mm/khugepaged.c

   1 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
   2
   3 #include <linux/mm.h>
   4 #include <linux/sched.h>
   5 #include <linux/sched/mm.h>
   6 #include <linux/sched/coredump.h>
   7 #include <linux/mmu_notifier.h>
   8 #include <linux/rmap.h>
   9 #include <linux/swap.h>
  10 #include <linux/mm_inline.h>
  11 #include <linux/kthread.h>
  12 #include <linux/khugepaged.h>
  13 #include <linux/freezer.h>
  14 #include <linux/mman.h>
  15 #include <linux/hashtable.h>
  16 #include <linux/userfaultfd_k.h>
  17 #include <linux/page_idle.h>
  18 #include <linux/swapops.h>
  19 #include <linux/shmem_fs.h>
  20
  21 #include <asm/tlb.h>
  22 #include <asm/pgalloc.h>
  23 #include "internal.h"
  24
  25 enum scan_result {
  26         SCAN_FAIL,
  27         SCAN_SUCCEED,
  28         SCAN_PMD_NULL,
  29         SCAN_EXCEED_NONE_PTE,
  30         SCAN_PTE_NON_PRESENT,
  31         SCAN_PAGE_RO,
  32         SCAN_LACK_REFERENCED_PAGE,
  33         SCAN_PAGE_NULL,
  34         SCAN_SCAN_ABORT,
  35         SCAN_PAGE_COUNT,
  36         SCAN_PAGE_LRU,
  37         SCAN_PAGE_LOCK,
  38         SCAN_PAGE_ANON,
  39         SCAN_PAGE_COMPOUND,
  40         SCAN_ANY_PROCESS,
  41         SCAN_VMA_NULL,
  42         SCAN_VMA_CHECK,
  43         SCAN_ADDRESS_RANGE,
  44         SCAN_SWAP_CACHE_PAGE,
  45         SCAN_DEL_PAGE_LRU,
  46         SCAN_ALLOC_HUGE_PAGE_FAIL,
  47         SCAN_CGROUP_CHARGE_FAIL,
  48         SCAN_EXCEED_SWAP_PTE,
  49         SCAN_TRUNCATED,
  50 };
  51
  52 #define CREATE_TRACE_POINTS
  53 #include <trace/events/huge_memory.h>
  54
  55 /* default scan 8*512 pte (or vmas) every 30 second */
  56 static unsigned int khugepaged_pages_to_scan __read_mostly;
  57 static unsigned int khugepaged_pages_collapsed;
  58 static unsigned int khugepaged_full_scans;
  59 static unsigned int khugepaged_scan_sleep_millisecs __read_mostly = 10000;
  60 /* during fragmentation poll the hugepage allocator once every minute */
  61 static unsigned int khugepaged_alloc_sleep_millisecs __read_mostly = 60000;
  62 static unsigned long khugepaged_sleep_expire;
  63 static DEFINE_SPINLOCK(khugepaged_mm_lock);
  64 static DECLARE_WAIT_QUEUE_HEAD(khugepaged_wait);
  65 /*
  66  * default collapse hugepages if there is at least one pte mapped like
  67  * it would have happened if the vma was large enough during page
  68  * fault.
  69  */
  70 static unsigned int khugepaged_max_ptes_none __read_mostly;
  71 static unsigned int khugepaged_max_ptes_swap __read_mostly;
  72
  73 #define MM_SLOTS_HASH_BITS 10
  74 static __read_mostly DEFINE_HASHTABLE(mm_slots_hash, MM_SLOTS_HASH_BITS);
  75
  76 static struct kmem_cache *mm_slot_cache __read_mostly;
  77
  78 /**
  79  * struct mm_slot - hash lookup from mm to mm_slot
  80  * @hash: hash collision list
  81  * @mm_node: khugepaged scan list headed in khugepaged_scan.mm_head
  82  * @mm: the mm that this information is valid for
  83  */
  84 struct mm_slot {
  85         struct hlist_node hash;
  86         struct list_head mm_node;
  87         struct mm_struct *mm;
  88 };
  89
  90 /**
  91  * struct khugepaged_scan - cursor for scanning
  92  * @mm_head: the head of the mm list to scan
  93  * @mm_slot: the current mm_slot we are scanning
  94  * @address: the next address inside that to be scanned
  95  *
  96  * There is only the one khugepaged_scan instance of this cursor structure.
  97  */
  98 struct khugepaged_scan {
  99         struct list_head mm_head;
 100         struct mm_slot *mm_slot;
 101         unsigned long address;
 102 };
 103
 104 static struct khugepaged_scan khugepaged_scan = {
 105         .mm_head = LIST_HEAD_INIT(khugepaged_scan.mm_head),
 106 };
 107
 108 #ifdef CONFIG_SYSFS
 109 static ssize_t scan_sleep_millisecs_show(struct kobject *kobj,
 110                                          struct kobj_attribute *attr,
 111                                          char *buf)
 112 {
 113         return sprintf(buf, "%u\n", khugepaged_scan_sleep_millisecs);
 114 }
 115
 116 static ssize_t scan_sleep_millisecs_store(struct kobject *kobj,
 117                                           struct kobj_attribute *attr,
 118                                           const char *buf, size_t count)
 119 {
 120         unsigned long msecs;
 121         int err;
 122
 123         err = kstrtoul(buf, 10, &msecs);
 124         if (err || msecs > UINT_MAX)
 125                 return -EINVAL;
 126
 127         khugepaged_scan_sleep_millisecs = msecs;
 128         khugepaged_sleep_expire = 0;
 129         wake_up_interruptible(&khugepaged_wait);
 130
 131         return count;
 132 }
 133 static struct kobj_attribute scan_sleep_millisecs_attr =
 134         __ATTR(scan_sleep_millisecs, 0644, scan_sleep_millisecs_show,
 135                scan_sleep_millisecs_store);
 136
 137 static ssize_t alloc_sleep_millisecs_show(struct kobject *kobj,
 138                                           struct kobj_attribute *attr,
 139                                           char *buf)
 140 {
 141         return sprintf(buf, "%u\n", khugepaged_alloc_sleep_millisecs);
 142 }
 143
 144 static ssize_t alloc_sleep_millisecs_store(struct kobject *kobj,
 145                                            struct kobj_attribute *attr,
 146                                            const char *buf, size_t count)
 147 {
 148         unsigned long msecs;
 149         int err;
 150
 151         err = kstrtoul(buf, 10, &msecs);
 152         if (err || msecs > UINT_MAX)
 153                 return -EINVAL;
 154
 155         khugepaged_alloc_sleep_millisecs = msecs;
 156         khugepaged_sleep_expire = 0;
 157         wake_up_interruptible(&khugepaged_wait);
 158
 159         return count;
 160 }
 161 static struct kobj_attribute alloc_sleep_millisecs_attr =
 162         __ATTR(alloc_sleep_millisecs, 0644, alloc_sleep_millisecs_show,
 163                alloc_sleep_millisecs_store);
 164
 165 static ssize_t pages_to_scan_show(struct kobject *kobj,
 166                                   struct kobj_attribute *attr,
 167                                   char *buf)
 168 {
 169         return sprintf(buf, "%u\n", khugepaged_pages_to_scan);
 170 }
 171 static ssize_t pages_to_scan_store(struct kobject *kobj,
 172                                    struct kobj_attribute *attr,
 173                                    const char *buf, size_t count)
 174 {
 175         int err;
 176         unsigned long pages;
 177
 178         err = kstrtoul(buf, 10, &pages);
 179         if (err || !pages || pages > UINT_MAX)
 180                 return -EINVAL;
 181
 182         khugepaged_pages_to_scan = pages;
 183
 184         return count;
 185 }
 186 static struct kobj_attribute pages_to_scan_attr =
 187         __ATTR(pages_to_scan, 0644, pages_to_scan_show,
 188                pages_to_scan_store);
 189
 190 static ssize_t pages_collapsed_show(struct kobject *kobj,
 191                                     struct kobj_attribute *attr,
 192                                     char *buf)
 193 {
 194         return sprintf(buf, "%u\n", khugepaged_pages_collapsed);
 195 }
 196 static struct kobj_attribute pages_collapsed_attr =
 197         __ATTR_RO(pages_collapsed);
 198
 199 static ssize_t full_scans_show(struct kobject *kobj,
 200                                struct kobj_attribute *attr,
 201                                char *buf)
 202 {
 203         return sprintf(buf, "%u\n", khugepaged_full_scans);
 204 }
 205 static struct kobj_attribute full_scans_attr =
 206         __ATTR_RO(full_scans);
 207
 208 static ssize_t khugepaged_defrag_show(struct kobject *kobj,
 209                                       struct kobj_attribute *attr, char *buf)
 210 {
 211         return single_hugepage_flag_show(kobj, attr, buf,
 212                                 TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG);
 213 }
 214 static ssize_t khugepaged_defrag_store(struct kobject *kobj,
 215                                        struct kobj_attribute *attr,
 216                                        const char *buf, size_t count)
 217 {
 218         return single_hugepage_flag_store(kobj, attr, buf, count,
 219                                  TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG);
 220 }
 221 static struct kobj_attribute khugepaged_defrag_attr =
 222         __ATTR(defrag, 0644, khugepaged_defrag_show,
 223                khugepaged_defrag_store);
 224
 225 /*
 226  * max_ptes_none controls if khugepaged should collapse hugepages over
 227  * any unmapped ptes in turn potentially increasing the memory
 228  * footprint of the vmas. When max_ptes_none is 0 khugepaged will not
 229  * reduce the available free memory in the system as it
 230  * runs. Increasing max_ptes_none will instead potentially reduce the
 231  * free memory in the system during the khugepaged scan.
 232  */
 233 static ssize_t khugepaged_max_ptes_none_show(struct kobject *kobj,
 234                                              struct kobj_attribute *attr,
 235                                              char *buf)
 236 {
 237         return sprintf(buf, "%u\n", khugepaged_max_ptes_none);
 238 }
 239 static ssize_t khugepaged_max_ptes_none_store(struct kobject *kobj,
 240                                               struct kobj_attribute *attr,
 241                                               const char *buf, size_t count)
 242 {
 243         int err;
 244         unsigned long max_ptes_none;
 245
 246         err = kstrtoul(buf, 10, &max_ptes_none);
 247         if (err || max_ptes_none > HPAGE_PMD_NR-1)
 248                 return -EINVAL;
 249
 250         khugepaged_max_ptes_none = max_ptes_none;
 251
 252         return count;
 253 }
 254 static struct kobj_attribute khugepaged_max_ptes_none_attr =
 255         __ATTR(max_ptes_none, 0644, khugepaged_max_ptes_none_show,
 256                khugepaged_max_ptes_none_store);
 257
 258 static ssize_t khugepaged_max_ptes_swap_show(struct kobject *kobj,
 259                                              struct kobj_attribute *attr,
 260                                              char *buf)
 261 {
 262         return sprintf(buf, "%u\n", khugepaged_max_ptes_swap);
 263 }
 264
 265 static ssize_t khugepaged_max_ptes_swap_store(struct kobject *kobj,
 266                                               struct kobj_attribute *attr,
 267                                               const char *buf, size_t count)
 268 {
 269         int err;
 270         unsigned long max_ptes_swap;
 271
 272         err  = kstrtoul(buf, 10, &max_ptes_swap);
 273         if (err || max_ptes_swap > HPAGE_PMD_NR-1)
 274                 return -EINVAL;
 275
 276         khugepaged_max_ptes_swap = max_ptes_swap;
 277
 278         return count;
 279 }
 280
 281 static struct kobj_attribute khugepaged_max_ptes_swap_attr =
 282         __ATTR(max_ptes_swap, 0644, khugepaged_max_ptes_swap_show,
 283                khugepaged_max_ptes_swap_store);
 284
 285 static struct attribute *khugepaged_attr[] = {
 286         &khugepaged_defrag_attr.attr,
 287         &khugepaged_max_ptes_none_attr.attr,
 288         &pages_to_scan_attr.attr,
 289         &pages_collapsed_attr.attr,
 290         &full_scans_attr.attr,
 291         &scan_sleep_millisecs_attr.attr,
 292         &alloc_sleep_millisecs_attr.attr,
 293         &khugepaged_max_ptes_swap_attr.attr,
 294         NULL,
 295 };
 296
 297 struct attribute_group khugepaged_attr_group = {
 298         .attrs = khugepaged_attr,
 299         .name = "khugepaged",
 300 };
 301 #endif /* CONFIG_SYSFS */
 302
 303 #define VM_NO_KHUGEPAGED (VM_SPECIAL | VM_HUGETLB)
 304
 305 int hugepage_madvise(struct vm_area_struct *vma,
 306                      unsigned long *vm_flags, int advice)
 307 {
 308         switch (advice) {
 309         case MADV_HUGEPAGE:
 310 #ifdef CONFIG_S390
 311                 /*
 312                  * qemu blindly sets MADV_HUGEPAGE on all allocations, but s390
 313                  * can't handle this properly after s390_enable_sie, so we simply
 314                  * ignore the madvise to prevent qemu from causing a SIGSEGV.
 315                  */
 316                 if (mm_has_pgste(vma->vm_mm))
 317                         return 0;
 318 #endif
 319                 *vm_flags &= ~VM_NOHUGEPAGE;
 320                 *vm_flags |= VM_HUGEPAGE;
 321                 /*
 322                  * If the vma become good for khugepaged to scan,
 323                  * register it here without waiting a page fault that
 324                  * may not happen any time soon.
 325                  */
 326                 if (!(*vm_flags & VM_NO_KHUGEPAGED) &&
 327                                 khugepaged_enter_vma_merge(vma, *vm_flags))
 328                         return -ENOMEM;
 329                 break;
 330         case MADV_NOHUGEPAGE:
 331                 *vm_flags &= ~VM_HUGEPAGE;
 332                 *vm_flags |= VM_NOHUGEPAGE;
 333                 /*
 334                  * Setting VM_NOHUGEPAGE will prevent khugepaged from scanning
 335                  * this vma even if we leave the mm registered in khugepaged if
 336                  * it got registered before VM_NOHUGEPAGE was set.
 337                  */
 338                 break;
 339         }
 340
 341         return 0;
 342 }
 343
 344 int __init khugepaged_init(void)
 345 {
 346         mm_slot_cache = kmem_cache_create("khugepaged_mm_slot",
 347                                           sizeof(struct mm_slot),
 348                                           __alignof__(struct mm_slot), 0, NULL);
 349         if (!mm_slot_cache)
 350                 return -ENOMEM;
 351
 352         khugepaged_pages_to_scan = HPAGE_PMD_NR * 8;
 353         khugepaged_max_ptes_none = HPAGE_PMD_NR - 1;
 354         khugepaged_max_ptes_swap = HPAGE_PMD_NR / 8;
 355
 356         return 0;
 357 }
 358
 359 void __init khugepaged_destroy(void)
 360 {
 361         kmem_cache_destroy(mm_slot_cache);
 362 }
 363
 364 static inline struct mm_slot *alloc_mm_slot(void)
 365 {
 366         if (!mm_slot_cache)     /* initialization failed */
 367                 return NULL;
 368         return kmem_cache_zalloc(mm_slot_cache, GFP_KERNEL);
 369 }
 370
 371 static inline void free_mm_slot(struct mm_slot *mm_slot)
 372 {
 373         kmem_cache_free(mm_slot_cache, mm_slot);
 374 }
 375
 376 static struct mm_slot *get_mm_slot(struct mm_struct *mm)
 377 {
 378         struct mm_slot *mm_slot;
 379
 380         hash_for_each_possible(mm_slots_hash, mm_slot, hash, (unsigned long)mm)
 381                 if (mm == mm_slot->mm)
 382                         return mm_slot;
 383
 384         return NULL;
 385 }
 386
 387 static void insert_to_mm_slots_hash(struct mm_struct *mm,
 388                                     struct mm_slot *mm_slot)
 389 {
 390         mm_slot->mm = mm;
 391         hash_add(mm_slots_hash, &mm_slot->hash, (long)mm);
 392 }
 393
 394 static inline int khugepaged_test_exit(struct mm_struct *mm)
 395 {
 396         return atomic_read(&mm->mm_users) == 0;
 397 }
 398
 399 int __khugepaged_enter(struct mm_struct *mm)
 400 {
 401         struct mm_slot *mm_slot;
 402         int wakeup;
 403
 404         mm_slot = alloc_mm_slot();
 405         if (!mm_slot)
 406                 return -ENOMEM;
 407
 408         /* __khugepaged_exit() must not run from under us */
 409         VM_BUG_ON_MM(khugepaged_test_exit(mm), mm);
 410         if (unlikely(test_and_set_bit(MMF_VM_HUGEPAGE, &mm->flags))) {
 411                 free_mm_slot(mm_slot);
 412                 return 0;
 413         }
 414
 415         spin_lock(&khugepaged_mm_lock);
 416         insert_to_mm_slots_hash(mm, mm_slot);
 417         /*
 418          * Insert just behind the scanning cursor, to let the area settle
 419          * down a little.
 420          */
 421         wakeup = list_empty(&khugepaged_scan.mm_head);
 422         list_add_tail(&mm_slot->mm_node, &khugepaged_scan.mm_head);
 423         spin_unlock(&khugepaged_mm_lock);
 424
 425         mmgrab(mm);
 426         if (wakeup)
 427                 wake_up_interruptible(&khugepaged_wait);
 428
 429         return 0;
 430 }
 431
 432 int khugepaged_enter_vma_merge(struct vm_area_struct *vma,
 433                                unsigned long vm_flags)
 434 {
 435         unsigned long hstart, hend;
 436         if (!vma->anon_vma)
 437                 /*
 438                  * Not yet faulted in so we will register later in the
 439                  * page fault if needed.
 440                  */
 441                 return 0;
 442         if (vma->vm_ops || (vm_flags & VM_NO_KHUGEPAGED))
 443                 /* khugepaged not yet working on file or special mappings */
 444                 return 0;
 445         hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK;
 446         hend = vma->vm_end & HPAGE_PMD_MASK;
 447         if (hstart < hend)
 448                 return khugepaged_enter(vma, vm_flags);
 449         return 0;
 450 }
 451
 452 void __khugepaged_exit(struct mm_struct *mm)
 453 {
 454         struct mm_slot *mm_slot;
 455         int free = 0;
 456
 457         spin_lock(&khugepaged_mm_lock);
 458         mm_slot = get_mm_slot(mm);
 459         if (mm_slot && khugepaged_scan.mm_slot != mm_slot) {
 460                 hash_del(&mm_slot->hash);
 461                 list_del(&mm_slot->mm_node);
 462                 free = 1;
 463         }
 464         spin_unlock(&khugepaged_mm_lock);
 465
 466         if (free) {
 467                 clear_bit(MMF_VM_HUGEPAGE, &mm->flags);
 468                 free_mm_slot(mm_slot);
 469                 mmdrop(mm);
 470         } else if (mm_slot) {
 471                 /*
 472                  * This is required to serialize against
 473                  * khugepaged_test_exit() (which is guaranteed to run
 474                  * under mmap sem read mode). Stop here (after we
 475                  * return all pagetables will be destroyed) until
 476                  * khugepaged has finished working on the pagetables
 477                  * under the mmap_sem.
 478                  */
 479                 down_write(&mm->mmap_sem);
 480                 up_write(&mm->mmap_sem);
 481         }
 482 }
 483
 484 static void release_pte_page(struct page *page)
 485 {
 486         dec_node_page_state(page, NR_ISOLATED_ANON + page_is_file_cache(page));
 487         unlock_page(page);
 488         putback_lru_page(page);
 489 }
 490
 491 static void release_pte_pages(pte_t *pte, pte_t *_pte)
 492 {
 493         while (--_pte >= pte) {
 494                 pte_t pteval = *_pte;
 495                 if (!pte_none(pteval) && !is_zero_pfn(pte_pfn(pteval)))
 496                         release_pte_page(pte_page(pteval));
 497         }
 498 }
 499
 500 static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
 501                                         unsigned long address,
 502                                         pte_t *pte)
 503 {
 504         struct page *page = NULL;
 505         pte_t *_pte;
 506         int none_or_zero = 0, result = 0, referenced = 0;
 507         bool writable = false;
 508
 509         for (_pte = pte; _pte < pte+HPAGE_PMD_NR;
 510              _pte++, address += PAGE_SIZE) {
 511                 pte_t pteval = *_pte;
 512                 if (pte_none(pteval) || (pte_present(pteval) &&
 513                                 is_zero_pfn(pte_pfn(pteval)))) {
 514                         if (!userfaultfd_armed(vma) &&
 515                             ++none_or_zero <= khugepaged_max_ptes_none) {
 516                                 continue;
 517                         } else {
 518                                 result = SCAN_EXCEED_NONE_PTE;
 519                                 goto out;
 520                         }
 521                 }
 522                 if (!pte_present(pteval)) {
 523                         result = SCAN_PTE_NON_PRESENT;
 524                         goto out;
 525                 }
 526                 page = vm_normal_page(vma, address, pteval);
 527                 if (unlikely(!page)) {
 528                         result = SCAN_PAGE_NULL;
 529                         goto out;
 530                 }
 531
 532                 VM_BUG_ON_PAGE(PageCompound(page), page);
 533                 VM_BUG_ON_PAGE(!PageAnon(page), page);
 534
 535                 /*
 536                  * We can do it before isolate_lru_page because the
 537                  * page can't be freed from under us. NOTE: PG_lock
 538                  * is needed to serialize against split_huge_page
 539                  * when invoked from the VM.
 540                  */
 541                 if (!trylock_page(page)) {
 542                         result = SCAN_PAGE_LOCK;
 543                         goto out;
 544                 }
 545
 546                 /*
 547                  * cannot use mapcount: can't collapse if there's a gup pin.
 548                  * The page must only be referenced by the scanned process
 549                  * and page swap cache.
 550                  */
 551                 if (page_count(page) != 1 + PageSwapCache(page)) {
 552                         unlock_page(page);
 553                         result = SCAN_PAGE_COUNT;
 554                         goto out;
 555                 }
 556                 if (pte_write(pteval)) {
 557                         writable = true;
 558                 } else {
 559                         if (PageSwapCache(page) &&
 560                             !reuse_swap_page(page, NULL)) {
 561                                 unlock_page(page);
 562                                 result = SCAN_SWAP_CACHE_PAGE;
 563                                 goto out;
 564                         }
 565                         /*
 566                          * Page is not in the swap cache. It can be collapsed
 567                          * into a THP.
 568                          */
 569                 }
 570
 571                 /*
 572                  * Isolate the page to avoid collapsing an hugepage
 573                  * currently in use by the VM.
 574                  */
 575                 if (isolate_lru_page(page)) {
 576                         unlock_page(page);
 577                         result = SCAN_DEL_PAGE_LRU;
 578                         goto out;
 579                 }
 580                 inc_node_page_state(page,
 581                                 NR_ISOLATED_ANON + page_is_file_cache(page));
 582                 VM_BUG_ON_PAGE(!PageLocked(page), page);
 583                 VM_BUG_ON_PAGE(PageLRU(page), page);
 584
 585                 /* There should be enough young pte to collapse the page */
 586                 if (pte_young(pteval) ||
 587                     page_is_young(page) || PageReferenced(page) ||
 588                     mmu_notifier_test_young(vma->vm_mm, address))
 589                         referenced++;
 590         }
 591         if (likely(writable)) {
 592                 if (likely(referenced)) {
 593                         result = SCAN_SUCCEED;
 594                         trace_mm_collapse_huge_page_isolate(page, none_or_zero,
 595                                                             referenced, writable, result);
 596                         return 1;
 597                 }
 598         } else {
 599                 result = SCAN_PAGE_RO;
 600         }
 601
 602 out:
 603         release_pte_pages(pte, _pte);
 604         trace_mm_collapse_huge_page_isolate(page, none_or_zero,
 605                                             referenced, writable, result);
 606         return 0;
 607 }
 608
 609 static void __collapse_huge_page_copy(pte_t *pte, struct page *page,
 610                                       struct vm_area_struct *vma,
 611                                       unsigned long address,
 612                                       spinlock_t *ptl)
 613 {
 614         pte_t *_pte;
 615         for (_pte = pte; _pte < pte + HPAGE_PMD_NR;
 616                                 _pte++, page++, address += PAGE_SIZE) {
 617                 pte_t pteval = *_pte;
 618                 struct page *src_page;
 619
 620                 if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) {
 621                         clear_user_highpage(page, address);
 622                         add_mm_counter(vma->vm_mm, MM_ANONPAGES, 1);
 623                         if (is_zero_pfn(pte_pfn(pteval))) {
 624                                 /*
 625                                  * ptl mostly unnecessary.
 626                                  */
 627                                 spin_lock(ptl);
 628                                 /*
 629                                  * paravirt calls inside pte_clear here are
 630                                  * superfluous.
 631                                  */
 632                                 pte_clear(vma->vm_mm, address, _pte);
 633                                 spin_unlock(ptl);
 634                         }
 635                 } else {
 636                         src_page = pte_page(pteval);
 637                         copy_user_highpage(page, src_page, address, vma);
 638                         VM_BUG_ON_PAGE(page_mapcount(src_page) != 1, src_page);
 639                         release_pte_page(src_page);
 640                         /*
 641                          * ptl mostly unnecessary, but preempt has to
 642                          * be disabled to update the per-cpu stats
 643                          * inside page_remove_rmap().
 644                          */
 645                         spin_lock(ptl);
 646                         /*
 647                          * paravirt calls inside pte_clear here are
 648                          * superfluous.
 649                          */
 650                         pte_clear(vma->vm_mm, address, _pte);
 651                         page_remove_rmap(src_page, false);
 652                         spin_unlock(ptl);
 653                         free_page_and_swap_cache(src_page);
 654                 }
 655         }
 656 }
 657
 658 static void khugepaged_alloc_sleep(void)
 659 {
 660         DEFINE_WAIT(wait);
 661
 662         add_wait_queue(&khugepaged_wait, &wait);
 663         freezable_schedule_timeout_interruptible(
 664                 msecs_to_jiffies(khugepaged_alloc_sleep_millisecs));
 665         remove_wait_queue(&khugepaged_wait, &wait);
 666 }
 667
 668 static int khugepaged_node_load[MAX_NUMNODES];
 669
 670 static bool khugepaged_scan_abort(int nid)
 671 {
 672         int i;
 673
 674         /*
 675          * If node_reclaim_mode is disabled, then no extra effort is made to
 676          * allocate memory locally.
 677          */
 678         if (!node_reclaim_mode)
 679                 return false;
 680
 681         /* If there is a count for this node already, it must be acceptable */
 682         if (khugepaged_node_load[nid])
 683                 return false;
 684
 685         for (i = 0; i < MAX_NUMNODES; i++) {
 686                 if (!khugepaged_node_load[i])
 687                         continue;
 688                 if (node_distance(nid, i) > RECLAIM_DISTANCE)
 689                         return true;
 690         }
 691         return false;
 692 }
 693
 694 /* Defrag for khugepaged will enter direct reclaim/compaction if necessary */
 695 static inline gfp_t alloc_hugepage_khugepaged_gfpmask(void)
 696 {
 697         return khugepaged_defrag() ? GFP_TRANSHUGE : GFP_TRANSHUGE_LIGHT;
 698 }
 699
 700 #ifdef CONFIG_NUMA
 701 static int khugepaged_find_target_node(void)
 702 {
 703         static int last_khugepaged_target_node = NUMA_NO_NODE;
 704         int nid, target_node = 0, max_value = 0;
 705
 706         /* find first node with max normal pages hit */
 707         for (nid = 0; nid < MAX_NUMNODES; nid++)
 708                 if (khugepaged_node_load[nid] > max_value) {
 709                         max_value = khugepaged_node_load[nid];
 710                         target_node = nid;
 711                 }
 712
 713         /* do some balance if several nodes have the same hit record */
 714         if (target_node <= last_khugepaged_target_node)
 715                 for (nid = last_khugepaged_target_node + 1; nid < MAX_NUMNODES;
 716                                 nid++)
 717                         if (max_value == khugepaged_node_load[nid]) {
 718                                 target_node = nid;
 719                                 break;
 720                         }
 721
 722         last_khugepaged_target_node = target_node;
 723         return target_node;
 724 }
 725
 726 static bool khugepaged_prealloc_page(struct page **hpage, bool *wait)
 727 {
 728         if (IS_ERR(*hpage)) {
 729                 if (!*wait)
 730                         return false;
 731
 732                 *wait = false;
 733                 *hpage = NULL;
 734                 khugepaged_alloc_sleep();
 735         } else if (*hpage) {
 736                 put_page(*hpage);
 737                 *hpage = NULL;
 738         }
 739
 740         return true;
 741 }
 742
 743 static struct page *
 744 khugepaged_alloc_page(struct page **hpage, gfp_t gfp, int node)
 745 {
 746         VM_BUG_ON_PAGE(*hpage, *hpage);
 747
 748         *hpage = __alloc_pages_node(node, gfp, HPAGE_PMD_ORDER);
 749         if (unlikely(!*hpage)) {
 750                 count_vm_event(THP_COLLAPSE_ALLOC_FAILED);
 751                 *hpage = ERR_PTR(-ENOMEM);
 752                 return NULL;
 753         }
 754
 755         prep_transhuge_page(*hpage);
 756         count_vm_event(THP_COLLAPSE_ALLOC);
 757         return *hpage;
 758 }
 759 #else
 760 static int khugepaged_find_target_node(void)
 761 {
 762         return 0;
 763 }
 764
 765 static inline struct page *alloc_khugepaged_hugepage(void)
 766 {
 767         struct page *page;
 768
 769         page = alloc_pages(alloc_hugepage_khugepaged_gfpmask(),
 770                            HPAGE_PMD_ORDER);
 771         if (page)
 772                 prep_transhuge_page(page);
 773         return page;
 774 }
 775
 776 static struct page *khugepaged_alloc_hugepage(bool *wait)
 777 {
 778         struct page *hpage;
 779
 780         do {
 781                 hpage = alloc_khugepaged_hugepage();
 782                 if (!hpage) {
 783                         count_vm_event(THP_COLLAPSE_ALLOC_FAILED);
 784                         if (!*wait)
 785                                 return NULL;
 786
 787                         *wait = false;
 788                         khugepaged_alloc_sleep();
 789                 } else
 790                         count_vm_event(THP_COLLAPSE_ALLOC);
 791         } while (unlikely(!hpage) && likely(khugepaged_enabled()));
 792
 793         return hpage;
 794 }
 795
 796 static bool khugepaged_prealloc_page(struct page **hpage, bool *wait)
 797 {
 798         if (!*hpage)
 799                 *hpage = khugepaged_alloc_hugepage(wait);
 800
 801         if (unlikely(!*hpage))
 802                 return false;
 803
 804         return true;
 805 }
 806
 807 static struct page *
 808 khugepaged_alloc_page(struct page **hpage, gfp_t gfp, int node)
 809 {
 810         VM_BUG_ON(!*hpage);
 811
 812         return  *hpage;
 813 }
 814 #endif
 815
 816 static bool hugepage_vma_check(struct vm_area_struct *vma)
 817 {
 818         if ((!(vma->vm_flags & VM_HUGEPAGE) && !khugepaged_always()) ||
 819             (vma->vm_flags & VM_NOHUGEPAGE) ||
 820             test_bit(MMF_DISABLE_THP, &vma->vm_mm->flags))
 821                 return false;
 822         if (shmem_file(vma->vm_file)) {
 823                 if (!IS_ENABLED(CONFIG_TRANSPARENT_HUGE_PAGECACHE))
 824                         return false;
 825                 return IS_ALIGNED((vma->vm_start >> PAGE_SHIFT) - vma->vm_pgoff,
 826                                 HPAGE_PMD_NR);
 827         }
 828         if (!vma->anon_vma || vma->vm_ops)
 829                 return false;
 830         if (is_vma_temporary_stack(vma))
 831                 return false;
 832         return !(vma->vm_flags & VM_NO_KHUGEPAGED);
 833 }
 834
 835 /*
 836  * If mmap_sem temporarily dropped, revalidate vma
 837  * before taking mmap_sem.
 838  * Return 0 if succeeds, otherwise return none-zero
 839  * value (scan code).
 840  */
 841
 842 static int hugepage_vma_revalidate(struct mm_struct *mm, unsigned long address,
 843                 struct vm_area_struct **vmap)
 844 {
 845         struct vm_area_struct *vma;
 846         unsigned long hstart, hend;
 847
 848         if (unlikely(khugepaged_test_exit(mm)))
 849                 return SCAN_ANY_PROCESS;
 850
 851         *vmap = vma = find_vma(mm, address);
 852         if (!vma)
 853                 return SCAN_VMA_NULL;
 854
 855         hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK;
 856         hend = vma->vm_end & HPAGE_PMD_MASK;
 857         if (address < hstart || address + HPAGE_PMD_SIZE > hend)
 858                 return SCAN_ADDRESS_RANGE;
 859         if (!hugepage_vma_check(vma))
 860                 return SCAN_VMA_CHECK;
 861         return 0;
 862 }
 863
 864 /*
 865  * Bring missing pages in from swap, to complete THP collapse.
 866  * Only done if khugepaged_scan_pmd believes it is worthwhile.
 867  *
 868  * Called and returns without pte mapped or spinlocks held,
 869  * but with mmap_sem held to protect against vma changes.
 870  */
 871
 872 static bool __collapse_huge_page_swapin(struct mm_struct *mm,
 873                                         struct vm_area_struct *vma,
 874                                         unsigned long address, pmd_t *pmd,
 875                                         int referenced)
 876 {
 877         int swapped_in = 0, ret = 0;
 878         struct vm_fault vmf = {
 879                 .vma = vma,
 880                 .address = address,
 881                 .flags = FAULT_FLAG_ALLOW_RETRY,
 882                 .pmd = pmd,
 883                 .pgoff = linear_page_index(vma, address),
 884         };
 885
 886         /* we only decide to swapin, if there is enough young ptes */
 887         if (referenced < HPAGE_PMD_NR/2) {
 888                 trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 0);
 889                 return false;
 890         }
 891         vmf.pte = pte_offset_map(pmd, address);
 892         for (; vmf.address < address + HPAGE_PMD_NR*PAGE_SIZE;
 893                         vmf.pte++, vmf.address += PAGE_SIZE) {
 894                 vmf.orig_pte = *vmf.pte;
 895                 if (!is_swap_pte(vmf.orig_pte))
 896                         continue;
 897                 swapped_in++;
 898                 ret = do_swap_page(&vmf);
 899
 900                 /* do_swap_page returns VM_FAULT_RETRY with released mmap_sem */
 901                 if (ret & VM_FAULT_RETRY) {
 902                         down_read(&mm->mmap_sem);
 903                         if (hugepage_vma_revalidate(mm, address, &vmf.vma)) {
 904                                 /* vma is no longer available, don't continue to swapin */
 905                                 trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 0);
 906                                 return false;
 907                         }
 908                         /* check if the pmd is still valid */
 909                         if (mm_find_pmd(mm, address) != pmd) {
 910                                 trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 0);
 911                                 return false;
 912                         }
 913                 }
 914                 if (ret & VM_FAULT_ERROR) {
 915                         trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 0);
 916                         return false;
 917                 }
 918                 /* pte is unmapped now, we need to map it */
 919                 vmf.pte = pte_offset_map(pmd, vmf.address);
 920         }
 921         vmf.pte--;
 922         pte_unmap(vmf.pte);
 923         trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 1);
 924         return true;
 925 }
 926
 927 static void collapse_huge_page(struct mm_struct *mm,
 928                                    unsigned long address,
 929                                    struct page **hpage,
 930                                    int node, int referenced)
 931 {
 932         pmd_t *pmd, _pmd;
 933         pte_t *pte;
 934         pgtable_t pgtable;
 935         struct page *new_page;
 936         spinlock_t *pmd_ptl, *pte_ptl;
 937         int isolated = 0, result = 0;
 938         struct mem_cgroup *memcg;
 939         struct vm_area_struct *vma;
 940         unsigned long mmun_start;       /* For mmu_notifiers */
 941         unsigned long mmun_end;         /* For mmu_notifiers */
 942         gfp_t gfp;
 943
 944         VM_BUG_ON(address & ~HPAGE_PMD_MASK);
 945
 946         /* Only allocate from the target node */
 947         gfp = alloc_hugepage_khugepaged_gfpmask() | __GFP_THISNODE;
 948
 949         /*
 950          * Before allocating the hugepage, release the mmap_sem read lock.
 951          * The allocation can take potentially a long time if it involves
 952          * sync compaction, and we do not need to hold the mmap_sem during
 953          * that. We will recheck the vma after taking it again in write mode.
 954          */
 955         up_read(&mm->mmap_sem);
 956         new_page = khugepaged_alloc_page(hpage, gfp, node);
 957         if (!new_page) {
 958                 result = SCAN_ALLOC_HUGE_PAGE_FAIL;
 959                 goto out_nolock;
 960         }
 961
 962         if (unlikely(mem_cgroup_try_charge(new_page, mm, gfp, &memcg, true))) {
 963                 result = SCAN_CGROUP_CHARGE_FAIL;
 964                 goto out_nolock;
 965         }
 966
 967         down_read(&mm->mmap_sem);
 968         result = hugepage_vma_revalidate(mm, address, &vma);
 969         if (result) {
 970                 mem_cgroup_cancel_charge(new_page, memcg, true);
 971                 up_read(&mm->mmap_sem);
 972                 goto out_nolock;
 973         }
 974
 975         pmd = mm_find_pmd(mm, address);
 976         if (!pmd) {
 977                 result = SCAN_PMD_NULL;
 978                 mem_cgroup_cancel_charge(new_page, memcg, true);
 979                 up_read(&mm->mmap_sem);
 980                 goto out_nolock;
 981         }
 982
 983         /*
 984          * __collapse_huge_page_swapin always returns with mmap_sem locked.
 985          * If it fails, we release mmap_sem and jump out_nolock.
 986          * Continuing to collapse causes inconsistency.
 987          */
 988         if (!__collapse_huge_page_swapin(mm, vma, address, pmd, referenced)) {
 989                 mem_cgroup_cancel_charge(new_page, memcg, true);
 990                 up_read(&mm->mmap_sem);
 991                 goto out_nolock;
 992         }
 993
 994         up_read(&mm->mmap_sem);
 995         /*
 996          * Prevent all access to pagetables with the exception of
 997          * gup_fast later handled by the ptep_clear_flush and the VM
 998          * handled by the anon_vma lock + PG_lock.
 999          */
1000         down_write(&mm->mmap_sem);
1001         result = hugepage_vma_revalidate(mm, address, &vma);
1002         if (result)
1003                 goto out;
1004         /* check if the pmd is still valid */
1005         if (mm_find_pmd(mm, address) != pmd)
1006                 goto out;
1007
1008         anon_vma_lock_write(vma->anon_vma);
1009
1010         pte = pte_offset_map(pmd, address);
1011         pte_ptl = pte_lockptr(mm, pmd);
1012
1013         mmun_start = address;
1014         mmun_end   = address + HPAGE_PMD_SIZE;
1015         mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
1016         pmd_ptl = pmd_lock(mm, pmd); /* probably unnecessary */
1017         /*
1018          * After this gup_fast can't run anymore. This also removes
1019          * any huge TLB entry from the CPU so we won't allow
1020          * huge and small TLB entries for the same virtual address
1021          * to avoid the risk of CPU bugs in that area.
1022          */
1023         _pmd = pmdp_collapse_flush(vma, address, pmd);
1024         spin_unlock(pmd_ptl);
1025         mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
1026
1027         spin_lock(pte_ptl);
1028         isolated = __collapse_huge_page_isolate(vma, address, pte);
1029         spin_unlock(pte_ptl);
1030
1031         if (unlikely(!isolated)) {
1032                 pte_unmap(pte);
1033                 spin_lock(pmd_ptl);
1034                 BUG_ON(!pmd_none(*pmd));
1035                 /*
1036                  * We can only use set_pmd_at when establishing
1037                  * hugepmds and never for establishing regular pmds that
1038                  * points to regular pagetables. Use pmd_populate for that
1039                  */
1040                 pmd_populate(mm, pmd, pmd_pgtable(_pmd));
1041                 spin_unlock(pmd_ptl);
1042                 anon_vma_unlock_write(vma->anon_vma);
1043                 result = SCAN_FAIL;
1044                 goto out;
1045         }
1046
1047         /*
1048          * All pages are isolated and locked so anon_vma rmap
1049          * can't run anymore.
1050          */
1051         anon_vma_unlock_write(vma->anon_vma);
1052
1053         __collapse_huge_page_copy(pte, new_page, vma, address, pte_ptl);
1054         pte_unmap(pte);
1055         __SetPageUptodate(new_page);
1056         pgtable = pmd_pgtable(_pmd);
1057
1058         _pmd = mk_huge_pmd(new_page, vma->vm_page_prot);
1059         _pmd = maybe_pmd_mkwrite(pmd_mkdirty(_pmd), vma);
1060
1061         /*
1062          * spin_lock() below is not the equivalent of smp_wmb(), so
1063          * this is needed to avoid the copy_huge_page writes to become
1064          * visible after the set_pmd_at() write.
1065          */
1066         smp_wmb();
1067
1068         spin_lock(pmd_ptl);
1069         BUG_ON(!pmd_none(*pmd));
1070         page_add_new_anon_rmap(new_page, vma, address, true);
1071         mem_cgroup_commit_charge(new_page, memcg, false, true);
1072         lru_cache_add_active_or_unevictable(new_page, vma);
1073         pgtable_trans_huge_deposit(mm, pmd, pgtable);
1074         set_pmd_at(mm, address, pmd, _pmd);
1075         update_mmu_cache_pmd(vma, address, pmd);
1076         spin_unlock(pmd_ptl);
1077
1078         *hpage = NULL;
1079
1080         khugepaged_pages_collapsed++;
1081         result = SCAN_SUCCEED;
1082 out_up_write:
1083         up_write(&mm->mmap_sem);
1084 out_nolock:
1085         trace_mm_collapse_huge_page(mm, isolated, result);
1086         return;
1087 out:
1088         mem_cgroup_cancel_charge(new_page, memcg, true);
1089         goto out_up_write;
1090 }
1091
1092 static int khugepaged_scan_pmd(struct mm_struct *mm,
1093                                struct vm_area_struct *vma,
1094                                unsigned long address,
1095                                struct page **hpage)
1096 {
1097         pmd_t *pmd;
1098         pte_t *pte, *_pte;
1099         int ret = 0, none_or_zero = 0, result = 0, referenced = 0;
1100         struct page *page = NULL;
1101         unsigned long _address;
1102         spinlock_t *ptl;
1103         int node = NUMA_NO_NODE, unmapped = 0;
1104         bool writable = false;
1105
1106         VM_BUG_ON(address & ~HPAGE_PMD_MASK);
1107
1108         pmd = mm_find_pmd(mm, address);
1109         if (!pmd) {
1110                 result = SCAN_PMD_NULL;
1111                 goto out;
1112         }
1113
1114         memset(khugepaged_node_load, 0, sizeof(khugepaged_node_load));
1115         pte = pte_offset_map_lock(mm, pmd, address, &ptl);
1116         for (_address = address, _pte = pte; _pte < pte+HPAGE_PMD_NR;
1117              _pte++, _address += PAGE_SIZE) {
1118                 pte_t pteval = *_pte;
1119                 if (is_swap_pte(pteval)) {
1120                         if (++unmapped <= khugepaged_max_ptes_swap) {
1121                                 continue;
1122                         } else {
1123                                 result = SCAN_EXCEED_SWAP_PTE;
1124                                 goto out_unmap;
1125                         }
1126                 }
1127                 if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) {
1128                         if (!userfaultfd_armed(vma) &&
1129                             ++none_or_zero <= khugepaged_max_ptes_none) {
1130                                 continue;
1131                         } else {
1132                                 result = SCAN_EXCEED_NONE_PTE;
1133                                 goto out_unmap;
1134                         }
1135                 }
1136                 if (!pte_present(pteval)) {
1137                         result = SCAN_PTE_NON_PRESENT;
1138                         goto out_unmap;
1139                 }
1140                 if (pte_write(pteval))
1141                         writable = true;
1142
1143                 page = vm_normal_page(vma, _address, pteval);
1144                 if (unlikely(!page)) {
1145                         result = SCAN_PAGE_NULL;
1146                         goto out_unmap;
1147                 }
1148
1149                 /* TODO: teach khugepaged to collapse THP mapped with pte */
1150                 if (PageCompound(page)) {
1151                         result = SCAN_PAGE_COMPOUND;
1152                         goto out_unmap;
1153                 }
1154
1155                 /*
1156                  * Record which node the original page is from and save this
1157                  * information to khugepaged_node_load[].
1158                  * Khupaged will allocate hugepage from the node has the max
1159                  * hit record.
1160                  */
1161                 node = page_to_nid(page);
1162                 if (khugepaged_scan_abort(node)) {
1163                         result = SCAN_SCAN_ABORT;
1164                         goto out_unmap;
1165                 }
1166                 khugepaged_node_load[node]++;
1167                 if (!PageLRU(page)) {
1168                         result = SCAN_PAGE_LRU;
1169                         goto out_unmap;
1170                 }
1171                 if (PageLocked(page)) {
1172                         result = SCAN_PAGE_LOCK;
1173                         goto out_unmap;
1174                 }
1175                 if (!PageAnon(page)) {
1176                         result = SCAN_PAGE_ANON;
1177                         goto out_unmap;
1178                 }
1179
1180                 /*
1181                  * cannot use mapcount: can't collapse if there's a gup pin.
1182                  * The page must only be referenced by the scanned process
1183                  * and page swap cache.
1184                  */
1185                 if (page_count(page) != 1 + PageSwapCache(page)) {
1186                         result = SCAN_PAGE_COUNT;
1187                         goto out_unmap;
1188                 }
1189                 if (pte_young(pteval) ||
1190                     page_is_young(page) || PageReferenced(page) ||
1191                     mmu_notifier_test_young(vma->vm_mm, address))
1192                         referenced++;
1193         }
1194         if (writable) {
1195                 if (referenced) {
1196                         result = SCAN_SUCCEED;
1197                         ret = 1;
1198                 } else {
1199                         result = SCAN_LACK_REFERENCED_PAGE;
1200                 }
1201         } else {
1202                 result = SCAN_PAGE_RO;
1203         }
1204 out_unmap:
1205         pte_unmap_unlock(pte, ptl);
1206         if (ret) {
1207                 node = khugepaged_find_target_node();
1208                 /* collapse_huge_page will return with the mmap_sem released */
1209                 collapse_huge_page(mm, address, hpage, node, referenced);
1210         }
1211 out:
1212         trace_mm_khugepaged_scan_pmd(mm, page, writable, referenced,
1213                                      none_or_zero, result, unmapped);
1214         return ret;
1215 }
1216
1217 static void collect_mm_slot(struct mm_slot *mm_slot)
1218 {
1219         struct mm_struct *mm = mm_slot->mm;
1220
1221         VM_BUG_ON(NR_CPUS != 1 && !spin_is_locked(&khugepaged_mm_lock));
1222
1223         if (khugepaged_test_exit(mm)) {
1224                 /* free mm_slot */
1225                 hash_del(&mm_slot->hash);
1226                 list_del(&mm_slot->mm_node);
1227
1228                 /*
1229                  * Not strictly needed because the mm exited already.
1230                  *
1231                  * clear_bit(MMF_VM_HUGEPAGE, &mm->flags);
1232                  */
1233
1234                 /* khugepaged_mm_lock actually not necessary for the below */
1235                 free_mm_slot(mm_slot);
1236                 mmdrop(mm);
1237         }
1238 }
1239
1240 #if defined(CONFIG_SHMEM) && defined(CONFIG_TRANSPARENT_HUGE_PAGECACHE)
1241 static void retract_page_tables(struct address_space *mapping, pgoff_t pgoff)
1242 {
1243         struct vm_area_struct *vma;
1244         unsigned long addr;
1245         pmd_t *pmd, _pmd;
1246
1247         i_mmap_lock_write(mapping);
1248         vma_interval_tree_foreach(vma, &mapping->i_mmap, pgoff, pgoff) {
1249                 /* probably overkill */
1250                 if (vma->anon_vma)
1251                         continue;
1252                 addr = vma->vm_start + ((pgoff - vma->vm_pgoff) << PAGE_SHIFT);
1253                 if (addr & ~HPAGE_PMD_MASK)
1254                         continue;
1255                 if (vma->vm_end < addr + HPAGE_PMD_SIZE)
1256                         continue;
1257                 pmd = mm_find_pmd(vma->vm_mm, addr);
1258                 if (!pmd)
1259                         continue;
1260                 /*
1261                  * We need exclusive mmap_sem to retract page table.
1262                  * If trylock fails we would end up with pte-mapped THP after
1263                  * re-fault. Not ideal, but it's more important to not disturb
1264                  * the system too much.
1265                  */
1266                 if (down_write_trylock(&vma->vm_mm->mmap_sem)) {
1267                         spinlock_t *ptl = pmd_lock(vma->vm_mm, pmd);
1268                         /* assume page table is clear */
1269                         _pmd = pmdp_collapse_flush(vma, addr, pmd);
1270                         spin_unlock(ptl);
1271                         up_write(&vma->vm_mm->mmap_sem);
1272                         atomic_long_dec(&vma->vm_mm->nr_ptes);
1273                         pte_free(vma->vm_mm, pmd_pgtable(_pmd));
1274                 }
1275         }
1276         i_mmap_unlock_write(mapping);
1277 }
1278
1279 /**
1280  * collapse_shmem - collapse small tmpfs/shmem pages into huge one.
1281  *
1282  * Basic scheme is simple, details are more complex:
1283  *  - allocate and freeze a new huge page;
1284  *  - scan over radix tree replacing old pages the new one
1285  *    + swap in pages if necessary;
1286  *    + fill in gaps;
1287  *    + keep old pages around in case if rollback is required;
1288  *  - if replacing succeed:
1289  *    + copy data over;
1290  *    + free old pages;
1291  *    + unfreeze huge page;
1292  *  - if replacing failed;
1293  *    + put all pages back and unfreeze them;
1294  *    + restore gaps in the radix-tree;
1295  *    + free huge page;
1296  */
1297 static void collapse_shmem(struct mm_struct *mm,
1298                 struct address_space *mapping, pgoff_t start,
1299                 struct page **hpage, int node)
1300 {
1301         gfp_t gfp;
1302         struct page *page, *new_page, *tmp;
1303         struct mem_cgroup *memcg;
1304         pgoff_t index, end = start + HPAGE_PMD_NR;
1305         LIST_HEAD(pagelist);
1306         struct radix_tree_iter iter;
1307         void **slot;
1308         int nr_none = 0, result = SCAN_SUCCEED;
1309
1310         VM_BUG_ON(start & (HPAGE_PMD_NR - 1));
1311
1312         /* Only allocate from the target node */
1313         gfp = alloc_hugepage_khugepaged_gfpmask() | __GFP_THISNODE;
1314
1315         new_page = khugepaged_alloc_page(hpage, gfp, node);
1316         if (!new_page) {
1317                 result = SCAN_ALLOC_HUGE_PAGE_FAIL;
1318                 goto out;
1319         }
1320
1321         if (unlikely(mem_cgroup_try_charge(new_page, mm, gfp, &memcg, true))) {
1322                 result = SCAN_CGROUP_CHARGE_FAIL;
1323                 goto out;
1324         }
1325
1326         new_page->index = start;
1327         new_page->mapping = mapping;
1328         __SetPageSwapBacked(new_page);
1329         __SetPageLocked(new_page);
1330         BUG_ON(!page_ref_freeze(new_page, 1));
1331
1332
1333         /*
1334          * At this point the new_page is 'frozen' (page_count() is zero), locked
1335          * and not up-to-date. It's safe to insert it into radix tree, because
1336          * nobody would be able to map it or use it in other way until we
1337          * unfreeze it.
1338          */
1339
1340         index = start;
1341         spin_lock_irq(&mapping->tree_lock);
1342         radix_tree_for_each_slot(slot, &mapping->page_tree, &iter, start) {
1343                 int n = min(iter.index, end) - index;
1344
1345                 /*
1346                  * Handle holes in the radix tree: charge it from shmem and
1347                  * insert relevant subpage of new_page into the radix-tree.
1348                  */
1349                 if (n && !shmem_charge(mapping->host, n)) {
1350                         result = SCAN_FAIL;
1351                         break;
1352                 }
1353                 nr_none += n;
1354                 for (; index < min(iter.index, end); index++) {
1355                         radix_tree_insert(&mapping->page_tree, index,
1356                                         new_page + (index % HPAGE_PMD_NR));
1357                 }
1358
1359                 /* We are done. */
1360                 if (index >= end)
1361                         break;
1362
1363                 page = radix_tree_deref_slot_protected(slot,
1364                                 &mapping->tree_lock);
1365                 if (radix_tree_exceptional_entry(page) || !PageUptodate(page)) {
1366                         spin_unlock_irq(&mapping->tree_lock);
1367                         /* swap in or instantiate fallocated page */
1368                         if (shmem_getpage(mapping->host, index, &page,
1369                                                 SGP_NOHUGE)) {
1370                                 result = SCAN_FAIL;
1371                                 goto tree_unlocked;
1372                         }
1373                         spin_lock_irq(&mapping->tree_lock);
1374                 } else if (trylock_page(page)) {
1375                         get_page(page);
1376                 } else {
1377                         result = SCAN_PAGE_LOCK;
1378                         break;
1379                 }
1380
1381                 /*
1382                  * The page must be locked, so we can drop the tree_lock
1383                  * without racing with truncate.
1384                  */
1385                 VM_BUG_ON_PAGE(!PageLocked(page), page);
1386                 VM_BUG_ON_PAGE(!PageUptodate(page), page);
1387                 VM_BUG_ON_PAGE(PageTransCompound(page), page);
1388
1389                 if (page_mapping(page) != mapping) {
1390                         result = SCAN_TRUNCATED;
1391                         goto out_unlock;
1392                 }
1393                 spin_unlock_irq(&mapping->tree_lock);
1394
1395                 if (isolate_lru_page(page)) {
1396                         result = SCAN_DEL_PAGE_LRU;
1397                         goto out_isolate_failed;
1398                 }
1399
1400                 if (page_mapped(page))
1401                         unmap_mapping_range(mapping, index << PAGE_SHIFT,
1402                                         PAGE_SIZE, 0);
1403
1404                 spin_lock_irq(&mapping->tree_lock);
1405
1406                 slot = radix_tree_lookup_slot(&mapping->page_tree, index);
1407                 VM_BUG_ON_PAGE(page != radix_tree_deref_slot_protected(slot,
1408                                         &mapping->tree_lock), page);
1409                 VM_BUG_ON_PAGE(page_mapped(page), page);
1410
1411                 /*
1412                  * The page is expected to have page_count() == 3:
1413                  *  - we hold a pin on it;
1414                  *  - one reference from radix tree;
1415                  *  - one from isolate_lru_page;
1416                  */
1417                 if (!page_ref_freeze(page, 3)) {
1418                         result = SCAN_PAGE_COUNT;
1419                         goto out_lru;
1420                 }
1421
1422                 /*
1423                  * Add the page to the list to be able to undo the collapse if
1424                  * something go wrong.
1425                  */
1426                 list_add_tail(&page->lru, &pagelist);
1427
1428                 /* Finally, replace with the new page. */
1429                 radix_tree_replace_slot(&mapping->page_tree, slot,
1430                                 new_page + (index % HPAGE_PMD_NR));
1431
1432                 slot = radix_tree_iter_resume(slot, &iter);
1433                 index++;
1434                 continue;
1435 out_lru:
1436                 spin_unlock_irq(&mapping->tree_lock);
1437                 putback_lru_page(page);
1438 out_isolate_failed:
1439                 unlock_page(page);
1440                 put_page(page);
1441                 goto tree_unlocked;
1442 out_unlock:
1443                 unlock_page(page);
1444                 put_page(page);
1445                 break;
1446         }
1447
1448         /*
1449          * Handle hole in radix tree at the end of the range.
1450          * This code only triggers if there's nothing in radix tree
1451          * beyond 'end'.
1452          */
1453         if (result == SCAN_SUCCEED && index < end) {
1454                 int n = end - index;
1455
1456                 if (!shmem_charge(mapping->host, n)) {
1457                         result = SCAN_FAIL;
1458                         goto tree_locked;
1459                 }
1460
1461                 for (; index < end; index++) {
1462                         radix_tree_insert(&mapping->page_tree, index,
1463                                         new_page + (index % HPAGE_PMD_NR));
1464                 }
1465                 nr_none += n;
1466         }
1467
1468 tree_locked:
1469         spin_unlock_irq(&mapping->tree_lock);
1470 tree_unlocked:
1471
1472         if (result == SCAN_SUCCEED) {
1473                 unsigned long flags;
1474                 struct zone *zone = page_zone(new_page);
1475
1476                 /*
1477                  * Replacing old pages with new one has succeed, now we need to
1478                  * copy the content and free old pages.
1479                  */
1480                 list_for_each_entry_safe(page, tmp, &pagelist, lru) {
1481                         copy_highpage(new_page + (page->index % HPAGE_PMD_NR),
1482                                         page);
1483                         list_del(&page->lru);
1484                         unlock_page(page);
1485                         page_ref_unfreeze(page, 1);
1486                         page->mapping = NULL;
1487                         ClearPageActive(page);
1488                         ClearPageUnevictable(page);
1489                         put_page(page);
1490                 }
1491
1492                 local_irq_save(flags);
1493                 __inc_node_page_state(new_page, NR_SHMEM_THPS);
1494                 if (nr_none) {
1495                         __mod_node_page_state(zone->zone_pgdat, NR_FILE_PAGES, nr_none);
1496                         __mod_node_page_state(zone->zone_pgdat, NR_SHMEM, nr_none);
1497                 }
1498                 local_irq_restore(flags);
1499
1500                 /*
1501                  * Remove pte page tables, so we can re-faulti
1502                  * the page as huge.
1503                  */
1504                 retract_page_tables(mapping, start);
1505
1506                 /* Everything is ready, let's unfreeze the new_page */
1507                 set_page_dirty(new_page);
1508                 SetPageUptodate(new_page);
1509                 page_ref_unfreeze(new_page, HPAGE_PMD_NR);
1510                 mem_cgroup_commit_charge(new_page, memcg, false, true);
1511                 lru_cache_add_anon(new_page);
1512                 unlock_page(new_page);
1513
1514                 *hpage = NULL;
1515         } else {
1516                 /* Something went wrong: rollback changes to the radix-tree */
1517                 shmem_uncharge(mapping->host, nr_none);
1518                 spin_lock_irq(&mapping->tree_lock);
1519                 radix_tree_for_each_slot(slot, &mapping->page_tree, &iter,
1520                                 start) {
1521                         if (iter.index >= end)
1522                                 break;
1523                         page = list_first_entry_or_null(&pagelist,
1524                                         struct page, lru);
1525                         if (!page || iter.index < page->index) {
1526                                 if (!nr_none)
1527                                         break;
1528                                 nr_none--;
1529                                 /* Put holes back where they were */
1530                                 radix_tree_delete(&mapping->page_tree,
1531                                                   iter.index);
1532                                 continue;
1533                         }
1534
1535                         VM_BUG_ON_PAGE(page->index != iter.index, page);
1536
1537                         /* Unfreeze the page. */
1538                         list_del(&page->lru);
1539                         page_ref_unfreeze(page, 2);
1540                         radix_tree_replace_slot(&mapping->page_tree,
1541                                                 slot, page);
1542                         slot = radix_tree_iter_resume(slot, &iter);
1543                         spin_unlock_irq(&mapping->tree_lock);
1544                         putback_lru_page(page);
1545                         unlock_page(page);
1546                         spin_lock_irq(&mapping->tree_lock);
1547                 }
1548                 VM_BUG_ON(nr_none);
1549                 spin_unlock_irq(&mapping->tree_lock);
1550
1551                 /* Unfreeze new_page, caller would take care about freeing it */
1552                 page_ref_unfreeze(new_page, 1);
1553                 mem_cgroup_cancel_charge(new_page, memcg, true);
1554                 unlock_page(new_page);
1555                 new_page->mapping = NULL;
1556         }
1557 out:
1558         VM_BUG_ON(!list_empty(&pagelist));
1559         /* TODO: tracepoints */
1560 }
1561
1562 static void khugepaged_scan_shmem(struct mm_struct *mm,
1563                 struct address_space *mapping,
1564                 pgoff_t start, struct page **hpage)
1565 {
1566         struct page *page = NULL;
1567         struct radix_tree_iter iter;
1568         void **slot;
1569         int present, swap;
1570         int node = NUMA_NO_NODE;
1571         int result = SCAN_SUCCEED;
1572
1573         present = 0;
1574         swap = 0;
1575         memset(khugepaged_node_load, 0, sizeof(khugepaged_node_load));
1576         rcu_read_lock();
1577         radix_tree_for_each_slot(slot, &mapping->page_tree, &iter, start) {
1578                 if (iter.index >= start + HPAGE_PMD_NR)
1579                         break;
1580
1581                 page = radix_tree_deref_slot(slot);
1582                 if (radix_tree_deref_retry(page)) {
1583                         slot = radix_tree_iter_retry(&iter);
1584                         continue;
1585                 }
1586
1587                 if (radix_tree_exception(page)) {
1588                         if (++swap > khugepaged_max_ptes_swap) {
1589                                 result = SCAN_EXCEED_SWAP_PTE;
1590                                 break;
1591                         }
1592                         continue;
1593                 }
1594
1595                 if (PageTransCompound(page)) {
1596                         result = SCAN_PAGE_COMPOUND;
1597                         break;
1598                 }
1599
1600                 node = page_to_nid(page);
1601                 if (khugepaged_scan_abort(node)) {
1602                         result = SCAN_SCAN_ABORT;
1603                         break;
1604                 }
1605                 khugepaged_node_load[node]++;
1606
1607                 if (!PageLRU(page)) {
1608                         result = SCAN_PAGE_LRU;
1609                         break;
1610                 }
1611
1612                 if (page_count(page) != 1 + page_mapcount(page)) {
1613                         result = SCAN_PAGE_COUNT;
1614                         break;
1615                 }
1616
1617                 /*
1618                  * We probably should check if the page is referenced here, but
1619                  * nobody would transfer pte_young() to PageReferenced() for us.
1620                  * And rmap walk here is just too costly...
1621                  */
1622
1623                 present++;
1624
1625                 if (need_resched()) {
1626                         slot = radix_tree_iter_resume(slot, &iter);
1627                         cond_resched_rcu();
1628                 }
1629         }
1630         rcu_read_unlock();
1631
1632         if (result == SCAN_SUCCEED) {
1633                 if (present < HPAGE_PMD_NR - khugepaged_max_ptes_none) {
1634                         result = SCAN_EXCEED_NONE_PTE;
1635                 } else {
1636                         node = khugepaged_find_target_node();
1637                         collapse_shmem(mm, mapping, start, hpage, node);
1638                 }
1639         }
1640
1641         /* TODO: tracepoints */
1642 }
1643 #else
1644 static void khugepaged_scan_shmem(struct mm_struct *mm,
1645                 struct address_space *mapping,
1646                 pgoff_t start, struct page **hpage)
1647 {
1648         BUILD_BUG();
1649 }
1650 #endif
1651
1652 static unsigned int khugepaged_scan_mm_slot(unsigned int pages,
1653                                             struct page **hpage)
1654         __releases(&khugepaged_mm_lock)
1655         __acquires(&khugepaged_mm_lock)
1656 {
1657         struct mm_slot *mm_slot;
1658         struct mm_struct *mm;
1659         struct vm_area_struct *vma;
1660         int progress = 0;
1661
1662         VM_BUG_ON(!pages);
1663         VM_BUG_ON(NR_CPUS != 1 && !spin_is_locked(&khugepaged_mm_lock));
1664
1665         if (khugepaged_scan.mm_slot)
1666                 mm_slot = khugepaged_scan.mm_slot;
1667         else {
1668                 mm_slot = list_entry(khugepaged_scan.mm_head.next,
1669                                      struct mm_slot, mm_node);
1670                 khugepaged_scan.address = 0;
1671                 khugepaged_scan.mm_slot = mm_slot;
1672         }
1673         spin_unlock(&khugepaged_mm_lock);
1674
1675         mm = mm_slot->mm;
1676         down_read(&mm->mmap_sem);
1677         if (unlikely(khugepaged_test_exit(mm)))
1678                 vma = NULL;
1679         else
1680                 vma = find_vma(mm, khugepaged_scan.address);
1681
1682         progress++;
1683         for (; vma; vma = vma->vm_next) {
1684                 unsigned long hstart, hend;
1685
1686                 cond_resched();
1687                 if (unlikely(khugepaged_test_exit(mm))) {
1688                         progress++;
1689                         break;
1690                 }
1691                 if (!hugepage_vma_check(vma)) {
1692 skip:
1693                         progress++;
1694                         continue;
1695                 }
1696                 hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK;
1697                 hend = vma->vm_end & HPAGE_PMD_MASK;
1698                 if (hstart >= hend)
1699                         goto skip;
1700                 if (khugepaged_scan.address > hend)
1701                         goto skip;
1702                 if (khugepaged_scan.address < hstart)
1703                         khugepaged_scan.address = hstart;
1704                 VM_BUG_ON(khugepaged_scan.address & ~HPAGE_PMD_MASK);
1705
1706                 while (khugepaged_scan.address < hend) {
1707                         int ret;
1708                         cond_resched();
1709                         if (unlikely(khugepaged_test_exit(mm)))
1710                                 goto breakouterloop;
1711
1712                         VM_BUG_ON(khugepaged_scan.address < hstart ||
1713                                   khugepaged_scan.address + HPAGE_PMD_SIZE >
1714                                   hend);
1715                         if (shmem_file(vma->vm_file)) {
1716                                 struct file *file;
1717                                 pgoff_t pgoff = linear_page_index(vma,
1718                                                 khugepaged_scan.address);
1719                                 if (!shmem_huge_enabled(vma))
1720                                         goto skip;
1721                                 file = get_file(vma->vm_file);
1722                                 up_read(&mm->mmap_sem);
1723                                 ret = 1;
1724                                 khugepaged_scan_shmem(mm, file->f_mapping,
1725                                                 pgoff, hpage);
1726                                 fput(file);
1727                         } else {
1728                                 ret = khugepaged_scan_pmd(mm, vma,
1729                                                 khugepaged_scan.address,
1730                                                 hpage);
1731                         }
1732                         /* move to next address */
1733                         khugepaged_scan.address += HPAGE_PMD_SIZE;
1734                         progress += HPAGE_PMD_NR;
1735                         if (ret)
1736                                 /* we released mmap_sem so break loop */
1737                                 goto breakouterloop_mmap_sem;
1738                         if (progress >= pages)
1739                                 goto breakouterloop;
1740                 }
1741         }
1742 breakouterloop:
1743         up_read(&mm->mmap_sem); /* exit_mmap will destroy ptes after this */
1744 breakouterloop_mmap_sem:
1745
1746         spin_lock(&khugepaged_mm_lock);
1747         VM_BUG_ON(khugepaged_scan.mm_slot != mm_slot);
1748         /*
1749          * Release the current mm_slot if this mm is about to die, or
1750          * if we scanned all vmas of this mm.
1751          */
1752         if (khugepaged_test_exit(mm) || !vma) {
1753                 /*
1754                  * Make sure that if mm_users is reaching zero while
1755                  * khugepaged runs here, khugepaged_exit will find
1756                  * mm_slot not pointing to the exiting mm.
1757                  */
1758                 if (mm_slot->mm_node.next != &khugepaged_scan.mm_head) {
1759                         khugepaged_scan.mm_slot = list_entry(
1760                                 mm_slot->mm_node.next,
1761                                 struct mm_slot, mm_node);
1762                         khugepaged_scan.address = 0;
1763                 } else {
1764                         khugepaged_scan.mm_slot = NULL;
1765                         khugepaged_full_scans++;
1766                 }
1767
1768                 collect_mm_slot(mm_slot);
1769         }
1770
1771         return progress;
1772 }
1773
1774 static int khugepaged_has_work(void)
1775 {
1776         return !list_empty(&khugepaged_scan.mm_head) &&
1777                 khugepaged_enabled();
1778 }
1779
1780 static int khugepaged_wait_event(void)
1781 {
1782         return !list_empty(&khugepaged_scan.mm_head) ||
1783                 kthread_should_stop();
1784 }
1785
1786 static void khugepaged_do_scan(void)
1787 {
1788         struct page *hpage = NULL;
1789         unsigned int progress = 0, pass_through_head = 0;
1790         unsigned int pages = khugepaged_pages_to_scan;
1791         bool wait = true;
1792
1793         barrier(); /* write khugepaged_pages_to_scan to local stack */
1794
1795         while (progress < pages) {
1796                 if (!khugepaged_prealloc_page(&hpage, &wait))
1797                         break;
1798
1799                 cond_resched();
1800
1801                 if (unlikely(kthread_should_stop() || try_to_freeze()))
1802                         break;
1803
1804                 spin_lock(&khugepaged_mm_lock);
1805                 if (!khugepaged_scan.mm_slot)
1806                         pass_through_head++;
1807                 if (khugepaged_has_work() &&
1808                     pass_through_head < 2)
1809                         progress += khugepaged_scan_mm_slot(pages - progress,
1810                                                             &hpage);
1811                 else
1812                         progress = pages;
1813                 spin_unlock(&khugepaged_mm_lock);
1814         }
1815
1816         if (!IS_ERR_OR_NULL(hpage))
1817                 put_page(hpage);
1818 }
1819
1820 static bool khugepaged_should_wakeup(void)
1821 {
1822         return kthread_should_stop() ||
1823                time_after_eq(jiffies, khugepaged_sleep_expire);
1824 }
1825
1826 static void khugepaged_wait_work(void)
1827 {
1828         if (khugepaged_has_work()) {
1829                 const unsigned long scan_sleep_jiffies =
1830                         msecs_to_jiffies(khugepaged_scan_sleep_millisecs);
1831
1832                 if (!scan_sleep_jiffies)
1833                         return;
1834
1835                 khugepaged_sleep_expire = jiffies + scan_sleep_jiffies;
1836                 wait_event_freezable_timeout(khugepaged_wait,
1837                                              khugepaged_should_wakeup(),
1838                                              scan_sleep_jiffies);
1839                 return;
1840         }
1841
1842         if (khugepaged_enabled())
1843                 wait_event_freezable(khugepaged_wait, khugepaged_wait_event());
1844 }
1845
1846 static int khugepaged(void *none)
1847 {
1848         struct mm_slot *mm_slot;
1849
1850         set_freezable();
1851         set_user_nice(current, MAX_NICE);
1852
1853         while (!kthread_should_stop()) {
1854                 khugepaged_do_scan();
1855                 khugepaged_wait_work();
1856         }
1857
1858         spin_lock(&khugepaged_mm_lock);
1859         mm_slot = khugepaged_scan.mm_slot;
1860         khugepaged_scan.mm_slot = NULL;
1861         if (mm_slot)
1862                 collect_mm_slot(mm_slot);
1863         spin_unlock(&khugepaged_mm_lock);
1864         return 0;
1865 }
1866
1867 static void set_recommended_min_free_kbytes(void)
1868 {
1869         struct zone *zone;
1870         int nr_zones = 0;
1871         unsigned long recommended_min;
1872
1873         for_each_populated_zone(zone)
1874                 nr_zones++;
1875
1876         /* Ensure 2 pageblocks are free to assist fragmentation avoidance */
1877         recommended_min = pageblock_nr_pages * nr_zones * 2;
1878
1879         /*
1880          * Make sure that on average at least two pageblocks are almost free
1881          * of another type, one for a migratetype to fall back to and a
1882          * second to avoid subsequent fallbacks of other types There are 3
1883          * MIGRATE_TYPES we care about.
1884          */
1885         recommended_min += pageblock_nr_pages * nr_zones *
1886                            MIGRATE_PCPTYPES * MIGRATE_PCPTYPES;
1887
1888         /* don't ever allow to reserve more than 5% of the lowmem */
1889         recommended_min = min(recommended_min,
1890                               (unsigned long) nr_free_buffer_pages() / 20);
1891         recommended_min <<= (PAGE_SHIFT-10);
1892
1893         if (recommended_min > min_free_kbytes) {
1894                 if (user_min_free_kbytes >= 0)
1895                         pr_info("raising min_free_kbytes from %d to %lu to help transparent hugepage allocations\n",
1896                                 min_free_kbytes, recommended_min);
1897
1898                 min_free_kbytes = recommended_min;
1899         }
1900         setup_per_zone_wmarks();
1901 }
1902
1903 int start_stop_khugepaged(void)
1904 {
1905         static struct task_struct *khugepaged_thread __read_mostly;
1906         static DEFINE_MUTEX(khugepaged_mutex);
1907         int err = 0;
1908
1909         mutex_lock(&khugepaged_mutex);
1910         if (khugepaged_enabled()) {
1911                 if (!khugepaged_thread)
1912                         khugepaged_thread = kthread_run(khugepaged, NULL,
1913                                                         "khugepaged");
1914                 if (IS_ERR(khugepaged_thread)) {
1915                         pr_err("khugepaged: kthread_run(khugepaged) failed\n");
1916                         err = PTR_ERR(khugepaged_thread);
1917                         khugepaged_thread = NULL;
1918                         goto fail;
1919                 }
1920
1921                 if (!list_empty(&khugepaged_scan.mm_head))
1922                         wake_up_interruptible(&khugepaged_wait);
1923
1924                 set_recommended_min_free_kbytes();
1925         } else if (khugepaged_thread) {
1926                 kthread_stop(khugepaged_thread);
1927                 khugepaged_thread = NULL;
1928         }
1929 fail:
1930         mutex_unlock(&khugepaged_mutex);
1931         return err;
1932 }