mm/huge_memory.c

   1 /*
   2  *  Copyright (C) 2009  Red Hat, Inc.
   3  *
   4  *  This work is licensed under the terms of the GNU GPL, version 2. See
   5  *  the COPYING file in the top-level directory.
   6  */
   7
   8 #include <linux/mm.h>
   9 #include <linux/sched.h>
  10 #include <linux/highmem.h>
  11 #include <linux/hugetlb.h>
  12 #include <linux/mmu_notifier.h>
  13 #include <linux/rmap.h>
  14 #include <linux/swap.h>
  15 #include <linux/shrinker.h>
  16 #include <linux/mm_inline.h>
  17 #include <linux/kthread.h>
  18 #include <linux/khugepaged.h>
  19 #include <linux/freezer.h>
  20 #include <linux/mman.h>
  21 #include <linux/pagemap.h>
  22
  23 #include <asm/tlb.h>
  24 #include <asm/pgalloc.h>
  25 #include "internal.h"
  26
  27 /*
  28  * By default transparent hugepage support is enabled for all mappings
  29  * and khugepaged scans all mappings. Defrag is only invoked by
  30  * khugepaged hugepage allocations and by page faults inside
  31  * MADV_HUGEPAGE regions to avoid the risk of slowing down short lived
  32  * allocations.
  33  */
  34 unsigned long transparent_hugepage_flags __read_mostly =
  35 #ifdef CONFIG_TRANSPARENT_HUGEPAGE_ALWAYS
  36         (1<<TRANSPARENT_HUGEPAGE_FLAG)|
  37 #endif
  38 #ifdef CONFIG_TRANSPARENT_HUGEPAGE_MADVISE
  39         (1<<TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG)|
  40 #endif
  41         (1<<TRANSPARENT_HUGEPAGE_DEFRAG_FLAG)|
  42         (1<<TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG);
  43
  44 /* default scan 8*512 pte (or vmas) every 30 second */
  45 static unsigned int khugepaged_pages_to_scan __read_mostly = HPAGE_PMD_NR*8;
  46 static unsigned int khugepaged_pages_collapsed;
  47 static unsigned int khugepaged_full_scans;
  48 static unsigned int khugepaged_scan_sleep_millisecs __read_mostly = 10000;
  49 /* during fragmentation poll the hugepage allocator once every minute */
  50 static unsigned int khugepaged_alloc_sleep_millisecs __read_mostly = 60000;
  51 static struct task_struct *khugepaged_thread __read_mostly;
  52 static DEFINE_MUTEX(khugepaged_mutex);
  53 static DEFINE_SPINLOCK(khugepaged_mm_lock);
  54 static DECLARE_WAIT_QUEUE_HEAD(khugepaged_wait);
  55 /*
  56  * default collapse hugepages if there is at least one pte mapped like
  57  * it would have happened if the vma was large enough during page
  58  * fault.
  59  */
  60 static unsigned int khugepaged_max_ptes_none __read_mostly = HPAGE_PMD_NR-1;
  61
  62 static int khugepaged(void *none);
  63 static int mm_slots_hash_init(void);
  64 static int khugepaged_slab_init(void);
  65 static void khugepaged_slab_free(void);
  66
  67 #define MM_SLOTS_HASH_HEADS 1024
  68 static struct hlist_head *mm_slots_hash __read_mostly;
  69 static struct kmem_cache *mm_slot_cache __read_mostly;
  70
  71 /**
  72  * struct mm_slot - hash lookup from mm to mm_slot
  73  * @hash: hash collision list
  74  * @mm_node: khugepaged scan list headed in khugepaged_scan.mm_head
  75  * @mm: the mm that this information is valid for
  76  */
  77 struct mm_slot {
  78         struct hlist_node hash;
  79         struct list_head mm_node;
  80         struct mm_struct *mm;
  81 };
  82
  83 /**
  84  * struct khugepaged_scan - cursor for scanning
  85  * @mm_head: the head of the mm list to scan
  86  * @mm_slot: the current mm_slot we are scanning
  87  * @address: the next address inside that to be scanned
  88  *
  89  * There is only the one khugepaged_scan instance of this cursor structure.
  90  */
  91 struct khugepaged_scan {
  92         struct list_head mm_head;
  93         struct mm_slot *mm_slot;
  94         unsigned long address;
  95 };
  96 static struct khugepaged_scan khugepaged_scan = {
  97         .mm_head = LIST_HEAD_INIT(khugepaged_scan.mm_head),
  98 };
  99
 100
 101 static int set_recommended_min_free_kbytes(void)
 102 {
 103         struct zone *zone;
 104         int nr_zones = 0;
 105         unsigned long recommended_min;
 106         extern int min_free_kbytes;
 107
 108         if (!khugepaged_enabled())
 109                 return 0;
 110
 111         for_each_populated_zone(zone)
 112                 nr_zones++;
 113
 114         /* Make sure at least 2 hugepages are free for MIGRATE_RESERVE */
 115         recommended_min = pageblock_nr_pages * nr_zones * 2;
 116
 117         /*
 118          * Make sure that on average at least two pageblocks are almost free
 119          * of another type, one for a migratetype to fall back to and a
 120          * second to avoid subsequent fallbacks of other types There are 3
 121          * MIGRATE_TYPES we care about.
 122          */
 123         recommended_min += pageblock_nr_pages * nr_zones *
 124                            MIGRATE_PCPTYPES * MIGRATE_PCPTYPES;
 125
 126         /* don't ever allow to reserve more than 5% of the lowmem */
 127         recommended_min = min(recommended_min,
 128                               (unsigned long) nr_free_buffer_pages() / 20);
 129         recommended_min <<= (PAGE_SHIFT-10);
 130
 131         if (recommended_min > min_free_kbytes)
 132                 min_free_kbytes = recommended_min;
 133         setup_per_zone_wmarks();
 134         return 0;
 135 }
 136 late_initcall(set_recommended_min_free_kbytes);
 137
 138 static int start_khugepaged(void)
 139 {
 140         int err = 0;
 141         if (khugepaged_enabled()) {
 142                 if (!khugepaged_thread)
 143                         khugepaged_thread = kthread_run(khugepaged, NULL,
 144                                                         "khugepaged");
 145                 if (unlikely(IS_ERR(khugepaged_thread))) {
 146                         printk(KERN_ERR
 147                                "khugepaged: kthread_run(khugepaged) failed\n");
 148                         err = PTR_ERR(khugepaged_thread);
 149                         khugepaged_thread = NULL;
 150                 }
 151
 152                 if (!list_empty(&khugepaged_scan.mm_head))
 153                         wake_up_interruptible(&khugepaged_wait);
 154
 155                 set_recommended_min_free_kbytes();
 156         } else if (khugepaged_thread) {
 157                 kthread_stop(khugepaged_thread);
 158                 khugepaged_thread = NULL;
 159         }
 160
 161         return err;
 162 }
 163
 164 static atomic_t huge_zero_refcount;
 165 static unsigned long huge_zero_pfn __read_mostly;
 166
 167 static inline bool is_huge_zero_pfn(unsigned long pfn)
 168 {
 169         unsigned long zero_pfn = ACCESS_ONCE(huge_zero_pfn);
 170         return zero_pfn && pfn == zero_pfn;
 171 }
 172
 173 static inline bool is_huge_zero_pmd(pmd_t pmd)
 174 {
 175         return is_huge_zero_pfn(pmd_pfn(pmd));
 176 }
 177
 178 static unsigned long get_huge_zero_page(void)
 179 {
 180         struct page *zero_page;
 181 retry:
 182         if (likely(atomic_inc_not_zero(&huge_zero_refcount)))
 183                 return ACCESS_ONCE(huge_zero_pfn);
 184
 185         zero_page = alloc_pages((GFP_TRANSHUGE | __GFP_ZERO) & ~__GFP_MOVABLE,
 186                         HPAGE_PMD_ORDER);
 187         if (!zero_page)
 188                 return 0;
 189         preempt_disable();
 190         if (cmpxchg(&huge_zero_pfn, 0, page_to_pfn(zero_page))) {
 191                 preempt_enable();
 192                 __free_page(zero_page);
 193                 goto retry;
 194         }
 195
 196         /* We take additional reference here. It will be put back by shrinker */
 197         atomic_set(&huge_zero_refcount, 2);
 198         preempt_enable();
 199         return ACCESS_ONCE(huge_zero_pfn);
 200 }
 201
 202 static void put_huge_zero_page(void)
 203 {
 204         /*
 205          * Counter should never go to zero here. Only shrinker can put
 206          * last reference.
 207          */
 208         BUG_ON(atomic_dec_and_test(&huge_zero_refcount));
 209 }
 210
 211 static int shrink_huge_zero_page(struct shrinker *shrink,
 212                 struct shrink_control *sc)
 213 {
 214         if (!sc->nr_to_scan)
 215                 /* we can free zero page only if last reference remains */
 216                 return atomic_read(&huge_zero_refcount) == 1 ? HPAGE_PMD_NR : 0;
 217
 218         if (atomic_cmpxchg(&huge_zero_refcount, 1, 0) == 1) {
 219                 unsigned long zero_pfn = xchg(&huge_zero_pfn, 0);
 220                 BUG_ON(zero_pfn == 0);
 221                 __free_page(__pfn_to_page(zero_pfn));
 222         }
 223
 224         return 0;
 225 }
 226
 227 static struct shrinker huge_zero_page_shrinker = {
 228         .shrink = shrink_huge_zero_page,
 229         .seeks = DEFAULT_SEEKS,
 230 };
 231
 232 #ifdef CONFIG_SYSFS
 233
 234 static ssize_t double_flag_show(struct kobject *kobj,
 235                                 struct kobj_attribute *attr, char *buf,
 236                                 enum transparent_hugepage_flag enabled,
 237                                 enum transparent_hugepage_flag req_madv)
 238 {
 239         if (test_bit(enabled, &transparent_hugepage_flags)) {
 240                 VM_BUG_ON(test_bit(req_madv, &transparent_hugepage_flags));
 241                 return sprintf(buf, "[always] madvise never\n");
 242         } else if (test_bit(req_madv, &transparent_hugepage_flags))
 243                 return sprintf(buf, "always [madvise] never\n");
 244         else
 245                 return sprintf(buf, "always madvise [never]\n");
 246 }
 247 static ssize_t double_flag_store(struct kobject *kobj,
 248                                  struct kobj_attribute *attr,
 249                                  const char *buf, size_t count,
 250                                  enum transparent_hugepage_flag enabled,
 251                                  enum transparent_hugepage_flag req_madv)
 252 {
 253         if (!memcmp("always", buf,
 254                     min(sizeof("always")-1, count))) {
 255                 set_bit(enabled, &transparent_hugepage_flags);
 256                 clear_bit(req_madv, &transparent_hugepage_flags);
 257         } else if (!memcmp("madvise", buf,
 258                            min(sizeof("madvise")-1, count))) {
 259                 clear_bit(enabled, &transparent_hugepage_flags);
 260                 set_bit(req_madv, &transparent_hugepage_flags);
 261         } else if (!memcmp("never", buf,
 262                            min(sizeof("never")-1, count))) {
 263                 clear_bit(enabled, &transparent_hugepage_flags);
 264                 clear_bit(req_madv, &transparent_hugepage_flags);
 265         } else
 266                 return -EINVAL;
 267
 268         return count;
 269 }
 270
 271 static ssize_t enabled_show(struct kobject *kobj,
 272                             struct kobj_attribute *attr, char *buf)
 273 {
 274         return double_flag_show(kobj, attr, buf,
 275                                 TRANSPARENT_HUGEPAGE_FLAG,
 276                                 TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG);
 277 }
 278 static ssize_t enabled_store(struct kobject *kobj,
 279                              struct kobj_attribute *attr,
 280                              const char *buf, size_t count)
 281 {
 282         ssize_t ret;
 283
 284         ret = double_flag_store(kobj, attr, buf, count,
 285                                 TRANSPARENT_HUGEPAGE_FLAG,
 286                                 TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG);
 287
 288         if (ret > 0) {
 289                 int err;
 290
 291                 mutex_lock(&khugepaged_mutex);
 292                 err = start_khugepaged();
 293                 mutex_unlock(&khugepaged_mutex);
 294
 295                 if (err)
 296                         ret = err;
 297         }
 298
 299         return ret;
 300 }
 301 static struct kobj_attribute enabled_attr =
 302         __ATTR(enabled, 0644, enabled_show, enabled_store);
 303
 304 static ssize_t single_flag_show(struct kobject *kobj,
 305                                 struct kobj_attribute *attr, char *buf,
 306                                 enum transparent_hugepage_flag flag)
 307 {
 308         return sprintf(buf, "%d\n",
 309                        !!test_bit(flag, &transparent_hugepage_flags));
 310 }
 311
 312 static ssize_t single_flag_store(struct kobject *kobj,
 313                                  struct kobj_attribute *attr,
 314                                  const char *buf, size_t count,
 315                                  enum transparent_hugepage_flag flag)
 316 {
 317         unsigned long value;
 318         int ret;
 319
 320         ret = kstrtoul(buf, 10, &value);
 321         if (ret < 0)
 322                 return ret;
 323         if (value > 1)
 324                 return -EINVAL;
 325
 326         if (value)
 327                 set_bit(flag, &transparent_hugepage_flags);
 328         else
 329                 clear_bit(flag, &transparent_hugepage_flags);
 330
 331         return count;
 332 }
 333
 334 /*
 335  * Currently defrag only disables __GFP_NOWAIT for allocation. A blind
 336  * __GFP_REPEAT is too aggressive, it's never worth swapping tons of
 337  * memory just to allocate one more hugepage.
 338  */
 339 static ssize_t defrag_show(struct kobject *kobj,
 340                            struct kobj_attribute *attr, char *buf)
 341 {
 342         return double_flag_show(kobj, attr, buf,
 343                                 TRANSPARENT_HUGEPAGE_DEFRAG_FLAG,
 344                                 TRANSPARENT_HUGEPAGE_DEFRAG_REQ_MADV_FLAG);
 345 }
 346 static ssize_t defrag_store(struct kobject *kobj,
 347                             struct kobj_attribute *attr,
 348                             const char *buf, size_t count)
 349 {
 350         return double_flag_store(kobj, attr, buf, count,
 351                                  TRANSPARENT_HUGEPAGE_DEFRAG_FLAG,
 352                                  TRANSPARENT_HUGEPAGE_DEFRAG_REQ_MADV_FLAG);
 353 }
 354 static struct kobj_attribute defrag_attr =
 355         __ATTR(defrag, 0644, defrag_show, defrag_store);
 356
 357 #ifdef CONFIG_DEBUG_VM
 358 static ssize_t debug_cow_show(struct kobject *kobj,
 359                                 struct kobj_attribute *attr, char *buf)
 360 {
 361         return single_flag_show(kobj, attr, buf,
 362                                 TRANSPARENT_HUGEPAGE_DEBUG_COW_FLAG);
 363 }
 364 static ssize_t debug_cow_store(struct kobject *kobj,
 365                                struct kobj_attribute *attr,
 366                                const char *buf, size_t count)
 367 {
 368         return single_flag_store(kobj, attr, buf, count,
 369                                  TRANSPARENT_HUGEPAGE_DEBUG_COW_FLAG);
 370 }
 371 static struct kobj_attribute debug_cow_attr =
 372         __ATTR(debug_cow, 0644, debug_cow_show, debug_cow_store);
 373 #endif /* CONFIG_DEBUG_VM */
 374
 375 static struct attribute *hugepage_attr[] = {
 376         &enabled_attr.attr,
 377         &defrag_attr.attr,
 378 #ifdef CONFIG_DEBUG_VM
 379         &debug_cow_attr.attr,
 380 #endif
 381         NULL,
 382 };
 383
 384 static struct attribute_group hugepage_attr_group = {
 385         .attrs = hugepage_attr,
 386 };
 387
 388 static ssize_t scan_sleep_millisecs_show(struct kobject *kobj,
 389                                          struct kobj_attribute *attr,
 390                                          char *buf)
 391 {
 392         return sprintf(buf, "%u\n", khugepaged_scan_sleep_millisecs);
 393 }
 394
 395 static ssize_t scan_sleep_millisecs_store(struct kobject *kobj,
 396                                           struct kobj_attribute *attr,
 397                                           const char *buf, size_t count)
 398 {
 399         unsigned long msecs;
 400         int err;
 401
 402         err = strict_strtoul(buf, 10, &msecs);
 403         if (err || msecs > UINT_MAX)
 404                 return -EINVAL;
 405
 406         khugepaged_scan_sleep_millisecs = msecs;
 407         wake_up_interruptible(&khugepaged_wait);
 408
 409         return count;
 410 }
 411 static struct kobj_attribute scan_sleep_millisecs_attr =
 412         __ATTR(scan_sleep_millisecs, 0644, scan_sleep_millisecs_show,
 413                scan_sleep_millisecs_store);
 414
 415 static ssize_t alloc_sleep_millisecs_show(struct kobject *kobj,
 416                                           struct kobj_attribute *attr,
 417                                           char *buf)
 418 {
 419         return sprintf(buf, "%u\n", khugepaged_alloc_sleep_millisecs);
 420 }
 421
 422 static ssize_t alloc_sleep_millisecs_store(struct kobject *kobj,
 423                                            struct kobj_attribute *attr,
 424                                            const char *buf, size_t count)
 425 {
 426         unsigned long msecs;
 427         int err;
 428
 429         err = strict_strtoul(buf, 10, &msecs);
 430         if (err || msecs > UINT_MAX)
 431                 return -EINVAL;
 432
 433         khugepaged_alloc_sleep_millisecs = msecs;
 434         wake_up_interruptible(&khugepaged_wait);
 435
 436         return count;
 437 }
 438 static struct kobj_attribute alloc_sleep_millisecs_attr =
 439         __ATTR(alloc_sleep_millisecs, 0644, alloc_sleep_millisecs_show,
 440                alloc_sleep_millisecs_store);
 441
 442 static ssize_t pages_to_scan_show(struct kobject *kobj,
 443                                   struct kobj_attribute *attr,
 444                                   char *buf)
 445 {
 446         return sprintf(buf, "%u\n", khugepaged_pages_to_scan);
 447 }
 448 static ssize_t pages_to_scan_store(struct kobject *kobj,
 449                                    struct kobj_attribute *attr,
 450                                    const char *buf, size_t count)
 451 {
 452         int err;
 453         unsigned long pages;
 454
 455         err = strict_strtoul(buf, 10, &pages);
 456         if (err || !pages || pages > UINT_MAX)
 457                 return -EINVAL;
 458
 459         khugepaged_pages_to_scan = pages;
 460
 461         return count;
 462 }
 463 static struct kobj_attribute pages_to_scan_attr =
 464         __ATTR(pages_to_scan, 0644, pages_to_scan_show,
 465                pages_to_scan_store);
 466
 467 static ssize_t pages_collapsed_show(struct kobject *kobj,
 468                                     struct kobj_attribute *attr,
 469                                     char *buf)
 470 {
 471         return sprintf(buf, "%u\n", khugepaged_pages_collapsed);
 472 }
 473 static struct kobj_attribute pages_collapsed_attr =
 474         __ATTR_RO(pages_collapsed);
 475
 476 static ssize_t full_scans_show(struct kobject *kobj,
 477                                struct kobj_attribute *attr,
 478                                char *buf)
 479 {
 480         return sprintf(buf, "%u\n", khugepaged_full_scans);
 481 }
 482 static struct kobj_attribute full_scans_attr =
 483         __ATTR_RO(full_scans);
 484
 485 static ssize_t khugepaged_defrag_show(struct kobject *kobj,
 486                                       struct kobj_attribute *attr, char *buf)
 487 {
 488         return single_flag_show(kobj, attr, buf,
 489                                 TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG);
 490 }
 491 static ssize_t khugepaged_defrag_store(struct kobject *kobj,
 492                                        struct kobj_attribute *attr,
 493                                        const char *buf, size_t count)
 494 {
 495         return single_flag_store(kobj, attr, buf, count,
 496                                  TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG);
 497 }
 498 static struct kobj_attribute khugepaged_defrag_attr =
 499         __ATTR(defrag, 0644, khugepaged_defrag_show,
 500                khugepaged_defrag_store);
 501
 502 /*
 503  * max_ptes_none controls if khugepaged should collapse hugepages over
 504  * any unmapped ptes in turn potentially increasing the memory
 505  * footprint of the vmas. When max_ptes_none is 0 khugepaged will not
 506  * reduce the available free memory in the system as it
 507  * runs. Increasing max_ptes_none will instead potentially reduce the
 508  * free memory in the system during the khugepaged scan.
 509  */
 510 static ssize_t khugepaged_max_ptes_none_show(struct kobject *kobj,
 511                                              struct kobj_attribute *attr,
 512                                              char *buf)
 513 {
 514         return sprintf(buf, "%u\n", khugepaged_max_ptes_none);
 515 }
 516 static ssize_t khugepaged_max_ptes_none_store(struct kobject *kobj,
 517                                               struct kobj_attribute *attr,
 518                                               const char *buf, size_t count)
 519 {
 520         int err;
 521         unsigned long max_ptes_none;
 522
 523         err = strict_strtoul(buf, 10, &max_ptes_none);
 524         if (err || max_ptes_none > HPAGE_PMD_NR-1)
 525                 return -EINVAL;
 526
 527         khugepaged_max_ptes_none = max_ptes_none;
 528
 529         return count;
 530 }
 531 static struct kobj_attribute khugepaged_max_ptes_none_attr =
 532         __ATTR(max_ptes_none, 0644, khugepaged_max_ptes_none_show,
 533                khugepaged_max_ptes_none_store);
 534
 535 static struct attribute *khugepaged_attr[] = {
 536         &khugepaged_defrag_attr.attr,
 537         &khugepaged_max_ptes_none_attr.attr,
 538         &pages_to_scan_attr.attr,
 539         &pages_collapsed_attr.attr,
 540         &full_scans_attr.attr,
 541         &scan_sleep_millisecs_attr.attr,
 542         &alloc_sleep_millisecs_attr.attr,
 543         NULL,
 544 };
 545
 546 static struct attribute_group khugepaged_attr_group = {
 547         .attrs = khugepaged_attr,
 548         .name = "khugepaged",
 549 };
 550
 551 static int __init hugepage_init_sysfs(struct kobject **hugepage_kobj)
 552 {
 553         int err;
 554
 555         *hugepage_kobj = kobject_create_and_add("transparent_hugepage", mm_kobj);
 556         if (unlikely(!*hugepage_kobj)) {
 557                 printk(KERN_ERR "hugepage: failed kobject create\n");
 558                 return -ENOMEM;
 559         }
 560
 561         err = sysfs_create_group(*hugepage_kobj, &hugepage_attr_group);
 562         if (err) {
 563                 printk(KERN_ERR "hugepage: failed register hugeage group\n");
 564                 goto delete_obj;
 565         }
 566
 567         err = sysfs_create_group(*hugepage_kobj, &khugepaged_attr_group);
 568         if (err) {
 569                 printk(KERN_ERR "hugepage: failed register hugeage group\n");
 570                 goto remove_hp_group;
 571         }
 572
 573         return 0;
 574
 575 remove_hp_group:
 576         sysfs_remove_group(*hugepage_kobj, &hugepage_attr_group);
 577 delete_obj:
 578         kobject_put(*hugepage_kobj);
 579         return err;
 580 }
 581
 582 static void __init hugepage_exit_sysfs(struct kobject *hugepage_kobj)
 583 {
 584         sysfs_remove_group(hugepage_kobj, &khugepaged_attr_group);
 585         sysfs_remove_group(hugepage_kobj, &hugepage_attr_group);
 586         kobject_put(hugepage_kobj);
 587 }
 588 #else
 589 static inline int hugepage_init_sysfs(struct kobject **hugepage_kobj)
 590 {
 591         return 0;
 592 }
 593
 594 static inline void hugepage_exit_sysfs(struct kobject *hugepage_kobj)
 595 {
 596 }
 597 #endif /* CONFIG_SYSFS */
 598
 599 static int __init hugepage_init(void)
 600 {
 601         int err;
 602         struct kobject *hugepage_kobj;
 603
 604         if (!has_transparent_hugepage()) {
 605                 transparent_hugepage_flags = 0;
 606                 return -EINVAL;
 607         }
 608
 609         err = hugepage_init_sysfs(&hugepage_kobj);
 610         if (err)
 611                 return err;
 612
 613         err = khugepaged_slab_init();
 614         if (err)
 615                 goto out;
 616
 617         err = mm_slots_hash_init();
 618         if (err) {
 619                 khugepaged_slab_free();
 620                 goto out;
 621         }
 622
 623         register_shrinker(&huge_zero_page_shrinker);
 624
 625         /*
 626          * By default disable transparent hugepages on smaller systems,
 627          * where the extra memory used could hurt more than TLB overhead
 628          * is likely to save.  The admin can still enable it through /sys.
 629          */
 630         if (totalram_pages < (512 << (20 - PAGE_SHIFT)))
 631                 transparent_hugepage_flags = 0;
 632
 633         start_khugepaged();
 634
 635         return 0;
 636 out:
 637         hugepage_exit_sysfs(hugepage_kobj);
 638         return err;
 639 }
 640 module_init(hugepage_init)
 641
 642 static int __init setup_transparent_hugepage(char *str)
 643 {
 644         int ret = 0;
 645         if (!str)
 646                 goto out;
 647         if (!strcmp(str, "always")) {
 648                 set_bit(TRANSPARENT_HUGEPAGE_FLAG,
 649                         &transparent_hugepage_flags);
 650                 clear_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG,
 651                           &transparent_hugepage_flags);
 652                 ret = 1;
 653         } else if (!strcmp(str, "madvise")) {
 654                 clear_bit(TRANSPARENT_HUGEPAGE_FLAG,
 655                           &transparent_hugepage_flags);
 656                 set_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG,
 657                         &transparent_hugepage_flags);
 658                 ret = 1;
 659         } else if (!strcmp(str, "never")) {
 660                 clear_bit(TRANSPARENT_HUGEPAGE_FLAG,
 661                           &transparent_hugepage_flags);
 662                 clear_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG,
 663                           &transparent_hugepage_flags);
 664                 ret = 1;
 665         }
 666 out:
 667         if (!ret)
 668                 printk(KERN_WARNING
 669                        "transparent_hugepage= cannot parse, ignored\n");
 670         return ret;
 671 }
 672 __setup("transparent_hugepage=", setup_transparent_hugepage);
 673
 674 static inline pmd_t maybe_pmd_mkwrite(pmd_t pmd, struct vm_area_struct *vma)
 675 {
 676         if (likely(vma->vm_flags & VM_WRITE))
 677                 pmd = pmd_mkwrite(pmd);
 678         return pmd;
 679 }
 680
 681 static inline pmd_t mk_huge_pmd(struct page *page, struct vm_area_struct *vma)
 682 {
 683         pmd_t entry;
 684         entry = mk_pmd(page, vma->vm_page_prot);
 685         entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
 686         entry = pmd_mkhuge(entry);
 687         return entry;
 688 }
 689
 690 static int __do_huge_pmd_anonymous_page(struct mm_struct *mm,
 691                                         struct vm_area_struct *vma,
 692                                         unsigned long haddr, pmd_t *pmd,
 693                                         struct page *page)
 694 {
 695         pgtable_t pgtable;
 696
 697         VM_BUG_ON(!PageCompound(page));
 698         pgtable = pte_alloc_one(mm, haddr);
 699         if (unlikely(!pgtable))
 700                 return VM_FAULT_OOM;
 701
 702         clear_huge_page(page, haddr, HPAGE_PMD_NR);
 703         __SetPageUptodate(page);
 704
 705         spin_lock(&mm->page_table_lock);
 706         if (unlikely(!pmd_none(*pmd))) {
 707                 spin_unlock(&mm->page_table_lock);
 708                 mem_cgroup_uncharge_page(page);
 709                 put_page(page);
 710                 pte_free(mm, pgtable);
 711         } else {
 712                 pmd_t entry;
 713                 entry = mk_huge_pmd(page, vma);
 714                 /*
 715                  * The spinlocking to take the lru_lock inside
 716                  * page_add_new_anon_rmap() acts as a full memory
 717                  * barrier to be sure clear_huge_page writes become
 718                  * visible after the set_pmd_at() write.
 719                  */
 720                 page_add_new_anon_rmap(page, vma, haddr);
 721                 set_pmd_at(mm, haddr, pmd, entry);
 722                 pgtable_trans_huge_deposit(mm, pgtable);
 723                 add_mm_counter(mm, MM_ANONPAGES, HPAGE_PMD_NR);
 724                 mm->nr_ptes++;
 725                 spin_unlock(&mm->page_table_lock);
 726         }
 727
 728         return 0;
 729 }
 730
 731 static inline gfp_t alloc_hugepage_gfpmask(int defrag, gfp_t extra_gfp)
 732 {
 733         return (GFP_TRANSHUGE & ~(defrag ? 0 : __GFP_WAIT)) | extra_gfp;
 734 }
 735
 736 static inline struct page *alloc_hugepage_vma(int defrag,
 737                                               struct vm_area_struct *vma,
 738                                               unsigned long haddr, int nd,
 739                                               gfp_t extra_gfp)
 740 {
 741         return alloc_pages_vma(alloc_hugepage_gfpmask(defrag, extra_gfp),
 742                                HPAGE_PMD_ORDER, vma, haddr, nd);
 743 }
 744
 745 #ifndef CONFIG_NUMA
 746 static inline struct page *alloc_hugepage(int defrag)
 747 {
 748         return alloc_pages(alloc_hugepage_gfpmask(defrag, 0),
 749                            HPAGE_PMD_ORDER);
 750 }
 751 #endif
 752
 753 static void set_huge_zero_page(pgtable_t pgtable, struct mm_struct *mm,
 754                 struct vm_area_struct *vma, unsigned long haddr, pmd_t *pmd,
 755                 unsigned long zero_pfn)
 756 {
 757         pmd_t entry;
 758         entry = pfn_pmd(zero_pfn, vma->vm_page_prot);
 759         entry = pmd_wrprotect(entry);
 760         entry = pmd_mkhuge(entry);
 761         set_pmd_at(mm, haddr, pmd, entry);
 762         pgtable_trans_huge_deposit(mm, pgtable);
 763         mm->nr_ptes++;
 764 }
 765
 766 int do_huge_pmd_anonymous_page(struct mm_struct *mm, struct vm_area_struct *vma,
 767                                unsigned long address, pmd_t *pmd,
 768                                unsigned int flags)
 769 {
 770         struct page *page;
 771         unsigned long haddr = address & HPAGE_PMD_MASK;
 772         pte_t *pte;
 773
 774         if (haddr >= vma->vm_start && haddr + HPAGE_PMD_SIZE <= vma->vm_end) {
 775                 if (unlikely(anon_vma_prepare(vma)))
 776                         return VM_FAULT_OOM;
 777                 if (unlikely(khugepaged_enter(vma)))
 778                         return VM_FAULT_OOM;
 779                 if (!(flags & FAULT_FLAG_WRITE)) {
 780                         pgtable_t pgtable;
 781                         unsigned long zero_pfn;
 782                         pgtable = pte_alloc_one(mm, haddr);
 783                         if (unlikely(!pgtable))
 784                                 return VM_FAULT_OOM;
 785                         zero_pfn = get_huge_zero_page();
 786                         if (unlikely(!zero_pfn)) {
 787                                 pte_free(mm, pgtable);
 788                                 count_vm_event(THP_FAULT_FALLBACK);
 789                                 goto out;
 790                         }
 791                         spin_lock(&mm->page_table_lock);
 792                         set_huge_zero_page(pgtable, mm, vma, haddr, pmd,
 793                                         zero_pfn);
 794                         spin_unlock(&mm->page_table_lock);
 795                         return 0;
 796                 }
 797                 page = alloc_hugepage_vma(transparent_hugepage_defrag(vma),
 798                                           vma, haddr, numa_node_id(), 0);
 799                 if (unlikely(!page)) {
 800                         count_vm_event(THP_FAULT_FALLBACK);
 801                         goto out;
 802                 }
 803                 count_vm_event(THP_FAULT_ALLOC);
 804                 if (unlikely(mem_cgroup_newpage_charge(page, mm, GFP_KERNEL))) {
 805                         put_page(page);
 806                         goto out;
 807                 }
 808                 if (unlikely(__do_huge_pmd_anonymous_page(mm, vma, haddr, pmd,
 809                                                           page))) {
 810                         mem_cgroup_uncharge_page(page);
 811                         put_page(page);
 812                         goto out;
 813                 }
 814
 815                 return 0;
 816         }
 817 out:
 818         /*
 819          * Use __pte_alloc instead of pte_alloc_map, because we can't
 820          * run pte_offset_map on the pmd, if an huge pmd could
 821          * materialize from under us from a different thread.
 822          */
 823         if (unlikely(__pte_alloc(mm, vma, pmd, address)))
 824                 return VM_FAULT_OOM;
 825         /* if an huge pmd materialized from under us just retry later */
 826         if (unlikely(pmd_trans_huge(*pmd)))
 827                 return 0;
 828         /*
 829          * A regular pmd is established and it can't morph into a huge pmd
 830          * from under us anymore at this point because we hold the mmap_sem
 831          * read mode and khugepaged takes it in write mode. So now it's
 832          * safe to run pte_offset_map().
 833          */
 834         pte = pte_offset_map(pmd, address);
 835         return handle_pte_fault(mm, vma, address, pte, pmd, flags);
 836 }
 837
 838 int copy_huge_pmd(struct mm_struct *dst_mm, struct mm_struct *src_mm,
 839                   pmd_t *dst_pmd, pmd_t *src_pmd, unsigned long addr,
 840                   struct vm_area_struct *vma)
 841 {
 842         struct page *src_page;
 843         pmd_t pmd;
 844         pgtable_t pgtable;
 845         int ret;
 846
 847         ret = -ENOMEM;
 848         pgtable = pte_alloc_one(dst_mm, addr);
 849         if (unlikely(!pgtable))
 850                 goto out;
 851
 852         spin_lock(&dst_mm->page_table_lock);
 853         spin_lock_nested(&src_mm->page_table_lock, SINGLE_DEPTH_NESTING);
 854
 855         ret = -EAGAIN;
 856         pmd = *src_pmd;
 857         if (unlikely(!pmd_trans_huge(pmd))) {
 858                 pte_free(dst_mm, pgtable);
 859                 goto out_unlock;
 860         }
 861         /*
 862          * mm->page_table_lock is enough to be sure that huge zero pmd is not
 863          * under splitting since we don't split the page itself, only pmd to
 864          * a page table.
 865          */
 866         if (is_huge_zero_pmd(pmd)) {
 867                 unsigned long zero_pfn;
 868                 /*
 869                  * get_huge_zero_page() will never allocate a new page here,
 870                  * since we already have a zero page to copy. It just takes a
 871                  * reference.
 872                  */
 873                 zero_pfn = get_huge_zero_page();
 874                 set_huge_zero_page(pgtable, dst_mm, vma, addr, dst_pmd,
 875                                 zero_pfn);
 876                 ret = 0;
 877                 goto out_unlock;
 878         }
 879         if (unlikely(pmd_trans_splitting(pmd))) {
 880                 /* split huge page running from under us */
 881                 spin_unlock(&src_mm->page_table_lock);
 882                 spin_unlock(&dst_mm->page_table_lock);
 883                 pte_free(dst_mm, pgtable);
 884
 885                 wait_split_huge_page(vma->anon_vma, src_pmd); /* src_vma */
 886                 goto out;
 887         }
 888         src_page = pmd_page(pmd);
 889         VM_BUG_ON(!PageHead(src_page));
 890         get_page(src_page);
 891         page_dup_rmap(src_page);
 892         add_mm_counter(dst_mm, MM_ANONPAGES, HPAGE_PMD_NR);
 893
 894         pmdp_set_wrprotect(src_mm, addr, src_pmd);
 895         pmd = pmd_mkold(pmd_wrprotect(pmd));
 896         set_pmd_at(dst_mm, addr, dst_pmd, pmd);
 897         pgtable_trans_huge_deposit(dst_mm, pgtable);
 898         dst_mm->nr_ptes++;
 899
 900         ret = 0;
 901 out_unlock:
 902         spin_unlock(&src_mm->page_table_lock);
 903         spin_unlock(&dst_mm->page_table_lock);
 904 out:
 905         return ret;
 906 }
 907
 908 void huge_pmd_set_accessed(struct mm_struct *mm,
 909                            struct vm_area_struct *vma,
 910                            unsigned long address,
 911                            pmd_t *pmd, pmd_t orig_pmd,
 912                            int dirty)
 913 {
 914         pmd_t entry;
 915         unsigned long haddr;
 916
 917         spin_lock(&mm->page_table_lock);
 918         if (unlikely(!pmd_same(*pmd, orig_pmd)))
 919                 goto unlock;
 920
 921         entry = pmd_mkyoung(orig_pmd);
 922         haddr = address & HPAGE_PMD_MASK;
 923         if (pmdp_set_access_flags(vma, haddr, pmd, entry, dirty))
 924                 update_mmu_cache_pmd(vma, address, pmd);
 925
 926 unlock:
 927         spin_unlock(&mm->page_table_lock);
 928 }
 929
 930 static int do_huge_pmd_wp_zero_page_fallback(struct mm_struct *mm,
 931                 struct vm_area_struct *vma, unsigned long address,
 932                 pmd_t *pmd, unsigned long haddr)
 933 {
 934         pgtable_t pgtable;
 935         pmd_t _pmd;
 936         struct page *page;
 937         int i, ret = 0;
 938         unsigned long mmun_start;       /* For mmu_notifiers */
 939         unsigned long mmun_end;         /* For mmu_notifiers */
 940
 941         page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma, address);
 942         if (!page) {
 943                 ret |= VM_FAULT_OOM;
 944                 goto out;
 945         }
 946
 947         if (mem_cgroup_newpage_charge(page, mm, GFP_KERNEL)) {
 948                 put_page(page);
 949                 ret |= VM_FAULT_OOM;
 950                 goto out;
 951         }
 952
 953         clear_user_highpage(page, address);
 954         __SetPageUptodate(page);
 955
 956         mmun_start = haddr;
 957         mmun_end   = haddr + HPAGE_PMD_SIZE;
 958         mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
 959
 960         spin_lock(&mm->page_table_lock);
 961         pmdp_clear_flush(vma, haddr, pmd);
 962         /* leave pmd empty until pte is filled */
 963
 964         pgtable = pgtable_trans_huge_withdraw(mm);
 965         pmd_populate(mm, &_pmd, pgtable);
 966
 967         for (i = 0; i < HPAGE_PMD_NR; i++, haddr += PAGE_SIZE) {
 968                 pte_t *pte, entry;
 969                 if (haddr == (address & PAGE_MASK)) {
 970                         entry = mk_pte(page, vma->vm_page_prot);
 971                         entry = maybe_mkwrite(pte_mkdirty(entry), vma);
 972                         page_add_new_anon_rmap(page, vma, haddr);
 973                 } else {
 974                         entry = pfn_pte(my_zero_pfn(haddr), vma->vm_page_prot);
 975                         entry = pte_mkspecial(entry);
 976                 }
 977                 pte = pte_offset_map(&_pmd, haddr);
 978                 VM_BUG_ON(!pte_none(*pte));
 979                 set_pte_at(mm, haddr, pte, entry);
 980                 pte_unmap(pte);
 981         }
 982         smp_wmb(); /* make pte visible before pmd */
 983         pmd_populate(mm, pmd, pgtable);
 984         spin_unlock(&mm->page_table_lock);
 985         put_huge_zero_page();
 986         inc_mm_counter(mm, MM_ANONPAGES);
 987
 988         mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
 989
 990         ret |= VM_FAULT_WRITE;
 991 out:
 992         return ret;
 993 }
 994
 995 static int do_huge_pmd_wp_page_fallback(struct mm_struct *mm,
 996                                         struct vm_area_struct *vma,
 997                                         unsigned long address,
 998                                         pmd_t *pmd, pmd_t orig_pmd,
 999                                         struct page *page,
1000                                         unsigned long haddr)
1001 {
1002         pgtable_t pgtable;
1003         pmd_t _pmd;
1004         int ret = 0, i;
1005         struct page **pages;
1006         unsigned long mmun_start;       /* For mmu_notifiers */
1007         unsigned long mmun_end;         /* For mmu_notifiers */
1008
1009         pages = kmalloc(sizeof(struct page *) * HPAGE_PMD_NR,
1010                         GFP_KERNEL);
1011         if (unlikely(!pages)) {
1012                 ret |= VM_FAULT_OOM;
1013                 goto out;
1014         }
1015
1016         for (i = 0; i < HPAGE_PMD_NR; i++) {
1017                 pages[i] = alloc_page_vma_node(GFP_HIGHUSER_MOVABLE |
1018                                                __GFP_OTHER_NODE,
1019                                                vma, address, page_to_nid(page));
1020                 if (unlikely(!pages[i] ||
1021                              mem_cgroup_newpage_charge(pages[i], mm,
1022                                                        GFP_KERNEL))) {
1023                         if (pages[i])
1024                                 put_page(pages[i]);
1025                         mem_cgroup_uncharge_start();
1026                         while (--i >= 0) {
1027                                 mem_cgroup_uncharge_page(pages[i]);
1028                                 put_page(pages[i]);
1029                         }
1030                         mem_cgroup_uncharge_end();
1031                         kfree(pages);
1032                         ret |= VM_FAULT_OOM;
1033                         goto out;
1034                 }
1035         }
1036
1037         for (i = 0; i < HPAGE_PMD_NR; i++) {
1038                 copy_user_highpage(pages[i], page + i,
1039                                    haddr + PAGE_SIZE * i, vma);
1040                 __SetPageUptodate(pages[i]);
1041                 cond_resched();
1042         }
1043
1044         mmun_start = haddr;
1045         mmun_end   = haddr + HPAGE_PMD_SIZE;
1046         mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
1047
1048         spin_lock(&mm->page_table_lock);
1049         if (unlikely(!pmd_same(*pmd, orig_pmd)))
1050                 goto out_free_pages;
1051         VM_BUG_ON(!PageHead(page));
1052
1053         pmdp_clear_flush(vma, haddr, pmd);
1054         /* leave pmd empty until pte is filled */
1055
1056         pgtable = pgtable_trans_huge_withdraw(mm);
1057         pmd_populate(mm, &_pmd, pgtable);
1058
1059         for (i = 0; i < HPAGE_PMD_NR; i++, haddr += PAGE_SIZE) {
1060                 pte_t *pte, entry;
1061                 entry = mk_pte(pages[i], vma->vm_page_prot);
1062                 entry = maybe_mkwrite(pte_mkdirty(entry), vma);
1063                 page_add_new_anon_rmap(pages[i], vma, haddr);
1064                 pte = pte_offset_map(&_pmd, haddr);
1065                 VM_BUG_ON(!pte_none(*pte));
1066                 set_pte_at(mm, haddr, pte, entry);
1067                 pte_unmap(pte);
1068         }
1069         kfree(pages);
1070
1071         smp_wmb(); /* make pte visible before pmd */
1072         pmd_populate(mm, pmd, pgtable);
1073         page_remove_rmap(page);
1074         spin_unlock(&mm->page_table_lock);
1075
1076         mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
1077
1078         ret |= VM_FAULT_WRITE;
1079         put_page(page);
1080
1081 out:
1082         return ret;
1083
1084 out_free_pages:
1085         spin_unlock(&mm->page_table_lock);
1086         mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
1087         mem_cgroup_uncharge_start();
1088         for (i = 0; i < HPAGE_PMD_NR; i++) {
1089                 mem_cgroup_uncharge_page(pages[i]);
1090                 put_page(pages[i]);
1091         }
1092         mem_cgroup_uncharge_end();
1093         kfree(pages);
1094         goto out;
1095 }
1096
1097 int do_huge_pmd_wp_page(struct mm_struct *mm, struct vm_area_struct *vma,
1098                         unsigned long address, pmd_t *pmd, pmd_t orig_pmd)
1099 {
1100         int ret = 0;
1101         struct page *page = NULL, *new_page;
1102         unsigned long haddr;
1103         unsigned long mmun_start;       /* For mmu_notifiers */
1104         unsigned long mmun_end;         /* For mmu_notifiers */
1105
1106         VM_BUG_ON(!vma->anon_vma);
1107         haddr = address & HPAGE_PMD_MASK;
1108         if (is_huge_zero_pmd(orig_pmd))
1109                 goto alloc;
1110         spin_lock(&mm->page_table_lock);
1111         if (unlikely(!pmd_same(*pmd, orig_pmd)))
1112                 goto out_unlock;
1113
1114         page = pmd_page(orig_pmd);
1115         VM_BUG_ON(!PageCompound(page) || !PageHead(page));
1116         if (page_mapcount(page) == 1) {
1117                 pmd_t entry;
1118                 entry = pmd_mkyoung(orig_pmd);
1119                 entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
1120                 if (pmdp_set_access_flags(vma, haddr, pmd, entry,  1))
1121                         update_mmu_cache_pmd(vma, address, pmd);
1122                 ret |= VM_FAULT_WRITE;
1123                 goto out_unlock;
1124         }
1125         get_page(page);
1126         spin_unlock(&mm->page_table_lock);
1127 alloc:
1128         if (transparent_hugepage_enabled(vma) &&
1129             !transparent_hugepage_debug_cow())
1130                 new_page = alloc_hugepage_vma(transparent_hugepage_defrag(vma),
1131                                               vma, haddr, numa_node_id(), 0);
1132         else
1133                 new_page = NULL;
1134
1135         if (unlikely(!new_page)) {
1136                 count_vm_event(THP_FAULT_FALLBACK);
1137                 if (is_huge_zero_pmd(orig_pmd)) {
1138                         ret = do_huge_pmd_wp_zero_page_fallback(mm, vma,
1139                                         address, pmd, haddr);
1140                 } else {
1141                         ret = do_huge_pmd_wp_page_fallback(mm, vma, address,
1142                                         pmd, orig_pmd, page, haddr);
1143                         if (ret & VM_FAULT_OOM)
1144                                 split_huge_page(page);
1145                         put_page(page);
1146                 }
1147                 goto out;
1148         }
1149         count_vm_event(THP_FAULT_ALLOC);
1150
1151         if (unlikely(mem_cgroup_newpage_charge(new_page, mm, GFP_KERNEL))) {
1152                 put_page(new_page);
1153                 if (page) {
1154                         split_huge_page(page);
1155                         put_page(page);
1156                 }
1157                 ret |= VM_FAULT_OOM;
1158                 goto out;
1159         }
1160
1161         if (is_huge_zero_pmd(orig_pmd))
1162                 clear_huge_page(new_page, haddr, HPAGE_PMD_NR);
1163         else
1164                 copy_user_huge_page(new_page, page, haddr, vma, HPAGE_PMD_NR);
1165         __SetPageUptodate(new_page);
1166
1167         mmun_start = haddr;
1168         mmun_end   = haddr + HPAGE_PMD_SIZE;
1169         mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
1170
1171         spin_lock(&mm->page_table_lock);
1172         if (page)
1173                 put_page(page);
1174         if (unlikely(!pmd_same(*pmd, orig_pmd))) {
1175                 spin_unlock(&mm->page_table_lock);
1176                 mem_cgroup_uncharge_page(new_page);
1177                 put_page(new_page);
1178                 goto out_mn;
1179         } else {
1180                 pmd_t entry;
1181                 entry = mk_huge_pmd(new_page, vma);
1182                 pmdp_clear_flush(vma, haddr, pmd);
1183                 page_add_new_anon_rmap(new_page, vma, haddr);
1184                 set_pmd_at(mm, haddr, pmd, entry);
1185                 update_mmu_cache_pmd(vma, address, pmd);
1186                 if (is_huge_zero_pmd(orig_pmd)) {
1187                         add_mm_counter(mm, MM_ANONPAGES, HPAGE_PMD_NR);
1188                         put_huge_zero_page();
1189                 } else {
1190                         VM_BUG_ON(!PageHead(page));
1191                         page_remove_rmap(page);
1192                         put_page(page);
1193                 }
1194                 ret |= VM_FAULT_WRITE;
1195         }
1196         spin_unlock(&mm->page_table_lock);
1197 out_mn:
1198         mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
1199 out:
1200         return ret;
1201 out_unlock:
1202         spin_unlock(&mm->page_table_lock);
1203         return ret;
1204 }
1205
1206 struct page *follow_trans_huge_pmd(struct vm_area_struct *vma,
1207                                    unsigned long addr,
1208                                    pmd_t *pmd,
1209                                    unsigned int flags)
1210 {
1211         struct mm_struct *mm = vma->vm_mm;
1212         struct page *page = NULL;
1213
1214         assert_spin_locked(&mm->page_table_lock);
1215
1216         if (flags & FOLL_WRITE && !pmd_write(*pmd))
1217                 goto out;
1218
1219         page = pmd_page(*pmd);
1220         VM_BUG_ON(!PageHead(page));
1221         if (flags & FOLL_TOUCH) {
1222                 pmd_t _pmd;
1223                 /*
1224                  * We should set the dirty bit only for FOLL_WRITE but
1225                  * for now the dirty bit in the pmd is meaningless.
1226                  * And if the dirty bit will become meaningful and
1227                  * we'll only set it with FOLL_WRITE, an atomic
1228                  * set_bit will be required on the pmd to set the
1229                  * young bit, instead of the current set_pmd_at.
1230                  */
1231                 _pmd = pmd_mkyoung(pmd_mkdirty(*pmd));
1232                 set_pmd_at(mm, addr & HPAGE_PMD_MASK, pmd, _pmd);
1233         }
1234         if ((flags & FOLL_MLOCK) && (vma->vm_flags & VM_LOCKED)) {
1235                 if (page->mapping && trylock_page(page)) {
1236                         lru_add_drain();
1237                         if (page->mapping)
1238                                 mlock_vma_page(page);
1239                         unlock_page(page);
1240                 }
1241         }
1242         page += (addr & ~HPAGE_PMD_MASK) >> PAGE_SHIFT;
1243         VM_BUG_ON(!PageCompound(page));
1244         if (flags & FOLL_GET)
1245                 get_page_foll(page);
1246
1247 out:
1248         return page;
1249 }
1250
1251 int zap_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
1252                  pmd_t *pmd, unsigned long addr)
1253 {
1254         int ret = 0;
1255
1256         if (__pmd_trans_huge_lock(pmd, vma) == 1) {
1257                 struct page *page;
1258                 pgtable_t pgtable;
1259                 pmd_t orig_pmd;
1260                 pgtable = pgtable_trans_huge_withdraw(tlb->mm);
1261                 orig_pmd = pmdp_get_and_clear(tlb->mm, addr, pmd);
1262                 tlb_remove_pmd_tlb_entry(tlb, pmd, addr);
1263                 if (is_huge_zero_pmd(orig_pmd)) {
1264                         tlb->mm->nr_ptes--;
1265                         spin_unlock(&tlb->mm->page_table_lock);
1266                         put_huge_zero_page();
1267                 } else {
1268                         page = pmd_page(orig_pmd);
1269                         page_remove_rmap(page);
1270                         VM_BUG_ON(page_mapcount(page) < 0);
1271                         add_mm_counter(tlb->mm, MM_ANONPAGES, -HPAGE_PMD_NR);
1272                         VM_BUG_ON(!PageHead(page));
1273                         tlb->mm->nr_ptes--;
1274                         spin_unlock(&tlb->mm->page_table_lock);
1275                         tlb_remove_page(tlb, page);
1276                 }
1277                 pte_free(tlb->mm, pgtable);
1278                 ret = 1;
1279         }
1280         return ret;
1281 }
1282
1283 int mincore_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
1284                 unsigned long addr, unsigned long end,
1285                 unsigned char *vec)
1286 {
1287         int ret = 0;
1288
1289         if (__pmd_trans_huge_lock(pmd, vma) == 1) {
1290                 /*
1291                  * All logical pages in the range are present
1292                  * if backed by a huge page.
1293                  */
1294                 spin_unlock(&vma->vm_mm->page_table_lock);
1295                 memset(vec, 1, (end - addr) >> PAGE_SHIFT);
1296                 ret = 1;
1297         }
1298
1299         return ret;
1300 }
1301
1302 int move_huge_pmd(struct vm_area_struct *vma, struct vm_area_struct *new_vma,
1303                   unsigned long old_addr,
1304                   unsigned long new_addr, unsigned long old_end,
1305                   pmd_t *old_pmd, pmd_t *new_pmd)
1306 {
1307         int ret = 0;
1308         pmd_t pmd;
1309
1310         struct mm_struct *mm = vma->vm_mm;
1311
1312         if ((old_addr & ~HPAGE_PMD_MASK) ||
1313             (new_addr & ~HPAGE_PMD_MASK) ||
1314             old_end - old_addr < HPAGE_PMD_SIZE ||
1315             (new_vma->vm_flags & VM_NOHUGEPAGE))
1316                 goto out;
1317
1318         /*
1319          * The destination pmd shouldn't be established, free_pgtables()
1320          * should have release it.
1321          */
1322         if (WARN_ON(!pmd_none(*new_pmd))) {
1323                 VM_BUG_ON(pmd_trans_huge(*new_pmd));
1324                 goto out;
1325         }
1326
1327         ret = __pmd_trans_huge_lock(old_pmd, vma);
1328         if (ret == 1) {
1329                 pmd = pmdp_get_and_clear(mm, old_addr, old_pmd);
1330                 VM_BUG_ON(!pmd_none(*new_pmd));
1331                 set_pmd_at(mm, new_addr, new_pmd, pmd);
1332                 spin_unlock(&mm->page_table_lock);
1333         }
1334 out:
1335         return ret;
1336 }
1337
1338 int change_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
1339                 unsigned long addr, pgprot_t newprot)
1340 {
1341         struct mm_struct *mm = vma->vm_mm;
1342         int ret = 0;
1343
1344         if (__pmd_trans_huge_lock(pmd, vma) == 1) {
1345                 pmd_t entry;
1346                 entry = pmdp_get_and_clear(mm, addr, pmd);
1347                 entry = pmd_modify(entry, newprot);
1348                 BUG_ON(pmd_write(entry));
1349                 set_pmd_at(mm, addr, pmd, entry);
1350                 spin_unlock(&vma->vm_mm->page_table_lock);
1351                 ret = 1;
1352         }
1353
1354         return ret;
1355 }
1356
1357 /*
1358  * Returns 1 if a given pmd maps a stable (not under splitting) thp.
1359  * Returns -1 if it maps a thp under splitting. Returns 0 otherwise.
1360  *
1361  * Note that if it returns 1, this routine returns without unlocking page
1362  * table locks. So callers must unlock them.
1363  */
1364 int __pmd_trans_huge_lock(pmd_t *pmd, struct vm_area_struct *vma)
1365 {
1366         spin_lock(&vma->vm_mm->page_table_lock);
1367         if (likely(pmd_trans_huge(*pmd))) {
1368                 if (unlikely(pmd_trans_splitting(*pmd))) {
1369                         spin_unlock(&vma->vm_mm->page_table_lock);
1370                         wait_split_huge_page(vma->anon_vma, pmd);
1371                         return -1;
1372                 } else {
1373                         /* Thp mapped by 'pmd' is stable, so we can
1374                          * handle it as it is. */
1375                         return 1;
1376                 }
1377         }
1378         spin_unlock(&vma->vm_mm->page_table_lock);
1379         return 0;
1380 }
1381
1382 pmd_t *page_check_address_pmd(struct page *page,
1383                               struct mm_struct *mm,
1384                               unsigned long address,
1385                               enum page_check_address_pmd_flag flag)
1386 {
1387         pmd_t *pmd, *ret = NULL;
1388
1389         if (address & ~HPAGE_PMD_MASK)
1390                 goto out;
1391
1392         pmd = mm_find_pmd(mm, address);
1393         if (!pmd)
1394                 goto out;
1395         if (pmd_none(*pmd))
1396                 goto out;
1397         if (pmd_page(*pmd) != page)
1398                 goto out;
1399         /*
1400          * split_vma() may create temporary aliased mappings. There is
1401          * no risk as long as all huge pmd are found and have their
1402          * splitting bit set before __split_huge_page_refcount
1403          * runs. Finding the same huge pmd more than once during the
1404          * same rmap walk is not a problem.
1405          */
1406         if (flag == PAGE_CHECK_ADDRESS_PMD_NOTSPLITTING_FLAG &&
1407             pmd_trans_splitting(*pmd))
1408                 goto out;
1409         if (pmd_trans_huge(*pmd)) {
1410                 VM_BUG_ON(flag == PAGE_CHECK_ADDRESS_PMD_SPLITTING_FLAG &&
1411                           !pmd_trans_splitting(*pmd));
1412                 ret = pmd;
1413         }
1414 out:
1415         return ret;
1416 }
1417
1418 static int __split_huge_page_splitting(struct page *page,
1419                                        struct vm_area_struct *vma,
1420                                        unsigned long address)
1421 {
1422         struct mm_struct *mm = vma->vm_mm;
1423         pmd_t *pmd;
1424         int ret = 0;
1425         /* For mmu_notifiers */
1426         const unsigned long mmun_start = address;
1427         const unsigned long mmun_end   = address + HPAGE_PMD_SIZE;
1428
1429         mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
1430         spin_lock(&mm->page_table_lock);
1431         pmd = page_check_address_pmd(page, mm, address,
1432                                      PAGE_CHECK_ADDRESS_PMD_NOTSPLITTING_FLAG);
1433         if (pmd) {
1434                 /*
1435                  * We can't temporarily set the pmd to null in order
1436                  * to split it, the pmd must remain marked huge at all
1437                  * times or the VM won't take the pmd_trans_huge paths
1438                  * and it won't wait on the anon_vma->root->mutex to
1439                  * serialize against split_huge_page*.
1440                  */
1441                 pmdp_splitting_flush(vma, address, pmd);
1442                 ret = 1;
1443         }
1444         spin_unlock(&mm->page_table_lock);
1445         mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
1446
1447         return ret;
1448 }
1449
1450 static void __split_huge_page_refcount(struct page *page)
1451 {
1452         int i;
1453         struct zone *zone = page_zone(page);
1454         struct lruvec *lruvec;
1455         int tail_count = 0;
1456
1457         /* prevent PageLRU to go away from under us, and freeze lru stats */
1458         spin_lock_irq(&zone->lru_lock);
1459         lruvec = mem_cgroup_page_lruvec(page, zone);
1460
1461         compound_lock(page);
1462         /* complete memcg works before add pages to LRU */
1463         mem_cgroup_split_huge_fixup(page);
1464
1465         for (i = HPAGE_PMD_NR - 1; i >= 1; i--) {
1466                 struct page *page_tail = page + i;
1467
1468                 /* tail_page->_mapcount cannot change */
1469                 BUG_ON(page_mapcount(page_tail) < 0);
1470                 tail_count += page_mapcount(page_tail);
1471                 /* check for overflow */
1472                 BUG_ON(tail_count < 0);
1473                 BUG_ON(atomic_read(&page_tail->_count) != 0);
1474                 /*
1475                  * tail_page->_count is zero and not changing from
1476                  * under us. But get_page_unless_zero() may be running
1477                  * from under us on the tail_page. If we used
1478                  * atomic_set() below instead of atomic_add(), we
1479                  * would then run atomic_set() concurrently with
1480                  * get_page_unless_zero(), and atomic_set() is
1481                  * implemented in C not using locked ops. spin_unlock
1482                  * on x86 sometime uses locked ops because of PPro
1483                  * errata 66, 92, so unless somebody can guarantee
1484                  * atomic_set() here would be safe on all archs (and
1485                  * not only on x86), it's safer to use atomic_add().
1486                  */
1487                 atomic_add(page_mapcount(page) + page_mapcount(page_tail) + 1,
1488                            &page_tail->_count);
1489
1490                 /* after clearing PageTail the gup refcount can be released */
1491                 smp_mb();
1492
1493                 /*
1494                  * retain hwpoison flag of the poisoned tail page:
1495                  *   fix for the unsuitable process killed on Guest Machine(KVM)
1496                  *   by the memory-failure.
1497                  */
1498                 page_tail->flags &= ~PAGE_FLAGS_CHECK_AT_PREP | __PG_HWPOISON;
1499                 page_tail->flags |= (page->flags &
1500                                      ((1L << PG_referenced) |
1501                                       (1L << PG_swapbacked) |
1502                                       (1L << PG_mlocked) |
1503                                       (1L << PG_uptodate)));
1504                 page_tail->flags |= (1L << PG_dirty);
1505
1506                 /* clear PageTail before overwriting first_page */
1507                 smp_wmb();
1508
1509                 /*
1510                  * __split_huge_page_splitting() already set the
1511                  * splitting bit in all pmd that could map this
1512                  * hugepage, that will ensure no CPU can alter the
1513                  * mapcount on the head page. The mapcount is only
1514                  * accounted in the head page and it has to be
1515                  * transferred to all tail pages in the below code. So
1516                  * for this code to be safe, the split the mapcount
1517                  * can't change. But that doesn't mean userland can't
1518                  * keep changing and reading the page contents while
1519                  * we transfer the mapcount, so the pmd splitting
1520                  * status is achieved setting a reserved bit in the
1521                  * pmd, not by clearing the present bit.
1522                 */
1523                 page_tail->_mapcount = page->_mapcount;
1524
1525                 BUG_ON(page_tail->mapping);
1526                 page_tail->mapping = page->mapping;
1527
1528                 page_tail->index = page->index + i;
1529
1530                 BUG_ON(!PageAnon(page_tail));
1531                 BUG_ON(!PageUptodate(page_tail));
1532                 BUG_ON(!PageDirty(page_tail));
1533                 BUG_ON(!PageSwapBacked(page_tail));
1534
1535                 lru_add_page_tail(page, page_tail, lruvec);
1536         }
1537         atomic_sub(tail_count, &page->_count);
1538         BUG_ON(atomic_read(&page->_count) <= 0);
1539
1540         __mod_zone_page_state(zone, NR_ANON_TRANSPARENT_HUGEPAGES, -1);
1541         __mod_zone_page_state(zone, NR_ANON_PAGES, HPAGE_PMD_NR);
1542
1543         ClearPageCompound(page);
1544         compound_unlock(page);
1545         spin_unlock_irq(&zone->lru_lock);
1546
1547         for (i = 1; i < HPAGE_PMD_NR; i++) {
1548                 struct page *page_tail = page + i;
1549                 BUG_ON(page_count(page_tail) <= 0);
1550                 /*
1551                  * Tail pages may be freed if there wasn't any mapping
1552                  * like if add_to_swap() is running on a lru page that
1553                  * had its mapping zapped. And freeing these pages
1554                  * requires taking the lru_lock so we do the put_page
1555                  * of the tail pages after the split is complete.
1556                  */
1557                 put_page(page_tail);
1558         }
1559
1560         /*
1561          * Only the head page (now become a regular page) is required
1562          * to be pinned by the caller.
1563          */
1564         BUG_ON(page_count(page) <= 0);
1565 }
1566
1567 static int __split_huge_page_map(struct page *page,
1568                                  struct vm_area_struct *vma,
1569                                  unsigned long address)
1570 {
1571         struct mm_struct *mm = vma->vm_mm;
1572         pmd_t *pmd, _pmd;
1573         int ret = 0, i;
1574         pgtable_t pgtable;
1575         unsigned long haddr;
1576
1577         spin_lock(&mm->page_table_lock);
1578         pmd = page_check_address_pmd(page, mm, address,
1579                                      PAGE_CHECK_ADDRESS_PMD_SPLITTING_FLAG);
1580         if (pmd) {
1581                 pgtable = pgtable_trans_huge_withdraw(mm);
1582                 pmd_populate(mm, &_pmd, pgtable);
1583
1584                 haddr = address;
1585                 for (i = 0; i < HPAGE_PMD_NR; i++, haddr += PAGE_SIZE) {
1586                         pte_t *pte, entry;
1587                         BUG_ON(PageCompound(page+i));
1588                         entry = mk_pte(page + i, vma->vm_page_prot);
1589                         entry = maybe_mkwrite(pte_mkdirty(entry), vma);
1590                         if (!pmd_write(*pmd))
1591                                 entry = pte_wrprotect(entry);
1592                         else
1593                                 BUG_ON(page_mapcount(page) != 1);
1594                         if (!pmd_young(*pmd))
1595                                 entry = pte_mkold(entry);
1596                         pte = pte_offset_map(&_pmd, haddr);
1597                         BUG_ON(!pte_none(*pte));
1598                         set_pte_at(mm, haddr, pte, entry);
1599                         pte_unmap(pte);
1600                 }
1601
1602                 smp_wmb(); /* make pte visible before pmd */
1603                 /*
1604                  * Up to this point the pmd is present and huge and
1605                  * userland has the whole access to the hugepage
1606                  * during the split (which happens in place). If we
1607                  * overwrite the pmd with the not-huge version
1608                  * pointing to the pte here (which of course we could
1609                  * if all CPUs were bug free), userland could trigger
1610                  * a small page size TLB miss on the small sized TLB
1611                  * while the hugepage TLB entry is still established
1612                  * in the huge TLB. Some CPU doesn't like that. See
1613                  * http://support.amd.com/us/Processor_TechDocs/41322.pdf,
1614                  * Erratum 383 on page 93. Intel should be safe but is
1615                  * also warns that it's only safe if the permission
1616                  * and cache attributes of the two entries loaded in
1617                  * the two TLB is identical (which should be the case
1618                  * here). But it is generally safer to never allow
1619                  * small and huge TLB entries for the same virtual
1620                  * address to be loaded simultaneously. So instead of
1621                  * doing "pmd_populate(); flush_tlb_range();" we first
1622                  * mark the current pmd notpresent (atomically because
1623                  * here the pmd_trans_huge and pmd_trans_splitting
1624                  * must remain set at all times on the pmd until the
1625                  * split is complete for this pmd), then we flush the
1626                  * SMP TLB and finally we write the non-huge version
1627                  * of the pmd entry with pmd_populate.
1628                  */
1629                 pmdp_invalidate(vma, address, pmd);
1630                 pmd_populate(mm, pmd, pgtable);
1631                 ret = 1;
1632         }
1633         spin_unlock(&mm->page_table_lock);
1634
1635         return ret;
1636 }
1637
1638 /* must be called with anon_vma->root->mutex hold */
1639 static void __split_huge_page(struct page *page,
1640                               struct anon_vma *anon_vma)
1641 {
1642         int mapcount, mapcount2;
1643         pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
1644         struct anon_vma_chain *avc;
1645
1646         BUG_ON(!PageHead(page));
1647         BUG_ON(PageTail(page));
1648
1649         mapcount = 0;
1650         anon_vma_interval_tree_foreach(avc, &anon_vma->rb_root, pgoff, pgoff) {
1651                 struct vm_area_struct *vma = avc->vma;
1652                 unsigned long addr = vma_address(page, vma);
1653                 BUG_ON(is_vma_temporary_stack(vma));
1654                 mapcount += __split_huge_page_splitting(page, vma, addr);
1655         }
1656         /*
1657          * It is critical that new vmas are added to the tail of the
1658          * anon_vma list. This guarantes that if copy_huge_pmd() runs
1659          * and establishes a child pmd before
1660          * __split_huge_page_splitting() freezes the parent pmd (so if
1661          * we fail to prevent copy_huge_pmd() from running until the
1662          * whole __split_huge_page() is complete), we will still see
1663          * the newly established pmd of the child later during the
1664          * walk, to be able to set it as pmd_trans_splitting too.
1665          */
1666         if (mapcount != page_mapcount(page))
1667                 printk(KERN_ERR "mapcount %d page_mapcount %d\n",
1668                        mapcount, page_mapcount(page));
1669         BUG_ON(mapcount != page_mapcount(page));
1670
1671         __split_huge_page_refcount(page);
1672
1673         mapcount2 = 0;
1674         anon_vma_interval_tree_foreach(avc, &anon_vma->rb_root, pgoff, pgoff) {
1675                 struct vm_area_struct *vma = avc->vma;
1676                 unsigned long addr = vma_address(page, vma);
1677                 BUG_ON(is_vma_temporary_stack(vma));
1678                 mapcount2 += __split_huge_page_map(page, vma, addr);
1679         }
1680         if (mapcount != mapcount2)
1681                 printk(KERN_ERR "mapcount %d mapcount2 %d page_mapcount %d\n",
1682                        mapcount, mapcount2, page_mapcount(page));
1683         BUG_ON(mapcount != mapcount2);
1684 }
1685
1686 int split_huge_page(struct page *page)
1687 {
1688         struct anon_vma *anon_vma;
1689         int ret = 1;
1690
1691         BUG_ON(is_huge_zero_pfn(page_to_pfn(page)));
1692         BUG_ON(!PageAnon(page));
1693         anon_vma = page_lock_anon_vma(page);
1694         if (!anon_vma)
1695                 goto out;
1696         ret = 0;
1697         if (!PageCompound(page))
1698                 goto out_unlock;
1699
1700         BUG_ON(!PageSwapBacked(page));
1701         __split_huge_page(page, anon_vma);
1702         count_vm_event(THP_SPLIT);
1703
1704         BUG_ON(PageCompound(page));
1705 out_unlock:
1706         page_unlock_anon_vma(anon_vma);
1707 out:
1708         return ret;
1709 }
1710
1711 #define VM_NO_THP (VM_SPECIAL|VM_MIXEDMAP|VM_HUGETLB|VM_SHARED|VM_MAYSHARE)
1712
1713 int hugepage_madvise(struct vm_area_struct *vma,
1714                      unsigned long *vm_flags, int advice)
1715 {
1716         struct mm_struct *mm = vma->vm_mm;
1717
1718         switch (advice) {
1719         case MADV_HUGEPAGE:
1720                 /*
1721                  * Be somewhat over-protective like KSM for now!
1722                  */
1723                 if (*vm_flags & (VM_HUGEPAGE | VM_NO_THP))
1724                         return -EINVAL;
1725                 if (mm->def_flags & VM_NOHUGEPAGE)
1726                         return -EINVAL;
1727                 *vm_flags &= ~VM_NOHUGEPAGE;
1728                 *vm_flags |= VM_HUGEPAGE;
1729                 /*
1730                  * If the vma become good for khugepaged to scan,
1731                  * register it here without waiting a page fault that
1732                  * may not happen any time soon.
1733                  */
1734                 if (unlikely(khugepaged_enter_vma_merge(vma)))
1735                         return -ENOMEM;
1736                 break;
1737         case MADV_NOHUGEPAGE:
1738                 /*
1739                  * Be somewhat over-protective like KSM for now!
1740                  */
1741                 if (*vm_flags & (VM_NOHUGEPAGE | VM_NO_THP))
1742                         return -EINVAL;
1743                 *vm_flags &= ~VM_HUGEPAGE;
1744                 *vm_flags |= VM_NOHUGEPAGE;
1745                 /*
1746                  * Setting VM_NOHUGEPAGE will prevent khugepaged from scanning
1747                  * this vma even if we leave the mm registered in khugepaged if
1748                  * it got registered before VM_NOHUGEPAGE was set.
1749                  */
1750                 break;
1751         }
1752
1753         return 0;
1754 }
1755
1756 static int __init khugepaged_slab_init(void)
1757 {
1758         mm_slot_cache = kmem_cache_create("khugepaged_mm_slot",
1759                                           sizeof(struct mm_slot),
1760                                           __alignof__(struct mm_slot), 0, NULL);
1761         if (!mm_slot_cache)
1762                 return -ENOMEM;
1763
1764         return 0;
1765 }
1766
1767 static void __init khugepaged_slab_free(void)
1768 {
1769         kmem_cache_destroy(mm_slot_cache);
1770         mm_slot_cache = NULL;
1771 }
1772
1773 static inline struct mm_slot *alloc_mm_slot(void)
1774 {
1775         if (!mm_slot_cache)     /* initialization failed */
1776                 return NULL;
1777         return kmem_cache_zalloc(mm_slot_cache, GFP_KERNEL);
1778 }
1779
1780 static inline void free_mm_slot(struct mm_slot *mm_slot)
1781 {
1782         kmem_cache_free(mm_slot_cache, mm_slot);
1783 }
1784
1785 static int __init mm_slots_hash_init(void)
1786 {
1787         mm_slots_hash = kzalloc(MM_SLOTS_HASH_HEADS * sizeof(struct hlist_head),
1788                                 GFP_KERNEL);
1789         if (!mm_slots_hash)
1790                 return -ENOMEM;
1791         return 0;
1792 }
1793
1794 #if 0
1795 static void __init mm_slots_hash_free(void)
1796 {
1797         kfree(mm_slots_hash);
1798         mm_slots_hash = NULL;
1799 }
1800 #endif
1801
1802 static struct mm_slot *get_mm_slot(struct mm_struct *mm)
1803 {
1804         struct mm_slot *mm_slot;
1805         struct hlist_head *bucket;
1806         struct hlist_node *node;
1807
1808         bucket = &mm_slots_hash[((unsigned long)mm / sizeof(struct mm_struct))
1809                                 % MM_SLOTS_HASH_HEADS];
1810         hlist_for_each_entry(mm_slot, node, bucket, hash) {
1811                 if (mm == mm_slot->mm)
1812                         return mm_slot;
1813         }
1814         return NULL;
1815 }
1816
1817 static void insert_to_mm_slots_hash(struct mm_struct *mm,
1818                                     struct mm_slot *mm_slot)
1819 {
1820         struct hlist_head *bucket;
1821
1822         bucket = &mm_slots_hash[((unsigned long)mm / sizeof(struct mm_struct))
1823                                 % MM_SLOTS_HASH_HEADS];
1824         mm_slot->mm = mm;
1825         hlist_add_head(&mm_slot->hash, bucket);
1826 }
1827
1828 static inline int khugepaged_test_exit(struct mm_struct *mm)
1829 {
1830         return atomic_read(&mm->mm_users) == 0;
1831 }
1832
1833 int __khugepaged_enter(struct mm_struct *mm)
1834 {
1835         struct mm_slot *mm_slot;
1836         int wakeup;
1837
1838         mm_slot = alloc_mm_slot();
1839         if (!mm_slot)
1840                 return -ENOMEM;
1841
1842         /* __khugepaged_exit() must not run from under us */
1843         VM_BUG_ON(khugepaged_test_exit(mm));
1844         if (unlikely(test_and_set_bit(MMF_VM_HUGEPAGE, &mm->flags))) {
1845                 free_mm_slot(mm_slot);
1846                 return 0;
1847         }
1848
1849         spin_lock(&khugepaged_mm_lock);
1850         insert_to_mm_slots_hash(mm, mm_slot);
1851         /*
1852          * Insert just behind the scanning cursor, to let the area settle
1853          * down a little.
1854          */
1855         wakeup = list_empty(&khugepaged_scan.mm_head);
1856         list_add_tail(&mm_slot->mm_node, &khugepaged_scan.mm_head);
1857         spin_unlock(&khugepaged_mm_lock);
1858
1859         atomic_inc(&mm->mm_count);
1860         if (wakeup)
1861                 wake_up_interruptible(&khugepaged_wait);
1862
1863         return 0;
1864 }
1865
1866 int khugepaged_enter_vma_merge(struct vm_area_struct *vma)
1867 {
1868         unsigned long hstart, hend;
1869         if (!vma->anon_vma)
1870                 /*
1871                  * Not yet faulted in so we will register later in the
1872                  * page fault if needed.
1873                  */
1874                 return 0;
1875         if (vma->vm_ops)
1876                 /* khugepaged not yet working on file or special mappings */
1877                 return 0;
1878         VM_BUG_ON(vma->vm_flags & VM_NO_THP);
1879         hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK;
1880         hend = vma->vm_end & HPAGE_PMD_MASK;
1881         if (hstart < hend)
1882                 return khugepaged_enter(vma);
1883         return 0;
1884 }
1885
1886 void __khugepaged_exit(struct mm_struct *mm)
1887 {
1888         struct mm_slot *mm_slot;
1889         int free = 0;
1890
1891         spin_lock(&khugepaged_mm_lock);
1892         mm_slot = get_mm_slot(mm);
1893         if (mm_slot && khugepaged_scan.mm_slot != mm_slot) {
1894                 hlist_del(&mm_slot->hash);
1895                 list_del(&mm_slot->mm_node);
1896                 free = 1;
1897         }
1898         spin_unlock(&khugepaged_mm_lock);
1899
1900         if (free) {
1901                 clear_bit(MMF_VM_HUGEPAGE, &mm->flags);
1902                 free_mm_slot(mm_slot);
1903                 mmdrop(mm);
1904         } else if (mm_slot) {
1905                 /*
1906                  * This is required to serialize against
1907                  * khugepaged_test_exit() (which is guaranteed to run
1908                  * under mmap sem read mode). Stop here (after we
1909                  * return all pagetables will be destroyed) until
1910                  * khugepaged has finished working on the pagetables
1911                  * under the mmap_sem.
1912                  */
1913                 down_write(&mm->mmap_sem);
1914                 up_write(&mm->mmap_sem);
1915         }
1916 }
1917
1918 static void release_pte_page(struct page *page)
1919 {
1920         /* 0 stands for page_is_file_cache(page) == false */
1921         dec_zone_page_state(page, NR_ISOLATED_ANON + 0);
1922         unlock_page(page);
1923         putback_lru_page(page);
1924 }
1925
1926 static void release_pte_pages(pte_t *pte, pte_t *_pte)
1927 {
1928         while (--_pte >= pte) {
1929                 pte_t pteval = *_pte;
1930                 if (!pte_none(pteval))
1931                         release_pte_page(pte_page(pteval));
1932         }
1933 }
1934
1935 static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
1936                                         unsigned long address,
1937                                         pte_t *pte)
1938 {
1939         struct page *page;
1940         pte_t *_pte;
1941         int referenced = 0, none = 0;
1942         for (_pte = pte; _pte < pte+HPAGE_PMD_NR;
1943              _pte++, address += PAGE_SIZE) {
1944                 pte_t pteval = *_pte;
1945                 if (pte_none(pteval)) {
1946                         if (++none <= khugepaged_max_ptes_none)
1947                                 continue;
1948                         else
1949                                 goto out;
1950                 }
1951                 if (!pte_present(pteval) || !pte_write(pteval))
1952                         goto out;
1953                 page = vm_normal_page(vma, address, pteval);
1954                 if (unlikely(!page))
1955                         goto out;
1956
1957                 VM_BUG_ON(PageCompound(page));
1958                 BUG_ON(!PageAnon(page));
1959                 VM_BUG_ON(!PageSwapBacked(page));
1960
1961                 /* cannot use mapcount: can't collapse if there's a gup pin */
1962                 if (page_count(page) != 1)
1963                         goto out;
1964                 /*
1965                  * We can do it before isolate_lru_page because the
1966                  * page can't be freed from under us. NOTE: PG_lock
1967                  * is needed to serialize against split_huge_page
1968                  * when invoked from the VM.
1969                  */
1970                 if (!trylock_page(page))
1971                         goto out;
1972                 /*
1973                  * Isolate the page to avoid collapsing an hugepage
1974                  * currently in use by the VM.
1975                  */
1976                 if (isolate_lru_page(page)) {
1977                         unlock_page(page);
1978                         goto out;
1979                 }
1980                 /* 0 stands for page_is_file_cache(page) == false */
1981                 inc_zone_page_state(page, NR_ISOLATED_ANON + 0);
1982                 VM_BUG_ON(!PageLocked(page));
1983                 VM_BUG_ON(PageLRU(page));
1984
1985                 /* If there is no mapped pte young don't collapse the page */
1986                 if (pte_young(pteval) || PageReferenced(page) ||
1987                     mmu_notifier_test_young(vma->vm_mm, address))
1988                         referenced = 1;
1989         }
1990         if (likely(referenced))
1991                 return 1;
1992 out:
1993         release_pte_pages(pte, _pte);
1994         return 0;
1995 }
1996
1997 static void __collapse_huge_page_copy(pte_t *pte, struct page *page,
1998                                       struct vm_area_struct *vma,
1999                                       unsigned long address,
2000                                       spinlock_t *ptl)
2001 {
2002         pte_t *_pte;
2003         for (_pte = pte; _pte < pte+HPAGE_PMD_NR; _pte++) {
2004                 pte_t pteval = *_pte;
2005                 struct page *src_page;
2006
2007                 if (pte_none(pteval)) {
2008                         clear_user_highpage(page, address);
2009                         add_mm_counter(vma->vm_mm, MM_ANONPAGES, 1);
2010                 } else {
2011                         src_page = pte_page(pteval);
2012                         copy_user_highpage(page, src_page, address, vma);
2013                         VM_BUG_ON(page_mapcount(src_page) != 1);
2014                         release_pte_page(src_page);
2015                         /*
2016                          * ptl mostly unnecessary, but preempt has to
2017                          * be disabled to update the per-cpu stats
2018                          * inside page_remove_rmap().
2019                          */
2020                         spin_lock(ptl);
2021                         /*
2022                          * paravirt calls inside pte_clear here are
2023                          * superfluous.
2024                          */
2025                         pte_clear(vma->vm_mm, address, _pte);
2026                         page_remove_rmap(src_page);
2027                         spin_unlock(ptl);
2028                         free_page_and_swap_cache(src_page);
2029                 }
2030
2031                 address += PAGE_SIZE;
2032                 page++;
2033         }
2034 }
2035
2036 static void khugepaged_alloc_sleep(void)
2037 {
2038         wait_event_freezable_timeout(khugepaged_wait, false,
2039                         msecs_to_jiffies(khugepaged_alloc_sleep_millisecs));
2040 }
2041
2042 #ifdef CONFIG_NUMA
2043 static bool khugepaged_prealloc_page(struct page **hpage, bool *wait)
2044 {
2045         if (IS_ERR(*hpage)) {
2046                 if (!*wait)
2047                         return false;
2048
2049                 *wait = false;
2050                 *hpage = NULL;
2051                 khugepaged_alloc_sleep();
2052         } else if (*hpage) {
2053                 put_page(*hpage);
2054                 *hpage = NULL;
2055         }
2056
2057         return true;
2058 }
2059
2060 static struct page
2061 *khugepaged_alloc_page(struct page **hpage, struct mm_struct *mm,
2062                        struct vm_area_struct *vma, unsigned long address,
2063                        int node)
2064 {
2065         VM_BUG_ON(*hpage);
2066         /*
2067          * Allocate the page while the vma is still valid and under
2068          * the mmap_sem read mode so there is no memory allocation
2069          * later when we take the mmap_sem in write mode. This is more
2070          * friendly behavior (OTOH it may actually hide bugs) to
2071          * filesystems in userland with daemons allocating memory in
2072          * the userland I/O paths.  Allocating memory with the
2073          * mmap_sem in read mode is good idea also to allow greater
2074          * scalability.
2075          */
2076         *hpage  = alloc_hugepage_vma(khugepaged_defrag(), vma, address,
2077                                       node, __GFP_OTHER_NODE);
2078
2079         /*
2080          * After allocating the hugepage, release the mmap_sem read lock in
2081          * preparation for taking it in write mode.
2082          */
2083         up_read(&mm->mmap_sem);
2084         if (unlikely(!*hpage)) {
2085                 count_vm_event(THP_COLLAPSE_ALLOC_FAILED);
2086                 *hpage = ERR_PTR(-ENOMEM);
2087                 return NULL;
2088         }
2089
2090         count_vm_event(THP_COLLAPSE_ALLOC);
2091         return *hpage;
2092 }
2093 #else
2094 static struct page *khugepaged_alloc_hugepage(bool *wait)
2095 {
2096         struct page *hpage;
2097
2098         do {
2099                 hpage = alloc_hugepage(khugepaged_defrag());
2100                 if (!hpage) {
2101                         count_vm_event(THP_COLLAPSE_ALLOC_FAILED);
2102                         if (!*wait)
2103                                 return NULL;
2104
2105                         *wait = false;
2106                         khugepaged_alloc_sleep();
2107                 } else
2108                         count_vm_event(THP_COLLAPSE_ALLOC);
2109         } while (unlikely(!hpage) && likely(khugepaged_enabled()));
2110
2111         return hpage;
2112 }
2113
2114 static bool khugepaged_prealloc_page(struct page **hpage, bool *wait)
2115 {
2116         if (!*hpage)
2117                 *hpage = khugepaged_alloc_hugepage(wait);
2118
2119         if (unlikely(!*hpage))
2120                 return false;
2121
2122         return true;
2123 }
2124
2125 static struct page
2126 *khugepaged_alloc_page(struct page **hpage, struct mm_struct *mm,
2127                        struct vm_area_struct *vma, unsigned long address,
2128                        int node)
2129 {
2130         up_read(&mm->mmap_sem);
2131         VM_BUG_ON(!*hpage);
2132         return  *hpage;
2133 }
2134 #endif
2135
2136 static bool hugepage_vma_check(struct vm_area_struct *vma)
2137 {
2138         if ((!(vma->vm_flags & VM_HUGEPAGE) && !khugepaged_always()) ||
2139             (vma->vm_flags & VM_NOHUGEPAGE))
2140                 return false;
2141
2142         if (!vma->anon_vma || vma->vm_ops)
2143                 return false;
2144         if (is_vma_temporary_stack(vma))
2145                 return false;
2146         VM_BUG_ON(vma->vm_flags & VM_NO_THP);
2147         return true;
2148 }
2149
2150 static void collapse_huge_page(struct mm_struct *mm,
2151                                    unsigned long address,
2152                                    struct page **hpage,
2153                                    struct vm_area_struct *vma,
2154                                    int node)
2155 {
2156         pmd_t *pmd, _pmd;
2157         pte_t *pte;
2158         pgtable_t pgtable;
2159         struct page *new_page;
2160         spinlock_t *ptl;
2161         int isolated;
2162         unsigned long hstart, hend;
2163         unsigned long mmun_start;       /* For mmu_notifiers */
2164         unsigned long mmun_end;         /* For mmu_notifiers */
2165
2166         VM_BUG_ON(address & ~HPAGE_PMD_MASK);
2167
2168         /* release the mmap_sem read lock. */
2169         new_page = khugepaged_alloc_page(hpage, mm, vma, address, node);
2170         if (!new_page)
2171                 return;
2172
2173         if (unlikely(mem_cgroup_newpage_charge(new_page, mm, GFP_KERNEL)))
2174                 return;
2175
2176         /*
2177          * Prevent all access to pagetables with the exception of
2178          * gup_fast later hanlded by the ptep_clear_flush and the VM
2179          * handled by the anon_vma lock + PG_lock.
2180          */
2181         down_write(&mm->mmap_sem);
2182         if (unlikely(khugepaged_test_exit(mm)))
2183                 goto out;
2184
2185         vma = find_vma(mm, address);
2186         hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK;
2187         hend = vma->vm_end & HPAGE_PMD_MASK;
2188         if (address < hstart || address + HPAGE_PMD_SIZE > hend)
2189                 goto out;
2190         if (!hugepage_vma_check(vma))
2191                 goto out;
2192         pmd = mm_find_pmd(mm, address);
2193         if (!pmd)
2194                 goto out;
2195         if (pmd_trans_huge(*pmd))
2196                 goto out;
2197
2198         anon_vma_lock(vma->anon_vma);
2199
2200         pte = pte_offset_map(pmd, address);
2201         ptl = pte_lockptr(mm, pmd);
2202
2203         mmun_start = address;
2204         mmun_end   = address + HPAGE_PMD_SIZE;
2205         mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
2206         spin_lock(&mm->page_table_lock); /* probably unnecessary */
2207         /*
2208          * After this gup_fast can't run anymore. This also removes
2209          * any huge TLB entry from the CPU so we won't allow
2210          * huge and small TLB entries for the same virtual address
2211          * to avoid the risk of CPU bugs in that area.
2212          */
2213         _pmd = pmdp_clear_flush(vma, address, pmd);
2214         spin_unlock(&mm->page_table_lock);
2215         mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
2216
2217         spin_lock(ptl);
2218         isolated = __collapse_huge_page_isolate(vma, address, pte);
2219         spin_unlock(ptl);
2220
2221         if (unlikely(!isolated)) {
2222                 pte_unmap(pte);
2223                 spin_lock(&mm->page_table_lock);
2224                 BUG_ON(!pmd_none(*pmd));
2225                 set_pmd_at(mm, address, pmd, _pmd);
2226                 spin_unlock(&mm->page_table_lock);
2227                 anon_vma_unlock(vma->anon_vma);
2228                 goto out;
2229         }
2230
2231         /*
2232          * All pages are isolated and locked so anon_vma rmap
2233          * can't run anymore.
2234          */
2235         anon_vma_unlock(vma->anon_vma);
2236
2237         __collapse_huge_page_copy(pte, new_page, vma, address, ptl);
2238         pte_unmap(pte);
2239         __SetPageUptodate(new_page);
2240         pgtable = pmd_pgtable(_pmd);
2241
2242         _pmd = mk_huge_pmd(new_page, vma);
2243
2244         /*
2245          * spin_lock() below is not the equivalent of smp_wmb(), so
2246          * this is needed to avoid the copy_huge_page writes to become
2247          * visible after the set_pmd_at() write.
2248          */
2249         smp_wmb();
2250
2251         spin_lock(&mm->page_table_lock);
2252         BUG_ON(!pmd_none(*pmd));
2253         page_add_new_anon_rmap(new_page, vma, address);
2254         set_pmd_at(mm, address, pmd, _pmd);
2255         update_mmu_cache_pmd(vma, address, pmd);
2256         pgtable_trans_huge_deposit(mm, pgtable);
2257         spin_unlock(&mm->page_table_lock);
2258
2259         *hpage = NULL;
2260
2261         khugepaged_pages_collapsed++;
2262 out_up_write:
2263         up_write(&mm->mmap_sem);
2264         return;
2265
2266 out:
2267         mem_cgroup_uncharge_page(new_page);
2268         goto out_up_write;
2269 }
2270
2271 static int khugepaged_scan_pmd(struct mm_struct *mm,
2272                                struct vm_area_struct *vma,
2273                                unsigned long address,
2274                                struct page **hpage)
2275 {
2276         pmd_t *pmd;
2277         pte_t *pte, *_pte;
2278         int ret = 0, referenced = 0, none = 0;
2279         struct page *page;
2280         unsigned long _address;
2281         spinlock_t *ptl;
2282         int node = -1;
2283
2284         VM_BUG_ON(address & ~HPAGE_PMD_MASK);
2285
2286         pmd = mm_find_pmd(mm, address);
2287         if (!pmd)
2288                 goto out;
2289         if (pmd_trans_huge(*pmd))
2290                 goto out;
2291
2292         pte = pte_offset_map_lock(mm, pmd, address, &ptl);
2293         for (_address = address, _pte = pte; _pte < pte+HPAGE_PMD_NR;
2294              _pte++, _address += PAGE_SIZE) {
2295                 pte_t pteval = *_pte;
2296                 if (pte_none(pteval)) {
2297                         if (++none <= khugepaged_max_ptes_none)
2298                                 continue;
2299                         else
2300                                 goto out_unmap;
2301                 }
2302                 if (!pte_present(pteval) || !pte_write(pteval))
2303                         goto out_unmap;
2304                 page = vm_normal_page(vma, _address, pteval);
2305                 if (unlikely(!page))
2306                         goto out_unmap;
2307                 /*
2308                  * Chose the node of the first page. This could
2309                  * be more sophisticated and look at more pages,
2310                  * but isn't for now.
2311                  */
2312                 if (node == -1)
2313                         node = page_to_nid(page);
2314                 VM_BUG_ON(PageCompound(page));
2315                 if (!PageLRU(page) || PageLocked(page) || !PageAnon(page))
2316                         goto out_unmap;
2317                 /* cannot use mapcount: can't collapse if there's a gup pin */
2318                 if (page_count(page) != 1)
2319                         goto out_unmap;
2320                 if (pte_young(pteval) || PageReferenced(page) ||
2321                     mmu_notifier_test_young(vma->vm_mm, address))
2322                         referenced = 1;
2323         }
2324         if (referenced)
2325                 ret = 1;
2326 out_unmap:
2327         pte_unmap_unlock(pte, ptl);
2328         if (ret)
2329                 /* collapse_huge_page will return with the mmap_sem released */
2330                 collapse_huge_page(mm, address, hpage, vma, node);
2331 out:
2332         return ret;
2333 }
2334
2335 static void collect_mm_slot(struct mm_slot *mm_slot)
2336 {
2337         struct mm_struct *mm = mm_slot->mm;
2338
2339         VM_BUG_ON(NR_CPUS != 1 && !spin_is_locked(&khugepaged_mm_lock));
2340
2341         if (khugepaged_test_exit(mm)) {
2342                 /* free mm_slot */
2343                 hlist_del(&mm_slot->hash);
2344                 list_del(&mm_slot->mm_node);
2345
2346                 /*
2347                  * Not strictly needed because the mm exited already.
2348                  *
2349                  * clear_bit(MMF_VM_HUGEPAGE, &mm->flags);
2350                  */
2351
2352                 /* khugepaged_mm_lock actually not necessary for the below */
2353                 free_mm_slot(mm_slot);
2354                 mmdrop(mm);
2355         }
2356 }
2357
2358 static unsigned int khugepaged_scan_mm_slot(unsigned int pages,
2359                                             struct page **hpage)
2360         __releases(&khugepaged_mm_lock)
2361         __acquires(&khugepaged_mm_lock)
2362 {
2363         struct mm_slot *mm_slot;
2364         struct mm_struct *mm;
2365         struct vm_area_struct *vma;
2366         int progress = 0;
2367
2368         VM_BUG_ON(!pages);
2369         VM_BUG_ON(NR_CPUS != 1 && !spin_is_locked(&khugepaged_mm_lock));
2370
2371         if (khugepaged_scan.mm_slot)
2372                 mm_slot = khugepaged_scan.mm_slot;
2373         else {
2374                 mm_slot = list_entry(khugepaged_scan.mm_head.next,
2375                                      struct mm_slot, mm_node);
2376                 khugepaged_scan.address = 0;
2377                 khugepaged_scan.mm_slot = mm_slot;
2378         }
2379         spin_unlock(&khugepaged_mm_lock);
2380
2381         mm = mm_slot->mm;
2382         down_read(&mm->mmap_sem);
2383         if (unlikely(khugepaged_test_exit(mm)))
2384                 vma = NULL;
2385         else
2386                 vma = find_vma(mm, khugepaged_scan.address);
2387
2388         progress++;
2389         for (; vma; vma = vma->vm_next) {
2390                 unsigned long hstart, hend;
2391
2392                 cond_resched();
2393                 if (unlikely(khugepaged_test_exit(mm))) {
2394                         progress++;
2395                         break;
2396                 }
2397                 if (!hugepage_vma_check(vma)) {
2398 skip:
2399                         progress++;
2400                         continue;
2401                 }
2402                 hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK;
2403                 hend = vma->vm_end & HPAGE_PMD_MASK;
2404                 if (hstart >= hend)
2405                         goto skip;
2406                 if (khugepaged_scan.address > hend)
2407                         goto skip;
2408                 if (khugepaged_scan.address < hstart)
2409                         khugepaged_scan.address = hstart;
2410                 VM_BUG_ON(khugepaged_scan.address & ~HPAGE_PMD_MASK);
2411
2412                 while (khugepaged_scan.address < hend) {
2413                         int ret;
2414                         cond_resched();
2415                         if (unlikely(khugepaged_test_exit(mm)))
2416                                 goto breakouterloop;
2417
2418                         VM_BUG_ON(khugepaged_scan.address < hstart ||
2419                                   khugepaged_scan.address + HPAGE_PMD_SIZE >
2420                                   hend);
2421                         ret = khugepaged_scan_pmd(mm, vma,
2422                                                   khugepaged_scan.address,
2423                                                   hpage);
2424                         /* move to next address */
2425                         khugepaged_scan.address += HPAGE_PMD_SIZE;
2426                         progress += HPAGE_PMD_NR;
2427                         if (ret)
2428                                 /* we released mmap_sem so break loop */
2429                                 goto breakouterloop_mmap_sem;
2430                         if (progress >= pages)
2431                                 goto breakouterloop;
2432                 }
2433         }
2434 breakouterloop:
2435         up_read(&mm->mmap_sem); /* exit_mmap will destroy ptes after this */
2436 breakouterloop_mmap_sem:
2437
2438         spin_lock(&khugepaged_mm_lock);
2439         VM_BUG_ON(khugepaged_scan.mm_slot != mm_slot);
2440         /*
2441          * Release the current mm_slot if this mm is about to die, or
2442          * if we scanned all vmas of this mm.
2443          */
2444         if (khugepaged_test_exit(mm) || !vma) {
2445                 /*
2446                  * Make sure that if mm_users is reaching zero while
2447                  * khugepaged runs here, khugepaged_exit will find
2448                  * mm_slot not pointing to the exiting mm.
2449                  */
2450                 if (mm_slot->mm_node.next != &khugepaged_scan.mm_head) {
2451                         khugepaged_scan.mm_slot = list_entry(
2452                                 mm_slot->mm_node.next,
2453                                 struct mm_slot, mm_node);
2454                         khugepaged_scan.address = 0;
2455                 } else {
2456                         khugepaged_scan.mm_slot = NULL;
2457                         khugepaged_full_scans++;
2458                 }
2459
2460                 collect_mm_slot(mm_slot);
2461         }
2462
2463         return progress;
2464 }
2465
2466 static int khugepaged_has_work(void)
2467 {
2468         return !list_empty(&khugepaged_scan.mm_head) &&
2469                 khugepaged_enabled();
2470 }
2471
2472 static int khugepaged_wait_event(void)
2473 {
2474         return !list_empty(&khugepaged_scan.mm_head) ||
2475                 kthread_should_stop();
2476 }
2477
2478 static void khugepaged_do_scan(void)
2479 {
2480         struct page *hpage = NULL;
2481         unsigned int progress = 0, pass_through_head = 0;
2482         unsigned int pages = khugepaged_pages_to_scan;
2483         bool wait = true;
2484
2485         barrier(); /* write khugepaged_pages_to_scan to local stack */
2486
2487         while (progress < pages) {
2488                 if (!khugepaged_prealloc_page(&hpage, &wait))
2489                         break;
2490
2491                 cond_resched();
2492
2493                 if (unlikely(kthread_should_stop() || freezing(current)))
2494                         break;
2495
2496                 spin_lock(&khugepaged_mm_lock);
2497                 if (!khugepaged_scan.mm_slot)
2498                         pass_through_head++;
2499                 if (khugepaged_has_work() &&
2500                     pass_through_head < 2)
2501                         progress += khugepaged_scan_mm_slot(pages - progress,
2502                                                             &hpage);
2503                 else
2504                         progress = pages;
2505                 spin_unlock(&khugepaged_mm_lock);
2506         }
2507
2508         if (!IS_ERR_OR_NULL(hpage))
2509                 put_page(hpage);
2510 }
2511
2512 static void khugepaged_wait_work(void)
2513 {
2514         try_to_freeze();
2515
2516         if (khugepaged_has_work()) {
2517                 if (!khugepaged_scan_sleep_millisecs)
2518                         return;
2519
2520                 wait_event_freezable_timeout(khugepaged_wait,
2521                                              kthread_should_stop(),
2522                         msecs_to_jiffies(khugepaged_scan_sleep_millisecs));
2523                 return;
2524         }
2525
2526         if (khugepaged_enabled())
2527                 wait_event_freezable(khugepaged_wait, khugepaged_wait_event());
2528 }
2529
2530 static int khugepaged(void *none)
2531 {
2532         struct mm_slot *mm_slot;
2533
2534         set_freezable();
2535         set_user_nice(current, 19);
2536
2537         while (!kthread_should_stop()) {
2538                 khugepaged_do_scan();
2539                 khugepaged_wait_work();
2540         }
2541
2542         spin_lock(&khugepaged_mm_lock);
2543         mm_slot = khugepaged_scan.mm_slot;
2544         khugepaged_scan.mm_slot = NULL;
2545         if (mm_slot)
2546                 collect_mm_slot(mm_slot);
2547         spin_unlock(&khugepaged_mm_lock);
2548         return 0;
2549 }
2550
2551 static void __split_huge_zero_page_pmd(struct vm_area_struct *vma,
2552                 unsigned long haddr, pmd_t *pmd)
2553 {
2554         struct mm_struct *mm = vma->vm_mm;
2555         pgtable_t pgtable;
2556         pmd_t _pmd;
2557         int i;
2558
2559         pmdp_clear_flush(vma, haddr, pmd);
2560         /* leave pmd empty until pte is filled */
2561
2562         pgtable = pgtable_trans_huge_withdraw(mm);
2563         pmd_populate(mm, &_pmd, pgtable);
2564
2565         for (i = 0; i < HPAGE_PMD_NR; i++, haddr += PAGE_SIZE) {
2566                 pte_t *pte, entry;
2567                 entry = pfn_pte(my_zero_pfn(haddr), vma->vm_page_prot);
2568                 entry = pte_mkspecial(entry);
2569                 pte = pte_offset_map(&_pmd, haddr);
2570                 VM_BUG_ON(!pte_none(*pte));
2571                 set_pte_at(mm, haddr, pte, entry);
2572                 pte_unmap(pte);
2573         }
2574         smp_wmb(); /* make pte visible before pmd */
2575         pmd_populate(mm, pmd, pgtable);
2576         put_huge_zero_page();
2577 }
2578
2579 void __split_huge_page_pmd(struct vm_area_struct *vma, unsigned long address,
2580                 pmd_t *pmd)
2581 {
2582         struct page *page;
2583         struct mm_struct *mm = vma->vm_mm;
2584         unsigned long haddr = address & HPAGE_PMD_MASK;
2585         unsigned long mmun_start;       /* For mmu_notifiers */
2586         unsigned long mmun_end;         /* For mmu_notifiers */
2587
2588         BUG_ON(vma->vm_start > haddr || vma->vm_end < haddr + HPAGE_PMD_SIZE);
2589
2590         mmun_start = haddr;
2591         mmun_end   = haddr + HPAGE_PMD_SIZE;
2592         mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
2593         spin_lock(&mm->page_table_lock);
2594         if (unlikely(!pmd_trans_huge(*pmd))) {
2595                 spin_unlock(&mm->page_table_lock);
2596                 mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
2597                 return;
2598         }
2599         if (is_huge_zero_pmd(*pmd)) {
2600                 __split_huge_zero_page_pmd(vma, haddr, pmd);
2601                 spin_unlock(&mm->page_table_lock);
2602                 mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
2603                 return;
2604         }
2605         page = pmd_page(*pmd);
2606         VM_BUG_ON(!page_count(page));
2607         get_page(page);
2608         spin_unlock(&mm->page_table_lock);
2609         mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
2610
2611         split_huge_page(page);
2612
2613         put_page(page);
2614         BUG_ON(pmd_trans_huge(*pmd));
2615 }
2616
2617 void split_huge_page_pmd_mm(struct mm_struct *mm, unsigned long address,
2618                 pmd_t *pmd)
2619 {
2620         struct vm_area_struct *vma;
2621
2622         vma = find_vma(mm, address);
2623         BUG_ON(vma == NULL);
2624         split_huge_page_pmd(vma, address, pmd);
2625 }
2626
2627 static void split_huge_page_address(struct mm_struct *mm,
2628                                     unsigned long address)
2629 {
2630         pmd_t *pmd;
2631
2632         VM_BUG_ON(!(address & ~HPAGE_PMD_MASK));
2633
2634         pmd = mm_find_pmd(mm, address);
2635         if (!pmd)
2636                 return;
2637         /*
2638          * Caller holds the mmap_sem write mode, so a huge pmd cannot
2639          * materialize from under us.
2640          */
2641         split_huge_page_pmd_mm(mm, address, pmd);
2642 }
2643
2644 void __vma_adjust_trans_huge(struct vm_area_struct *vma,
2645                              unsigned long start,
2646                              unsigned long end,
2647                              long adjust_next)
2648 {
2649         /*
2650          * If the new start address isn't hpage aligned and it could
2651          * previously contain an hugepage: check if we need to split
2652          * an huge pmd.
2653          */
2654         if (start & ~HPAGE_PMD_MASK &&
2655             (start & HPAGE_PMD_MASK) >= vma->vm_start &&
2656             (start & HPAGE_PMD_MASK) + HPAGE_PMD_SIZE <= vma->vm_end)
2657                 split_huge_page_address(vma->vm_mm, start);
2658
2659         /*
2660          * If the new end address isn't hpage aligned and it could
2661          * previously contain an hugepage: check if we need to split
2662          * an huge pmd.
2663          */
2664         if (end & ~HPAGE_PMD_MASK &&
2665             (end & HPAGE_PMD_MASK) >= vma->vm_start &&
2666             (end & HPAGE_PMD_MASK) + HPAGE_PMD_SIZE <= vma->vm_end)
2667                 split_huge_page_address(vma->vm_mm, end);
2668
2669         /*
2670          * If we're also updating the vma->vm_next->vm_start, if the new
2671          * vm_next->vm_start isn't page aligned and it could previously
2672          * contain an hugepage: check if we need to split an huge pmd.
2673          */
2674         if (adjust_next > 0) {
2675                 struct vm_area_struct *next = vma->vm_next;
2676                 unsigned long nstart = next->vm_start;
2677                 nstart += adjust_next << PAGE_SHIFT;
2678                 if (nstart & ~HPAGE_PMD_MASK &&
2679                     (nstart & HPAGE_PMD_MASK) >= next->vm_start &&
2680                     (nstart & HPAGE_PMD_MASK) + HPAGE_PMD_SIZE <= next->vm_end)
2681                         split_huge_page_address(next->vm_mm, nstart);
2682         }
2683 }