS],
  			     node_page_state(pgdat, i));

  
  	return n;

  }

  static DEVICE_ATTR(vmstat, S_IRUGO, node_read_vmstat, NULL);

  static ssize_t node_read_distance(struct device *dev,

  			struct device_attribute *attr, char *buf)

  {
  	int nid = dev->id;
  	int len = 0;
  	int i;

  	/*
  	 * buf is currently PAGE_SIZE in length and each node needs 4 chars
  	 * at the most (distance + space or newline).
  	 */
  	BUILD_BUG_ON(MAX_NUMNODES * 4 > PAGE_SIZE);

  
  	for_each_online_node(i)
  		len += sprintf(buf + len, "%s%d", i ? " " : "", node_distance(nid, i));
  
  	len += sprintf(buf + len, "
  ");
  	return len;
  }

  static DEVICE_ATTR(distance, S_IRUGO, node_read_distance, NULL);

  static struct attribute *node_dev_attrs[] = {
  	&dev_attr_cpumap.attr,
  	&dev_attr_cpulist.attr,
  	&dev_attr_meminfo.attr,
  	&dev_attr_numastat.attr,
  	&dev_attr_distance.attr,
  	&dev_attr_vmstat.attr,
  	NULL
  };

  ATTRIBUTE_GROUPS(node_dev);

  #ifdef CONFIG_HUGETLBFS
  /*
   * hugetlbfs per node attributes registration interface:
   * When/if hugetlb[fs] subsystem initializes [sometime after this module],

   * it will register its per node attributes for all online nodes with
   * memory.  It will also call register_hugetlbfs_with_node(), below, to

   * register its attribute registration functions with this node driver.
   * Once these hooks have been initialized, the node driver will call into
   * the hugetlb module to [un]register attributes for hot-plugged nodes.
   */
  static node_registration_func_t __hugetlb_register_node;
  static node_registration_func_t __hugetlb_unregister_node;

  static inline bool hugetlb_register_node(struct node *node)

  {

  	if (__hugetlb_register_node &&

  			node_state(node->dev.id, N_MEMORY)) {

  		__hugetlb_register_node(node);

  		return true;
  	}
  	return false;

  }
  
  static inline void hugetlb_unregister_node(struct node *node)
  {
  	if (__hugetlb_unregister_node)
  		__hugetlb_unregister_node(node);
  }
  
  void register_hugetlbfs_with_node(node_registration_func_t doregister,
  				  node_registration_func_t unregister)
  {
  	__hugetlb_register_node   = doregister;
  	__hugetlb_unregister_node = unregister;
  }
  #else
  static inline void hugetlb_register_node(struct node *node) {}
  
  static inline void hugetlb_unregister_node(struct node *node) {}
  #endif

  static void node_device_release(struct device *dev)
  {
  	struct node *node = to_node(dev);
  
  #if defined(CONFIG_MEMORY_HOTPLUG_SPARSE) && defined(CONFIG_HUGETLBFS)
  	/*
  	 * We schedule the work only when a memory section is
  	 * onlined/offlined on this node. When we come here,
  	 * all the memory on this node has been offlined,
  	 * so we won't enqueue new work to this work.
  	 *
  	 * The work is using node->node_work, so we should
  	 * flush work before freeing the memory.
  	 */
  	flush_work(&node->node_work);
  #endif
  	kfree(node);
  }

  
  /*

   * register_node - Setup a sysfs device for a node.

   * @num - Node number to use when creating the device.
   *
   * Initialize and register the node device.
   */

  static int register_node(struct node *node, int num, struct node *parent)

  {
  	int error;

  	node->dev.id = num;
  	node->dev.bus = &node_subsys;

  	node->dev.release = node_device_release;

  	node->dev.groups = node_dev_groups;

  	error = device_register(&node->dev);

  
  	if (!error){

  		hugetlb_register_node(node);

  
  		compaction_register_node(node);

  	}
  	return error;
  }

  /**
   * unregister_node - unregister a node device
   * @node: node going away
   *
   * Unregisters a node device @node.  All the devices on the node must be
   * unregistered before calling this function.
   */
  void unregister_node(struct node *node)
  {

  	hugetlb_unregister_node(node);		/* no-op, if memoryless node */

  	device_unregister(&node->dev);

  }

  struct node *node_devices[MAX_NUMNODES];

  /*
   * register cpu under node
   */
  int register_cpu_under_node(unsigned int cpu, unsigned int nid)
  {

  	int ret;

  	struct device *obj;

  	if (!node_online(nid))
  		return 0;

  	obj = get_cpu_device(cpu);

  	if (!obj)
  		return 0;

  	ret = sysfs_create_link(&node_devices[nid]->dev.kobj,

  				&obj->kobj,
  				kobject_name(&obj->kobj));

  	if (ret)
  		return ret;
  
  	return sysfs_create_link(&obj->kobj,

  				 &node_devices[nid]->dev.kobj,
  				 kobject_name(&node_devices[nid]->dev.kobj));

  }
  
  int unregister_cpu_under_node(unsigned int cpu, unsigned int nid)
  {

  	struct device *obj;

  
  	if (!node_online(nid))
  		return 0;

  	obj = get_cpu_device(cpu);

  	if (!obj)
  		return 0;

  	sysfs_remove_link(&node_devices[nid]->dev.kobj,

  			  kobject_name(&obj->kobj));

  	sysfs_remove_link(&obj->kobj,

  			  kobject_name(&node_devices[nid]->dev.kobj));

  	return 0;
  }

  #ifdef CONFIG_MEMORY_HOTPLUG_SPARSE
  #define page_initialized(page)  (page->lru.next)

  static int __ref get_nid_for_pfn(unsigned long pfn)

  {
  	struct page *page;
  
  	if (!pfn_valid_within(pfn))
  		return -1;

  #ifdef CONFIG_DEFERRED_STRUCT_PAGE_INIT
  	if (system_state == SYSTEM_BOOTING)
  		return early_pfn_to_nid(pfn);
  #endif

  	page = pfn_to_page(pfn);
  	if (!page_initialized(page))
  		return -1;
  	return pfn_to_nid(pfn);
  }
  
  /* register memory section under specified node if it spans that node */
  int register_mem_sect_under_node(struct memory_block *mem_blk, int nid)
  {

  	int ret;

  	unsigned long pfn, sect_start_pfn, sect_end_pfn;
  
  	if (!mem_blk)
  		return -EFAULT;
  	if (!node_online(nid))
  		return 0;

  
  	sect_start_pfn = section_nr_to_pfn(mem_blk->start_section_nr);
  	sect_end_pfn = section_nr_to_pfn(mem_blk->end_section_nr);
  	sect_end_pfn += PAGES_PER_SECTION - 1;

  	for (pfn = sect_start_pfn; pfn <= sect_end_pfn; pfn++) {
  		int page_nid;

  		/*
  		 * memory block could have several absent sections from start.
  		 * skip pfn range from absent section
  		 */
  		if (!pfn_present(pfn)) {
  			pfn = round_down(pfn + PAGES_PER_SECTION,
  					 PAGES_PER_SECTION) - 1;
  			continue;
  		}

  		page_nid = get_nid_for_pfn(pfn);
  		if (page_nid < 0)
  			continue;
  		if (page_nid != nid)
  			continue;

  		ret = sysfs_create_link_nowarn(&node_devices[nid]->dev.kobj,

  					&mem_blk->dev.kobj,
  					kobject_name(&mem_blk->dev.kobj));

  		if (ret)
  			return ret;

  		return sysfs_create_link_nowarn(&mem_blk->dev.kobj,

  				&node_devices[nid]->dev.kobj,
  				kobject_name(&node_devices[nid]->dev.kobj));

  	}
  	/* mem section does not span the specified node */
  	return 0;
  }
  
  /* unregister memory section under all nodes that it spans */

  int unregister_mem_sect_under_nodes(struct memory_block *mem_blk,
  				    unsigned long phys_index)

  {

  	NODEMASK_ALLOC(nodemask_t, unlinked_nodes, GFP_KERNEL);

  	unsigned long pfn, sect_start_pfn, sect_end_pfn;

  	if (!mem_blk) {
  		NODEMASK_FREE(unlinked_nodes);

  		return -EFAULT;

  	}
  	if (!unlinked_nodes)
  		return -ENOMEM;
  	nodes_clear(*unlinked_nodes);

  
  	sect_start_pfn = section_nr_to_pfn(phys_index);

  	sect_end_pfn = sect_start_pfn + PAGES_PER_SECTION - 1;
  	for (pfn = sect_start_pfn; pfn <= sect_end_pfn; pfn++) {

  		int nid;

  
  		nid = get_nid_for_pfn(pfn);
  		if (nid < 0)
  			continue;
  		if (!node_online(nid))
  			continue;

  		if (node_test_and_set(nid, *unlinked_nodes))

  			continue;

  		sysfs_remove_link(&node_devices[nid]->dev.kobj,

  			 kobject_name(&mem_blk->dev.kobj));
  		sysfs_remove_link(&mem_blk->dev.kobj,

  			 kobject_name(&node_devices[nid]->dev.kobj));

  	}

  	NODEMASK_FREE(unlinked_nodes);

  	return 0;
  }
  
  static int link_mem_sections(int nid)
  {
  	unsigned long start_pfn = NODE_DATA(nid)->node_start_pfn;
  	unsigned long end_pfn = start_pfn + NODE_DATA(nid)->node_spanned_pages;
  	unsigned long pfn;

  	struct memory_block *mem_blk = NULL;

  	int err = 0;
  
  	for (pfn = start_pfn; pfn < end_pfn; pfn += PAGES_PER_SECTION) {
  		unsigned long section_nr = pfn_to_section_nr(pfn);
  		struct mem_section *mem_sect;

  		int ret;
  
  		if (!present_section_nr(section_nr))
  			continue;
  		mem_sect = __nr_to_section(section_nr);

  
  		/* same memblock ? */
  		if (mem_blk)
  			if ((section_nr >= mem_blk->start_section_nr) &&
  			    (section_nr <= mem_blk->end_section_nr))
  				continue;

  		mem_blk = find_memory_block_hinted(mem_sect, mem_blk);

  		ret = register_mem_sect_under_node(mem_blk, nid);
  		if (!err)
  			err = ret;
  
  		/* discard ref obtained in find_memory_block() */

  	}

  
  	if (mem_blk)

  		kobject_put(&mem_blk->dev.kobj);

  	return err;
  }

  #ifdef CONFIG_HUGETLBFS

  /*
   * Handle per node hstate attribute [un]registration on transistions
   * to/from memoryless state.
   */

  static void node_hugetlb_work(struct work_struct *work)
  {
  	struct node *node = container_of(work, struct node, node_work);
  
  	/*
  	 * We only get here when a node transitions to/from memoryless state.
  	 * We can detect which transition occurred by examining whether the
  	 * node has memory now.  hugetlb_register_node() already check this
  	 * so we try to register the attributes.  If that fails, then the
  	 * node has transitioned to memoryless, try to unregister the
  	 * attributes.
  	 */
  	if (!hugetlb_register_node(node))
  		hugetlb_unregister_node(node);
  }
  
  static void init_node_hugetlb_work(int nid)
  {

  	INIT_WORK(&node_devices[nid]->node_work, node_hugetlb_work);

  }

  
  static int node_memory_callback(struct notifier_block *self,
  				unsigned long action, void *arg)
  {
  	struct memory_notify *mnb = arg;
  	int nid = mnb->status_change_nid;
  
  	switch (action) {

  	case MEM_ONLINE:
  	case MEM_OFFLINE:
  		/*
  		 * offload per node hstate [un]registration to a work thread
  		 * when transitioning to/from memoryless state.
  		 */

  		if (nid != NUMA_NO_NODE)

  			schedule_work(&node_devices[nid]->node_work);

  		break;

  	case MEM_GOING_ONLINE:
  	case MEM_GOING_OFFLINE:
  	case MEM_CANCEL_ONLINE:
  	case MEM_CANCEL_OFFLINE:
  	default:
  		break;
  	}
  
  	return NOTIFY_OK;
  }

  #endif	/* CONFIG_HUGETLBFS */
  #else	/* !CONFIG_MEMORY_HOTPLUG_SPARSE */

  static int link_mem_sections(int nid) { return 0; }

  #endif	/* CONFIG_MEMORY_HOTPLUG_SPARSE */

  #if !defined(CONFIG_MEMORY_HOTPLUG_SPARSE) || \
      !defined(CONFIG_HUGETLBFS)

  static inline int node_memory_callback(struct notifier_block *self,
  				unsigned long action, void *arg)
  {
  	return NOTIFY_OK;
  }

  
  static void init_node_hugetlb_work(int nid) { }
  
  #endif

  int register_one_node(int nid)
  {
  	int error = 0;

  	int cpu;

  
  	if (node_online(nid)) {
  		int p_node = parent_node(nid);
  		struct node *parent = NULL;
  
  		if (p_node != nid)

  			parent = node_devices[p_node];

  		node_devices[nid] = kzalloc(sizeof(struct node), GFP_KERNEL);
  		if (!node_devices[nid])
  			return -ENOMEM;
  
  		error = register_node(node_devices[nid], nid, parent);

  
  		/* link cpu under this node */
  		for_each_present_cpu(cpu) {
  			if (cpu_to_node(cpu) == nid)
  				register_cpu_under_node(cpu, nid);
  		}

  
  		/* link memory sections under this node */
  		error = link_mem_sections(nid);

  
  		/* initialize work queue for memory hot plug */
  		init_node_hugetlb_work(nid);

  	}
  
  	return error;
  
  }
  
  void unregister_one_node(int nid)
  {

  	if (!node_devices[nid])
  		return;

  	unregister_node(node_devices[nid]);

  	node_devices[nid] = NULL;

  }

  /*
   * node states attributes
   */
  
  static ssize_t print_nodes_state(enum node_states state, char *buf)
  {
  	int n;

  	n = scnprintf(buf, PAGE_SIZE - 1, "%*pbl",
  		      nodemask_pr_args(&node_states[state]));

  	buf[n++] = '
  ';
  	buf[n] = '\0';

  	return n;
  }

  struct node_attr {

  	struct device_attribute attr;

  	enum node_states state;
  };

  static ssize_t show_node_state(struct device *dev,
  			       struct device_attribute *attr, char *buf)

  {

  	struct node_attr *na = container_of(attr, struct node_attr, attr);
  	return print_nodes_state(na->state, buf);

  }

  #define _NODE_ATTR(name, state) \

  	{ __ATTR(name, 0444, show_node_state, NULL), state }

  static struct node_attr node_state_attr[] = {

  	[N_POSSIBLE] = _NODE_ATTR(possible, N_POSSIBLE),
  	[N_ONLINE] = _NODE_ATTR(online, N_ONLINE),
  	[N_NORMAL_MEMORY] = _NODE_ATTR(has_normal_memory, N_NORMAL_MEMORY),

  #ifdef CONFIG_HIGHMEM

  	[N_HIGH_MEMORY] = _NODE_ATTR(has_high_memory, N_HIGH_MEMORY),

  #endif

  #ifdef CONFIG_MOVABLE_NODE
  	[N_MEMORY] = _NODE_ATTR(has_memory, N_MEMORY),
  #endif

  	[N_CPU] = _NODE_ATTR(has_cpu, N_CPU),

  };

  static struct attribute *node_state_attrs[] = {

  	&node_state_attr[N_POSSIBLE].attr.attr,
  	&node_state_attr[N_ONLINE].attr.attr,
  	&node_state_attr[N_NORMAL_MEMORY].attr.attr,

  #ifdef CONFIG_HIGHMEM

  	&node_state_attr[N_HIGH_MEMORY].attr.attr,

  #endif

  #ifdef CONFIG_MOVABLE_NODE
  	&node_state_attr[N_MEMORY].attr.attr,
  #endif

  	&node_state_attr[N_CPU].attr.attr,

  	NULL
  };

  static struct attribute_group memory_root_attr_group = {
  	.attrs = node_state_attrs,
  };
  
  static const struct attribute_group *cpu_root_attr_groups[] = {
  	&memory_root_attr_group,
  	NULL,
  };

  #define NODE_CALLBACK_PRI	2	/* lower than SLAB */

  static int __init register_node_type(void)

  {

  	int ret;

   	BUILD_BUG_ON(ARRAY_SIZE(node_state_attr) != NR_NODE_STATES);
   	BUILD_BUG_ON(ARRAY_SIZE(node_state_attrs)-1 != NR_NODE_STATES);

  	ret = subsys_system_register(&node_subsys, cpu_root_attr_groups);

  	if (!ret) {

  		static struct notifier_block node_memory_callback_nb = {
  			.notifier_call = node_memory_callback,
  			.priority = NODE_CALLBACK_PRI,
  		};
  		register_hotmemory_notifier(&node_memory_callback_nb);

  	}

  
  	/*
  	 * Note:  we're not going to unregister the node class if we fail
  	 * to register the node state class attribute files.
  	 */
  	return ret;

  }
  postcore_initcall(register_node_type);