linux/mm/huge_memory.c
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   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#include <linux/migrate.h>
  23#include <linux/hashtable.h>
  24
  25#include <asm/tlb.h>
  26#include <asm/pgalloc.h>
  27#include "internal.h"
  28
  29/*
  30 * By default transparent hugepage support is enabled for all mappings
  31 * and khugepaged scans all mappings. Defrag is only invoked by
  32 * khugepaged hugepage allocations and by page faults inside
  33 * MADV_HUGEPAGE regions to avoid the risk of slowing down short lived
  34 * allocations.
  35 */
  36unsigned long transparent_hugepage_flags __read_mostly =
  37#ifdef CONFIG_TRANSPARENT_HUGEPAGE_ALWAYS
  38        (1<<TRANSPARENT_HUGEPAGE_FLAG)|
  39#endif
  40#ifdef CONFIG_TRANSPARENT_HUGEPAGE_MADVISE
  41        (1<<TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG)|
  42#endif
  43        (1<<TRANSPARENT_HUGEPAGE_DEFRAG_FLAG)|
  44        (1<<TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG)|
  45        (1<<TRANSPARENT_HUGEPAGE_USE_ZERO_PAGE_FLAG);
  46
  47/* default scan 8*512 pte (or vmas) every 30 second */
  48static unsigned int khugepaged_pages_to_scan __read_mostly = HPAGE_PMD_NR*8;
  49static unsigned int khugepaged_pages_collapsed;
  50static unsigned int khugepaged_full_scans;
  51static unsigned int khugepaged_scan_sleep_millisecs __read_mostly = 10000;
  52/* during fragmentation poll the hugepage allocator once every minute */
  53static unsigned int khugepaged_alloc_sleep_millisecs __read_mostly = 60000;
  54static struct task_struct *khugepaged_thread __read_mostly;
  55static DEFINE_MUTEX(khugepaged_mutex);
  56static DEFINE_SPINLOCK(khugepaged_mm_lock);
  57static DECLARE_WAIT_QUEUE_HEAD(khugepaged_wait);
  58/*
  59 * default collapse hugepages if there is at least one pte mapped like
  60 * it would have happened if the vma was large enough during page
  61 * fault.
  62 */
  63static unsigned int khugepaged_max_ptes_none __read_mostly = HPAGE_PMD_NR-1;
  64
  65static int khugepaged(void *none);
  66static int khugepaged_slab_init(void);
  67
  68#define MM_SLOTS_HASH_BITS 10
  69static __read_mostly DEFINE_HASHTABLE(mm_slots_hash, MM_SLOTS_HASH_BITS);
  70
  71static struct kmem_cache *mm_slot_cache __read_mostly;
  72
  73/**
  74 * struct mm_slot - hash lookup from mm to mm_slot
  75 * @hash: hash collision list
  76 * @mm_node: khugepaged scan list headed in khugepaged_scan.mm_head
  77 * @mm: the mm that this information is valid for
  78 */
  79struct mm_slot {
  80        struct hlist_node hash;
  81        struct list_head mm_node;
  82        struct mm_struct *mm;
  83};
  84
  85/**
  86 * struct khugepaged_scan - cursor for scanning
  87 * @mm_head: the head of the mm list to scan
  88 * @mm_slot: the current mm_slot we are scanning
  89 * @address: the next address inside that to be scanned
  90 *
  91 * There is only the one khugepaged_scan instance of this cursor structure.
  92 */
  93struct khugepaged_scan {
  94        struct list_head mm_head;
  95        struct mm_slot *mm_slot;
  96        unsigned long address;
  97};
  98static struct khugepaged_scan khugepaged_scan = {
  99        .mm_head = LIST_HEAD_INIT(khugepaged_scan.mm_head),
 100};
 101
 102
 103static int set_recommended_min_free_kbytes(void)
 104{
 105        struct zone *zone;
 106        int nr_zones = 0;
 107        unsigned long recommended_min;
 108
 109        if (!khugepaged_enabled())
 110                return 0;
 111
 112        for_each_populated_zone(zone)
 113                nr_zones++;
 114
 115        /* Make sure at least 2 hugepages are free for MIGRATE_RESERVE */
 116        recommended_min = pageblock_nr_pages * nr_zones * 2;
 117
 118        /*
 119         * Make sure that on average at least two pageblocks are almost free
 120         * of another type, one for a migratetype to fall back to and a
 121         * second to avoid subsequent fallbacks of other types There are 3
 122         * MIGRATE_TYPES we care about.
 123         */
 124        recommended_min += pageblock_nr_pages * nr_zones *
 125                           MIGRATE_PCPTYPES * MIGRATE_PCPTYPES;
 126
 127        /* don't ever allow to reserve more than 5% of the lowmem */
 128        recommended_min = min(recommended_min,
 129                              (unsigned long) nr_free_buffer_pages() / 20);
 130        recommended_min <<= (PAGE_SHIFT-10);
 131
 132        if (recommended_min > min_free_kbytes)
 133                min_free_kbytes = recommended_min;
 134        setup_per_zone_wmarks();
 135        return 0;
 136}
 137late_initcall(set_recommended_min_free_kbytes);
 138
 139static int start_khugepaged(void)
 140{
 141        int err = 0;
 142        if (khugepaged_enabled()) {
 143                if (!khugepaged_thread)
 144                        khugepaged_thread = kthread_run(khugepaged, NULL,
 145                                                        "khugepaged");
 146                if (unlikely(IS_ERR(khugepaged_thread))) {
 147                        printk(KERN_ERR
 148                               "khugepaged: kthread_run(khugepaged) failed\n");
 149                        err = PTR_ERR(khugepaged_thread);
 150                        khugepaged_thread = NULL;
 151                }
 152
 153                if (!list_empty(&khugepaged_scan.mm_head))
 154                        wake_up_interruptible(&khugepaged_wait);
 155
 156                set_recommended_min_free_kbytes();
 157        } else if (khugepaged_thread) {
 158                kthread_stop(khugepaged_thread);
 159                khugepaged_thread = NULL;
 160        }
 161
 162        return err;
 163}
 164
 165static atomic_t huge_zero_refcount;
 166static unsigned long huge_zero_pfn __read_mostly;
 167
 168static inline bool is_huge_zero_pfn(unsigned long pfn)
 169{
 170        unsigned long zero_pfn = ACCESS_ONCE(huge_zero_pfn);
 171        return zero_pfn && pfn == zero_pfn;
 172}
 173
 174static inline bool is_huge_zero_pmd(pmd_t pmd)
 175{
 176        return is_huge_zero_pfn(pmd_pfn(pmd));
 177}
 178
 179static unsigned long get_huge_zero_page(void)
 180{
 181        struct page *zero_page;
 182retry:
 183        if (likely(atomic_inc_not_zero(&huge_zero_refcount)))
 184                return ACCESS_ONCE(huge_zero_pfn);
 185
 186        zero_page = alloc_pages((GFP_TRANSHUGE | __GFP_ZERO) & ~__GFP_MOVABLE,
 187                        HPAGE_PMD_ORDER);
 188        if (!zero_page) {
 189                count_vm_event(THP_ZERO_PAGE_ALLOC_FAILED);
 190                return 0;
 191        }
 192        count_vm_event(THP_ZERO_PAGE_ALLOC);
 193        preempt_disable();
 194        if (cmpxchg(&huge_zero_pfn, 0, page_to_pfn(zero_page))) {
 195                preempt_enable();
 196                __free_page(zero_page);
 197                goto retry;
 198        }
 199
 200        /* We take additional reference here. It will be put back by shrinker */
 201        atomic_set(&huge_zero_refcount, 2);
 202        preempt_enable();
 203        return ACCESS_ONCE(huge_zero_pfn);
 204}
 205
 206static void put_huge_zero_page(void)
 207{
 208        /*
 209         * Counter should never go to zero here. Only shrinker can put
 210         * last reference.
 211         */
 212        BUG_ON(atomic_dec_and_test(&huge_zero_refcount));
 213}
 214
 215static int shrink_huge_zero_page(struct shrinker *shrink,
 216                struct shrink_control *sc)
 217{
 218        if (!sc->nr_to_scan)
 219                /* we can free zero page only if last reference remains */
 220                return atomic_read(&huge_zero_refcount) == 1 ? HPAGE_PMD_NR : 0;
 221
 222        if (atomic_cmpxchg(&huge_zero_refcount, 1, 0) == 1) {
 223                unsigned long zero_pfn = xchg(&huge_zero_pfn, 0);
 224                BUG_ON(zero_pfn == 0);
 225                __free_page(__pfn_to_page(zero_pfn));
 226        }
 227
 228        return 0;
 229}
 230
 231static struct shrinker huge_zero_page_shrinker = {
 232        .shrink = shrink_huge_zero_page,
 233        .seeks = DEFAULT_SEEKS,
 234};
 235
 236#ifdef CONFIG_SYSFS
 237
 238static ssize_t double_flag_show(struct kobject *kobj,
 239                                struct kobj_attribute *attr, char *buf,
 240                                enum transparent_hugepage_flag enabled,
 241                                enum transparent_hugepage_flag req_madv)
 242{
 243        if (test_bit(enabled, &transparent_hugepage_flags)) {
 244                VM_BUG_ON(test_bit(req_madv, &transparent_hugepage_flags));
 245                return sprintf(buf, "[always] madvise never\n");
 246        } else if (test_bit(req_madv, &transparent_hugepage_flags))
 247                return sprintf(buf, "always [madvise] never\n");
 248        else
 249                return sprintf(buf, "always madvise [never]\n");
 250}
 251static ssize_t double_flag_store(struct kobject *kobj,
 252                                 struct kobj_attribute *attr,
 253                                 const char *buf, size_t count,
 254                                 enum transparent_hugepage_flag enabled,
 255                                 enum transparent_hugepage_flag req_madv)
 256{
 257        if (!memcmp("always", buf,
 258                    min(sizeof("always")-1, count))) {
 259                set_bit(enabled, &transparent_hugepage_flags);
 260                clear_bit(req_madv, &transparent_hugepage_flags);
 261        } else if (!memcmp("madvise", buf,
 262                           min(sizeof("madvise")-1, count))) {
 263                clear_bit(enabled, &transparent_hugepage_flags);
 264                set_bit(req_madv, &transparent_hugepage_flags);
 265        } else if (!memcmp("never", buf,
 266                           min(sizeof("never")-1, count))) {
 267                clear_bit(enabled, &transparent_hugepage_flags);
 268                clear_bit(req_madv, &transparent_hugepage_flags);
 269        } else
 270                return -EINVAL;
 271
 272        return count;
 273}
 274
 275static ssize_t enabled_show(struct kobject *kobj,
 276                            struct kobj_attribute *attr, char *buf)
 277{
 278        return double_flag_show(kobj, attr, buf,
 279                                TRANSPARENT_HUGEPAGE_FLAG,
 280                                TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG);
 281}
 282static ssize_t enabled_store(struct kobject *kobj,
 283                             struct kobj_attribute *attr,
 284                             const char *buf, size_t count)
 285{
 286        ssize_t ret;
 287
 288        ret = double_flag_store(kobj, attr, buf, count,
 289                                TRANSPARENT_HUGEPAGE_FLAG,
 290                                TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG);
 291
 292        if (ret > 0) {
 293                int err;
 294
 295                mutex_lock(&khugepaged_mutex);
 296                err = start_khugepaged();
 297                mutex_unlock(&khugepaged_mutex);
 298
 299                if (err)
 300                        ret = err;
 301        }
 302
 303        return ret;
 304}
 305static struct kobj_attribute enabled_attr =
 306        __ATTR(enabled, 0644, enabled_show, enabled_store);
 307
 308static ssize_t single_flag_show(struct kobject *kobj,
 309                                struct kobj_attribute *attr, char *buf,
 310                                enum transparent_hugepage_flag flag)
 311{
 312        return sprintf(buf, "%d\n",
 313                       !!test_bit(flag, &transparent_hugepage_flags));
 314}
 315
 316static ssize_t single_flag_store(struct kobject *kobj,
 317                                 struct kobj_attribute *attr,
 318                                 const char *buf, size_t count,
 319                                 enum transparent_hugepage_flag flag)
 320{
 321        unsigned long value;
 322        int ret;
 323
 324        ret = kstrtoul(buf, 10, &value);
 325        if (ret < 0)
 326                return ret;
 327        if (value > 1)
 328                return -EINVAL;
 329
 330        if (value)
 331                set_bit(flag, &transparent_hugepage_flags);
 332        else
 333                clear_bit(flag, &transparent_hugepage_flags);
 334
 335        return count;
 336}
 337
 338/*
 339 * Currently defrag only disables __GFP_NOWAIT for allocation. A blind
 340 * __GFP_REPEAT is too aggressive, it's never worth swapping tons of
 341 * memory just to allocate one more hugepage.
 342 */
 343static ssize_t defrag_show(struct kobject *kobj,
 344                           struct kobj_attribute *attr, char *buf)
 345{
 346        return double_flag_show(kobj, attr, buf,
 347                                TRANSPARENT_HUGEPAGE_DEFRAG_FLAG,
 348                                TRANSPARENT_HUGEPAGE_DEFRAG_REQ_MADV_FLAG);
 349}
 350static ssize_t defrag_store(struct kobject *kobj,
 351                            struct kobj_attribute *attr,
 352                            const char *buf, size_t count)
 353{
 354        return double_flag_store(kobj, attr, buf, count,
 355                                 TRANSPARENT_HUGEPAGE_DEFRAG_FLAG,
 356                                 TRANSPARENT_HUGEPAGE_DEFRAG_REQ_MADV_FLAG);
 357}
 358static struct kobj_attribute defrag_attr =
 359        __ATTR(defrag, 0644, defrag_show, defrag_store);
 360
 361static ssize_t use_zero_page_show(struct kobject *kobj,
 362                struct kobj_attribute *attr, char *buf)
 363{
 364        return single_flag_show(kobj, attr, buf,
 365                                TRANSPARENT_HUGEPAGE_USE_ZERO_PAGE_FLAG);
 366}
 367static ssize_t use_zero_page_store(struct kobject *kobj,
 368                struct kobj_attribute *attr, const char *buf, size_t count)
 369{
 370        return single_flag_store(kobj, attr, buf, count,
 371                                 TRANSPARENT_HUGEPAGE_USE_ZERO_PAGE_FLAG);
 372}
 373static struct kobj_attribute use_zero_page_attr =
 374        __ATTR(use_zero_page, 0644, use_zero_page_show, use_zero_page_store);
 375#ifdef CONFIG_DEBUG_VM
 376static ssize_t debug_cow_show(struct kobject *kobj,
 377                                struct kobj_attribute *attr, char *buf)
 378{
 379        return single_flag_show(kobj, attr, buf,
 380                                TRANSPARENT_HUGEPAGE_DEBUG_COW_FLAG);
 381}
 382static ssize_t debug_cow_store(struct kobject *kobj,
 383                               struct kobj_attribute *attr,
 384                               const char *buf, size_t count)
 385{
 386        return single_flag_store(kobj, attr, buf, count,
 387                                 TRANSPARENT_HUGEPAGE_DEBUG_COW_FLAG);
 388}
 389static struct kobj_attribute debug_cow_attr =
 390        __ATTR(debug_cow, 0644, debug_cow_show, debug_cow_store);
 391#endif /* CONFIG_DEBUG_VM */
 392
 393static struct attribute *hugepage_attr[] = {
 394        &enabled_attr.attr,
 395        &defrag_attr.attr,
 396        &use_zero_page_attr.attr,
 397#ifdef CONFIG_DEBUG_VM
 398        &debug_cow_attr.attr,
 399#endif
 400        NULL,
 401};
 402
 403static struct attribute_group hugepage_attr_group = {
 404        .attrs = hugepage_attr,
 405};
 406
 407static ssize_t scan_sleep_millisecs_show(struct kobject *kobj,
 408                                         struct kobj_attribute *attr,
 409                                         char *buf)
 410{
 411        return sprintf(buf, "%u\n", khugepaged_scan_sleep_millisecs);
 412}
 413
 414static ssize_t scan_sleep_millisecs_store(struct kobject *kobj,
 415                                          struct kobj_attribute *attr,
 416                                          const char *buf, size_t count)
 417{
 418        unsigned long msecs;
 419        int err;
 420
 421        err = strict_strtoul(buf, 10, &msecs);
 422        if (err || msecs > UINT_MAX)
 423                return -EINVAL;
 424
 425        khugepaged_scan_sleep_millisecs = msecs;
 426        wake_up_interruptible(&khugepaged_wait);
 427
 428        return count;
 429}
 430static struct kobj_attribute scan_sleep_millisecs_attr =
 431        __ATTR(scan_sleep_millisecs, 0644, scan_sleep_millisecs_show,
 432               scan_sleep_millisecs_store);
 433
 434static ssize_t alloc_sleep_millisecs_show(struct kobject *kobj,
 435                                          struct kobj_attribute *attr,
 436                                          char *buf)
 437{
 438        return sprintf(buf, "%u\n", khugepaged_alloc_sleep_millisecs);
 439}
 440
 441static ssize_t alloc_sleep_millisecs_store(struct kobject *kobj,
 442                                           struct kobj_attribute *attr,
 443                                           const char *buf, size_t count)
 444{
 445        unsigned long msecs;
 446        int err;
 447
 448        err = strict_strtoul(buf, 10, &msecs);
 449        if (err || msecs > UINT_MAX)
 450                return -EINVAL;
 451
 452        khugepaged_alloc_sleep_millisecs = msecs;
 453        wake_up_interruptible(&khugepaged_wait);
 454
 455        return count;
 456}
 457static struct kobj_attribute alloc_sleep_millisecs_attr =
 458        __ATTR(alloc_sleep_millisecs, 0644, alloc_sleep_millisecs_show,
 459               alloc_sleep_millisecs_store);
 460
 461static ssize_t pages_to_scan_show(struct kobject *kobj,
 462                                  struct kobj_attribute *attr,
 463                                  char *buf)
 464{
 465        return sprintf(buf, "%u\n", khugepaged_pages_to_scan);
 466}
 467static ssize_t pages_to_scan_store(struct kobject *kobj,
 468                                   struct kobj_attribute *attr,
 469                                   const char *buf, size_t count)
 470{
 471        int err;
 472        unsigned long pages;
 473
 474        err = strict_strtoul(buf, 10, &pages);
 475        if (err || !pages || pages > UINT_MAX)
 476                return -EINVAL;
 477
 478        khugepaged_pages_to_scan = pages;
 479
 480        return count;
 481}
 482static struct kobj_attribute pages_to_scan_attr =
 483        __ATTR(pages_to_scan, 0644, pages_to_scan_show,
 484               pages_to_scan_store);
 485
 486static ssize_t pages_collapsed_show(struct kobject *kobj,
 487                                    struct kobj_attribute *attr,
 488                                    char *buf)
 489{
 490        return sprintf(buf, "%u\n", khugepaged_pages_collapsed);
 491}
 492static struct kobj_attribute pages_collapsed_attr =
 493        __ATTR_RO(pages_collapsed);
 494
 495static ssize_t full_scans_show(struct kobject *kobj,
 496                               struct kobj_attribute *attr,
 497                               char *buf)
 498{
 499        return sprintf(buf, "%u\n", khugepaged_full_scans);
 500}
 501static struct kobj_attribute full_scans_attr =
 502        __ATTR_RO(full_scans);
 503
 504static ssize_t khugepaged_defrag_show(struct kobject *kobj,
 505                                      struct kobj_attribute *attr, char *buf)
 506{
 507        return single_flag_show(kobj, attr, buf,
 508                                TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG);
 509}
 510static ssize_t khugepaged_defrag_store(struct kobject *kobj,
 511                                       struct kobj_attribute *attr,
 512                                       const char *buf, size_t count)
 513{
 514        return single_flag_store(kobj, attr, buf, count,
 515                                 TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG);
 516}
 517static struct kobj_attribute khugepaged_defrag_attr =
 518        __ATTR(defrag, 0644, khugepaged_defrag_show,
 519               khugepaged_defrag_store);
 520
 521/*
 522 * max_ptes_none controls if khugepaged should collapse hugepages over
 523 * any unmapped ptes in turn potentially increasing the memory
 524 * footprint of the vmas. When max_ptes_none is 0 khugepaged will not
 525 * reduce the available free memory in the system as it
 526 * runs. Increasing max_ptes_none will instead potentially reduce the
 527 * free memory in the system during the khugepaged scan.
 528 */
 529static ssize_t khugepaged_max_ptes_none_show(struct kobject *kobj,
 530                                             struct kobj_attribute *attr,
 531                                             char *buf)
 532{
 533        return sprintf(buf, "%u\n", khugepaged_max_ptes_none);
 534}
 535static ssize_t khugepaged_max_ptes_none_store(struct kobject *kobj,
 536                                              struct kobj_attribute *attr,
 537                                              const char *buf, size_t count)
 538{
 539        int err;
 540        unsigned long max_ptes_none;
 541
 542        err = strict_strtoul(buf, 10, &max_ptes_none);
 543        if (err || max_ptes_none > HPAGE_PMD_NR-1)
 544                return -EINVAL;
 545
 546        khugepaged_max_ptes_none = max_ptes_none;
 547
 548        return count;
 549}
 550static struct kobj_attribute khugepaged_max_ptes_none_attr =
 551        __ATTR(max_ptes_none, 0644, khugepaged_max_ptes_none_show,
 552               khugepaged_max_ptes_none_store);
 553
 554static struct attribute *khugepaged_attr[] = {
 555        &khugepaged_defrag_attr.attr,
 556        &khugepaged_max_ptes_none_attr.attr,
 557        &pages_to_scan_attr.attr,
 558        &pages_collapsed_attr.attr,
 559        &full_scans_attr.attr,
 560        &scan_sleep_millisecs_attr.attr,
 561        &alloc_sleep_millisecs_attr.attr,
 562        NULL,
 563};
 564
 565static struct attribute_group khugepaged_attr_group = {
 566        .attrs = khugepaged_attr,
 567        .name = "khugepaged",
 568};
 569
 570static int __init hugepage_init_sysfs(struct kobject **hugepage_kobj)
 571{
 572        int err;
 573
 574        *hugepage_kobj = kobject_create_and_add("transparent_hugepage", mm_kobj);
 575        if (unlikely(!*hugepage_kobj)) {
 576                printk(KERN_ERR "hugepage: failed to create transparent hugepage kobject\n");
 577                return -ENOMEM;
 578        }
 579
 580        err = sysfs_create_group(*hugepage_kobj, &hugepage_attr_group);
 581        if (err) {
 582                printk(KERN_ERR "hugepage: failed to register transparent hugepage group\n");
 583                goto delete_obj;
 584        }
 585
 586        err = sysfs_create_group(*hugepage_kobj, &khugepaged_attr_group);
 587        if (err) {
 588                printk(KERN_ERR "hugepage: failed to register transparent hugepage group\n");
 589                goto remove_hp_group;
 590        }
 591
 592        return 0;
 593
 594remove_hp_group:
 595        sysfs_remove_group(*hugepage_kobj, &hugepage_attr_group);
 596delete_obj:
 597        kobject_put(*hugepage_kobj);
 598        return err;
 599}
 600
 601static void __init hugepage_exit_sysfs(struct kobject *hugepage_kobj)
 602{
 603        sysfs_remove_group(hugepage_kobj, &khugepaged_attr_group);
 604        sysfs_remove_group(hugepage_kobj, &hugepage_attr_group);
 605        kobject_put(hugepage_kobj);
 606}
 607#else
 608static inline int hugepage_init_sysfs(struct kobject **hugepage_kobj)
 609{
 610        return 0;
 611}
 612
 613static inline void hugepage_exit_sysfs(struct kobject *hugepage_kobj)
 614{
 615}
 616#endif /* CONFIG_SYSFS */
 617
 618static int __init hugepage_init(void)
 619{
 620        int err;
 621        struct kobject *hugepage_kobj;
 622
 623        if (!has_transparent_hugepage()) {
 624                transparent_hugepage_flags = 0;
 625                return -EINVAL;
 626        }
 627
 628        err = hugepage_init_sysfs(&hugepage_kobj);
 629        if (err)
 630                return err;
 631
 632        err = khugepaged_slab_init();
 633        if (err)
 634                goto out;
 635
 636        register_shrinker(&huge_zero_page_shrinker);
 637
 638        /*
 639         * By default disable transparent hugepages on smaller systems,
 640         * where the extra memory used could hurt more than TLB overhead
 641         * is likely to save.  The admin can still enable it through /sys.
 642         */
 643        if (totalram_pages < (512 << (20 - PAGE_SHIFT)))
 644                transparent_hugepage_flags = 0;
 645
 646        start_khugepaged();
 647
 648        return 0;
 649out:
 650        hugepage_exit_sysfs(hugepage_kobj);
 651        return err;
 652}
 653module_init(hugepage_init)
 654
 655static int __init setup_transparent_hugepage(char *str)
 656{
 657        int ret = 0;
 658        if (!str)
 659                goto out;
 660        if (!strcmp(str, "always")) {
 661                set_bit(TRANSPARENT_HUGEPAGE_FLAG,
 662                        &transparent_hugepage_flags);
 663                clear_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG,
 664                          &transparent_hugepage_flags);
 665                ret = 1;
 666        } else if (!strcmp(str, "madvise")) {
 667                clear_bit(TRANSPARENT_HUGEPAGE_FLAG,
 668                          &transparent_hugepage_flags);
 669                set_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG,
 670                        &transparent_hugepage_flags);
 671                ret = 1;
 672        } else if (!strcmp(str, "never")) {
 673                clear_bit(TRANSPARENT_HUGEPAGE_FLAG,
 674                          &transparent_hugepage_flags);
 675                clear_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG,
 676                          &transparent_hugepage_flags);
 677                ret = 1;
 678        }
 679out:
 680        if (!ret)
 681                printk(KERN_WARNING
 682                       "transparent_hugepage= cannot parse, ignored\n");
 683        return ret;
 684}
 685__setup("transparent_hugepage=", setup_transparent_hugepage);
 686
 687pmd_t maybe_pmd_mkwrite(pmd_t pmd, struct vm_area_struct *vma)
 688{
 689        if (likely(vma->vm_flags & VM_WRITE))
 690                pmd = pmd_mkwrite(pmd);
 691        return pmd;
 692}
 693
 694static inline pmd_t mk_huge_pmd(struct page *page, struct vm_area_struct *vma)
 695{
 696        pmd_t entry;
 697        entry = mk_pmd(page, vma->vm_page_prot);
 698        entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
 699        entry = pmd_mkhuge(entry);
 700        return entry;
 701}
 702
 703static int __do_huge_pmd_anonymous_page(struct mm_struct *mm,
 704                                        struct vm_area_struct *vma,
 705                                        unsigned long haddr, pmd_t *pmd,
 706                                        struct page *page)
 707{
 708        pgtable_t pgtable;
 709
 710        VM_BUG_ON(!PageCompound(page));
 711        pgtable = pte_alloc_one(mm, haddr);
 712        if (unlikely(!pgtable))
 713                return VM_FAULT_OOM;
 714
 715        clear_huge_page(page, haddr, HPAGE_PMD_NR);
 716        __SetPageUptodate(page);
 717
 718        spin_lock(&mm->page_table_lock);
 719        if (unlikely(!pmd_none(*pmd))) {
 720                spin_unlock(&mm->page_table_lock);
 721                mem_cgroup_uncharge_page(page);
 722                put_page(page);
 723                pte_free(mm, pgtable);
 724        } else {
 725                pmd_t entry;
 726                entry = mk_huge_pmd(page, vma);
 727                /*
 728                 * The spinlocking to take the lru_lock inside
 729                 * page_add_new_anon_rmap() acts as a full memory
 730                 * barrier to be sure clear_huge_page writes become
 731                 * visible after the set_pmd_at() write.
 732                 */
 733                page_add_new_anon_rmap(page, vma, haddr);
 734                set_pmd_at(mm, haddr, pmd, entry);
 735                pgtable_trans_huge_deposit(mm, pgtable);
 736                add_mm_counter(mm, MM_ANONPAGES, HPAGE_PMD_NR);
 737                mm->nr_ptes++;
 738                spin_unlock(&mm->page_table_lock);
 739        }
 740
 741        return 0;
 742}
 743
 744static inline gfp_t alloc_hugepage_gfpmask(int defrag, gfp_t extra_gfp)
 745{
 746        return (GFP_TRANSHUGE & ~(defrag ? 0 : __GFP_WAIT)) | extra_gfp;
 747}
 748
 749static inline struct page *alloc_hugepage_vma(int defrag,
 750                                              struct vm_area_struct *vma,
 751                                              unsigned long haddr, int nd,
 752                                              gfp_t extra_gfp)
 753{
 754        return alloc_pages_vma(alloc_hugepage_gfpmask(defrag, extra_gfp),
 755                               HPAGE_PMD_ORDER, vma, haddr, nd);
 756}
 757
 758#ifndef CONFIG_NUMA
 759static inline struct page *alloc_hugepage(int defrag)
 760{
 761        return alloc_pages(alloc_hugepage_gfpmask(defrag, 0),
 762                           HPAGE_PMD_ORDER);
 763}
 764#endif
 765
 766static bool set_huge_zero_page(pgtable_t pgtable, struct mm_struct *mm,
 767                struct vm_area_struct *vma, unsigned long haddr, pmd_t *pmd,
 768                unsigned long zero_pfn)
 769{
 770        pmd_t entry;
 771        if (!pmd_none(*pmd))
 772                return false;
 773        entry = pfn_pmd(zero_pfn, vma->vm_page_prot);
 774        entry = pmd_wrprotect(entry);
 775        entry = pmd_mkhuge(entry);
 776        set_pmd_at(mm, haddr, pmd, entry);
 777        pgtable_trans_huge_deposit(mm, pgtable);
 778        mm->nr_ptes++;
 779        return true;
 780}
 781
 782int do_huge_pmd_anonymous_page(struct mm_struct *mm, struct vm_area_struct *vma,
 783                               unsigned long address, pmd_t *pmd,
 784                               unsigned int flags)
 785{
 786        struct page *page;
 787        unsigned long haddr = address & HPAGE_PMD_MASK;
 788        pte_t *pte;
 789
 790        if (haddr >= vma->vm_start && haddr + HPAGE_PMD_SIZE <= vma->vm_end) {
 791                if (unlikely(anon_vma_prepare(vma)))
 792                        return VM_FAULT_OOM;
 793                if (unlikely(khugepaged_enter(vma)))
 794                        return VM_FAULT_OOM;
 795                if (!(flags & FAULT_FLAG_WRITE) &&
 796                                transparent_hugepage_use_zero_page()) {
 797                        pgtable_t pgtable;
 798                        unsigned long zero_pfn;
 799                        bool set;
 800                        pgtable = pte_alloc_one(mm, haddr);
 801                        if (unlikely(!pgtable))
 802                                return VM_FAULT_OOM;
 803                        zero_pfn = get_huge_zero_page();
 804                        if (unlikely(!zero_pfn)) {
 805                                pte_free(mm, pgtable);
 806                                count_vm_event(THP_FAULT_FALLBACK);
 807                                goto out;
 808                        }
 809                        spin_lock(&mm->page_table_lock);
 810                        set = set_huge_zero_page(pgtable, mm, vma, haddr, pmd,
 811                                        zero_pfn);
 812                        spin_unlock(&mm->page_table_lock);
 813                        if (!set) {
 814                                pte_free(mm, pgtable);
 815                                put_huge_zero_page();
 816                        }
 817                        return 0;
 818                }
 819                page = alloc_hugepage_vma(transparent_hugepage_defrag(vma),
 820                                          vma, haddr, numa_node_id(), 0);
 821                if (unlikely(!page)) {
 822                        count_vm_event(THP_FAULT_FALLBACK);
 823                        goto out;
 824                }
 825                count_vm_event(THP_FAULT_ALLOC);
 826                if (unlikely(mem_cgroup_newpage_charge(page, mm, GFP_KERNEL))) {
 827                        put_page(page);
 828                        goto out;
 829                }
 830                if (unlikely(__do_huge_pmd_anonymous_page(mm, vma, haddr, pmd,
 831                                                          page))) {
 832                        mem_cgroup_uncharge_page(page);
 833                        put_page(page);
 834                        goto out;
 835                }
 836
 837                return 0;
 838        }
 839out:
 840        /*
 841         * Use __pte_alloc instead of pte_alloc_map, because we can't
 842         * run pte_offset_map on the pmd, if an huge pmd could
 843         * materialize from under us from a different thread.
 844         */
 845        if (unlikely(pmd_none(*pmd)) &&
 846            unlikely(__pte_alloc(mm, vma, pmd, address)))
 847                return VM_FAULT_OOM;
 848        /* if an huge pmd materialized from under us just retry later */
 849        if (unlikely(pmd_trans_huge(*pmd)))
 850                return 0;
 851        /*
 852         * A regular pmd is established and it can't morph into a huge pmd
 853         * from under us anymore at this point because we hold the mmap_sem
 854         * read mode and khugepaged takes it in write mode. So now it's
 855         * safe to run pte_offset_map().
 856         */
 857        pte = pte_offset_map(pmd, address);
 858        return handle_pte_fault(mm, vma, address, pte, pmd, flags);
 859}
 860
 861int copy_huge_pmd(struct mm_struct *dst_mm, struct mm_struct *src_mm,
 862                  pmd_t *dst_pmd, pmd_t *src_pmd, unsigned long addr,
 863                  struct vm_area_struct *vma)
 864{
 865        struct page *src_page;
 866        pmd_t pmd;
 867        pgtable_t pgtable;
 868        int ret;
 869
 870        ret = -ENOMEM;
 871        pgtable = pte_alloc_one(dst_mm, addr);
 872        if (unlikely(!pgtable))
 873                goto out;
 874
 875        spin_lock(&dst_mm->page_table_lock);
 876        spin_lock_nested(&src_mm->page_table_lock, SINGLE_DEPTH_NESTING);
 877
 878        ret = -EAGAIN;
 879        pmd = *src_pmd;
 880        if (unlikely(!pmd_trans_huge(pmd))) {
 881                pte_free(dst_mm, pgtable);
 882                goto out_unlock;
 883        }
 884        /*
 885         * mm->page_table_lock is enough to be sure that huge zero pmd is not
 886         * under splitting since we don't split the page itself, only pmd to
 887         * a page table.
 888         */
 889        if (is_huge_zero_pmd(pmd)) {
 890                unsigned long zero_pfn;
 891                bool set;
 892                /*
 893                 * get_huge_zero_page() will never allocate a new page here,
 894                 * since we already have a zero page to copy. It just takes a
 895                 * reference.
 896                 */
 897                zero_pfn = get_huge_zero_page();
 898                set = set_huge_zero_page(pgtable, dst_mm, vma, addr, dst_pmd,
 899                                zero_pfn);
 900                BUG_ON(!set); /* unexpected !pmd_none(dst_pmd) */
 901                ret = 0;
 902                goto out_unlock;
 903        }
 904        if (unlikely(pmd_trans_splitting(pmd))) {
 905                /* split huge page running from under us */
 906                spin_unlock(&src_mm->page_table_lock);
 907                spin_unlock(&dst_mm->page_table_lock);
 908                pte_free(dst_mm, pgtable);
 909
 910                wait_split_huge_page(vma->anon_vma, src_pmd); /* src_vma */
 911                goto out;
 912        }
 913        src_page = pmd_page(pmd);
 914        VM_BUG_ON(!PageHead(src_page));
 915        get_page(src_page);
 916        page_dup_rmap(src_page);
 917        add_mm_counter(dst_mm, MM_ANONPAGES, HPAGE_PMD_NR);
 918
 919        pmdp_set_wrprotect(src_mm, addr, src_pmd);
 920        pmd = pmd_mkold(pmd_wrprotect(pmd));
 921        set_pmd_at(dst_mm, addr, dst_pmd, pmd);
 922        pgtable_trans_huge_deposit(dst_mm, pgtable);
 923        dst_mm->nr_ptes++;
 924
 925        ret = 0;
 926out_unlock:
 927        spin_unlock(&src_mm->page_table_lock);
 928        spin_unlock(&dst_mm->page_table_lock);
 929out:
 930        return ret;
 931}
 932
 933void huge_pmd_set_accessed(struct mm_struct *mm,
 934                           struct vm_area_struct *vma,
 935                           unsigned long address,
 936                           pmd_t *pmd, pmd_t orig_pmd,
 937                           int dirty)
 938{
 939        pmd_t entry;
 940        unsigned long haddr;
 941
 942        spin_lock(&mm->page_table_lock);
 943        if (unlikely(!pmd_same(*pmd, orig_pmd)))
 944                goto unlock;
 945
 946        entry = pmd_mkyoung(orig_pmd);
 947        haddr = address & HPAGE_PMD_MASK;
 948        if (pmdp_set_access_flags(vma, haddr, pmd, entry, dirty))
 949                update_mmu_cache_pmd(vma, address, pmd);
 950
 951unlock:
 952        spin_unlock(&mm->page_table_lock);
 953}
 954
 955static int do_huge_pmd_wp_zero_page_fallback(struct mm_struct *mm,
 956                struct vm_area_struct *vma, unsigned long address,
 957                pmd_t *pmd, pmd_t orig_pmd, unsigned long haddr)
 958{
 959        pgtable_t pgtable;
 960        pmd_t _pmd;
 961        struct page *page;
 962        int i, ret = 0;
 963        unsigned long mmun_start;       /* For mmu_notifiers */
 964        unsigned long mmun_end;         /* For mmu_notifiers */
 965
 966        page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma, address);
 967        if (!page) {
 968                ret |= VM_FAULT_OOM;
 969                goto out;
 970        }
 971
 972        if (mem_cgroup_newpage_charge(page, mm, GFP_KERNEL)) {
 973                put_page(page);
 974                ret |= VM_FAULT_OOM;
 975                goto out;
 976        }
 977
 978        clear_user_highpage(page, address);
 979        __SetPageUptodate(page);
 980
 981        mmun_start = haddr;
 982        mmun_end   = haddr + HPAGE_PMD_SIZE;
 983        mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
 984
 985        spin_lock(&mm->page_table_lock);
 986        if (unlikely(!pmd_same(*pmd, orig_pmd)))
 987                goto out_free_page;
 988
 989        pmdp_clear_flush(vma, haddr, pmd);
 990        /* leave pmd empty until pte is filled */
 991
 992        pgtable = pgtable_trans_huge_withdraw(mm);
 993        pmd_populate(mm, &_pmd, pgtable);
 994
 995        for (i = 0; i < HPAGE_PMD_NR; i++, haddr += PAGE_SIZE) {
 996                pte_t *pte, entry;
 997                if (haddr == (address & PAGE_MASK)) {
 998                        entry = mk_pte(page, vma->vm_page_prot);
 999                        entry = maybe_mkwrite(pte_mkdirty(entry), vma);
1000                        page_add_new_anon_rmap(page, vma, haddr);
1001                } else {
1002                        entry = pfn_pte(my_zero_pfn(haddr), vma->vm_page_prot);
1003                        entry = pte_mkspecial(entry);
1004                }
1005                pte = pte_offset_map(&_pmd, haddr);
1006                VM_BUG_ON(!pte_none(*pte));
1007                set_pte_at(mm, haddr, pte, entry);
1008                pte_unmap(pte);
1009        }
1010        smp_wmb(); /* make pte visible before pmd */
1011        pmd_populate(mm, pmd, pgtable);
1012        spin_unlock(&mm->page_table_lock);
1013        put_huge_zero_page();
1014        inc_mm_counter(mm, MM_ANONPAGES);
1015
1016        mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
1017
1018        ret |= VM_FAULT_WRITE;
1019out:
1020        return ret;
1021out_free_page:
1022        spin_unlock(&mm->page_table_lock);
1023        mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
1024        mem_cgroup_uncharge_page(page);
1025        put_page(page);
1026        goto out;
1027}
1028
1029static int do_huge_pmd_wp_page_fallback(struct mm_struct *mm,
1030                                        struct vm_area_struct *vma,
1031                                        unsigned long address,
1032                                        pmd_t *pmd, pmd_t orig_pmd,
1033                                        struct page *page,
1034                                        unsigned long haddr)
1035{
1036        pgtable_t pgtable;
1037        pmd_t _pmd;
1038        int ret = 0, i;
1039        struct page **pages;
1040        unsigned long mmun_start;       /* For mmu_notifiers */
1041        unsigned long mmun_end;         /* For mmu_notifiers */
1042
1043        pages = kmalloc(sizeof(struct page *) * HPAGE_PMD_NR,
1044                        GFP_KERNEL);
1045        if (unlikely(!pages)) {
1046                ret |= VM_FAULT_OOM;
1047                goto out;
1048        }
1049
1050        for (i = 0; i < HPAGE_PMD_NR; i++) {
1051                pages[i] = alloc_page_vma_node(GFP_HIGHUSER_MOVABLE |
1052                                               __GFP_OTHER_NODE,
1053                                               vma, address, page_to_nid(page));
1054                if (unlikely(!pages[i] ||
1055                             mem_cgroup_newpage_charge(pages[i], mm,
1056                                                       GFP_KERNEL))) {
1057                        if (pages[i])
1058                                put_page(pages[i]);
1059                        mem_cgroup_uncharge_start();
1060                        while (--i >= 0) {
1061                                mem_cgroup_uncharge_page(pages[i]);
1062                                put_page(pages[i]);
1063                        }
1064                        mem_cgroup_uncharge_end();
1065                        kfree(pages);
1066                        ret |= VM_FAULT_OOM;
1067                        goto out;
1068                }
1069        }
1070
1071        for (i = 0; i < HPAGE_PMD_NR; i++) {
1072                copy_user_highpage(pages[i], page + i,
1073                                   haddr + PAGE_SIZE * i, vma);
1074                __SetPageUptodate(pages[i]);
1075                cond_resched();
1076        }
1077
1078        mmun_start = haddr;
1079        mmun_end   = haddr + HPAGE_PMD_SIZE;
1080        mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
1081
1082        spin_lock(&mm->page_table_lock);
1083        if (unlikely(!pmd_same(*pmd, orig_pmd)))
1084                goto out_free_pages;
1085        VM_BUG_ON(!PageHead(page));
1086
1087        pmdp_clear_flush(vma, haddr, pmd);
1088        /* leave pmd empty until pte is filled */
1089
1090        pgtable = pgtable_trans_huge_withdraw(mm);
1091        pmd_populate(mm, &_pmd, pgtable);
1092
1093        for (i = 0; i < HPAGE_PMD_NR; i++, haddr += PAGE_SIZE) {
1094                pte_t *pte, entry;
1095                entry = mk_pte(pages[i], vma->vm_page_prot);
1096                entry = maybe_mkwrite(pte_mkdirty(entry), vma);
1097                page_add_new_anon_rmap(pages[i], vma, haddr);
1098                pte = pte_offset_map(&_pmd, haddr);
1099                VM_BUG_ON(!pte_none(*pte));
1100                set_pte_at(mm, haddr, pte, entry);
1101                pte_unmap(pte);
1102        }
1103        kfree(pages);
1104
1105        smp_wmb(); /* make pte visible before pmd */
1106        pmd_populate(mm, pmd, pgtable);
1107        page_remove_rmap(page);
1108        spin_unlock(&mm->page_table_lock);
1109
1110        mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
1111
1112        ret |= VM_FAULT_WRITE;
1113        put_page(page);
1114
1115out:
1116        return ret;
1117
1118out_free_pages:
1119        spin_unlock(&mm->page_table_lock);
1120        mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
1121        mem_cgroup_uncharge_start();
1122        for (i = 0; i < HPAGE_PMD_NR; i++) {
1123                mem_cgroup_uncharge_page(pages[i]);
1124                put_page(pages[i]);
1125        }
1126        mem_cgroup_uncharge_end();
1127        kfree(pages);
1128        goto out;
1129}
1130
1131int do_huge_pmd_wp_page(struct mm_struct *mm, struct vm_area_struct *vma,
1132                        unsigned long address, pmd_t *pmd, pmd_t orig_pmd)
1133{
1134        int ret = 0;
1135        struct page *page = NULL, *new_page;
1136        unsigned long haddr;
1137        unsigned long mmun_start;       /* For mmu_notifiers */
1138        unsigned long mmun_end;         /* For mmu_notifiers */
1139
1140        VM_BUG_ON(!vma->anon_vma);
1141        haddr = address & HPAGE_PMD_MASK;
1142        if (is_huge_zero_pmd(orig_pmd))
1143                goto alloc;
1144        spin_lock(&mm->page_table_lock);
1145        if (unlikely(!pmd_same(*pmd, orig_pmd)))
1146                goto out_unlock;
1147
1148        page = pmd_page(orig_pmd);
1149        VM_BUG_ON(!PageCompound(page) || !PageHead(page));
1150        if (page_mapcount(page) == 1) {
1151                pmd_t entry;
1152                entry = pmd_mkyoung(orig_pmd);
1153                entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
1154                if (pmdp_set_access_flags(vma, haddr, pmd, entry,  1))
1155                        update_mmu_cache_pmd(vma, address, pmd);
1156                ret |= VM_FAULT_WRITE;
1157                goto out_unlock;
1158        }
1159        get_page(page);
1160        spin_unlock(&mm->page_table_lock);
1161alloc:
1162        if (transparent_hugepage_enabled(vma) &&
1163            !transparent_hugepage_debug_cow())
1164                new_page = alloc_hugepage_vma(transparent_hugepage_defrag(vma),
1165                                              vma, haddr, numa_node_id(), 0);
1166        else
1167                new_page = NULL;
1168
1169        if (unlikely(!new_page)) {
1170                count_vm_event(THP_FAULT_FALLBACK);
1171                if (is_huge_zero_pmd(orig_pmd)) {
1172                        ret = do_huge_pmd_wp_zero_page_fallback(mm, vma,
1173                                        address, pmd, orig_pmd, haddr);
1174                } else {
1175                        ret = do_huge_pmd_wp_page_fallback(mm, vma, address,
1176                                        pmd, orig_pmd, page, haddr);
1177                        if (ret & VM_FAULT_OOM)
1178                                split_huge_page(page);
1179                        put_page(page);
1180                }
1181                goto out;
1182        }
1183        count_vm_event(THP_FAULT_ALLOC);
1184
1185        if (unlikely(mem_cgroup_newpage_charge(new_page, mm, GFP_KERNEL))) {
1186                put_page(new_page);
1187                if (page) {
1188                        split_huge_page(page);
1189                        put_page(page);
1190                }
1191                ret |= VM_FAULT_OOM;
1192                goto out;
1193        }
1194
1195        if (is_huge_zero_pmd(orig_pmd))
1196                clear_huge_page(new_page, haddr, HPAGE_PMD_NR);
1197        else
1198                copy_user_huge_page(new_page, page, haddr, vma, HPAGE_PMD_NR);
1199        __SetPageUptodate(new_page);
1200
1201        mmun_start = haddr;
1202        mmun_end   = haddr + HPAGE_PMD_SIZE;
1203        mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
1204
1205        spin_lock(&mm->page_table_lock);
1206        if (page)
1207                put_page(page);
1208        if (unlikely(!pmd_same(*pmd, orig_pmd))) {
1209                spin_unlock(&mm->page_table_lock);
1210                mem_cgroup_uncharge_page(new_page);
1211                put_page(new_page);
1212                goto out_mn;
1213        } else {
1214                pmd_t entry;
1215                entry = mk_huge_pmd(new_page, vma);
1216                pmdp_clear_flush(vma, haddr, pmd);
1217                page_add_new_anon_rmap(new_page, vma, haddr);
1218                set_pmd_at(mm, haddr, pmd, entry);
1219                update_mmu_cache_pmd(vma, address, pmd);
1220                if (is_huge_zero_pmd(orig_pmd)) {
1221                        add_mm_counter(mm, MM_ANONPAGES, HPAGE_PMD_NR);
1222                        put_huge_zero_page();
1223                } else {
1224                        VM_BUG_ON(!PageHead(page));
1225                        page_remove_rmap(page);
1226                        put_page(page);
1227                }
1228                ret |= VM_FAULT_WRITE;
1229        }
1230        spin_unlock(&mm->page_table_lock);
1231out_mn:
1232        mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
1233out:
1234        return ret;
1235out_unlock:
1236        spin_unlock(&mm->page_table_lock);
1237        return ret;
1238}
1239
1240struct page *follow_trans_huge_pmd(struct vm_area_struct *vma,
1241                                   unsigned long addr,
1242                                   pmd_t *pmd,
1243                                   unsigned int flags)
1244{
1245        struct mm_struct *mm = vma->vm_mm;
1246        struct page *page = NULL;
1247
1248        assert_spin_locked(&mm->page_table_lock);
1249
1250        if (flags & FOLL_WRITE && !pmd_write(*pmd))
1251                goto out;
1252
1253        /* Avoid dumping huge zero page */
1254        if ((flags & FOLL_DUMP) && is_huge_zero_pmd(*pmd))
1255                return ERR_PTR(-EFAULT);
1256
1257        page = pmd_page(*pmd);
1258        VM_BUG_ON(!PageHead(page));
1259        if (flags & FOLL_TOUCH) {
1260                pmd_t _pmd;
1261                /*
1262                 * We should set the dirty bit only for FOLL_WRITE but
1263                 * for now the dirty bit in the pmd is meaningless.
1264                 * And if the dirty bit will become meaningful and
1265                 * we'll only set it with FOLL_WRITE, an atomic
1266                 * set_bit will be required on the pmd to set the
1267                 * young bit, instead of the current set_pmd_at.
1268                 */
1269                _pmd = pmd_mkyoung(pmd_mkdirty(*pmd));
1270                set_pmd_at(mm, addr & HPAGE_PMD_MASK, pmd, _pmd);
1271        }
1272        if ((flags & FOLL_MLOCK) && (vma->vm_flags & VM_LOCKED)) {
1273                if (page->mapping && trylock_page(page)) {
1274                        lru_add_drain();
1275                        if (page->mapping)
1276                                mlock_vma_page(page);
1277                        unlock_page(page);
1278                }
1279        }
1280        page += (addr & ~HPAGE_PMD_MASK) >> PAGE_SHIFT;
1281        VM_BUG_ON(!PageCompound(page));
1282        if (flags & FOLL_GET)
1283                get_page_foll(page);
1284
1285out:
1286        return page;
1287}
1288
1289/* NUMA hinting page fault entry point for trans huge pmds */
1290int do_huge_pmd_numa_page(struct mm_struct *mm, struct vm_area_struct *vma,
1291                                unsigned long addr, pmd_t pmd, pmd_t *pmdp)
1292{
1293        struct page *page;
1294        unsigned long haddr = addr & HPAGE_PMD_MASK;
1295        int target_nid;
1296        int current_nid = -1;
1297        bool migrated;
1298
1299        spin_lock(&mm->page_table_lock);
1300        if (unlikely(!pmd_same(pmd, *pmdp)))
1301                goto out_unlock;
1302
1303        page = pmd_page(pmd);
1304        get_page(page);
1305        current_nid = page_to_nid(page);
1306        count_vm_numa_event(NUMA_HINT_FAULTS);
1307        if (current_nid == numa_node_id())
1308                count_vm_numa_event(NUMA_HINT_FAULTS_LOCAL);
1309
1310        target_nid = mpol_misplaced(page, vma, haddr);
1311        if (target_nid == -1) {
1312                put_page(page);
1313                goto clear_pmdnuma;
1314        }
1315
1316        /* Acquire the page lock to serialise THP migrations */
1317        spin_unlock(&mm->page_table_lock);
1318        lock_page(page);
1319
1320        /* Confirm the PTE did not while locked */
1321        spin_lock(&mm->page_table_lock);
1322        if (unlikely(!pmd_same(pmd, *pmdp))) {
1323                unlock_page(page);
1324                put_page(page);
1325                goto out_unlock;
1326        }
1327        spin_unlock(&mm->page_table_lock);
1328
1329        /* Migrate the THP to the requested node */
1330        migrated = migrate_misplaced_transhuge_page(mm, vma,
1331                                pmdp, pmd, addr, page, target_nid);
1332        if (!migrated)
1333                goto check_same;
1334
1335        task_numa_fault(target_nid, HPAGE_PMD_NR, true);
1336        return 0;
1337
1338check_same:
1339        spin_lock(&mm->page_table_lock);
1340        if (unlikely(!pmd_same(pmd, *pmdp)))
1341                goto out_unlock;
1342clear_pmdnuma:
1343        pmd = pmd_mknonnuma(pmd);
1344        set_pmd_at(mm, haddr, pmdp, pmd);
1345        VM_BUG_ON(pmd_numa(*pmdp));
1346        update_mmu_cache_pmd(vma, addr, pmdp);
1347out_unlock:
1348        spin_unlock(&mm->page_table_lock);
1349        if (current_nid != -1)
1350                task_numa_fault(current_nid, HPAGE_PMD_NR, false);
1351        return 0;
1352}
1353
1354int zap_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
1355                 pmd_t *pmd, unsigned long addr)
1356{
1357        int ret = 0;
1358
1359        if (__pmd_trans_huge_lock(pmd, vma) == 1) {
1360                struct page *page;
1361                pgtable_t pgtable;
1362                pmd_t orig_pmd;
1363                pgtable = pgtable_trans_huge_withdraw(tlb->mm);
1364                orig_pmd = pmdp_get_and_clear(tlb->mm, addr, pmd);
1365                tlb_remove_pmd_tlb_entry(tlb, pmd, addr);
1366                if (is_huge_zero_pmd(orig_pmd)) {
1367                        tlb->mm->nr_ptes--;
1368                        spin_unlock(&tlb->mm->page_table_lock);
1369                        put_huge_zero_page();
1370                } else {
1371                        page = pmd_page(orig_pmd);
1372                        page_remove_rmap(page);
1373                        VM_BUG_ON(page_mapcount(page) < 0);
1374                        add_mm_counter(tlb->mm, MM_ANONPAGES, -HPAGE_PMD_NR);
1375                        VM_BUG_ON(!PageHead(page));
1376                        tlb->mm->nr_ptes--;
1377                        spin_unlock(&tlb->mm->page_table_lock);
1378                        tlb_remove_page(tlb, page);
1379                }
1380                pte_free(tlb->mm, pgtable);
1381                ret = 1;
1382        }
1383        return ret;
1384}
1385
1386int mincore_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
1387                unsigned long addr, unsigned long end,
1388                unsigned char *vec)
1389{
1390        int ret = 0;
1391
1392        if (__pmd_trans_huge_lock(pmd, vma) == 1) {
1393                /*
1394                 * All logical pages in the range are present
1395                 * if backed by a huge page.
1396                 */
1397                spin_unlock(&vma->vm_mm->page_table_lock);
1398                memset(vec, 1, (end - addr) >> PAGE_SHIFT);
1399                ret = 1;
1400        }
1401
1402        return ret;
1403}
1404
1405int move_huge_pmd(struct vm_area_struct *vma, struct vm_area_struct *new_vma,
1406                  unsigned long old_addr,
1407                  unsigned long new_addr, unsigned long old_end,
1408                  pmd_t *old_pmd, pmd_t *new_pmd)
1409{
1410        int ret = 0;
1411        pmd_t pmd;
1412
1413        struct mm_struct *mm = vma->vm_mm;
1414
1415        if ((old_addr & ~HPAGE_PMD_MASK) ||
1416            (new_addr & ~HPAGE_PMD_MASK) ||
1417            old_end - old_addr < HPAGE_PMD_SIZE ||
1418            (new_vma->vm_flags & VM_NOHUGEPAGE))
1419                goto out;
1420
1421        /*
1422         * The destination pmd shouldn't be established, free_pgtables()
1423         * should have release it.
1424         */
1425        if (WARN_ON(!pmd_none(*new_pmd))) {
1426                VM_BUG_ON(pmd_trans_huge(*new_pmd));
1427                goto out;
1428        }
1429
1430        ret = __pmd_trans_huge_lock(old_pmd, vma);
1431        if (ret == 1) {
1432                pmd = pmdp_get_and_clear(mm, old_addr, old_pmd);
1433                VM_BUG_ON(!pmd_none(*new_pmd));
1434                set_pmd_at(mm, new_addr, new_pmd, pmd);
1435                spin_unlock(&mm->page_table_lock);
1436        }
1437out:
1438        return ret;
1439}
1440
1441int change_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
1442                unsigned long addr, pgprot_t newprot, int prot_numa)
1443{
1444        struct mm_struct *mm = vma->vm_mm;
1445        int ret = 0;
1446
1447        if (__pmd_trans_huge_lock(pmd, vma) == 1) {
1448                pmd_t entry;
1449                entry = pmdp_get_and_clear(mm, addr, pmd);
1450                if (!prot_numa) {
1451                        entry = pmd_modify(entry, newprot);
1452                        BUG_ON(pmd_write(entry));
1453                } else {
1454                        struct page *page = pmd_page(*pmd);
1455
1456                        /* only check non-shared pages */
1457                        if (page_mapcount(page) == 1 &&
1458                            !pmd_numa(*pmd)) {
1459                                entry = pmd_mknuma(entry);
1460                        }
1461                }
1462                set_pmd_at(mm, addr, pmd, entry);
1463                spin_unlock(&vma->vm_mm->page_table_lock);
1464                ret = 1;
1465        }
1466
1467        return ret;
1468}
1469
1470/*
1471 * Returns 1 if a given pmd maps a stable (not under splitting) thp.
1472 * Returns -1 if it maps a thp under splitting. Returns 0 otherwise.
1473 *
1474 * Note that if it returns 1, this routine returns without unlocking page
1475 * table locks. So callers must unlock them.
1476 */
1477int __pmd_trans_huge_lock(pmd_t *pmd, struct vm_area_struct *vma)
1478{
1479        spin_lock(&vma->vm_mm->page_table_lock);
1480        if (likely(pmd_trans_huge(*pmd))) {
1481                if (unlikely(pmd_trans_splitting(*pmd))) {
1482                        spin_unlock(&vma->vm_mm->page_table_lock);
1483                        wait_split_huge_page(vma->anon_vma, pmd);
1484                        return -1;
1485                } else {
1486                        /* Thp mapped by 'pmd' is stable, so we can
1487                         * handle it as it is. */
1488                        return 1;
1489                }
1490        }
1491        spin_unlock(&vma->vm_mm->page_table_lock);
1492        return 0;
1493}
1494
1495pmd_t *page_check_address_pmd(struct page *page,
1496                              struct mm_struct *mm,
1497                              unsigned long address,
1498                              enum page_check_address_pmd_flag flag)
1499{
1500        pmd_t *pmd, *ret = NULL;
1501
1502        if (address & ~HPAGE_PMD_MASK)
1503                goto out;
1504
1505        pmd = mm_find_pmd(mm, address);
1506        if (!pmd)
1507                goto out;
1508        if (pmd_none(*pmd))
1509                goto out;
1510        if (pmd_page(*pmd) != page)
1511                goto out;
1512        /*
1513         * split_vma() may create temporary aliased mappings. There is
1514         * no risk as long as all huge pmd are found and have their
1515         * splitting bit set before __split_huge_page_refcount
1516         * runs. Finding the same huge pmd more than once during the
1517         * same rmap walk is not a problem.
1518         */
1519        if (flag == PAGE_CHECK_ADDRESS_PMD_NOTSPLITTING_FLAG &&
1520            pmd_trans_splitting(*pmd))
1521                goto out;
1522        if (pmd_trans_huge(*pmd)) {
1523                VM_BUG_ON(flag == PAGE_CHECK_ADDRESS_PMD_SPLITTING_FLAG &&
1524                          !pmd_trans_splitting(*pmd));
1525                ret = pmd;
1526        }
1527out:
1528        return ret;
1529}
1530
1531static int __split_huge_page_splitting(struct page *page,
1532                                       struct vm_area_struct *vma,
1533                                       unsigned long address)
1534{
1535        struct mm_struct *mm = vma->vm_mm;
1536        pmd_t *pmd;
1537        int ret = 0;
1538        /* For mmu_notifiers */
1539        const unsigned long mmun_start = address;
1540        const unsigned long mmun_end   = address + HPAGE_PMD_SIZE;
1541
1542        mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
1543        spin_lock(&mm->page_table_lock);
1544        pmd = page_check_address_pmd(page, mm, address,
1545                                     PAGE_CHECK_ADDRESS_PMD_NOTSPLITTING_FLAG);
1546        if (pmd) {
1547                /*
1548                 * We can't temporarily set the pmd to null in order
1549                 * to split it, the pmd must remain marked huge at all
1550                 * times or the VM won't take the pmd_trans_huge paths
1551                 * and it won't wait on the anon_vma->root->rwsem to
1552                 * serialize against split_huge_page*.
1553                 */
1554                pmdp_splitting_flush(vma, address, pmd);
1555                ret = 1;
1556        }
1557        spin_unlock(&mm->page_table_lock);
1558        mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
1559
1560        return ret;
1561}
1562
1563static void __split_huge_page_refcount(struct page *page)
1564{
1565        int i;
1566        struct zone *zone = page_zone(page);
1567        struct lruvec *lruvec;
1568        int tail_count = 0;
1569
1570        /* prevent PageLRU to go away from under us, and freeze lru stats */
1571        spin_lock_irq(&zone->lru_lock);
1572        lruvec = mem_cgroup_page_lruvec(page, zone);
1573
1574        compound_lock(page);
1575        /* complete memcg works before add pages to LRU */
1576        mem_cgroup_split_huge_fixup(page);
1577
1578        for (i = HPAGE_PMD_NR - 1; i >= 1; i--) {
1579                struct page *page_tail = page + i;
1580
1581                /* tail_page->_mapcount cannot change */
1582                BUG_ON(page_mapcount(page_tail) < 0);
1583                tail_count += page_mapcount(page_tail);
1584                /* check for overflow */
1585                BUG_ON(tail_count < 0);
1586                BUG_ON(atomic_read(&page_tail->_count) != 0);
1587                /*
1588                 * tail_page->_count is zero and not changing from
1589                 * under us. But get_page_unless_zero() may be running
1590                 * from under us on the tail_page. If we used
1591                 * atomic_set() below instead of atomic_add(), we
1592                 * would then run atomic_set() concurrently with
1593                 * get_page_unless_zero(), and atomic_set() is
1594                 * implemented in C not using locked ops. spin_unlock
1595                 * on x86 sometime uses locked ops because of PPro
1596                 * errata 66, 92, so unless somebody can guarantee
1597                 * atomic_set() here would be safe on all archs (and
1598                 * not only on x86), it's safer to use atomic_add().
1599                 */
1600                atomic_add(page_mapcount(page) + page_mapcount(page_tail) + 1,
1601                           &page_tail->_count);
1602
1603                /* after clearing PageTail the gup refcount can be released */
1604                smp_mb();
1605
1606                /*
1607                 * retain hwpoison flag of the poisoned tail page:
1608                 *   fix for the unsuitable process killed on Guest Machine(KVM)
1609                 *   by the memory-failure.
1610                 */
1611                page_tail->flags &= ~PAGE_FLAGS_CHECK_AT_PREP | __PG_HWPOISON;
1612                page_tail->flags |= (page->flags &
1613                                     ((1L << PG_referenced) |
1614                                      (1L << PG_swapbacked) |
1615                                      (1L << PG_mlocked) |
1616                                      (1L << PG_uptodate)));
1617                page_tail->flags |= (1L << PG_dirty);
1618
1619                /* clear PageTail before overwriting first_page */
1620                smp_wmb();
1621
1622                /*
1623                 * __split_huge_page_splitting() already set the
1624                 * splitting bit in all pmd that could map this
1625                 * hugepage, that will ensure no CPU can alter the
1626                 * mapcount on the head page. The mapcount is only
1627                 * accounted in the head page and it has to be
1628                 * transferred to all tail pages in the below code. So
1629                 * for this code to be safe, the split the mapcount
1630                 * can't change. But that doesn't mean userland can't
1631                 * keep changing and reading the page contents while
1632                 * we transfer the mapcount, so the pmd splitting
1633                 * status is achieved setting a reserved bit in the
1634                 * pmd, not by clearing the present bit.
1635                */
1636                page_tail->_mapcount = page->_mapcount;
1637
1638                BUG_ON(page_tail->mapping);
1639                page_tail->mapping = page->mapping;
1640
1641                page_tail->index = page->index + i;
1642                page_nid_xchg_last(page_tail, page_nid_last(page));
1643
1644                BUG_ON(!PageAnon(page_tail));
1645                BUG_ON(!PageUptodate(page_tail));
1646                BUG_ON(!PageDirty(page_tail));
1647                BUG_ON(!PageSwapBacked(page_tail));
1648
1649                lru_add_page_tail(page, page_tail, lruvec);
1650        }
1651        atomic_sub(tail_count, &page->_count);
1652        BUG_ON(atomic_read(&page->_count) <= 0);
1653
1654        __mod_zone_page_state(zone, NR_ANON_TRANSPARENT_HUGEPAGES, -1);
1655        __mod_zone_page_state(zone, NR_ANON_PAGES, HPAGE_PMD_NR);
1656
1657        ClearPageCompound(page);
1658        compound_unlock(page);
1659        spin_unlock_irq(&zone->lru_lock);
1660
1661        for (i = 1; i < HPAGE_PMD_NR; i++) {
1662                struct page *page_tail = page + i;
1663                BUG_ON(page_count(page_tail) <= 0);
1664                /*
1665                 * Tail pages may be freed if there wasn't any mapping
1666                 * like if add_to_swap() is running on a lru page that
1667                 * had its mapping zapped. And freeing these pages
1668                 * requires taking the lru_lock so we do the put_page
1669                 * of the tail pages after the split is complete.
1670                 */
1671                put_page(page_tail);
1672        }
1673
1674        /*
1675         * Only the head page (now become a regular page) is required
1676         * to be pinned by the caller.
1677         */
1678        BUG_ON(page_count(page) <= 0);
1679}
1680
1681static int __split_huge_page_map(struct page *page,
1682                                 struct vm_area_struct *vma,
1683                                 unsigned long address)
1684{
1685        struct mm_struct *mm = vma->vm_mm;
1686        pmd_t *pmd, _pmd;
1687        int ret = 0, i;
1688        pgtable_t pgtable;
1689        unsigned long haddr;
1690
1691        spin_lock(&mm->page_table_lock);
1692        pmd = page_check_address_pmd(page, mm, address,
1693                                     PAGE_CHECK_ADDRESS_PMD_SPLITTING_FLAG);
1694        if (pmd) {
1695                pgtable = pgtable_trans_huge_withdraw(mm);
1696                pmd_populate(mm, &_pmd, pgtable);
1697
1698                haddr = address;
1699                for (i = 0; i < HPAGE_PMD_NR; i++, haddr += PAGE_SIZE) {
1700                        pte_t *pte, entry;
1701                        BUG_ON(PageCompound(page+i));
1702                        entry = mk_pte(page + i, vma->vm_page_prot);
1703                        entry = maybe_mkwrite(pte_mkdirty(entry), vma);
1704                        if (!pmd_write(*pmd))
1705                                entry = pte_wrprotect(entry);
1706                        else
1707                                BUG_ON(page_mapcount(page) != 1);
1708                        if (!pmd_young(*pmd))
1709                                entry = pte_mkold(entry);
1710                        if (pmd_numa(*pmd))
1711                                entry = pte_mknuma(entry);
1712                        pte = pte_offset_map(&_pmd, haddr);
1713                        BUG_ON(!pte_none(*pte));
1714                        set_pte_at(mm, haddr, pte, entry);
1715                        pte_unmap(pte);
1716                }
1717
1718                smp_wmb(); /* make pte visible before pmd */
1719                /*
1720                 * Up to this point the pmd is present and huge and
1721                 * userland has the whole access to the hugepage
1722                 * during the split (which happens in place). If we
1723                 * overwrite the pmd with the not-huge version
1724                 * pointing to the pte here (which of course we could
1725                 * if all CPUs were bug free), userland could trigger
1726                 * a small page size TLB miss on the small sized TLB
1727                 * while the hugepage TLB entry is still established
1728                 * in the huge TLB. Some CPU doesn't like that. See
1729                 * http://support.amd.com/us/Processor_TechDocs/41322.pdf,
1730                 * Erratum 383 on page 93. Intel should be safe but is
1731                 * also warns that it's only safe if the permission
1732                 * and cache attributes of the two entries loaded in
1733                 * the two TLB is identical (which should be the case
1734                 * here). But it is generally safer to never allow
1735                 * small and huge TLB entries for the same virtual
1736                 * address to be loaded simultaneously. So instead of
1737                 * doing "pmd_populate(); flush_tlb_range();" we first
1738                 * mark the current pmd notpresent (atomically because
1739                 * here the pmd_trans_huge and pmd_trans_splitting
1740                 * must remain set at all times on the pmd until the
1741                 * split is complete for this pmd), then we flush the
1742                 * SMP TLB and finally we write the non-huge version
1743                 * of the pmd entry with pmd_populate.
1744                 */
1745                pmdp_invalidate(vma, address, pmd);
1746                pmd_populate(mm, pmd, pgtable);
1747                ret = 1;
1748        }
1749        spin_unlock(&mm->page_table_lock);
1750
1751        return ret;
1752}
1753
1754/* must be called with anon_vma->root->rwsem held */
1755static void __split_huge_page(struct page *page,
1756                              struct anon_vma *anon_vma)
1757{
1758        int mapcount, mapcount2;
1759        pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
1760        struct anon_vma_chain *avc;
1761
1762        BUG_ON(!PageHead(page));
1763        BUG_ON(PageTail(page));
1764
1765        mapcount = 0;
1766        anon_vma_interval_tree_foreach(avc, &anon_vma->rb_root, pgoff, pgoff) {
1767                struct vm_area_struct *vma = avc->vma;
1768                unsigned long addr = vma_address(page, vma);
1769                BUG_ON(is_vma_temporary_stack(vma));
1770                mapcount += __split_huge_page_splitting(page, vma, addr);
1771        }
1772        /*
1773         * It is critical that new vmas are added to the tail of the
1774         * anon_vma list. This guarantes that if copy_huge_pmd() runs
1775         * and establishes a child pmd before
1776         * __split_huge_page_splitting() freezes the parent pmd (so if
1777         * we fail to prevent copy_huge_pmd() from running until the
1778         * whole __split_huge_page() is complete), we will still see
1779         * the newly established pmd of the child later during the
1780         * walk, to be able to set it as pmd_trans_splitting too.
1781         */
1782        if (mapcount != page_mapcount(page))
1783                printk(KERN_ERR "mapcount %d page_mapcount %d\n",
1784                       mapcount, page_mapcount(page));
1785        BUG_ON(mapcount != page_mapcount(page));
1786
1787        __split_huge_page_refcount(page);
1788
1789        mapcount2 = 0;
1790        anon_vma_interval_tree_foreach(avc, &anon_vma->rb_root, pgoff, pgoff) {
1791                struct vm_area_struct *vma = avc->vma;
1792                unsigned long addr = vma_address(page, vma);
1793                BUG_ON(is_vma_temporary_stack(vma));
1794                mapcount2 += __split_huge_page_map(page, vma, addr);
1795        }
1796        if (mapcount != mapcount2)
1797                printk(KERN_ERR "mapcount %d mapcount2 %d page_mapcount %d\n",
1798                       mapcount, mapcount2, page_mapcount(page));
1799        BUG_ON(mapcount != mapcount2);
1800}
1801
1802int split_huge_page(struct page *page)
1803{
1804        struct anon_vma *anon_vma;
1805        int ret = 1;
1806
1807        BUG_ON(is_huge_zero_pfn(page_to_pfn(page)));
1808        BUG_ON(!PageAnon(page));
1809
1810        /*
1811         * The caller does not necessarily hold an mmap_sem that would prevent
1812         * the anon_vma disappearing so we first we take a reference to it
1813         * and then lock the anon_vma for write. This is similar to
1814         * page_lock_anon_vma_read except the write lock is taken to serialise
1815         * against parallel split or collapse operations.
1816         */
1817        anon_vma = page_get_anon_vma(page);
1818        if (!anon_vma)
1819                goto out;
1820        anon_vma_lock_write(anon_vma);
1821
1822        ret = 0;
1823        if (!PageCompound(page))
1824                goto out_unlock;
1825
1826        BUG_ON(!PageSwapBacked(page));
1827        __split_huge_page(page, anon_vma);
1828        count_vm_event(THP_SPLIT);
1829
1830        BUG_ON(PageCompound(page));
1831out_unlock:
1832        anon_vma_unlock_write(anon_vma);
1833        put_anon_vma(anon_vma);
1834out:
1835        return ret;
1836}
1837
1838#define VM_NO_THP (VM_SPECIAL|VM_MIXEDMAP|VM_HUGETLB|VM_SHARED|VM_MAYSHARE)
1839
1840int hugepage_madvise(struct vm_area_struct *vma,
1841                     unsigned long *vm_flags, int advice)
1842{
1843        struct mm_struct *mm = vma->vm_mm;
1844
1845        switch (advice) {
1846        case MADV_HUGEPAGE:
1847                /*
1848                 * Be somewhat over-protective like KSM for now!
1849                 */
1850                if (*vm_flags & (VM_HUGEPAGE | VM_NO_THP))
1851                        return -EINVAL;
1852                if (mm->def_flags & VM_NOHUGEPAGE)
1853                        return -EINVAL;
1854                *vm_flags &= ~VM_NOHUGEPAGE;
1855                *vm_flags |= VM_HUGEPAGE;
1856                /*
1857                 * If the vma become good for khugepaged to scan,
1858                 * register it here without waiting a page fault that
1859                 * may not happen any time soon.
1860                 */
1861                if (unlikely(khugepaged_enter_vma_merge(vma)))
1862                        return -ENOMEM;
1863                break;
1864        case MADV_NOHUGEPAGE:
1865                /*
1866                 * Be somewhat over-protective like KSM for now!
1867                 */
1868                if (*vm_flags & (VM_NOHUGEPAGE | VM_NO_THP))
1869                        return -EINVAL;
1870                *vm_flags &= ~VM_HUGEPAGE;
1871                *vm_flags |= VM_NOHUGEPAGE;
1872                /*
1873                 * Setting VM_NOHUGEPAGE will prevent khugepaged from scanning
1874                 * this vma even if we leave the mm registered in khugepaged if
1875                 * it got registered before VM_NOHUGEPAGE was set.
1876                 */
1877                break;
1878        }
1879
1880        return 0;
1881}
1882
1883static int __init khugepaged_slab_init(void)
1884{
1885        mm_slot_cache = kmem_cache_create("khugepaged_mm_slot",
1886                                          sizeof(struct mm_slot),
1887                                          __alignof__(struct mm_slot), 0, NULL);
1888        if (!mm_slot_cache)
1889                return -ENOMEM;
1890
1891        return 0;
1892}
1893
1894static inline struct mm_slot *alloc_mm_slot(void)
1895{
1896        if (!mm_slot_cache)     /* initialization failed */
1897                return NULL;
1898        return kmem_cache_zalloc(mm_slot_cache, GFP_KERNEL);
1899}
1900
1901static inline void free_mm_slot(struct mm_slot *mm_slot)
1902{
1903        kmem_cache_free(mm_slot_cache, mm_slot);
1904}
1905
1906static struct mm_slot *get_mm_slot(struct mm_struct *mm)
1907{
1908        struct mm_slot *mm_slot;
1909
1910        hash_for_each_possible(mm_slots_hash, mm_slot, hash, (unsigned long)mm)
1911                if (mm == mm_slot->mm)
1912                        return mm_slot;
1913
1914        return NULL;
1915}
1916
1917static void insert_to_mm_slots_hash(struct mm_struct *mm,
1918                                    struct mm_slot *mm_slot)
1919{
1920        mm_slot->mm = mm;
1921        hash_add(mm_slots_hash, &mm_slot->hash, (long)mm);
1922}
1923
1924static inline int khugepaged_test_exit(struct mm_struct *mm)
1925{
1926        return atomic_read(&mm->mm_users) == 0;
1927}
1928
1929int __khugepaged_enter(struct mm_struct *mm)
1930{
1931        struct mm_slot *mm_slot;
1932        int wakeup;
1933
1934        mm_slot = alloc_mm_slot();
1935        if (!mm_slot)
1936                return -ENOMEM;
1937
1938        /* __khugepaged_exit() must not run from under us */
1939        VM_BUG_ON(khugepaged_test_exit(mm));
1940        if (unlikely(test_and_set_bit(MMF_VM_HUGEPAGE, &mm->flags))) {
1941                free_mm_slot(mm_slot);
1942                return 0;
1943        }
1944
1945        spin_lock(&khugepaged_mm_lock);
1946        insert_to_mm_slots_hash(mm, mm_slot);
1947        /*
1948         * Insert just behind the scanning cursor, to let the area settle
1949         * down a little.
1950         */
1951        wakeup = list_empty(&khugepaged_scan.mm_head);
1952        list_add_tail(&mm_slot->mm_node, &khugepaged_scan.mm_head);
1953        spin_unlock(&khugepaged_mm_lock);
1954
1955        atomic_inc(&mm->mm_count);
1956        if (wakeup)
1957                wake_up_interruptible(&khugepaged_wait);
1958
1959        return 0;
1960}
1961
1962int khugepaged_enter_vma_merge(struct vm_area_struct *vma)
1963{
1964        unsigned long hstart, hend;
1965        if (!vma->anon_vma)
1966                /*
1967                 * Not yet faulted in so we will register later in the
1968                 * page fault if needed.
1969                 */
1970                return 0;
1971        if (vma->vm_ops)
1972                /* khugepaged not yet working on file or special mappings */
1973                return 0;
1974        VM_BUG_ON(vma->vm_flags & VM_NO_THP);
1975        hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK;
1976        hend = vma->vm_end & HPAGE_PMD_MASK;
1977        if (hstart < hend)
1978                return khugepaged_enter(vma);
1979        return 0;
1980}
1981
1982void __khugepaged_exit(struct mm_struct *mm)
1983{
1984        struct mm_slot *mm_slot;
1985        int free = 0;
1986
1987        spin_lock(&khugepaged_mm_lock);
1988        mm_slot = get_mm_slot(mm);
1989        if (mm_slot && khugepaged_scan.mm_slot != mm_slot) {
1990                hash_del(&mm_slot->hash);
1991                list_del(&mm_slot->mm_node);
1992                free = 1;
1993        }
1994        spin_unlock(&khugepaged_mm_lock);
1995
1996        if (free) {
1997                clear_bit(MMF_VM_HUGEPAGE, &mm->flags);
1998                free_mm_slot(mm_slot);
1999                mmdrop(mm);
2000        } else if (mm_slot) {
2001                /*
2002                 * This is required to serialize against
2003                 * khugepaged_test_exit() (which is guaranteed to run
2004                 * under mmap sem read mode). Stop here (after we
2005                 * return all pagetables will be destroyed) until
2006                 * khugepaged has finished working on the pagetables
2007                 * under the mmap_sem.
2008                 */
2009                down_write(&mm->mmap_sem);
2010                up_write(&mm->mmap_sem);
2011        }
2012}
2013
2014static void release_pte_page(struct page *page)
2015{
2016        /* 0 stands for page_is_file_cache(page) == false */
2017        dec_zone_page_state(page, NR_ISOLATED_ANON + 0);
2018        unlock_page(page);
2019        putback_lru_page(page);
2020}
2021
2022static void release_pte_pages(pte_t *pte, pte_t *_pte)
2023{
2024        while (--_pte >= pte) {
2025                pte_t pteval = *_pte;
2026                if (!pte_none(pteval))
2027                        release_pte_page(pte_page(pteval));
2028        }
2029}
2030
2031static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
2032                                        unsigned long address,
2033                                        pte_t *pte)
2034{
2035        struct page *page;
2036        pte_t *_pte;
2037        int referenced = 0, none = 0;
2038        for (_pte = pte; _pte < pte+HPAGE_PMD_NR;
2039             _pte++, address += PAGE_SIZE) {
2040                pte_t pteval = *_pte;
2041                if (pte_none(pteval)) {
2042                        if (++none <= khugepaged_max_ptes_none)
2043                                continue;
2044                        else
2045                                goto out;
2046                }
2047                if (!pte_present(pteval) || !pte_write(pteval))
2048                        goto out;
2049                page = vm_normal_page(vma, address, pteval);
2050                if (unlikely(!page))
2051                        goto out;
2052
2053                VM_BUG_ON(PageCompound(page));
2054                BUG_ON(!PageAnon(page));
2055                VM_BUG_ON(!PageSwapBacked(page));
2056
2057                /* cannot use mapcount: can't collapse if there's a gup pin */
2058                if (page_count(page) != 1)
2059                        goto out;
2060                /*
2061                 * We can do it before isolate_lru_page because the
2062                 * page can't be freed from under us. NOTE: PG_lock
2063                 * is needed to serialize against split_huge_page
2064                 * when invoked from the VM.
2065                 */
2066                if (!trylock_page(page))
2067                        goto out;
2068                /*
2069                 * Isolate the page to avoid collapsing an hugepage
2070                 * currently in use by the VM.
2071                 */
2072                if (isolate_lru_page(page)) {
2073                        unlock_page(page);
2074                        goto out;
2075                }
2076                /* 0 stands for page_is_file_cache(page) == false */
2077                inc_zone_page_state(page, NR_ISOLATED_ANON + 0);
2078                VM_BUG_ON(!PageLocked(page));
2079                VM_BUG_ON(PageLRU(page));
2080
2081                /* If there is no mapped pte young don't collapse the page */
2082                if (pte_young(pteval) || PageReferenced(page) ||
2083                    mmu_notifier_test_young(vma->vm_mm, address))
2084                        referenced = 1;
2085        }
2086        if (likely(referenced))
2087                return 1;
2088out:
2089        release_pte_pages(pte, _pte);
2090        return 0;
2091}
2092
2093static void __collapse_huge_page_copy(pte_t *pte, struct page *page,
2094                                      struct vm_area_struct *vma,
2095                                      unsigned long address,
2096                                      spinlock_t *ptl)
2097{
2098        pte_t *_pte;
2099        for (_pte = pte; _pte < pte+HPAGE_PMD_NR; _pte++) {
2100                pte_t pteval = *_pte;
2101                struct page *src_page;
2102
2103                if (pte_none(pteval)) {
2104                        clear_user_highpage(page, address);
2105                        add_mm_counter(vma->vm_mm, MM_ANONPAGES, 1);
2106                } else {
2107                        src_page = pte_page(pteval);
2108                        copy_user_highpage(page, src_page, address, vma);
2109                        VM_BUG_ON(page_mapcount(src_page) != 1);
2110                        release_pte_page(src_page);
2111                        /*
2112                         * ptl mostly unnecessary, but preempt has to
2113                         * be disabled to update the per-cpu stats
2114                         * inside page_remove_rmap().
2115                         */
2116                        spin_lock(ptl);
2117                        /*
2118                         * paravirt calls inside pte_clear here are
2119                         * superfluous.
2120                         */
2121                        pte_clear(vma->vm_mm, address, _pte);
2122                        page_remove_rmap(src_page);
2123                        spin_unlock(ptl);
2124                        free_page_and_swap_cache(src_page);
2125                }
2126
2127                address += PAGE_SIZE;
2128                page++;
2129        }
2130}
2131
2132static void khugepaged_alloc_sleep(void)
2133{
2134        wait_event_freezable_timeout(khugepaged_wait, false,
2135                        msecs_to_jiffies(khugepaged_alloc_sleep_millisecs));
2136}
2137
2138#ifdef CONFIG_NUMA
2139static bool khugepaged_prealloc_page(struct page **hpage, bool *wait)
2140{
2141        if (IS_ERR(*hpage)) {
2142                if (!*wait)
2143                        return false;
2144
2145                *wait = false;
2146                *hpage = NULL;
2147                khugepaged_alloc_sleep();
2148        } else if (*hpage) {
2149                put_page(*hpage);
2150                *hpage = NULL;
2151        }
2152
2153        return true;
2154}
2155
2156static struct page
2157*khugepaged_alloc_page(struct page **hpage, struct mm_struct *mm,
2158                       struct vm_area_struct *vma, unsigned long address,
2159                       int node)
2160{
2161        VM_BUG_ON(*hpage);
2162        /*
2163         * Allocate the page while the vma is still valid and under
2164         * the mmap_sem read mode so there is no memory allocation
2165         * later when we take the mmap_sem in write mode. This is more
2166         * friendly behavior (OTOH it may actually hide bugs) to
2167         * filesystems in userland with daemons allocating memory in
2168         * the userland I/O paths.  Allocating memory with the
2169         * mmap_sem in read mode is good idea also to allow greater
2170         * scalability.
2171         */
2172        *hpage  = alloc_hugepage_vma(khugepaged_defrag(), vma, address,
2173                                      node, __GFP_OTHER_NODE);
2174
2175        /*
2176         * After allocating the hugepage, release the mmap_sem read lock in
2177         * preparation for taking it in write mode.
2178         */
2179        up_read(&mm->mmap_sem);
2180        if (unlikely(!*hpage)) {
2181                count_vm_event(THP_COLLAPSE_ALLOC_FAILED);
2182                *hpage = ERR_PTR(-ENOMEM);
2183                return NULL;
2184        }
2185
2186        count_vm_event(THP_COLLAPSE_ALLOC);
2187        return *hpage;
2188}
2189#else
2190static struct page *khugepaged_alloc_hugepage(bool *wait)
2191{
2192        struct page *hpage;
2193
2194        do {
2195                hpage = alloc_hugepage(khugepaged_defrag());
2196                if (!hpage) {
2197                        count_vm_event(THP_COLLAPSE_ALLOC_FAILED);
2198                        if (!*wait)
2199                                return NULL;
2200
2201                        *wait = false;
2202                        khugepaged_alloc_sleep();
2203                } else
2204                        count_vm_event(THP_COLLAPSE_ALLOC);
2205        } while (unlikely(!hpage) && likely(khugepaged_enabled()));
2206
2207        return hpage;
2208}
2209
2210static bool khugepaged_prealloc_page(struct page **hpage, bool *wait)
2211{
2212        if (!*hpage)
2213                *hpage = khugepaged_alloc_hugepage(wait);
2214
2215        if (unlikely(!*hpage))
2216                return false;
2217
2218        return true;
2219}
2220
2221static struct page
2222*khugepaged_alloc_page(struct page **hpage, struct mm_struct *mm,
2223                       struct vm_area_struct *vma, unsigned long address,
2224                       int node)
2225{
2226        up_read(&mm->mmap_sem);
2227        VM_BUG_ON(!*hpage);
2228        return  *hpage;
2229}
2230#endif
2231
2232static bool hugepage_vma_check(struct vm_area_struct *vma)
2233{
2234        if ((!(vma->vm_flags & VM_HUGEPAGE) && !khugepaged_always()) ||
2235            (vma->vm_flags & VM_NOHUGEPAGE))
2236                return false;
2237
2238        if (!vma->anon_vma || vma->vm_ops)
2239                return false;
2240        if (is_vma_temporary_stack(vma))
2241                return false;
2242        VM_BUG_ON(vma->vm_flags & VM_NO_THP);
2243        return true;
2244}
2245
2246static void collapse_huge_page(struct mm_struct *mm,
2247                                   unsigned long address,
2248                                   struct page **hpage,
2249                                   struct vm_area_struct *vma,
2250                                   int node)
2251{
2252        pmd_t *pmd, _pmd;
2253        pte_t *pte;
2254        pgtable_t pgtable;
2255        struct page *new_page;
2256        spinlock_t *ptl;
2257        int isolated;
2258        unsigned long hstart, hend;
2259        unsigned long mmun_start;       /* For mmu_notifiers */
2260        unsigned long mmun_end;         /* For mmu_notifiers */
2261
2262        VM_BUG_ON(address & ~HPAGE_PMD_MASK);
2263
2264        /* release the mmap_sem read lock. */
2265        new_page = khugepaged_alloc_page(hpage, mm, vma, address, node);
2266        if (!new_page)
2267                return;
2268
2269        if (unlikely(mem_cgroup_newpage_charge(new_page, mm, GFP_KERNEL)))
2270                return;
2271
2272        /*
2273         * Prevent all access to pagetables with the exception of
2274         * gup_fast later hanlded by the ptep_clear_flush and the VM
2275         * handled by the anon_vma lock + PG_lock.
2276         */
2277        down_write(&mm->mmap_sem);
2278        if (unlikely(khugepaged_test_exit(mm)))
2279                goto out;
2280
2281        vma = find_vma(mm, address);
2282        hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK;
2283        hend = vma->vm_end & HPAGE_PMD_MASK;
2284        if (address < hstart || address + HPAGE_PMD_SIZE > hend)
2285                goto out;
2286        if (!hugepage_vma_check(vma))
2287                goto out;
2288        pmd = mm_find_pmd(mm, address);
2289        if (!pmd)
2290                goto out;
2291        if (pmd_trans_huge(*pmd))
2292                goto out;
2293
2294        anon_vma_lock_write(vma->anon_vma);
2295
2296        pte = pte_offset_map(pmd, address);
2297        ptl = pte_lockptr(mm, pmd);
2298
2299        mmun_start = address;
2300        mmun_end   = address + HPAGE_PMD_SIZE;
2301        mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
2302        spin_lock(&mm->page_table_lock); /* probably unnecessary */
2303        /*
2304         * After this gup_fast can't run anymore. This also removes
2305         * any huge TLB entry from the CPU so we won't allow
2306         * huge and small TLB entries for the same virtual address
2307         * to avoid the risk of CPU bugs in that area.
2308         */
2309        _pmd = pmdp_clear_flush(vma, address, pmd);
2310        spin_unlock(&mm->page_table_lock);
2311        mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
2312
2313        spin_lock(ptl);
2314        isolated = __collapse_huge_page_isolate(vma, address, pte);
2315        spin_unlock(ptl);
2316
2317        if (unlikely(!isolated)) {
2318                pte_unmap(pte);
2319                spin_lock(&mm->page_table_lock);
2320                BUG_ON(!pmd_none(*pmd));
2321                /*
2322                 * We can only use set_pmd_at when establishing
2323                 * hugepmds and never for establishing regular pmds that
2324                 * points to regular pagetables. Use pmd_populate for that
2325                 */
2326                pmd_populate(mm, pmd, pmd_pgtable(_pmd));
2327                spin_unlock(&mm->page_table_lock);
2328                anon_vma_unlock_write(vma->anon_vma);
2329                goto out;
2330        }
2331
2332        /*
2333         * All pages are isolated and locked so anon_vma rmap
2334         * can't run anymore.
2335         */
2336        anon_vma_unlock_write(vma->anon_vma);
2337
2338        __collapse_huge_page_copy(pte, new_page, vma, address, ptl);
2339        pte_unmap(pte);
2340        __SetPageUptodate(new_page);
2341        pgtable = pmd_pgtable(_pmd);
2342
2343        _pmd = mk_huge_pmd(new_page, vma);
2344
2345        /*
2346         * spin_lock() below is not the equivalent of smp_wmb(), so
2347         * this is needed to avoid the copy_huge_page writes to become
2348         * visible after the set_pmd_at() write.
2349         */
2350        smp_wmb();
2351
2352        spin_lock(&mm->page_table_lock);
2353        BUG_ON(!pmd_none(*pmd));
2354        page_add_new_anon_rmap(new_page, vma, address);
2355        set_pmd_at(mm, address, pmd, _pmd);
2356        update_mmu_cache_pmd(vma, address, pmd);
2357        pgtable_trans_huge_deposit(mm, pgtable);
2358        spin_unlock(&mm->page_table_lock);
2359
2360        *hpage = NULL;
2361
2362        khugepaged_pages_collapsed++;
2363out_up_write:
2364        up_write(&mm->mmap_sem);
2365        return;
2366
2367out:
2368        mem_cgroup_uncharge_page(new_page);
2369        goto out_up_write;
2370}
2371
2372static int khugepaged_scan_pmd(struct mm_struct *mm,
2373                               struct vm_area_struct *vma,
2374                               unsigned long address,
2375                               struct page **hpage)
2376{
2377        pmd_t *pmd;
2378        pte_t *pte, *_pte;
2379        int ret = 0, referenced = 0, none = 0;
2380        struct page *page;
2381        unsigned long _address;
2382        spinlock_t *ptl;
2383        int node = NUMA_NO_NODE;
2384
2385        VM_BUG_ON(address & ~HPAGE_PMD_MASK);
2386
2387        pmd = mm_find_pmd(mm, address);
2388        if (!pmd)
2389                goto out;
2390        if (pmd_trans_huge(*pmd))
2391                goto out;
2392
2393        pte = pte_offset_map_lock(mm, pmd, address, &ptl);
2394        for (_address = address, _pte = pte; _pte < pte+HPAGE_PMD_NR;
2395             _pte++, _address += PAGE_SIZE) {
2396                pte_t pteval = *_pte;
2397                if (pte_none(pteval)) {
2398                        if (++none <= khugepaged_max_ptes_none)
2399                                continue;
2400                        else
2401                                goto out_unmap;
2402                }
2403                if (!pte_present(pteval) || !pte_write(pteval))
2404                        goto out_unmap;
2405                page = vm_normal_page(vma, _address, pteval);
2406                if (unlikely(!page))
2407                        goto out_unmap;
2408                /*
2409                 * Chose the node of the first page. This could
2410                 * be more sophisticated and look at more pages,
2411                 * but isn't for now.
2412                 */
2413                if (node == NUMA_NO_NODE)
2414                        node = page_to_nid(page);
2415                VM_BUG_ON(PageCompound(page));
2416                if (!PageLRU(page) || PageLocked(page) || !PageAnon(page))
2417                        goto out_unmap;
2418                /* cannot use mapcount: can't collapse if there's a gup pin */
2419                if (page_count(page) != 1)
2420                        goto out_unmap;
2421                if (pte_young(pteval) || PageReferenced(page) ||
2422                    mmu_notifier_test_young(vma->vm_mm, address))
2423                        referenced = 1;
2424        }
2425        if (referenced)
2426                ret = 1;
2427out_unmap:
2428        pte_unmap_unlock(pte, ptl);
2429        if (ret)
2430                /* collapse_huge_page will return with the mmap_sem released */
2431                collapse_huge_page(mm, address, hpage, vma, node);
2432out:
2433        return ret;
2434}
2435
2436static void collect_mm_slot(struct mm_slot *mm_slot)
2437{
2438        struct mm_struct *mm = mm_slot->mm;
2439
2440        VM_BUG_ON(NR_CPUS != 1 && !spin_is_locked(&khugepaged_mm_lock));
2441
2442        if (khugepaged_test_exit(mm)) {
2443                /* free mm_slot */
2444                hash_del(&mm_slot->hash);
2445                list_del(&mm_slot->mm_node);
2446
2447                /*
2448                 * Not strictly needed because the mm exited already.
2449                 *
2450                 * clear_bit(MMF_VM_HUGEPAGE, &mm->flags);
2451                 */
2452
2453                /* khugepaged_mm_lock actually not necessary for the below */
2454                free_mm_slot(mm_slot);
2455                mmdrop(mm);
2456        }
2457}
2458
2459static unsigned int khugepaged_scan_mm_slot(unsigned int pages,
2460                                            struct page **hpage)
2461        __releases(&khugepaged_mm_lock)
2462        __acquires(&khugepaged_mm_lock)
2463{
2464        struct mm_slot *mm_slot;
2465        struct mm_struct *mm;
2466        struct vm_area_struct *vma;
2467        int progress = 0;
2468
2469        VM_BUG_ON(!pages);
2470        VM_BUG_ON(NR_CPUS != 1 && !spin_is_locked(&khugepaged_mm_lock));
2471
2472        if (khugepaged_scan.mm_slot)
2473                mm_slot = khugepaged_scan.mm_slot;
2474        else {
2475                mm_slot = list_entry(khugepaged_scan.mm_head.next,
2476                                     struct mm_slot, mm_node);
2477                khugepaged_scan.address = 0;
2478                khugepaged_scan.mm_slot = mm_slot;
2479        }
2480        spin_unlock(&khugepaged_mm_lock);
2481
2482        mm = mm_slot->mm;
2483        down_read(&mm->mmap_sem);
2484        if (unlikely(khugepaged_test_exit(mm)))
2485                vma = NULL;
2486        else
2487                vma = find_vma(mm, khugepaged_scan.address);
2488
2489        progress++;
2490        for (; vma; vma = vma->vm_next) {
2491                unsigned long hstart, hend;
2492
2493                cond_resched();
2494                if (unlikely(khugepaged_test_exit(mm))) {
2495                        progress++;
2496                        break;
2497                }
2498                if (!hugepage_vma_check(vma)) {
2499skip:
2500                        progress++;
2501                        continue;
2502                }
2503                hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK;
2504                hend = vma->vm_end & HPAGE_PMD_MASK;
2505                if (hstart >= hend)
2506                        goto skip;
2507                if (khugepaged_scan.address > hend)
2508                        goto skip;
2509                if (khugepaged_scan.address < hstart)
2510                        khugepaged_scan.address = hstart;
2511                VM_BUG_ON(khugepaged_scan.address & ~HPAGE_PMD_MASK);
2512
2513                while (khugepaged_scan.address < hend) {
2514                        int ret;
2515                        cond_resched();
2516                        if (unlikely(khugepaged_test_exit(mm)))
2517                                goto breakouterloop;
2518
2519                        VM_BUG_ON(khugepaged_scan.address < hstart ||
2520                                  khugepaged_scan.address + HPAGE_PMD_SIZE >
2521                                  hend);
2522                        ret = khugepaged_scan_pmd(mm, vma,
2523                                                  khugepaged_scan.address,
2524                                                  hpage);
2525                        /* move to next address */
2526                        khugepaged_scan.address += HPAGE_PMD_SIZE;
2527                        progress += HPAGE_PMD_NR;
2528                        if (ret)
2529                                /* we released mmap_sem so break loop */
2530                                goto breakouterloop_mmap_sem;
2531                        if (progress >= pages)
2532                                goto breakouterloop;
2533                }
2534        }
2535breakouterloop:
2536        up_read(&mm->mmap_sem); /* exit_mmap will destroy ptes after this */
2537breakouterloop_mmap_sem:
2538
2539        spin_lock(&khugepaged_mm_lock);
2540        VM_BUG_ON(khugepaged_scan.mm_slot != mm_slot);
2541        /*
2542         * Release the current mm_slot if this mm is about to die, or
2543         * if we scanned all vmas of this mm.
2544         */
2545        if (khugepaged_test_exit(mm) || !vma) {
2546                /*
2547                 * Make sure that if mm_users is reaching zero while
2548                 * khugepaged runs here, khugepaged_exit will find
2549                 * mm_slot not pointing to the exiting mm.
2550                 */
2551                if (mm_slot->mm_node.next != &khugepaged_scan.mm_head) {
2552                        khugepaged_scan.mm_slot = list_entry(
2553                                mm_slot->mm_node.next,
2554                                struct mm_slot, mm_node);
2555                        khugepaged_scan.address = 0;
2556                } else {
2557                        khugepaged_scan.mm_slot = NULL;
2558                        khugepaged_full_scans++;
2559                }
2560
2561                collect_mm_slot(mm_slot);
2562        }
2563
2564        return progress;
2565}
2566
2567static int khugepaged_has_work(void)
2568{
2569        return !list_empty(&khugepaged_scan.mm_head) &&
2570                khugepaged_enabled();
2571}
2572
2573static int khugepaged_wait_event(void)
2574{
2575        return !list_empty(&khugepaged_scan.mm_head) ||
2576                kthread_should_stop();
2577}
2578
2579static void khugepaged_do_scan(void)
2580{
2581        struct page *hpage = NULL;
2582        unsigned int progress = 0, pass_through_head = 0;
2583        unsigned int pages = khugepaged_pages_to_scan;
2584        bool wait = true;
2585
2586        barrier(); /* write khugepaged_pages_to_scan to local stack */
2587
2588        while (progress < pages) {
2589                if (!khugepaged_prealloc_page(&hpage, &wait))
2590                        break;
2591
2592                cond_resched();
2593
2594                if (unlikely(kthread_should_stop() || freezing(current)))
2595                        break;
2596
2597                spin_lock(&khugepaged_mm_lock);
2598                if (!khugepaged_scan.mm_slot)
2599                        pass_through_head++;
2600                if (khugepaged_has_work() &&
2601                    pass_through_head < 2)
2602                        progress += khugepaged_scan_mm_slot(pages - progress,
2603                                                            &hpage);
2604                else
2605                        progress = pages;
2606                spin_unlock(&khugepaged_mm_lock);
2607        }
2608
2609        if (!IS_ERR_OR_NULL(hpage))
2610                put_page(hpage);
2611}
2612
2613static void khugepaged_wait_work(void)
2614{
2615        try_to_freeze();
2616
2617        if (khugepaged_has_work()) {
2618                if (!khugepaged_scan_sleep_millisecs)
2619                        return;
2620
2621                wait_event_freezable_timeout(khugepaged_wait,
2622                                             kthread_should_stop(),
2623                        msecs_to_jiffies(khugepaged_scan_sleep_millisecs));
2624                return;
2625        }
2626
2627        if (khugepaged_enabled())
2628                wait_event_freezable(khugepaged_wait, khugepaged_wait_event());
2629}
2630
2631static int khugepaged(void *none)
2632{
2633        struct mm_slot *mm_slot;
2634
2635        set_freezable();
2636        set_user_nice(current, 19);
2637
2638        while (!kthread_should_stop()) {
2639                khugepaged_do_scan();
2640                khugepaged_wait_work();
2641        }
2642
2643        spin_lock(&khugepaged_mm_lock);
2644        mm_slot = khugepaged_scan.mm_slot;
2645        khugepaged_scan.mm_slot = NULL;
2646        if (mm_slot)
2647                collect_mm_slot(mm_slot);
2648        spin_unlock(&khugepaged_mm_lock);
2649        return 0;
2650}
2651
2652static void __split_huge_zero_page_pmd(struct vm_area_struct *vma,
2653                unsigned long haddr, pmd_t *pmd)
2654{
2655        struct mm_struct *mm = vma->vm_mm;
2656        pgtable_t pgtable;
2657        pmd_t _pmd;
2658        int i;
2659
2660        pmdp_clear_flush(vma, haddr, pmd);
2661        /* leave pmd empty until pte is filled */
2662
2663        pgtable = pgtable_trans_huge_withdraw(mm);
2664        pmd_populate(mm, &_pmd, pgtable);
2665
2666        for (i = 0; i < HPAGE_PMD_NR; i++, haddr += PAGE_SIZE) {
2667                pte_t *pte, entry;
2668                entry = pfn_pte(my_zero_pfn(haddr), vma->vm_page_prot);
2669                entry = pte_mkspecial(entry);
2670                pte = pte_offset_map(&_pmd, haddr);
2671                VM_BUG_ON(!pte_none(*pte));
2672                set_pte_at(mm, haddr, pte, entry);
2673                pte_unmap(pte);
2674        }
2675        smp_wmb(); /* make pte visible before pmd */
2676        pmd_populate(mm, pmd, pgtable);
2677        put_huge_zero_page();
2678}
2679
2680void __split_huge_page_pmd(struct vm_area_struct *vma, unsigned long address,
2681                pmd_t *pmd)
2682{
2683        struct page *page;
2684        struct mm_struct *mm = vma->vm_mm;
2685        unsigned long haddr = address & HPAGE_PMD_MASK;
2686        unsigned long mmun_start;       /* For mmu_notifiers */
2687        unsigned long mmun_end;         /* For mmu_notifiers */
2688
2689        BUG_ON(vma->vm_start > haddr || vma->vm_end < haddr + HPAGE_PMD_SIZE);
2690
2691        mmun_start = haddr;
2692        mmun_end   = haddr + HPAGE_PMD_SIZE;
2693        mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
2694        spin_lock(&mm->page_table_lock);
2695        if (unlikely(!pmd_trans_huge(*pmd))) {
2696                spin_unlock(&mm->page_table_lock);
2697                mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
2698                return;
2699        }
2700        if (is_huge_zero_pmd(*pmd)) {
2701                __split_huge_zero_page_pmd(vma, haddr, pmd);
2702                spin_unlock(&mm->page_table_lock);
2703                mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
2704                return;
2705        }
2706        page = pmd_page(*pmd);
2707        VM_BUG_ON(!page_count(page));
2708        get_page(page);
2709        spin_unlock(&mm->page_table_lock);
2710        mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
2711
2712        split_huge_page(page);
2713
2714        put_page(page);
2715        BUG_ON(pmd_trans_huge(*pmd));
2716}
2717
2718void split_huge_page_pmd_mm(struct mm_struct *mm, unsigned long address,
2719                pmd_t *pmd)
2720{
2721        struct vm_area_struct *vma;
2722
2723        vma = find_vma(mm, address);
2724        BUG_ON(vma == NULL);
2725        split_huge_page_pmd(vma, address, pmd);
2726}
2727
2728static void split_huge_page_address(struct mm_struct *mm,
2729                                    unsigned long address)
2730{
2731        pmd_t *pmd;
2732
2733        VM_BUG_ON(!(address & ~HPAGE_PMD_MASK));
2734
2735        pmd = mm_find_pmd(mm, address);
2736        if (!pmd)
2737                return;
2738        /*
2739         * Caller holds the mmap_sem write mode, so a huge pmd cannot
2740         * materialize from under us.
2741         */
2742        split_huge_page_pmd_mm(mm, address, pmd);
2743}
2744
2745void __vma_adjust_trans_huge(struct vm_area_struct *vma,
2746                             unsigned long start,
2747                             unsigned long end,
2748                             long adjust_next)
2749{
2750        /*
2751         * If the new start address isn't hpage aligned and it could
2752         * previously contain an hugepage: check if we need to split
2753         * an huge pmd.
2754         */
2755        if (start & ~HPAGE_PMD_MASK &&
2756            (start & HPAGE_PMD_MASK) >= vma->vm_start &&
2757            (start & HPAGE_PMD_MASK) + HPAGE_PMD_SIZE <= vma->vm_end)
2758                split_huge_page_address(vma->vm_mm, start);
2759
2760        /*
2761         * If the new end address isn't hpage aligned and it could
2762         * previously contain an hugepage: check if we need to split
2763         * an huge pmd.
2764         */
2765        if (end & ~HPAGE_PMD_MASK &&
2766            (end & HPAGE_PMD_MASK) >= vma->vm_start &&
2767            (end & HPAGE_PMD_MASK) + HPAGE_PMD_SIZE <= vma->vm_end)
2768                split_huge_page_address(vma->vm_mm, end);
2769
2770        /*
2771         * If we're also updating the vma->vm_next->vm_start, if the new
2772         * vm_next->vm_start isn't page aligned and it could previously
2773         * contain an hugepage: check if we need to split an huge pmd.
2774         */
2775        if (adjust_next > 0) {
2776                struct vm_area_struct *next = vma->vm_next;
2777                unsigned long nstart = next->vm_start;
2778                nstart += adjust_next << PAGE_SHIFT;
2779                if (nstart & ~HPAGE_PMD_MASK &&
2780                    (nstart & HPAGE_PMD_MASK) >= next->vm_start &&
2781                    (nstart & HPAGE_PMD_MASK) + HPAGE_PMD_SIZE <= next->vm_end)
2782                        split_huge_page_address(next->vm_mm, nstart);
2783        }
2784}
2785
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