xref: /linux/drivers/base/node.c (revision b43ab901d671e3e3cad425ea5e9a3c74e266dcdd)
1 /*
2  * Basic Node interface support
3  */
4 
5 #include <linux/module.h>
6 #include <linux/init.h>
7 #include <linux/mm.h>
8 #include <linux/memory.h>
9 #include <linux/vmstat.h>
10 #include <linux/node.h>
11 #include <linux/hugetlb.h>
12 #include <linux/compaction.h>
13 #include <linux/cpumask.h>
14 #include <linux/topology.h>
15 #include <linux/nodemask.h>
16 #include <linux/cpu.h>
17 #include <linux/device.h>
18 #include <linux/swap.h>
19 #include <linux/slab.h>
20 
21 static struct bus_type node_subsys = {
22 	.name = "node",
23 	.dev_name = "node",
24 };
25 
26 
27 static ssize_t node_read_cpumap(struct device *dev, int type, char *buf)
28 {
29 	struct node *node_dev = to_node(dev);
30 	const struct cpumask *mask = cpumask_of_node(node_dev->dev.id);
31 	int len;
32 
33 	/* 2008/04/07: buf currently PAGE_SIZE, need 9 chars per 32 bits. */
34 	BUILD_BUG_ON((NR_CPUS/32 * 9) > (PAGE_SIZE-1));
35 
36 	len = type?
37 		cpulist_scnprintf(buf, PAGE_SIZE-2, mask) :
38 		cpumask_scnprintf(buf, PAGE_SIZE-2, mask);
39  	buf[len++] = '\n';
40  	buf[len] = '\0';
41 	return len;
42 }
43 
44 static inline ssize_t node_read_cpumask(struct device *dev,
45 				struct device_attribute *attr, char *buf)
46 {
47 	return node_read_cpumap(dev, 0, buf);
48 }
49 static inline ssize_t node_read_cpulist(struct device *dev,
50 				struct device_attribute *attr, char *buf)
51 {
52 	return node_read_cpumap(dev, 1, buf);
53 }
54 
55 static DEVICE_ATTR(cpumap,  S_IRUGO, node_read_cpumask, NULL);
56 static DEVICE_ATTR(cpulist, S_IRUGO, node_read_cpulist, NULL);
57 
58 #define K(x) ((x) << (PAGE_SHIFT - 10))
59 static ssize_t node_read_meminfo(struct device *dev,
60 			struct device_attribute *attr, char *buf)
61 {
62 	int n;
63 	int nid = dev->id;
64 	struct sysinfo i;
65 
66 	si_meminfo_node(&i, nid);
67 	n = sprintf(buf,
68 		       "Node %d MemTotal:       %8lu kB\n"
69 		       "Node %d MemFree:        %8lu kB\n"
70 		       "Node %d MemUsed:        %8lu kB\n"
71 		       "Node %d Active:         %8lu kB\n"
72 		       "Node %d Inactive:       %8lu kB\n"
73 		       "Node %d Active(anon):   %8lu kB\n"
74 		       "Node %d Inactive(anon): %8lu kB\n"
75 		       "Node %d Active(file):   %8lu kB\n"
76 		       "Node %d Inactive(file): %8lu kB\n"
77 		       "Node %d Unevictable:    %8lu kB\n"
78 		       "Node %d Mlocked:        %8lu kB\n",
79 		       nid, K(i.totalram),
80 		       nid, K(i.freeram),
81 		       nid, K(i.totalram - i.freeram),
82 		       nid, K(node_page_state(nid, NR_ACTIVE_ANON) +
83 				node_page_state(nid, NR_ACTIVE_FILE)),
84 		       nid, K(node_page_state(nid, NR_INACTIVE_ANON) +
85 				node_page_state(nid, NR_INACTIVE_FILE)),
86 		       nid, K(node_page_state(nid, NR_ACTIVE_ANON)),
87 		       nid, K(node_page_state(nid, NR_INACTIVE_ANON)),
88 		       nid, K(node_page_state(nid, NR_ACTIVE_FILE)),
89 		       nid, K(node_page_state(nid, NR_INACTIVE_FILE)),
90 		       nid, K(node_page_state(nid, NR_UNEVICTABLE)),
91 		       nid, K(node_page_state(nid, NR_MLOCK)));
92 
93 #ifdef CONFIG_HIGHMEM
94 	n += sprintf(buf + n,
95 		       "Node %d HighTotal:      %8lu kB\n"
96 		       "Node %d HighFree:       %8lu kB\n"
97 		       "Node %d LowTotal:       %8lu kB\n"
98 		       "Node %d LowFree:        %8lu kB\n",
99 		       nid, K(i.totalhigh),
100 		       nid, K(i.freehigh),
101 		       nid, K(i.totalram - i.totalhigh),
102 		       nid, K(i.freeram - i.freehigh));
103 #endif
104 	n += sprintf(buf + n,
105 		       "Node %d Dirty:          %8lu kB\n"
106 		       "Node %d Writeback:      %8lu kB\n"
107 		       "Node %d FilePages:      %8lu kB\n"
108 		       "Node %d Mapped:         %8lu kB\n"
109 		       "Node %d AnonPages:      %8lu kB\n"
110 		       "Node %d Shmem:          %8lu kB\n"
111 		       "Node %d KernelStack:    %8lu kB\n"
112 		       "Node %d PageTables:     %8lu kB\n"
113 		       "Node %d NFS_Unstable:   %8lu kB\n"
114 		       "Node %d Bounce:         %8lu kB\n"
115 		       "Node %d WritebackTmp:   %8lu kB\n"
116 		       "Node %d Slab:           %8lu kB\n"
117 		       "Node %d SReclaimable:   %8lu kB\n"
118 		       "Node %d SUnreclaim:     %8lu kB\n"
119 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
120 		       "Node %d AnonHugePages:  %8lu kB\n"
121 #endif
122 			,
123 		       nid, K(node_page_state(nid, NR_FILE_DIRTY)),
124 		       nid, K(node_page_state(nid, NR_WRITEBACK)),
125 		       nid, K(node_page_state(nid, NR_FILE_PAGES)),
126 		       nid, K(node_page_state(nid, NR_FILE_MAPPED)),
127 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
128 		       nid, K(node_page_state(nid, NR_ANON_PAGES)
129 			+ node_page_state(nid, NR_ANON_TRANSPARENT_HUGEPAGES) *
130 			HPAGE_PMD_NR),
131 #else
132 		       nid, K(node_page_state(nid, NR_ANON_PAGES)),
133 #endif
134 		       nid, K(node_page_state(nid, NR_SHMEM)),
135 		       nid, node_page_state(nid, NR_KERNEL_STACK) *
136 				THREAD_SIZE / 1024,
137 		       nid, K(node_page_state(nid, NR_PAGETABLE)),
138 		       nid, K(node_page_state(nid, NR_UNSTABLE_NFS)),
139 		       nid, K(node_page_state(nid, NR_BOUNCE)),
140 		       nid, K(node_page_state(nid, NR_WRITEBACK_TEMP)),
141 		       nid, K(node_page_state(nid, NR_SLAB_RECLAIMABLE) +
142 				node_page_state(nid, NR_SLAB_UNRECLAIMABLE)),
143 		       nid, K(node_page_state(nid, NR_SLAB_RECLAIMABLE)),
144 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
145 		       nid, K(node_page_state(nid, NR_SLAB_UNRECLAIMABLE))
146 			, nid,
147 			K(node_page_state(nid, NR_ANON_TRANSPARENT_HUGEPAGES) *
148 			HPAGE_PMD_NR));
149 #else
150 		       nid, K(node_page_state(nid, NR_SLAB_UNRECLAIMABLE)));
151 #endif
152 	n += hugetlb_report_node_meminfo(nid, buf + n);
153 	return n;
154 }
155 
156 #undef K
157 static DEVICE_ATTR(meminfo, S_IRUGO, node_read_meminfo, NULL);
158 
159 static ssize_t node_read_numastat(struct device *dev,
160 				struct device_attribute *attr, char *buf)
161 {
162 	return sprintf(buf,
163 		       "numa_hit %lu\n"
164 		       "numa_miss %lu\n"
165 		       "numa_foreign %lu\n"
166 		       "interleave_hit %lu\n"
167 		       "local_node %lu\n"
168 		       "other_node %lu\n",
169 		       node_page_state(dev->id, NUMA_HIT),
170 		       node_page_state(dev->id, NUMA_MISS),
171 		       node_page_state(dev->id, NUMA_FOREIGN),
172 		       node_page_state(dev->id, NUMA_INTERLEAVE_HIT),
173 		       node_page_state(dev->id, NUMA_LOCAL),
174 		       node_page_state(dev->id, NUMA_OTHER));
175 }
176 static DEVICE_ATTR(numastat, S_IRUGO, node_read_numastat, NULL);
177 
178 static ssize_t node_read_vmstat(struct device *dev,
179 				struct device_attribute *attr, char *buf)
180 {
181 	int nid = dev->id;
182 	int i;
183 	int n = 0;
184 
185 	for (i = 0; i < NR_VM_ZONE_STAT_ITEMS; i++)
186 		n += sprintf(buf+n, "%s %lu\n", vmstat_text[i],
187 			     node_page_state(nid, i));
188 
189 	return n;
190 }
191 static DEVICE_ATTR(vmstat, S_IRUGO, node_read_vmstat, NULL);
192 
193 static ssize_t node_read_distance(struct device *dev,
194 			struct device_attribute *attr, char * buf)
195 {
196 	int nid = dev->id;
197 	int len = 0;
198 	int i;
199 
200 	/*
201 	 * buf is currently PAGE_SIZE in length and each node needs 4 chars
202 	 * at the most (distance + space or newline).
203 	 */
204 	BUILD_BUG_ON(MAX_NUMNODES * 4 > PAGE_SIZE);
205 
206 	for_each_online_node(i)
207 		len += sprintf(buf + len, "%s%d", i ? " " : "", node_distance(nid, i));
208 
209 	len += sprintf(buf + len, "\n");
210 	return len;
211 }
212 static DEVICE_ATTR(distance, S_IRUGO, node_read_distance, NULL);
213 
214 #ifdef CONFIG_HUGETLBFS
215 /*
216  * hugetlbfs per node attributes registration interface:
217  * When/if hugetlb[fs] subsystem initializes [sometime after this module],
218  * it will register its per node attributes for all online nodes with
219  * memory.  It will also call register_hugetlbfs_with_node(), below, to
220  * register its attribute registration functions with this node driver.
221  * Once these hooks have been initialized, the node driver will call into
222  * the hugetlb module to [un]register attributes for hot-plugged nodes.
223  */
224 static node_registration_func_t __hugetlb_register_node;
225 static node_registration_func_t __hugetlb_unregister_node;
226 
227 static inline bool hugetlb_register_node(struct node *node)
228 {
229 	if (__hugetlb_register_node &&
230 			node_state(node->dev.id, N_HIGH_MEMORY)) {
231 		__hugetlb_register_node(node);
232 		return true;
233 	}
234 	return false;
235 }
236 
237 static inline void hugetlb_unregister_node(struct node *node)
238 {
239 	if (__hugetlb_unregister_node)
240 		__hugetlb_unregister_node(node);
241 }
242 
243 void register_hugetlbfs_with_node(node_registration_func_t doregister,
244 				  node_registration_func_t unregister)
245 {
246 	__hugetlb_register_node   = doregister;
247 	__hugetlb_unregister_node = unregister;
248 }
249 #else
250 static inline void hugetlb_register_node(struct node *node) {}
251 
252 static inline void hugetlb_unregister_node(struct node *node) {}
253 #endif
254 
255 
256 /*
257  * register_node - Setup a sysfs device for a node.
258  * @num - Node number to use when creating the device.
259  *
260  * Initialize and register the node device.
261  */
262 int register_node(struct node *node, int num, struct node *parent)
263 {
264 	int error;
265 
266 	node->dev.id = num;
267 	node->dev.bus = &node_subsys;
268 	error = device_register(&node->dev);
269 
270 	if (!error){
271 		device_create_file(&node->dev, &dev_attr_cpumap);
272 		device_create_file(&node->dev, &dev_attr_cpulist);
273 		device_create_file(&node->dev, &dev_attr_meminfo);
274 		device_create_file(&node->dev, &dev_attr_numastat);
275 		device_create_file(&node->dev, &dev_attr_distance);
276 		device_create_file(&node->dev, &dev_attr_vmstat);
277 
278 		scan_unevictable_register_node(node);
279 
280 		hugetlb_register_node(node);
281 
282 		compaction_register_node(node);
283 	}
284 	return error;
285 }
286 
287 /**
288  * unregister_node - unregister a node device
289  * @node: node going away
290  *
291  * Unregisters a node device @node.  All the devices on the node must be
292  * unregistered before calling this function.
293  */
294 void unregister_node(struct node *node)
295 {
296 	device_remove_file(&node->dev, &dev_attr_cpumap);
297 	device_remove_file(&node->dev, &dev_attr_cpulist);
298 	device_remove_file(&node->dev, &dev_attr_meminfo);
299 	device_remove_file(&node->dev, &dev_attr_numastat);
300 	device_remove_file(&node->dev, &dev_attr_distance);
301 	device_remove_file(&node->dev, &dev_attr_vmstat);
302 
303 	scan_unevictable_unregister_node(node);
304 	hugetlb_unregister_node(node);		/* no-op, if memoryless node */
305 
306 	device_unregister(&node->dev);
307 }
308 
309 struct node node_devices[MAX_NUMNODES];
310 
311 /*
312  * register cpu under node
313  */
314 int register_cpu_under_node(unsigned int cpu, unsigned int nid)
315 {
316 	int ret;
317 	struct device *obj;
318 
319 	if (!node_online(nid))
320 		return 0;
321 
322 	obj = get_cpu_device(cpu);
323 	if (!obj)
324 		return 0;
325 
326 	ret = sysfs_create_link(&node_devices[nid].dev.kobj,
327 				&obj->kobj,
328 				kobject_name(&obj->kobj));
329 	if (ret)
330 		return ret;
331 
332 	return sysfs_create_link(&obj->kobj,
333 				 &node_devices[nid].dev.kobj,
334 				 kobject_name(&node_devices[nid].dev.kobj));
335 }
336 
337 int unregister_cpu_under_node(unsigned int cpu, unsigned int nid)
338 {
339 	struct device *obj;
340 
341 	if (!node_online(nid))
342 		return 0;
343 
344 	obj = get_cpu_device(cpu);
345 	if (!obj)
346 		return 0;
347 
348 	sysfs_remove_link(&node_devices[nid].dev.kobj,
349 			  kobject_name(&obj->kobj));
350 	sysfs_remove_link(&obj->kobj,
351 			  kobject_name(&node_devices[nid].dev.kobj));
352 
353 	return 0;
354 }
355 
356 #ifdef CONFIG_MEMORY_HOTPLUG_SPARSE
357 #define page_initialized(page)  (page->lru.next)
358 
359 static int get_nid_for_pfn(unsigned long pfn)
360 {
361 	struct page *page;
362 
363 	if (!pfn_valid_within(pfn))
364 		return -1;
365 	page = pfn_to_page(pfn);
366 	if (!page_initialized(page))
367 		return -1;
368 	return pfn_to_nid(pfn);
369 }
370 
371 /* register memory section under specified node if it spans that node */
372 int register_mem_sect_under_node(struct memory_block *mem_blk, int nid)
373 {
374 	int ret;
375 	unsigned long pfn, sect_start_pfn, sect_end_pfn;
376 
377 	if (!mem_blk)
378 		return -EFAULT;
379 	if (!node_online(nid))
380 		return 0;
381 
382 	sect_start_pfn = section_nr_to_pfn(mem_blk->start_section_nr);
383 	sect_end_pfn = section_nr_to_pfn(mem_blk->end_section_nr);
384 	sect_end_pfn += PAGES_PER_SECTION - 1;
385 	for (pfn = sect_start_pfn; pfn <= sect_end_pfn; pfn++) {
386 		int page_nid;
387 
388 		page_nid = get_nid_for_pfn(pfn);
389 		if (page_nid < 0)
390 			continue;
391 		if (page_nid != nid)
392 			continue;
393 		ret = sysfs_create_link_nowarn(&node_devices[nid].dev.kobj,
394 					&mem_blk->dev.kobj,
395 					kobject_name(&mem_blk->dev.kobj));
396 		if (ret)
397 			return ret;
398 
399 		return sysfs_create_link_nowarn(&mem_blk->dev.kobj,
400 				&node_devices[nid].dev.kobj,
401 				kobject_name(&node_devices[nid].dev.kobj));
402 	}
403 	/* mem section does not span the specified node */
404 	return 0;
405 }
406 
407 /* unregister memory section under all nodes that it spans */
408 int unregister_mem_sect_under_nodes(struct memory_block *mem_blk,
409 				    unsigned long phys_index)
410 {
411 	NODEMASK_ALLOC(nodemask_t, unlinked_nodes, GFP_KERNEL);
412 	unsigned long pfn, sect_start_pfn, sect_end_pfn;
413 
414 	if (!mem_blk) {
415 		NODEMASK_FREE(unlinked_nodes);
416 		return -EFAULT;
417 	}
418 	if (!unlinked_nodes)
419 		return -ENOMEM;
420 	nodes_clear(*unlinked_nodes);
421 
422 	sect_start_pfn = section_nr_to_pfn(phys_index);
423 	sect_end_pfn = sect_start_pfn + PAGES_PER_SECTION - 1;
424 	for (pfn = sect_start_pfn; pfn <= sect_end_pfn; pfn++) {
425 		int nid;
426 
427 		nid = get_nid_for_pfn(pfn);
428 		if (nid < 0)
429 			continue;
430 		if (!node_online(nid))
431 			continue;
432 		if (node_test_and_set(nid, *unlinked_nodes))
433 			continue;
434 		sysfs_remove_link(&node_devices[nid].dev.kobj,
435 			 kobject_name(&mem_blk->dev.kobj));
436 		sysfs_remove_link(&mem_blk->dev.kobj,
437 			 kobject_name(&node_devices[nid].dev.kobj));
438 	}
439 	NODEMASK_FREE(unlinked_nodes);
440 	return 0;
441 }
442 
443 static int link_mem_sections(int nid)
444 {
445 	unsigned long start_pfn = NODE_DATA(nid)->node_start_pfn;
446 	unsigned long end_pfn = start_pfn + NODE_DATA(nid)->node_spanned_pages;
447 	unsigned long pfn;
448 	struct memory_block *mem_blk = NULL;
449 	int err = 0;
450 
451 	for (pfn = start_pfn; pfn < end_pfn; pfn += PAGES_PER_SECTION) {
452 		unsigned long section_nr = pfn_to_section_nr(pfn);
453 		struct mem_section *mem_sect;
454 		int ret;
455 
456 		if (!present_section_nr(section_nr))
457 			continue;
458 		mem_sect = __nr_to_section(section_nr);
459 		mem_blk = find_memory_block_hinted(mem_sect, mem_blk);
460 		ret = register_mem_sect_under_node(mem_blk, nid);
461 		if (!err)
462 			err = ret;
463 
464 		/* discard ref obtained in find_memory_block() */
465 	}
466 
467 	if (mem_blk)
468 		kobject_put(&mem_blk->dev.kobj);
469 	return err;
470 }
471 
472 #ifdef CONFIG_HUGETLBFS
473 /*
474  * Handle per node hstate attribute [un]registration on transistions
475  * to/from memoryless state.
476  */
477 static void node_hugetlb_work(struct work_struct *work)
478 {
479 	struct node *node = container_of(work, struct node, node_work);
480 
481 	/*
482 	 * We only get here when a node transitions to/from memoryless state.
483 	 * We can detect which transition occurred by examining whether the
484 	 * node has memory now.  hugetlb_register_node() already check this
485 	 * so we try to register the attributes.  If that fails, then the
486 	 * node has transitioned to memoryless, try to unregister the
487 	 * attributes.
488 	 */
489 	if (!hugetlb_register_node(node))
490 		hugetlb_unregister_node(node);
491 }
492 
493 static void init_node_hugetlb_work(int nid)
494 {
495 	INIT_WORK(&node_devices[nid].node_work, node_hugetlb_work);
496 }
497 
498 static int node_memory_callback(struct notifier_block *self,
499 				unsigned long action, void *arg)
500 {
501 	struct memory_notify *mnb = arg;
502 	int nid = mnb->status_change_nid;
503 
504 	switch (action) {
505 	case MEM_ONLINE:
506 	case MEM_OFFLINE:
507 		/*
508 		 * offload per node hstate [un]registration to a work thread
509 		 * when transitioning to/from memoryless state.
510 		 */
511 		if (nid != NUMA_NO_NODE)
512 			schedule_work(&node_devices[nid].node_work);
513 		break;
514 
515 	case MEM_GOING_ONLINE:
516 	case MEM_GOING_OFFLINE:
517 	case MEM_CANCEL_ONLINE:
518 	case MEM_CANCEL_OFFLINE:
519 	default:
520 		break;
521 	}
522 
523 	return NOTIFY_OK;
524 }
525 #endif	/* CONFIG_HUGETLBFS */
526 #else	/* !CONFIG_MEMORY_HOTPLUG_SPARSE */
527 
528 static int link_mem_sections(int nid) { return 0; }
529 #endif	/* CONFIG_MEMORY_HOTPLUG_SPARSE */
530 
531 #if !defined(CONFIG_MEMORY_HOTPLUG_SPARSE) || \
532     !defined(CONFIG_HUGETLBFS)
533 static inline int node_memory_callback(struct notifier_block *self,
534 				unsigned long action, void *arg)
535 {
536 	return NOTIFY_OK;
537 }
538 
539 static void init_node_hugetlb_work(int nid) { }
540 
541 #endif
542 
543 int register_one_node(int nid)
544 {
545 	int error = 0;
546 	int cpu;
547 
548 	if (node_online(nid)) {
549 		int p_node = parent_node(nid);
550 		struct node *parent = NULL;
551 
552 		if (p_node != nid)
553 			parent = &node_devices[p_node];
554 
555 		error = register_node(&node_devices[nid], nid, parent);
556 
557 		/* link cpu under this node */
558 		for_each_present_cpu(cpu) {
559 			if (cpu_to_node(cpu) == nid)
560 				register_cpu_under_node(cpu, nid);
561 		}
562 
563 		/* link memory sections under this node */
564 		error = link_mem_sections(nid);
565 
566 		/* initialize work queue for memory hot plug */
567 		init_node_hugetlb_work(nid);
568 	}
569 
570 	return error;
571 
572 }
573 
574 void unregister_one_node(int nid)
575 {
576 	unregister_node(&node_devices[nid]);
577 }
578 
579 /*
580  * node states attributes
581  */
582 
583 static ssize_t print_nodes_state(enum node_states state, char *buf)
584 {
585 	int n;
586 
587 	n = nodelist_scnprintf(buf, PAGE_SIZE, node_states[state]);
588 	if (n > 0 && PAGE_SIZE > n + 1) {
589 		*(buf + n++) = '\n';
590 		*(buf + n++) = '\0';
591 	}
592 	return n;
593 }
594 
595 struct node_attr {
596 	struct device_attribute attr;
597 	enum node_states state;
598 };
599 
600 static ssize_t show_node_state(struct device *dev,
601 			       struct device_attribute *attr, char *buf)
602 {
603 	struct node_attr *na = container_of(attr, struct node_attr, attr);
604 	return print_nodes_state(na->state, buf);
605 }
606 
607 #define _NODE_ATTR(name, state) \
608 	{ __ATTR(name, 0444, show_node_state, NULL), state }
609 
610 static struct node_attr node_state_attr[] = {
611 	_NODE_ATTR(possible, N_POSSIBLE),
612 	_NODE_ATTR(online, N_ONLINE),
613 	_NODE_ATTR(has_normal_memory, N_NORMAL_MEMORY),
614 	_NODE_ATTR(has_cpu, N_CPU),
615 #ifdef CONFIG_HIGHMEM
616 	_NODE_ATTR(has_high_memory, N_HIGH_MEMORY),
617 #endif
618 };
619 
620 static struct attribute *node_state_attrs[] = {
621 	&node_state_attr[0].attr.attr,
622 	&node_state_attr[1].attr.attr,
623 	&node_state_attr[2].attr.attr,
624 	&node_state_attr[3].attr.attr,
625 #ifdef CONFIG_HIGHMEM
626 	&node_state_attr[4].attr.attr,
627 #endif
628 	NULL
629 };
630 
631 static struct attribute_group memory_root_attr_group = {
632 	.attrs = node_state_attrs,
633 };
634 
635 static const struct attribute_group *cpu_root_attr_groups[] = {
636 	&memory_root_attr_group,
637 	NULL,
638 };
639 
640 #define NODE_CALLBACK_PRI	2	/* lower than SLAB */
641 static int __init register_node_type(void)
642 {
643 	int ret;
644 
645  	BUILD_BUG_ON(ARRAY_SIZE(node_state_attr) != NR_NODE_STATES);
646  	BUILD_BUG_ON(ARRAY_SIZE(node_state_attrs)-1 != NR_NODE_STATES);
647 
648 	ret = subsys_system_register(&node_subsys, cpu_root_attr_groups);
649 	if (!ret) {
650 		hotplug_memory_notifier(node_memory_callback,
651 					NODE_CALLBACK_PRI);
652 	}
653 
654 	/*
655 	 * Note:  we're not going to unregister the node class if we fail
656 	 * to register the node state class attribute files.
657 	 */
658 	return ret;
659 }
660 postcore_initcall(register_node_type);
661