drivers/base/memory.c

   1 /*
   2  * Memory subsystem support
   3  *
   4  * Written by Matt Tolentino <matthew.e.tolentino@intel.com>
   5  *            Dave Hansen <haveblue@us.ibm.com>
   6  *
   7  * This file provides the necessary infrastructure to represent
   8  * a SPARSEMEM-memory-model system's physical memory in /sysfs.
   9  * All arch-independent code that assumes MEMORY_HOTPLUG requires
  10  * SPARSEMEM should be contained here, or in mm/memory_hotplug.c.
  11  */
  12
  13 #include <linux/module.h>
  14 #include <linux/init.h>
  15 #include <linux/topology.h>
  16 #include <linux/capability.h>
  17 #include <linux/device.h>
  18 #include <linux/memory.h>
  19 #include <linux/kobject.h>
  20 #include <linux/memory_hotplug.h>
  21 #include <linux/mm.h>
  22 #include <linux/mutex.h>
  23 #include <linux/stat.h>
  24 #include <linux/slab.h>
  25
  26 #include <linux/atomic.h>
  27 #include <asm/uaccess.h>
  28
  29 static DEFINE_MUTEX(mem_sysfs_mutex);
  30
  31 #define MEMORY_CLASS_NAME       "memory"
  32
  33 static int sections_per_block;
  34
  35 static inline int base_memory_block_id(int section_nr)
  36 {
  37         return section_nr / sections_per_block;
  38 }
  39
  40 static struct bus_type memory_subsys = {
  41         .name = MEMORY_CLASS_NAME,
  42         .dev_name = MEMORY_CLASS_NAME,
  43 };
  44
  45 static BLOCKING_NOTIFIER_HEAD(memory_chain);
  46
  47 int register_memory_notifier(struct notifier_block *nb)
  48 {
  49         return blocking_notifier_chain_register(&memory_chain, nb);
  50 }
  51 EXPORT_SYMBOL(register_memory_notifier);
  52
  53 void unregister_memory_notifier(struct notifier_block *nb)
  54 {
  55         blocking_notifier_chain_unregister(&memory_chain, nb);
  56 }
  57 EXPORT_SYMBOL(unregister_memory_notifier);
  58
  59 static ATOMIC_NOTIFIER_HEAD(memory_isolate_chain);
  60
  61 int register_memory_isolate_notifier(struct notifier_block *nb)
  62 {
  63         return atomic_notifier_chain_register(&memory_isolate_chain, nb);
  64 }
  65 EXPORT_SYMBOL(register_memory_isolate_notifier);
  66
  67 void unregister_memory_isolate_notifier(struct notifier_block *nb)
  68 {
  69         atomic_notifier_chain_unregister(&memory_isolate_chain, nb);
  70 }
  71 EXPORT_SYMBOL(unregister_memory_isolate_notifier);
  72
  73 static void memory_block_release(struct device *dev)
  74 {
  75         struct memory_block *mem = container_of(dev, struct memory_block, dev);
  76
  77         kfree(mem);
  78 }
  79
  80 /*
  81  * register_memory - Setup a sysfs device for a memory block
  82  */
  83 static
  84 int register_memory(struct memory_block *memory)
  85 {
  86         int error;
  87
  88         memory->dev.bus = &memory_subsys;
  89         memory->dev.id = memory->start_section_nr / sections_per_block;
  90         memory->dev.release = memory_block_release;
  91
  92         error = device_register(&memory->dev);
  93         return error;
  94 }
  95
  96 unsigned long __weak memory_block_size_bytes(void)
  97 {
  98         return MIN_MEMORY_BLOCK_SIZE;
  99 }
 100
 101 static unsigned long get_memory_block_size(void)
 102 {
 103         unsigned long block_sz;
 104
 105         block_sz = memory_block_size_bytes();
 106
 107         /* Validate blk_sz is a power of 2 and not less than section size */
 108         if ((block_sz & (block_sz - 1)) || (block_sz < MIN_MEMORY_BLOCK_SIZE)) {
 109                 WARN_ON(1);
 110                 block_sz = MIN_MEMORY_BLOCK_SIZE;
 111         }
 112
 113         return block_sz;
 114 }
 115
 116 /*
 117  * use this as the physical section index that this memsection
 118  * uses.
 119  */
 120
 121 static ssize_t show_mem_start_phys_index(struct device *dev,
 122                         struct device_attribute *attr, char *buf)
 123 {
 124         struct memory_block *mem =
 125                 container_of(dev, struct memory_block, dev);
 126         unsigned long phys_index;
 127
 128         phys_index = mem->start_section_nr / sections_per_block;
 129         return sprintf(buf, "%08lx\n", phys_index);
 130 }
 131
 132 static ssize_t show_mem_end_phys_index(struct device *dev,
 133                         struct device_attribute *attr, char *buf)
 134 {
 135         struct memory_block *mem =
 136                 container_of(dev, struct memory_block, dev);
 137         unsigned long phys_index;
 138
 139         phys_index = mem->end_section_nr / sections_per_block;
 140         return sprintf(buf, "%08lx\n", phys_index);
 141 }
 142
 143 /*
 144  * Show whether the section of memory is likely to be hot-removable
 145  */
 146 static ssize_t show_mem_removable(struct device *dev,
 147                         struct device_attribute *attr, char *buf)
 148 {
 149         unsigned long i, pfn;
 150         int ret = 1;
 151         struct memory_block *mem =
 152                 container_of(dev, struct memory_block, dev);
 153
 154         for (i = 0; i < sections_per_block; i++) {
 155                 pfn = section_nr_to_pfn(mem->start_section_nr + i);
 156                 ret &= is_mem_section_removable(pfn, PAGES_PER_SECTION);
 157         }
 158
 159         return sprintf(buf, "%d\n", ret);
 160 }
 161
 162 /*
 163  * online, offline, going offline, etc.
 164  */
 165 static ssize_t show_mem_state(struct device *dev,
 166                         struct device_attribute *attr, char *buf)
 167 {
 168         struct memory_block *mem =
 169                 container_of(dev, struct memory_block, dev);
 170         ssize_t len = 0;
 171
 172         /*
 173          * We can probably put these states in a nice little array
 174          * so that they're not open-coded
 175          */
 176         switch (mem->state) {
 177                 case MEM_ONLINE:
 178                         len = sprintf(buf, "online\n");
 179                         break;
 180                 case MEM_OFFLINE:
 181                         len = sprintf(buf, "offline\n");
 182                         break;
 183                 case MEM_GOING_OFFLINE:
 184                         len = sprintf(buf, "going-offline\n");
 185                         break;
 186                 default:
 187                         len = sprintf(buf, "ERROR-UNKNOWN-%ld\n",
 188                                         mem->state);
 189                         WARN_ON(1);
 190                         break;
 191         }
 192
 193         return len;
 194 }
 195
 196 int memory_notify(unsigned long val, void *v)
 197 {
 198         return blocking_notifier_call_chain(&memory_chain, val, v);
 199 }
 200
 201 int memory_isolate_notify(unsigned long val, void *v)
 202 {
 203         return atomic_notifier_call_chain(&memory_isolate_chain, val, v);
 204 }
 205
 206 /*
 207  * The probe routines leave the pages reserved, just as the bootmem code does.
 208  * Make sure they're still that way.
 209  */
 210 static bool pages_correctly_reserved(unsigned long start_pfn,
 211                                         unsigned long nr_pages)
 212 {
 213         int i, j;
 214         struct page *page;
 215         unsigned long pfn = start_pfn;
 216
 217         /*
 218          * memmap between sections is not contiguous except with
 219          * SPARSEMEM_VMEMMAP. We lookup the page once per section
 220          * and assume memmap is contiguous within each section
 221          */
 222         for (i = 0; i < sections_per_block; i++, pfn += PAGES_PER_SECTION) {
 223                 if (WARN_ON_ONCE(!pfn_valid(pfn)))
 224                         return false;
 225                 page = pfn_to_page(pfn);
 226
 227                 for (j = 0; j < PAGES_PER_SECTION; j++) {
 228                         if (PageReserved(page + j))
 229                                 continue;
 230
 231                         printk(KERN_WARNING "section number %ld page number %d "
 232                                 "not reserved, was it already online?\n",
 233                                 pfn_to_section_nr(pfn), j);
 234
 235                         return false;
 236                 }
 237         }
 238
 239         return true;
 240 }
 241
 242 /*
 243  * MEMORY_HOTPLUG depends on SPARSEMEM in mm/Kconfig, so it is
 244  * OK to have direct references to sparsemem variables in here.
 245  */
 246 static int
 247 memory_block_action(unsigned long phys_index, unsigned long action, int online_type)
 248 {
 249         unsigned long start_pfn;
 250         unsigned long nr_pages = PAGES_PER_SECTION * sections_per_block;
 251         struct page *first_page;
 252         int ret;
 253
 254         first_page = pfn_to_page(phys_index << PFN_SECTION_SHIFT);
 255         start_pfn = page_to_pfn(first_page);
 256
 257         switch (action) {
 258                 case MEM_ONLINE:
 259                         if (!pages_correctly_reserved(start_pfn, nr_pages))
 260                                 return -EBUSY;
 261
 262                         ret = online_pages(start_pfn, nr_pages, online_type);
 263                         break;
 264                 case MEM_OFFLINE:
 265                         ret = offline_pages(start_pfn, nr_pages);
 266                         break;
 267                 default:
 268                         WARN(1, KERN_WARNING "%s(%ld, %ld) unknown action: "
 269                              "%ld\n", __func__, phys_index, action, action);
 270                         ret = -EINVAL;
 271         }
 272
 273         return ret;
 274 }
 275
 276 static int __memory_block_change_state(struct memory_block *mem,
 277                 unsigned long to_state, unsigned long from_state_req,
 278                 int online_type)
 279 {
 280         int ret = 0;
 281
 282         if (mem->state != from_state_req) {
 283                 ret = -EINVAL;
 284                 goto out;
 285         }
 286
 287         if (to_state == MEM_OFFLINE)
 288                 mem->state = MEM_GOING_OFFLINE;
 289
 290         ret = memory_block_action(mem->start_section_nr, to_state, online_type);
 291
 292         if (ret) {
 293                 mem->state = from_state_req;
 294                 goto out;
 295         }
 296
 297         mem->state = to_state;
 298         switch (mem->state) {
 299         case MEM_OFFLINE:
 300                 kobject_uevent(&mem->dev.kobj, KOBJ_OFFLINE);
 301                 break;
 302         case MEM_ONLINE:
 303                 kobject_uevent(&mem->dev.kobj, KOBJ_ONLINE);
 304                 break;
 305         default:
 306                 break;
 307         }
 308 out:
 309         return ret;
 310 }
 311
 312 static int memory_block_change_state(struct memory_block *mem,
 313                 unsigned long to_state, unsigned long from_state_req,
 314                 int online_type)
 315 {
 316         int ret;
 317
 318         mutex_lock(&mem->state_mutex);
 319         ret = __memory_block_change_state(mem, to_state, from_state_req,
 320                                           online_type);
 321         mutex_unlock(&mem->state_mutex);
 322
 323         return ret;
 324 }
 325 static ssize_t
 326 store_mem_state(struct device *dev,
 327                 struct device_attribute *attr, const char *buf, size_t count)
 328 {
 329         struct memory_block *mem;
 330         int ret = -EINVAL;
 331
 332         mem = container_of(dev, struct memory_block, dev);
 333
 334         if (!strncmp(buf, "online_kernel", min_t(int, count, 13)))
 335                 ret = memory_block_change_state(mem, MEM_ONLINE,
 336                                                 MEM_OFFLINE, ONLINE_KERNEL);
 337         else if (!strncmp(buf, "online_movable", min_t(int, count, 14)))
 338                 ret = memory_block_change_state(mem, MEM_ONLINE,
 339                                                 MEM_OFFLINE, ONLINE_MOVABLE);
 340         else if (!strncmp(buf, "online", min_t(int, count, 6)))
 341                 ret = memory_block_change_state(mem, MEM_ONLINE,
 342                                                 MEM_OFFLINE, ONLINE_KEEP);
 343         else if(!strncmp(buf, "offline", min_t(int, count, 7)))
 344                 ret = memory_block_change_state(mem, MEM_OFFLINE,
 345                                                 MEM_ONLINE, -1);
 346
 347         if (ret)
 348                 return ret;
 349         return count;
 350 }
 351
 352 /*
 353  * phys_device is a bad name for this.  What I really want
 354  * is a way to differentiate between memory ranges that
 355  * are part of physical devices that constitute
 356  * a complete removable unit or fru.
 357  * i.e. do these ranges belong to the same physical device,
 358  * s.t. if I offline all of these sections I can then
 359  * remove the physical device?
 360  */
 361 static ssize_t show_phys_device(struct device *dev,
 362                                 struct device_attribute *attr, char *buf)
 363 {
 364         struct memory_block *mem =
 365                 container_of(dev, struct memory_block, dev);
 366         return sprintf(buf, "%d\n", mem->phys_device);
 367 }
 368
 369 static DEVICE_ATTR(phys_index, 0444, show_mem_start_phys_index, NULL);
 370 static DEVICE_ATTR(end_phys_index, 0444, show_mem_end_phys_index, NULL);
 371 static DEVICE_ATTR(state, 0644, show_mem_state, store_mem_state);
 372 static DEVICE_ATTR(phys_device, 0444, show_phys_device, NULL);
 373 static DEVICE_ATTR(removable, 0444, show_mem_removable, NULL);
 374
 375 #define mem_create_simple_file(mem, attr_name)  \
 376         device_create_file(&mem->dev, &dev_attr_##attr_name)
 377 #define mem_remove_simple_file(mem, attr_name)  \
 378         device_remove_file(&mem->dev, &dev_attr_##attr_name)
 379
 380 /*
 381  * Block size attribute stuff
 382  */
 383 static ssize_t
 384 print_block_size(struct device *dev, struct device_attribute *attr,
 385                  char *buf)
 386 {
 387         return sprintf(buf, "%lx\n", get_memory_block_size());
 388 }
 389
 390 static DEVICE_ATTR(block_size_bytes, 0444, print_block_size, NULL);
 391
 392 static int block_size_init(void)
 393 {
 394         return device_create_file(memory_subsys.dev_root,
 395                                   &dev_attr_block_size_bytes);
 396 }
 397
 398 /*
 399  * Some architectures will have custom drivers to do this, and
 400  * will not need to do it from userspace.  The fake hot-add code
 401  * as well as ppc64 will do all of their discovery in userspace
 402  * and will require this interface.
 403  */
 404 #ifdef CONFIG_ARCH_MEMORY_PROBE
 405 static ssize_t
 406 memory_probe_store(struct device *dev, struct device_attribute *attr,
 407                    const char *buf, size_t count)
 408 {
 409         u64 phys_addr;
 410         int nid;
 411         int i, ret;
 412         unsigned long pages_per_block = PAGES_PER_SECTION * sections_per_block;
 413
 414         phys_addr = simple_strtoull(buf, NULL, 0);
 415
 416         if (phys_addr & ((pages_per_block << PAGE_SHIFT) - 1))
 417                 return -EINVAL;
 418
 419         for (i = 0; i < sections_per_block; i++) {
 420                 nid = memory_add_physaddr_to_nid(phys_addr);
 421                 ret = add_memory(nid, phys_addr,
 422                                  PAGES_PER_SECTION << PAGE_SHIFT);
 423                 if (ret)
 424                         goto out;
 425
 426                 phys_addr += MIN_MEMORY_BLOCK_SIZE;
 427         }
 428
 429         ret = count;
 430 out:
 431         return ret;
 432 }
 433 static DEVICE_ATTR(probe, S_IWUSR, NULL, memory_probe_store);
 434
 435 static int memory_probe_init(void)
 436 {
 437         return device_create_file(memory_subsys.dev_root, &dev_attr_probe);
 438 }
 439 #else
 440 static inline int memory_probe_init(void)
 441 {
 442         return 0;
 443 }
 444 #endif
 445
 446 #ifdef CONFIG_MEMORY_FAILURE
 447 /*
 448  * Support for offlining pages of memory
 449  */
 450
 451 /* Soft offline a page */
 452 static ssize_t
 453 store_soft_offline_page(struct device *dev,
 454                         struct device_attribute *attr,
 455                         const char *buf, size_t count)
 456 {
 457         int ret;
 458         u64 pfn;
 459         if (!capable(CAP_SYS_ADMIN))
 460                 return -EPERM;
 461         if (strict_strtoull(buf, 0, &pfn) < 0)
 462                 return -EINVAL;
 463         pfn >>= PAGE_SHIFT;
 464         if (!pfn_valid(pfn))
 465                 return -ENXIO;
 466         ret = soft_offline_page(pfn_to_page(pfn), 0);
 467         return ret == 0 ? count : ret;
 468 }
 469
 470 /* Forcibly offline a page, including killing processes. */
 471 static ssize_t
 472 store_hard_offline_page(struct device *dev,
 473                         struct device_attribute *attr,
 474                         const char *buf, size_t count)
 475 {
 476         int ret;
 477         u64 pfn;
 478         if (!capable(CAP_SYS_ADMIN))
 479                 return -EPERM;
 480         if (strict_strtoull(buf, 0, &pfn) < 0)
 481                 return -EINVAL;
 482         pfn >>= PAGE_SHIFT;
 483         ret = memory_failure(pfn, 0, 0);
 484         return ret ? ret : count;
 485 }
 486
 487 static DEVICE_ATTR(soft_offline_page, S_IWUSR, NULL, store_soft_offline_page);
 488 static DEVICE_ATTR(hard_offline_page, S_IWUSR, NULL, store_hard_offline_page);
 489
 490 static __init int memory_fail_init(void)
 491 {
 492         int err;
 493
 494         err = device_create_file(memory_subsys.dev_root,
 495                                 &dev_attr_soft_offline_page);
 496         if (!err)
 497                 err = device_create_file(memory_subsys.dev_root,
 498                                 &dev_attr_hard_offline_page);
 499         return err;
 500 }
 501 #else
 502 static inline int memory_fail_init(void)
 503 {
 504         return 0;
 505 }
 506 #endif
 507
 508 /*
 509  * Note that phys_device is optional.  It is here to allow for
 510  * differentiation between which *physical* devices each
 511  * section belongs to...
 512  */
 513 int __weak arch_get_memory_phys_device(unsigned long start_pfn)
 514 {
 515         return 0;
 516 }
 517
 518 /*
 519  * A reference for the returned object is held and the reference for the
 520  * hinted object is released.
 521  */
 522 struct memory_block *find_memory_block_hinted(struct mem_section *section,
 523                                               struct memory_block *hint)
 524 {
 525         int block_id = base_memory_block_id(__section_nr(section));
 526         struct device *hintdev = hint ? &hint->dev : NULL;
 527         struct device *dev;
 528
 529         dev = subsys_find_device_by_id(&memory_subsys, block_id, hintdev);
 530         if (hint)
 531                 put_device(&hint->dev);
 532         if (!dev)
 533                 return NULL;
 534         return container_of(dev, struct memory_block, dev);
 535 }
 536
 537 /*
 538  * For now, we have a linear search to go find the appropriate
 539  * memory_block corresponding to a particular phys_index. If
 540  * this gets to be a real problem, we can always use a radix
 541  * tree or something here.
 542  *
 543  * This could be made generic for all device subsystems.
 544  */
 545 struct memory_block *find_memory_block(struct mem_section *section)
 546 {
 547         return find_memory_block_hinted(section, NULL);
 548 }
 549
 550 static int init_memory_block(struct memory_block **memory,
 551                              struct mem_section *section, unsigned long state)
 552 {
 553         struct memory_block *mem;
 554         unsigned long start_pfn;
 555         int scn_nr;
 556         int ret = 0;
 557
 558         mem = kzalloc(sizeof(*mem), GFP_KERNEL);
 559         if (!mem)
 560                 return -ENOMEM;
 561
 562         scn_nr = __section_nr(section);
 563         mem->start_section_nr =
 564                         base_memory_block_id(scn_nr) * sections_per_block;
 565         mem->end_section_nr = mem->start_section_nr + sections_per_block - 1;
 566         mem->state = state;
 567         mem->section_count++;
 568         mutex_init(&mem->state_mutex);
 569         start_pfn = section_nr_to_pfn(mem->start_section_nr);
 570         mem->phys_device = arch_get_memory_phys_device(start_pfn);
 571
 572         ret = register_memory(mem);
 573         if (!ret)
 574                 ret = mem_create_simple_file(mem, phys_index);
 575         if (!ret)
 576                 ret = mem_create_simple_file(mem, end_phys_index);
 577         if (!ret)
 578                 ret = mem_create_simple_file(mem, state);
 579         if (!ret)
 580                 ret = mem_create_simple_file(mem, phys_device);
 581         if (!ret)
 582                 ret = mem_create_simple_file(mem, removable);
 583
 584         *memory = mem;
 585         return ret;
 586 }
 587
 588 static int add_memory_section(int nid, struct mem_section *section,
 589                         struct memory_block **mem_p,
 590                         unsigned long state, enum mem_add_context context)
 591 {
 592         struct memory_block *mem = NULL;
 593         int scn_nr = __section_nr(section);
 594         int ret = 0;
 595
 596         mutex_lock(&mem_sysfs_mutex);
 597
 598         if (context == BOOT) {
 599                 /* same memory block ? */
 600                 if (mem_p && *mem_p)
 601                         if (scn_nr >= (*mem_p)->start_section_nr &&
 602                             scn_nr <= (*mem_p)->end_section_nr) {
 603                                 mem = *mem_p;
 604                                 kobject_get(&mem->dev.kobj);
 605                         }
 606         } else
 607                 mem = find_memory_block(section);
 608
 609         if (mem) {
 610                 mem->section_count++;
 611                 kobject_put(&mem->dev.kobj);
 612         } else {
 613                 ret = init_memory_block(&mem, section, state);
 614                 /* store memory_block pointer for next loop */
 615                 if (!ret && context == BOOT)
 616                         if (mem_p)
 617                                 *mem_p = mem;
 618         }
 619
 620         if (!ret) {
 621                 if (context == HOTPLUG &&
 622                     mem->section_count == sections_per_block)
 623                         ret = register_mem_sect_under_node(mem, nid);
 624         }
 625
 626         mutex_unlock(&mem_sysfs_mutex);
 627         return ret;
 628 }
 629
 630 /*
 631  * need an interface for the VM to add new memory regions,
 632  * but without onlining it.
 633  */
 634 int register_new_memory(int nid, struct mem_section *section)
 635 {
 636         return add_memory_section(nid, section, NULL, MEM_OFFLINE, HOTPLUG);
 637 }
 638
 639 #ifdef CONFIG_MEMORY_HOTREMOVE
 640 static void
 641 unregister_memory(struct memory_block *memory)
 642 {
 643         BUG_ON(memory->dev.bus != &memory_subsys);
 644
 645         /* drop the ref. we got in remove_memory_block() */
 646         kobject_put(&memory->dev.kobj);
 647         device_unregister(&memory->dev);
 648 }
 649
 650 static int remove_memory_block(unsigned long node_id,
 651                                struct mem_section *section, int phys_device)
 652 {
 653         struct memory_block *mem;
 654
 655         mutex_lock(&mem_sysfs_mutex);
 656         mem = find_memory_block(section);
 657         unregister_mem_sect_under_nodes(mem, __section_nr(section));
 658
 659         mem->section_count--;
 660         if (mem->section_count == 0) {
 661                 mem_remove_simple_file(mem, phys_index);
 662                 mem_remove_simple_file(mem, end_phys_index);
 663                 mem_remove_simple_file(mem, state);
 664                 mem_remove_simple_file(mem, phys_device);
 665                 mem_remove_simple_file(mem, removable);
 666                 unregister_memory(mem);
 667         } else
 668                 kobject_put(&mem->dev.kobj);
 669
 670         mutex_unlock(&mem_sysfs_mutex);
 671         return 0;
 672 }
 673
 674 int unregister_memory_section(struct mem_section *section)
 675 {
 676         if (!present_section(section))
 677                 return -EINVAL;
 678
 679         return remove_memory_block(0, section, 0);
 680 }
 681 #endif /* CONFIG_MEMORY_HOTREMOVE */
 682
 683 /*
 684  * offline one memory block. If the memory block has been offlined, do nothing.
 685  */
 686 int offline_memory_block(struct memory_block *mem)
 687 {
 688         int ret = 0;
 689
 690         mutex_lock(&mem->state_mutex);
 691         if (mem->state != MEM_OFFLINE)
 692                 ret = __memory_block_change_state(mem, MEM_OFFLINE, MEM_ONLINE, -1);
 693         mutex_unlock(&mem->state_mutex);
 694
 695         return ret;
 696 }
 697
 698 /* return true if the memory block is offlined, otherwise, return false */
 699 bool is_memblock_offlined(struct memory_block *mem)
 700 {
 701         return mem->state == MEM_OFFLINE;
 702 }
 703
 704 /*
 705  * Initialize the sysfs support for memory devices...
 706  */
 707 int __init memory_dev_init(void)
 708 {
 709         unsigned int i;
 710         int ret;
 711         int err;
 712         unsigned long block_sz;
 713         struct memory_block *mem = NULL;
 714
 715         ret = subsys_system_register(&memory_subsys, NULL);
 716         if (ret)
 717                 goto out;
 718
 719         block_sz = get_memory_block_size();
 720         sections_per_block = block_sz / MIN_MEMORY_BLOCK_SIZE;
 721
 722         /*
 723          * Create entries for memory sections that were found
 724          * during boot and have been initialized
 725          */
 726         for (i = 0; i < NR_MEM_SECTIONS; i++) {
 727                 if (!present_section_nr(i))
 728                         continue;
 729                 /* don't need to reuse memory_block if only one per block */
 730                 err = add_memory_section(0, __nr_to_section(i),
 731                                  (sections_per_block == 1) ? NULL : &mem,
 732                                          MEM_ONLINE,
 733                                          BOOT);
 734                 if (!ret)
 735                         ret = err;
 736         }
 737
 738         err = memory_probe_init();
 739         if (!ret)
 740                 ret = err;
 741         err = memory_fail_init();
 742         if (!ret)
 743                 ret = err;
 744         err = block_size_init();
 745         if (!ret)
 746                 ret = err;
 747 out:
 748         if (ret)
 749                 printk(KERN_ERR "%s() failed: %d\n", __func__, ret);
 750         return ret;
 751 }