mm/page_owner.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 #include <linux/debugfs.h>
   3 #include <linux/mm.h>
   4 #include <linux/slab.h>
   5 #include <linux/uaccess.h>
   6 #include <linux/memblock.h>
   7 #include <linux/stacktrace.h>
   8 #include <linux/page_owner.h>
   9 #include <linux/jump_label.h>
  10 #include <linux/migrate.h>
  11 #include <linux/stackdepot.h>
  12 #include <linux/seq_file.h>
  13 #include <linux/memcontrol.h>
  14 #include <linux/sched/clock.h>
  15
  16 #include "internal.h"
  17
  18 /*
  19  * TODO: teach PAGE_OWNER_STACK_DEPTH (__dump_page_owner and save_stack)
  20  * to use off stack temporal storage
  21  */
  22 #define PAGE_OWNER_STACK_DEPTH (16)
  23
  24 struct page_owner {
  25         unsigned short order;
  26         short last_migrate_reason;
  27         gfp_t gfp_mask;
  28         depot_stack_handle_t handle;
  29         depot_stack_handle_t free_handle;
  30         u64 ts_nsec;
  31         u64 free_ts_nsec;
  32         char comm[TASK_COMM_LEN];
  33         pid_t pid;
  34         pid_t tgid;
  35 };
  36
  37 static bool page_owner_enabled = false;
  38 DEFINE_STATIC_KEY_FALSE(page_owner_inited);
  39
  40 static depot_stack_handle_t dummy_handle;
  41 static depot_stack_handle_t failure_handle;
  42 static depot_stack_handle_t early_handle;
  43
  44 static void init_early_allocated_pages(void);
  45
  46 static int __init early_page_owner_param(char *buf)
  47 {
  48         int ret = kstrtobool(buf, &page_owner_enabled);
  49
  50         if (page_owner_enabled)
  51                 stack_depot_want_early_init();
  52
  53         return ret;
  54 }
  55 early_param("page_owner", early_page_owner_param);
  56
  57 static __init bool need_page_owner(void)
  58 {
  59         return page_owner_enabled;
  60 }
  61
  62 static __always_inline depot_stack_handle_t create_dummy_stack(void)
  63 {
  64         unsigned long entries[4];
  65         unsigned int nr_entries;
  66
  67         nr_entries = stack_trace_save(entries, ARRAY_SIZE(entries), 0);
  68         return stack_depot_save(entries, nr_entries, GFP_KERNEL);
  69 }
  70
  71 static noinline void register_dummy_stack(void)
  72 {
  73         dummy_handle = create_dummy_stack();
  74 }
  75
  76 static noinline void register_failure_stack(void)
  77 {
  78         failure_handle = create_dummy_stack();
  79 }
  80
  81 static noinline void register_early_stack(void)
  82 {
  83         early_handle = create_dummy_stack();
  84 }
  85
  86 static __init void init_page_owner(void)
  87 {
  88         if (!page_owner_enabled)
  89                 return;
  90
  91         register_dummy_stack();
  92         register_failure_stack();
  93         register_early_stack();
  94         static_branch_enable(&page_owner_inited);
  95         init_early_allocated_pages();
  96 }
  97
  98 struct page_ext_operations page_owner_ops = {
  99         .size = sizeof(struct page_owner),
 100         .need = need_page_owner,
 101         .init = init_page_owner,
 102 };
 103
 104 static inline struct page_owner *get_page_owner(struct page_ext *page_ext)
 105 {
 106         return (void *)page_ext + page_owner_ops.offset;
 107 }
 108
 109 static noinline depot_stack_handle_t save_stack(gfp_t flags)
 110 {
 111         unsigned long entries[PAGE_OWNER_STACK_DEPTH];
 112         depot_stack_handle_t handle;
 113         unsigned int nr_entries;
 114
 115         /*
 116          * Avoid recursion.
 117          *
 118          * Sometimes page metadata allocation tracking requires more
 119          * memory to be allocated:
 120          * - when new stack trace is saved to stack depot
 121          * - when backtrace itself is calculated (ia64)
 122          */
 123         if (current->in_page_owner)
 124                 return dummy_handle;
 125         current->in_page_owner = 1;
 126
 127         nr_entries = stack_trace_save(entries, ARRAY_SIZE(entries), 2);
 128         handle = stack_depot_save(entries, nr_entries, flags);
 129         if (!handle)
 130                 handle = failure_handle;
 131
 132         current->in_page_owner = 0;
 133         return handle;
 134 }
 135
 136 void __reset_page_owner(struct page *page, unsigned short order)
 137 {
 138         int i;
 139         struct page_ext *page_ext;
 140         depot_stack_handle_t handle;
 141         struct page_owner *page_owner;
 142         u64 free_ts_nsec = local_clock();
 143
 144         page_ext = lookup_page_ext(page);
 145         if (unlikely(!page_ext))
 146                 return;
 147
 148         handle = save_stack(GFP_NOWAIT | __GFP_NOWARN);
 149         for (i = 0; i < (1 << order); i++) {
 150                 __clear_bit(PAGE_EXT_OWNER_ALLOCATED, &page_ext->flags);
 151                 page_owner = get_page_owner(page_ext);
 152                 page_owner->free_handle = handle;
 153                 page_owner->free_ts_nsec = free_ts_nsec;
 154                 page_ext = page_ext_next(page_ext);
 155         }
 156 }
 157
 158 static inline void __set_page_owner_handle(struct page_ext *page_ext,
 159                                         depot_stack_handle_t handle,
 160                                         unsigned short order, gfp_t gfp_mask)
 161 {
 162         struct page_owner *page_owner;
 163         int i;
 164
 165         for (i = 0; i < (1 << order); i++) {
 166                 page_owner = get_page_owner(page_ext);
 167                 page_owner->handle = handle;
 168                 page_owner->order = order;
 169                 page_owner->gfp_mask = gfp_mask;
 170                 page_owner->last_migrate_reason = -1;
 171                 page_owner->pid = current->pid;
 172                 page_owner->tgid = current->tgid;
 173                 page_owner->ts_nsec = local_clock();
 174                 strlcpy(page_owner->comm, current->comm,
 175                         sizeof(page_owner->comm));
 176                 __set_bit(PAGE_EXT_OWNER, &page_ext->flags);
 177                 __set_bit(PAGE_EXT_OWNER_ALLOCATED, &page_ext->flags);
 178
 179                 page_ext = page_ext_next(page_ext);
 180         }
 181 }
 182
 183 noinline void __set_page_owner(struct page *page, unsigned short order,
 184                                         gfp_t gfp_mask)
 185 {
 186         struct page_ext *page_ext = lookup_page_ext(page);
 187         depot_stack_handle_t handle;
 188
 189         if (unlikely(!page_ext))
 190                 return;
 191
 192         handle = save_stack(gfp_mask);
 193         __set_page_owner_handle(page_ext, handle, order, gfp_mask);
 194 }
 195
 196 void __set_page_owner_migrate_reason(struct page *page, int reason)
 197 {
 198         struct page_ext *page_ext = lookup_page_ext(page);
 199         struct page_owner *page_owner;
 200
 201         if (unlikely(!page_ext))
 202                 return;
 203
 204         page_owner = get_page_owner(page_ext);
 205         page_owner->last_migrate_reason = reason;
 206 }
 207
 208 void __split_page_owner(struct page *page, unsigned int nr)
 209 {
 210         int i;
 211         struct page_ext *page_ext = lookup_page_ext(page);
 212         struct page_owner *page_owner;
 213
 214         if (unlikely(!page_ext))
 215                 return;
 216
 217         for (i = 0; i < nr; i++) {
 218                 page_owner = get_page_owner(page_ext);
 219                 page_owner->order = 0;
 220                 page_ext = page_ext_next(page_ext);
 221         }
 222 }
 223
 224 void __folio_copy_owner(struct folio *newfolio, struct folio *old)
 225 {
 226         struct page_ext *old_ext = lookup_page_ext(&old->page);
 227         struct page_ext *new_ext = lookup_page_ext(&newfolio->page);
 228         struct page_owner *old_page_owner, *new_page_owner;
 229
 230         if (unlikely(!old_ext || !new_ext))
 231                 return;
 232
 233         old_page_owner = get_page_owner(old_ext);
 234         new_page_owner = get_page_owner(new_ext);
 235         new_page_owner->order = old_page_owner->order;
 236         new_page_owner->gfp_mask = old_page_owner->gfp_mask;
 237         new_page_owner->last_migrate_reason =
 238                 old_page_owner->last_migrate_reason;
 239         new_page_owner->handle = old_page_owner->handle;
 240         new_page_owner->pid = old_page_owner->pid;
 241         new_page_owner->tgid = old_page_owner->tgid;
 242         new_page_owner->ts_nsec = old_page_owner->ts_nsec;
 243         new_page_owner->free_ts_nsec = old_page_owner->ts_nsec;
 244         strcpy(new_page_owner->comm, old_page_owner->comm);
 245
 246         /*
 247          * We don't clear the bit on the old folio as it's going to be freed
 248          * after migration. Until then, the info can be useful in case of
 249          * a bug, and the overall stats will be off a bit only temporarily.
 250          * Also, migrate_misplaced_transhuge_page() can still fail the
 251          * migration and then we want the old folio to retain the info. But
 252          * in that case we also don't need to explicitly clear the info from
 253          * the new page, which will be freed.
 254          */
 255         __set_bit(PAGE_EXT_OWNER, &new_ext->flags);
 256         __set_bit(PAGE_EXT_OWNER_ALLOCATED, &new_ext->flags);
 257 }
 258
 259 void pagetypeinfo_showmixedcount_print(struct seq_file *m,
 260                                        pg_data_t *pgdat, struct zone *zone)
 261 {
 262         struct page *page;
 263         struct page_ext *page_ext;
 264         struct page_owner *page_owner;
 265         unsigned long pfn, block_end_pfn;
 266         unsigned long end_pfn = zone_end_pfn(zone);
 267         unsigned long count[MIGRATE_TYPES] = { 0, };
 268         int pageblock_mt, page_mt;
 269         int i;
 270
 271         /* Scan block by block. First and last block may be incomplete */
 272         pfn = zone->zone_start_pfn;
 273
 274         /*
 275          * Walk the zone in pageblock_nr_pages steps. If a page block spans
 276          * a zone boundary, it will be double counted between zones. This does
 277          * not matter as the mixed block count will still be correct
 278          */
 279         for (; pfn < end_pfn; ) {
 280                 page = pfn_to_online_page(pfn);
 281                 if (!page) {
 282                         pfn = ALIGN(pfn + 1, MAX_ORDER_NR_PAGES);
 283                         continue;
 284                 }
 285
 286                 block_end_pfn = ALIGN(pfn + 1, pageblock_nr_pages);
 287                 block_end_pfn = min(block_end_pfn, end_pfn);
 288
 289                 pageblock_mt = get_pageblock_migratetype(page);
 290
 291                 for (; pfn < block_end_pfn; pfn++) {
 292                         /* The pageblock is online, no need to recheck. */
 293                         page = pfn_to_page(pfn);
 294
 295                         if (page_zone(page) != zone)
 296                                 continue;
 297
 298                         if (PageBuddy(page)) {
 299                                 unsigned long freepage_order;
 300
 301                                 freepage_order = buddy_order_unsafe(page);
 302                                 if (freepage_order < MAX_ORDER)
 303                                         pfn += (1UL << freepage_order) - 1;
 304                                 continue;
 305                         }
 306
 307                         if (PageReserved(page))
 308                                 continue;
 309
 310                         page_ext = lookup_page_ext(page);
 311                         if (unlikely(!page_ext))
 312                                 continue;
 313
 314                         if (!test_bit(PAGE_EXT_OWNER_ALLOCATED, &page_ext->flags))
 315                                 continue;
 316
 317                         page_owner = get_page_owner(page_ext);
 318                         page_mt = gfp_migratetype(page_owner->gfp_mask);
 319                         if (pageblock_mt != page_mt) {
 320                                 if (is_migrate_cma(pageblock_mt))
 321                                         count[MIGRATE_MOVABLE]++;
 322                                 else
 323                                         count[pageblock_mt]++;
 324
 325                                 pfn = block_end_pfn;
 326                                 break;
 327                         }
 328                         pfn += (1UL << page_owner->order) - 1;
 329                 }
 330         }
 331
 332         /* Print counts */
 333         seq_printf(m, "Node %d, zone %8s ", pgdat->node_id, zone->name);
 334         for (i = 0; i < MIGRATE_TYPES; i++)
 335                 seq_printf(m, "%12lu ", count[i]);
 336         seq_putc(m, '\n');
 337 }
 338
 339 /*
 340  * Looking for memcg information and print it out
 341  */
 342 static inline int print_page_owner_memcg(char *kbuf, size_t count, int ret,
 343                                          struct page *page)
 344 {
 345 #ifdef CONFIG_MEMCG
 346         unsigned long memcg_data;
 347         struct mem_cgroup *memcg;
 348         bool online;
 349         char name[80];
 350
 351         rcu_read_lock();
 352         memcg_data = READ_ONCE(page->memcg_data);
 353         if (!memcg_data)
 354                 goto out_unlock;
 355
 356         if (memcg_data & MEMCG_DATA_OBJCGS)
 357                 ret += scnprintf(kbuf + ret, count - ret,
 358                                 "Slab cache page\n");
 359
 360         memcg = page_memcg_check(page);
 361         if (!memcg)
 362                 goto out_unlock;
 363
 364         online = (memcg->css.flags & CSS_ONLINE);
 365         cgroup_name(memcg->css.cgroup, name, sizeof(name));
 366         ret += scnprintf(kbuf + ret, count - ret,
 367                         "Charged %sto %smemcg %s\n",
 368                         PageMemcgKmem(page) ? "(via objcg) " : "",
 369                         online ? "" : "offline ",
 370                         name);
 371 out_unlock:
 372         rcu_read_unlock();
 373 #endif /* CONFIG_MEMCG */
 374
 375         return ret;
 376 }
 377
 378 static ssize_t
 379 print_page_owner(char __user *buf, size_t count, unsigned long pfn,
 380                 struct page *page, struct page_owner *page_owner,
 381                 depot_stack_handle_t handle)
 382 {
 383         int ret, pageblock_mt, page_mt;
 384         char *kbuf;
 385
 386         count = min_t(size_t, count, PAGE_SIZE);
 387         kbuf = kmalloc(count, GFP_KERNEL);
 388         if (!kbuf)
 389                 return -ENOMEM;
 390
 391         ret = scnprintf(kbuf, count,
 392                         "Page allocated via order %u, mask %#x(%pGg), pid %d, tgid %d (%s), ts %llu ns, free_ts %llu ns\n",
 393                         page_owner->order, page_owner->gfp_mask,
 394                         &page_owner->gfp_mask, page_owner->pid,
 395                         page_owner->tgid, page_owner->comm,
 396                         page_owner->ts_nsec, page_owner->free_ts_nsec);
 397
 398         /* Print information relevant to grouping pages by mobility */
 399         pageblock_mt = get_pageblock_migratetype(page);
 400         page_mt  = gfp_migratetype(page_owner->gfp_mask);
 401         ret += scnprintf(kbuf + ret, count - ret,
 402                         "PFN %lu type %s Block %lu type %s Flags %pGp\n",
 403                         pfn,
 404                         migratetype_names[page_mt],
 405                         pfn >> pageblock_order,
 406                         migratetype_names[pageblock_mt],
 407                         &page->flags);
 408
 409         ret += stack_depot_snprint(handle, kbuf + ret, count - ret, 0);
 410         if (ret >= count)
 411                 goto err;
 412
 413         if (page_owner->last_migrate_reason != -1) {
 414                 ret += scnprintf(kbuf + ret, count - ret,
 415                         "Page has been migrated, last migrate reason: %s\n",
 416                         migrate_reason_names[page_owner->last_migrate_reason]);
 417         }
 418
 419         ret = print_page_owner_memcg(kbuf, count, ret, page);
 420
 421         ret += snprintf(kbuf + ret, count - ret, "\n");
 422         if (ret >= count)
 423                 goto err;
 424
 425         if (copy_to_user(buf, kbuf, ret))
 426                 ret = -EFAULT;
 427
 428         kfree(kbuf);
 429         return ret;
 430
 431 err:
 432         kfree(kbuf);
 433         return -ENOMEM;
 434 }
 435
 436 void __dump_page_owner(const struct page *page)
 437 {
 438         struct page_ext *page_ext = lookup_page_ext(page);
 439         struct page_owner *page_owner;
 440         depot_stack_handle_t handle;
 441         gfp_t gfp_mask;
 442         int mt;
 443
 444         if (unlikely(!page_ext)) {
 445                 pr_alert("There is not page extension available.\n");
 446                 return;
 447         }
 448
 449         page_owner = get_page_owner(page_ext);
 450         gfp_mask = page_owner->gfp_mask;
 451         mt = gfp_migratetype(gfp_mask);
 452
 453         if (!test_bit(PAGE_EXT_OWNER, &page_ext->flags)) {
 454                 pr_alert("page_owner info is not present (never set?)\n");
 455                 return;
 456         }
 457
 458         if (test_bit(PAGE_EXT_OWNER_ALLOCATED, &page_ext->flags))
 459                 pr_alert("page_owner tracks the page as allocated\n");
 460         else
 461                 pr_alert("page_owner tracks the page as freed\n");
 462
 463         pr_alert("page last allocated via order %u, migratetype %s, gfp_mask %#x(%pGg), pid %d, tgid %d (%s), ts %llu, free_ts %llu\n",
 464                  page_owner->order, migratetype_names[mt], gfp_mask, &gfp_mask,
 465                  page_owner->pid, page_owner->tgid, page_owner->comm,
 466                  page_owner->ts_nsec, page_owner->free_ts_nsec);
 467
 468         handle = READ_ONCE(page_owner->handle);
 469         if (!handle)
 470                 pr_alert("page_owner allocation stack trace missing\n");
 471         else
 472                 stack_depot_print(handle);
 473
 474         handle = READ_ONCE(page_owner->free_handle);
 475         if (!handle) {
 476                 pr_alert("page_owner free stack trace missing\n");
 477         } else {
 478                 pr_alert("page last free stack trace:\n");
 479                 stack_depot_print(handle);
 480         }
 481
 482         if (page_owner->last_migrate_reason != -1)
 483                 pr_alert("page has been migrated, last migrate reason: %s\n",
 484                         migrate_reason_names[page_owner->last_migrate_reason]);
 485 }
 486
 487 static ssize_t
 488 read_page_owner(struct file *file, char __user *buf, size_t count, loff_t *ppos)
 489 {
 490         unsigned long pfn;
 491         struct page *page;
 492         struct page_ext *page_ext;
 493         struct page_owner *page_owner;
 494         depot_stack_handle_t handle;
 495
 496         if (!static_branch_unlikely(&page_owner_inited))
 497                 return -EINVAL;
 498
 499         page = NULL;
 500         pfn = min_low_pfn + *ppos;
 501
 502         /* Find a valid PFN or the start of a MAX_ORDER_NR_PAGES area */
 503         while (!pfn_valid(pfn) && (pfn & (MAX_ORDER_NR_PAGES - 1)) != 0)
 504                 pfn++;
 505
 506         drain_all_pages(NULL);
 507
 508         /* Find an allocated page */
 509         for (; pfn < max_pfn; pfn++) {
 510                 /*
 511                  * If the new page is in a new MAX_ORDER_NR_PAGES area,
 512                  * validate the area as existing, skip it if not
 513                  */
 514                 if ((pfn & (MAX_ORDER_NR_PAGES - 1)) == 0 && !pfn_valid(pfn)) {
 515                         pfn += MAX_ORDER_NR_PAGES - 1;
 516                         continue;
 517                 }
 518
 519                 page = pfn_to_page(pfn);
 520                 if (PageBuddy(page)) {
 521                         unsigned long freepage_order = buddy_order_unsafe(page);
 522
 523                         if (freepage_order < MAX_ORDER)
 524                                 pfn += (1UL << freepage_order) - 1;
 525                         continue;
 526                 }
 527
 528                 page_ext = lookup_page_ext(page);
 529                 if (unlikely(!page_ext))
 530                         continue;
 531
 532                 /*
 533                  * Some pages could be missed by concurrent allocation or free,
 534                  * because we don't hold the zone lock.
 535                  */
 536                 if (!test_bit(PAGE_EXT_OWNER, &page_ext->flags))
 537                         continue;
 538
 539                 /*
 540                  * Although we do have the info about past allocation of free
 541                  * pages, it's not relevant for current memory usage.
 542                  */
 543                 if (!test_bit(PAGE_EXT_OWNER_ALLOCATED, &page_ext->flags))
 544                         continue;
 545
 546                 page_owner = get_page_owner(page_ext);
 547
 548                 /*
 549                  * Don't print "tail" pages of high-order allocations as that
 550                  * would inflate the stats.
 551                  */
 552                 if (!IS_ALIGNED(pfn, 1 << page_owner->order))
 553                         continue;
 554
 555                 /*
 556                  * Access to page_ext->handle isn't synchronous so we should
 557                  * be careful to access it.
 558                  */
 559                 handle = READ_ONCE(page_owner->handle);
 560                 if (!handle)
 561                         continue;
 562
 563                 /* Record the next PFN to read in the file offset */
 564                 *ppos = (pfn - min_low_pfn) + 1;
 565
 566                 return print_page_owner(buf, count, pfn, page,
 567                                 page_owner, handle);
 568         }
 569
 570         return 0;
 571 }
 572
 573 static void init_pages_in_zone(pg_data_t *pgdat, struct zone *zone)
 574 {
 575         unsigned long pfn = zone->zone_start_pfn;
 576         unsigned long end_pfn = zone_end_pfn(zone);
 577         unsigned long count = 0;
 578
 579         /*
 580          * Walk the zone in pageblock_nr_pages steps. If a page block spans
 581          * a zone boundary, it will be double counted between zones. This does
 582          * not matter as the mixed block count will still be correct
 583          */
 584         for (; pfn < end_pfn; ) {
 585                 unsigned long block_end_pfn;
 586
 587                 if (!pfn_valid(pfn)) {
 588                         pfn = ALIGN(pfn + 1, MAX_ORDER_NR_PAGES);
 589                         continue;
 590                 }
 591
 592                 block_end_pfn = ALIGN(pfn + 1, pageblock_nr_pages);
 593                 block_end_pfn = min(block_end_pfn, end_pfn);
 594
 595                 for (; pfn < block_end_pfn; pfn++) {
 596                         struct page *page = pfn_to_page(pfn);
 597                         struct page_ext *page_ext;
 598
 599                         if (page_zone(page) != zone)
 600                                 continue;
 601
 602                         /*
 603                          * To avoid having to grab zone->lock, be a little
 604                          * careful when reading buddy page order. The only
 605                          * danger is that we skip too much and potentially miss
 606                          * some early allocated pages, which is better than
 607                          * heavy lock contention.
 608                          */
 609                         if (PageBuddy(page)) {
 610                                 unsigned long order = buddy_order_unsafe(page);
 611
 612                                 if (order > 0 && order < MAX_ORDER)
 613                                         pfn += (1UL << order) - 1;
 614                                 continue;
 615                         }
 616
 617                         if (PageReserved(page))
 618                                 continue;
 619
 620                         page_ext = lookup_page_ext(page);
 621                         if (unlikely(!page_ext))
 622                                 continue;
 623
 624                         /* Maybe overlapping zone */
 625                         if (test_bit(PAGE_EXT_OWNER, &page_ext->flags))
 626                                 continue;
 627
 628                         /* Found early allocated page */
 629                         __set_page_owner_handle(page_ext, early_handle,
 630                                                 0, 0);
 631                         count++;
 632                 }
 633                 cond_resched();
 634         }
 635
 636         pr_info("Node %d, zone %8s: page owner found early allocated %lu pages\n",
 637                 pgdat->node_id, zone->name, count);
 638 }
 639
 640 static void init_zones_in_node(pg_data_t *pgdat)
 641 {
 642         struct zone *zone;
 643         struct zone *node_zones = pgdat->node_zones;
 644
 645         for (zone = node_zones; zone - node_zones < MAX_NR_ZONES; ++zone) {
 646                 if (!populated_zone(zone))
 647                         continue;
 648
 649                 init_pages_in_zone(pgdat, zone);
 650         }
 651 }
 652
 653 static void init_early_allocated_pages(void)
 654 {
 655         pg_data_t *pgdat;
 656
 657         for_each_online_pgdat(pgdat)
 658                 init_zones_in_node(pgdat);
 659 }
 660
 661 static const struct file_operations proc_page_owner_operations = {
 662         .read           = read_page_owner,
 663 };
 664
 665 static int __init pageowner_init(void)
 666 {
 667         if (!static_branch_unlikely(&page_owner_inited)) {
 668                 pr_info("page_owner is disabled\n");
 669                 return 0;
 670         }
 671
 672         debugfs_create_file("page_owner", 0400, NULL, NULL,
 673                             &proc_page_owner_operations);
 674
 675         return 0;
 676 }
 677 late_initcall(pageowner_init)