mm/khugepaged.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
   3
   4 #include <linux/mm.h>
   5 #include <linux/sched.h>
   6 #include <linux/sched/mm.h>
   7 #include <linux/sched/coredump.h>
   8 #include <linux/mmu_notifier.h>
   9 #include <linux/rmap.h>
  10 #include <linux/swap.h>
  11 #include <linux/mm_inline.h>
  12 #include <linux/kthread.h>
  13 #include <linux/khugepaged.h>
  14 #include <linux/freezer.h>
  15 #include <linux/mman.h>
  16 #include <linux/hashtable.h>
  17 #include <linux/userfaultfd_k.h>
  18 #include <linux/page_idle.h>
  19 #include <linux/swapops.h>
  20 #include <linux/shmem_fs.h>
  21
  22 #include <asm/tlb.h>
  23 #include <asm/pgalloc.h>
  24 #include "internal.h"
  25
  26 enum scan_result {
  27         SCAN_FAIL,
  28         SCAN_SUCCEED,
  29         SCAN_PMD_NULL,
  30         SCAN_EXCEED_NONE_PTE,
  31         SCAN_PTE_NON_PRESENT,
  32         SCAN_PAGE_RO,
  33         SCAN_LACK_REFERENCED_PAGE,
  34         SCAN_PAGE_NULL,
  35         SCAN_SCAN_ABORT,
  36         SCAN_PAGE_COUNT,
  37         SCAN_PAGE_LRU,
  38         SCAN_PAGE_LOCK,
  39         SCAN_PAGE_ANON,
  40         SCAN_PAGE_COMPOUND,
  41         SCAN_ANY_PROCESS,
  42         SCAN_VMA_NULL,
  43         SCAN_VMA_CHECK,
  44         SCAN_ADDRESS_RANGE,
  45         SCAN_SWAP_CACHE_PAGE,
  46         SCAN_DEL_PAGE_LRU,
  47         SCAN_ALLOC_HUGE_PAGE_FAIL,
  48         SCAN_CGROUP_CHARGE_FAIL,
  49         SCAN_EXCEED_SWAP_PTE,
  50         SCAN_TRUNCATED,
  51 };
  52
  53 #define CREATE_TRACE_POINTS
  54 #include <trace/events/huge_memory.h>
  55
  56 /* default scan 8*512 pte (or vmas) every 30 second */
  57 static unsigned int khugepaged_pages_to_scan __read_mostly;
  58 static unsigned int khugepaged_pages_collapsed;
  59 static unsigned int khugepaged_full_scans;
  60 static unsigned int khugepaged_scan_sleep_millisecs __read_mostly = 10000;
  61 /* during fragmentation poll the hugepage allocator once every minute */
  62 static unsigned int khugepaged_alloc_sleep_millisecs __read_mostly = 60000;
  63 static unsigned long khugepaged_sleep_expire;
  64 static DEFINE_SPINLOCK(khugepaged_mm_lock);
  65 static DECLARE_WAIT_QUEUE_HEAD(khugepaged_wait);
  66 /*
  67  * default collapse hugepages if there is at least one pte mapped like
  68  * it would have happened if the vma was large enough during page
  69  * fault.
  70  */
  71 static unsigned int khugepaged_max_ptes_none __read_mostly;
  72 static unsigned int khugepaged_max_ptes_swap __read_mostly;
  73
  74 #define MM_SLOTS_HASH_BITS 10
  75 static __read_mostly DEFINE_HASHTABLE(mm_slots_hash, MM_SLOTS_HASH_BITS);
  76
  77 static struct kmem_cache *mm_slot_cache __read_mostly;
  78
  79 /**
  80  * struct mm_slot - hash lookup from mm to mm_slot
  81  * @hash: hash collision list
  82  * @mm_node: khugepaged scan list headed in khugepaged_scan.mm_head
  83  * @mm: the mm that this information is valid for
  84  */
  85 struct mm_slot {
  86         struct hlist_node hash;
  87         struct list_head mm_node;
  88         struct mm_struct *mm;
  89 };
  90
  91 /**
  92  * struct khugepaged_scan - cursor for scanning
  93  * @mm_head: the head of the mm list to scan
  94  * @mm_slot: the current mm_slot we are scanning
  95  * @address: the next address inside that to be scanned
  96  *
  97  * There is only the one khugepaged_scan instance of this cursor structure.
  98  */
  99 struct khugepaged_scan {
 100         struct list_head mm_head;
 101         struct mm_slot *mm_slot;
 102         unsigned long address;
 103 };
 104
 105 static struct khugepaged_scan khugepaged_scan = {
 106         .mm_head = LIST_HEAD_INIT(khugepaged_scan.mm_head),
 107 };
 108
 109 #ifdef CONFIG_SYSFS
 110 static ssize_t scan_sleep_millisecs_show(struct kobject *kobj,
 111                                          struct kobj_attribute *attr,
 112                                          char *buf)
 113 {
 114         return sprintf(buf, "%u\n", khugepaged_scan_sleep_millisecs);
 115 }
 116
 117 static ssize_t scan_sleep_millisecs_store(struct kobject *kobj,
 118                                           struct kobj_attribute *attr,
 119                                           const char *buf, size_t count)
 120 {
 121         unsigned long msecs;
 122         int err;
 123
 124         err = kstrtoul(buf, 10, &msecs);
 125         if (err || msecs > UINT_MAX)
 126                 return -EINVAL;
 127
 128         khugepaged_scan_sleep_millisecs = msecs;
 129         khugepaged_sleep_expire = 0;
 130         wake_up_interruptible(&khugepaged_wait);
 131
 132         return count;
 133 }
 134 static struct kobj_attribute scan_sleep_millisecs_attr =
 135         __ATTR(scan_sleep_millisecs, 0644, scan_sleep_millisecs_show,
 136                scan_sleep_millisecs_store);
 137
 138 static ssize_t alloc_sleep_millisecs_show(struct kobject *kobj,
 139                                           struct kobj_attribute *attr,
 140                                           char *buf)
 141 {
 142         return sprintf(buf, "%u\n", khugepaged_alloc_sleep_millisecs);
 143 }
 144
 145 static ssize_t alloc_sleep_millisecs_store(struct kobject *kobj,
 146                                            struct kobj_attribute *attr,
 147                                            const char *buf, size_t count)
 148 {
 149         unsigned long msecs;
 150         int err;
 151
 152         err = kstrtoul(buf, 10, &msecs);
 153         if (err || msecs > UINT_MAX)
 154                 return -EINVAL;
 155
 156         khugepaged_alloc_sleep_millisecs = msecs;
 157         khugepaged_sleep_expire = 0;
 158         wake_up_interruptible(&khugepaged_wait);
 159
 160         return count;
 161 }
 162 static struct kobj_attribute alloc_sleep_millisecs_attr =
 163         __ATTR(alloc_sleep_millisecs, 0644, alloc_sleep_millisecs_show,
 164                alloc_sleep_millisecs_store);
 165
 166 static ssize_t pages_to_scan_show(struct kobject *kobj,
 167                                   struct kobj_attribute *attr,
 168                                   char *buf)
 169 {
 170         return sprintf(buf, "%u\n", khugepaged_pages_to_scan);
 171 }
 172 static ssize_t pages_to_scan_store(struct kobject *kobj,
 173                                    struct kobj_attribute *attr,
 174                                    const char *buf, size_t count)
 175 {
 176         int err;
 177         unsigned long pages;
 178
 179         err = kstrtoul(buf, 10, &pages);
 180         if (err || !pages || pages > UINT_MAX)
 181                 return -EINVAL;
 182
 183         khugepaged_pages_to_scan = pages;
 184
 185         return count;
 186 }
 187 static struct kobj_attribute pages_to_scan_attr =
 188         __ATTR(pages_to_scan, 0644, pages_to_scan_show,
 189                pages_to_scan_store);
 190
 191 static ssize_t pages_collapsed_show(struct kobject *kobj,
 192                                     struct kobj_attribute *attr,
 193                                     char *buf)
 194 {
 195         return sprintf(buf, "%u\n", khugepaged_pages_collapsed);
 196 }
 197 static struct kobj_attribute pages_collapsed_attr =
 198         __ATTR_RO(pages_collapsed);
 199
 200 static ssize_t full_scans_show(struct kobject *kobj,
 201                                struct kobj_attribute *attr,
 202                                char *buf)
 203 {
 204         return sprintf(buf, "%u\n", khugepaged_full_scans);
 205 }
 206 static struct kobj_attribute full_scans_attr =
 207         __ATTR_RO(full_scans);
 208
 209 static ssize_t khugepaged_defrag_show(struct kobject *kobj,
 210                                       struct kobj_attribute *attr, char *buf)
 211 {
 212         return single_hugepage_flag_show(kobj, attr, buf,
 213                                 TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG);
 214 }
 215 static ssize_t khugepaged_defrag_store(struct kobject *kobj,
 216                                        struct kobj_attribute *attr,
 217                                        const char *buf, size_t count)
 218 {
 219         return single_hugepage_flag_store(kobj, attr, buf, count,
 220                                  TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG);
 221 }
 222 static struct kobj_attribute khugepaged_defrag_attr =
 223         __ATTR(defrag, 0644, khugepaged_defrag_show,
 224                khugepaged_defrag_store);
 225
 226 /*
 227  * max_ptes_none controls if khugepaged should collapse hugepages over
 228  * any unmapped ptes in turn potentially increasing the memory
 229  * footprint of the vmas. When max_ptes_none is 0 khugepaged will not
 230  * reduce the available free memory in the system as it
 231  * runs. Increasing max_ptes_none will instead potentially reduce the
 232  * free memory in the system during the khugepaged scan.
 233  */
 234 static ssize_t khugepaged_max_ptes_none_show(struct kobject *kobj,
 235                                              struct kobj_attribute *attr,
 236                                              char *buf)
 237 {
 238         return sprintf(buf, "%u\n", khugepaged_max_ptes_none);
 239 }
 240 static ssize_t khugepaged_max_ptes_none_store(struct kobject *kobj,
 241                                               struct kobj_attribute *attr,
 242                                               const char *buf, size_t count)
 243 {
 244         int err;
 245         unsigned long max_ptes_none;
 246
 247         err = kstrtoul(buf, 10, &max_ptes_none);
 248         if (err || max_ptes_none > HPAGE_PMD_NR-1)
 249                 return -EINVAL;
 250
 251         khugepaged_max_ptes_none = max_ptes_none;
 252
 253         return count;
 254 }
 255 static struct kobj_attribute khugepaged_max_ptes_none_attr =
 256         __ATTR(max_ptes_none, 0644, khugepaged_max_ptes_none_show,
 257                khugepaged_max_ptes_none_store);
 258
 259 static ssize_t khugepaged_max_ptes_swap_show(struct kobject *kobj,
 260                                              struct kobj_attribute *attr,
 261                                              char *buf)
 262 {
 263         return sprintf(buf, "%u\n", khugepaged_max_ptes_swap);
 264 }
 265
 266 static ssize_t khugepaged_max_ptes_swap_store(struct kobject *kobj,
 267                                               struct kobj_attribute *attr,
 268                                               const char *buf, size_t count)
 269 {
 270         int err;
 271         unsigned long max_ptes_swap;
 272
 273         err  = kstrtoul(buf, 10, &max_ptes_swap);
 274         if (err || max_ptes_swap > HPAGE_PMD_NR-1)
 275                 return -EINVAL;
 276
 277         khugepaged_max_ptes_swap = max_ptes_swap;
 278
 279         return count;
 280 }
 281
 282 static struct kobj_attribute khugepaged_max_ptes_swap_attr =
 283         __ATTR(max_ptes_swap, 0644, khugepaged_max_ptes_swap_show,
 284                khugepaged_max_ptes_swap_store);
 285
 286 static struct attribute *khugepaged_attr[] = {
 287         &khugepaged_defrag_attr.attr,
 288         &khugepaged_max_ptes_none_attr.attr,
 289         &pages_to_scan_attr.attr,
 290         &pages_collapsed_attr.attr,
 291         &full_scans_attr.attr,
 292         &scan_sleep_millisecs_attr.attr,
 293         &alloc_sleep_millisecs_attr.attr,
 294         &khugepaged_max_ptes_swap_attr.attr,
 295         NULL,
 296 };
 297
 298 struct attribute_group khugepaged_attr_group = {
 299         .attrs = khugepaged_attr,
 300         .name = "khugepaged",
 301 };
 302 #endif /* CONFIG_SYSFS */
 303
 304 #define VM_NO_KHUGEPAGED (VM_SPECIAL | VM_HUGETLB)
 305
 306 int hugepage_madvise(struct vm_area_struct *vma,
 307                      unsigned long *vm_flags, int advice)
 308 {
 309         switch (advice) {
 310         case MADV_HUGEPAGE:
 311 #ifdef CONFIG_S390
 312                 /*
 313                  * qemu blindly sets MADV_HUGEPAGE on all allocations, but s390
 314                  * can't handle this properly after s390_enable_sie, so we simply
 315                  * ignore the madvise to prevent qemu from causing a SIGSEGV.
 316                  */
 317                 if (mm_has_pgste(vma->vm_mm))
 318                         return 0;
 319 #endif
 320                 *vm_flags &= ~VM_NOHUGEPAGE;
 321                 *vm_flags |= VM_HUGEPAGE;
 322                 /*
 323                  * If the vma become good for khugepaged to scan,
 324                  * register it here without waiting a page fault that
 325                  * may not happen any time soon.
 326                  */
 327                 if (!(*vm_flags & VM_NO_KHUGEPAGED) &&
 328                                 khugepaged_enter_vma_merge(vma, *vm_flags))
 329                         return -ENOMEM;
 330                 break;
 331         case MADV_NOHUGEPAGE:
 332                 *vm_flags &= ~VM_HUGEPAGE;
 333                 *vm_flags |= VM_NOHUGEPAGE;
 334                 /*
 335                  * Setting VM_NOHUGEPAGE will prevent khugepaged from scanning
 336                  * this vma even if we leave the mm registered in khugepaged if
 337                  * it got registered before VM_NOHUGEPAGE was set.
 338                  */
 339                 break;
 340         }
 341
 342         return 0;
 343 }
 344
 345 int __init khugepaged_init(void)
 346 {
 347         mm_slot_cache = kmem_cache_create("khugepaged_mm_slot",
 348                                           sizeof(struct mm_slot),
 349                                           __alignof__(struct mm_slot), 0, NULL);
 350         if (!mm_slot_cache)
 351                 return -ENOMEM;
 352
 353         khugepaged_pages_to_scan = HPAGE_PMD_NR * 8;
 354         khugepaged_max_ptes_none = HPAGE_PMD_NR - 1;
 355         khugepaged_max_ptes_swap = HPAGE_PMD_NR / 8;
 356
 357         return 0;
 358 }
 359
 360 void __init khugepaged_destroy(void)
 361 {
 362         kmem_cache_destroy(mm_slot_cache);
 363 }
 364
 365 static inline struct mm_slot *alloc_mm_slot(void)
 366 {
 367         if (!mm_slot_cache)     /* initialization failed */
 368                 return NULL;
 369         return kmem_cache_zalloc(mm_slot_cache, GFP_KERNEL);
 370 }
 371
 372 static inline void free_mm_slot(struct mm_slot *mm_slot)
 373 {
 374         kmem_cache_free(mm_slot_cache, mm_slot);
 375 }
 376
 377 static struct mm_slot *get_mm_slot(struct mm_struct *mm)
 378 {
 379         struct mm_slot *mm_slot;
 380
 381         hash_for_each_possible(mm_slots_hash, mm_slot, hash, (unsigned long)mm)
 382                 if (mm == mm_slot->mm)
 383                         return mm_slot;
 384
 385         return NULL;
 386 }
 387
 388 static void insert_to_mm_slots_hash(struct mm_struct *mm,
 389                                     struct mm_slot *mm_slot)
 390 {
 391         mm_slot->mm = mm;
 392         hash_add(mm_slots_hash, &mm_slot->hash, (long)mm);
 393 }
 394
 395 static inline int khugepaged_test_exit(struct mm_struct *mm)
 396 {
 397         return atomic_read(&mm->mm_users) == 0;
 398 }
 399
 400 static bool hugepage_vma_check(struct vm_area_struct *vma,
 401                                unsigned long vm_flags)
 402 {
 403         if ((!(vm_flags & VM_HUGEPAGE) && !khugepaged_always()) ||
 404             (vm_flags & VM_NOHUGEPAGE) ||
 405             test_bit(MMF_DISABLE_THP, &vma->vm_mm->flags))
 406                 return false;
 407         if (shmem_file(vma->vm_file)) {
 408                 if (!IS_ENABLED(CONFIG_TRANSPARENT_HUGE_PAGECACHE))
 409                         return false;
 410                 return IS_ALIGNED((vma->vm_start >> PAGE_SHIFT) - vma->vm_pgoff,
 411                                 HPAGE_PMD_NR);
 412         }
 413         if (!vma->anon_vma || vma->vm_ops)
 414                 return false;
 415         if (is_vma_temporary_stack(vma))
 416                 return false;
 417         return !(vm_flags & VM_NO_KHUGEPAGED);
 418 }
 419
 420 int __khugepaged_enter(struct mm_struct *mm)
 421 {
 422         struct mm_slot *mm_slot;
 423         int wakeup;
 424
 425         mm_slot = alloc_mm_slot();
 426         if (!mm_slot)
 427                 return -ENOMEM;
 428
 429         /* __khugepaged_exit() must not run from under us */
 430         VM_BUG_ON_MM(khugepaged_test_exit(mm), mm);
 431         if (unlikely(test_and_set_bit(MMF_VM_HUGEPAGE, &mm->flags))) {
 432                 free_mm_slot(mm_slot);
 433                 return 0;
 434         }
 435
 436         spin_lock(&khugepaged_mm_lock);
 437         insert_to_mm_slots_hash(mm, mm_slot);
 438         /*
 439          * Insert just behind the scanning cursor, to let the area settle
 440          * down a little.
 441          */
 442         wakeup = list_empty(&khugepaged_scan.mm_head);
 443         list_add_tail(&mm_slot->mm_node, &khugepaged_scan.mm_head);
 444         spin_unlock(&khugepaged_mm_lock);
 445
 446         mmgrab(mm);
 447         if (wakeup)
 448                 wake_up_interruptible(&khugepaged_wait);
 449
 450         return 0;
 451 }
 452
 453 int khugepaged_enter_vma_merge(struct vm_area_struct *vma,
 454                                unsigned long vm_flags)
 455 {
 456         unsigned long hstart, hend;
 457
 458         /*
 459          * khugepaged does not yet work on non-shmem files or special
 460          * mappings. And file-private shmem THP is not supported.
 461          */
 462         if (!hugepage_vma_check(vma, vm_flags))
 463                 return 0;
 464
 465         hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK;
 466         hend = vma->vm_end & HPAGE_PMD_MASK;
 467         if (hstart < hend)
 468                 return khugepaged_enter(vma, vm_flags);
 469         return 0;
 470 }
 471
 472 void __khugepaged_exit(struct mm_struct *mm)
 473 {
 474         struct mm_slot *mm_slot;
 475         int free = 0;
 476
 477         spin_lock(&khugepaged_mm_lock);
 478         mm_slot = get_mm_slot(mm);
 479         if (mm_slot && khugepaged_scan.mm_slot != mm_slot) {
 480                 hash_del(&mm_slot->hash);
 481                 list_del(&mm_slot->mm_node);
 482                 free = 1;
 483         }
 484         spin_unlock(&khugepaged_mm_lock);
 485
 486         if (free) {
 487                 clear_bit(MMF_VM_HUGEPAGE, &mm->flags);
 488                 free_mm_slot(mm_slot);
 489                 mmdrop(mm);
 490         } else if (mm_slot) {
 491                 /*
 492                  * This is required to serialize against
 493                  * khugepaged_test_exit() (which is guaranteed to run
 494                  * under mmap sem read mode). Stop here (after we
 495                  * return all pagetables will be destroyed) until
 496                  * khugepaged has finished working on the pagetables
 497                  * under the mmap_sem.
 498                  */
 499                 down_write(&mm->mmap_sem);
 500                 up_write(&mm->mmap_sem);
 501         }
 502 }
 503
 504 static void release_pte_page(struct page *page)
 505 {
 506         dec_node_page_state(page, NR_ISOLATED_ANON + page_is_file_cache(page));
 507         unlock_page(page);
 508         putback_lru_page(page);
 509 }
 510
 511 static void release_pte_pages(pte_t *pte, pte_t *_pte)
 512 {
 513         while (--_pte >= pte) {
 514                 pte_t pteval = *_pte;
 515                 if (!pte_none(pteval) && !is_zero_pfn(pte_pfn(pteval)))
 516                         release_pte_page(pte_page(pteval));
 517         }
 518 }
 519
 520 static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
 521                                         unsigned long address,
 522                                         pte_t *pte)
 523 {
 524         struct page *page = NULL;
 525         pte_t *_pte;
 526         int none_or_zero = 0, result = 0, referenced = 0;
 527         bool writable = false;
 528
 529         for (_pte = pte; _pte < pte+HPAGE_PMD_NR;
 530              _pte++, address += PAGE_SIZE) {
 531                 pte_t pteval = *_pte;
 532                 if (pte_none(pteval) || (pte_present(pteval) &&
 533                                 is_zero_pfn(pte_pfn(pteval)))) {
 534                         if (!userfaultfd_armed(vma) &&
 535                             ++none_or_zero <= khugepaged_max_ptes_none) {
 536                                 continue;
 537                         } else {
 538                                 result = SCAN_EXCEED_NONE_PTE;
 539                                 goto out;
 540                         }
 541                 }
 542                 if (!pte_present(pteval)) {
 543                         result = SCAN_PTE_NON_PRESENT;
 544                         goto out;
 545                 }
 546                 page = vm_normal_page(vma, address, pteval);
 547                 if (unlikely(!page)) {
 548                         result = SCAN_PAGE_NULL;
 549                         goto out;
 550                 }
 551
 552                 /* TODO: teach khugepaged to collapse THP mapped with pte */
 553                 if (PageCompound(page)) {
 554                         result = SCAN_PAGE_COMPOUND;
 555                         goto out;
 556                 }
 557
 558                 VM_BUG_ON_PAGE(!PageAnon(page), page);
 559
 560                 /*
 561                  * We can do it before isolate_lru_page because the
 562                  * page can't be freed from under us. NOTE: PG_lock
 563                  * is needed to serialize against split_huge_page
 564                  * when invoked from the VM.
 565                  */
 566                 if (!trylock_page(page)) {
 567                         result = SCAN_PAGE_LOCK;
 568                         goto out;
 569                 }
 570
 571                 /*
 572                  * cannot use mapcount: can't collapse if there's a gup pin.
 573                  * The page must only be referenced by the scanned process
 574                  * and page swap cache.
 575                  */
 576                 if (page_count(page) != 1 + PageSwapCache(page)) {
 577                         unlock_page(page);
 578                         result = SCAN_PAGE_COUNT;
 579                         goto out;
 580                 }
 581                 if (pte_write(pteval)) {
 582                         writable = true;
 583                 } else {
 584                         if (PageSwapCache(page) &&
 585                             !reuse_swap_page(page, NULL)) {
 586                                 unlock_page(page);
 587                                 result = SCAN_SWAP_CACHE_PAGE;
 588                                 goto out;
 589                         }
 590                         /*
 591                          * Page is not in the swap cache. It can be collapsed
 592                          * into a THP.
 593                          */
 594                 }
 595
 596                 /*
 597                  * Isolate the page to avoid collapsing an hugepage
 598                  * currently in use by the VM.
 599                  */
 600                 if (isolate_lru_page(page)) {
 601                         unlock_page(page);
 602                         result = SCAN_DEL_PAGE_LRU;
 603                         goto out;
 604                 }
 605                 inc_node_page_state(page,
 606                                 NR_ISOLATED_ANON + page_is_file_cache(page));
 607                 VM_BUG_ON_PAGE(!PageLocked(page), page);
 608                 VM_BUG_ON_PAGE(PageLRU(page), page);
 609
 610                 /* There should be enough young pte to collapse the page */
 611                 if (pte_young(pteval) ||
 612                     page_is_young(page) || PageReferenced(page) ||
 613                     mmu_notifier_test_young(vma->vm_mm, address))
 614                         referenced++;
 615         }
 616         if (likely(writable)) {
 617                 if (likely(referenced)) {
 618                         result = SCAN_SUCCEED;
 619                         trace_mm_collapse_huge_page_isolate(page, none_or_zero,
 620                                                             referenced, writable, result);
 621                         return 1;
 622                 }
 623         } else {
 624                 result = SCAN_PAGE_RO;
 625         }
 626
 627 out:
 628         release_pte_pages(pte, _pte);
 629         trace_mm_collapse_huge_page_isolate(page, none_or_zero,
 630                                             referenced, writable, result);
 631         return 0;
 632 }
 633
 634 static void __collapse_huge_page_copy(pte_t *pte, struct page *page,
 635                                       struct vm_area_struct *vma,
 636                                       unsigned long address,
 637                                       spinlock_t *ptl)
 638 {
 639         pte_t *_pte;
 640         for (_pte = pte; _pte < pte + HPAGE_PMD_NR;
 641                                 _pte++, page++, address += PAGE_SIZE) {
 642                 pte_t pteval = *_pte;
 643                 struct page *src_page;
 644
 645                 if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) {
 646                         clear_user_highpage(page, address);
 647                         add_mm_counter(vma->vm_mm, MM_ANONPAGES, 1);
 648                         if (is_zero_pfn(pte_pfn(pteval))) {
 649                                 /*
 650                                  * ptl mostly unnecessary.
 651                                  */
 652                                 spin_lock(ptl);
 653                                 /*
 654                                  * paravirt calls inside pte_clear here are
 655                                  * superfluous.
 656                                  */
 657                                 pte_clear(vma->vm_mm, address, _pte);
 658                                 spin_unlock(ptl);
 659                         }
 660                 } else {
 661                         src_page = pte_page(pteval);
 662                         copy_user_highpage(page, src_page, address, vma);
 663                         VM_BUG_ON_PAGE(page_mapcount(src_page) != 1, src_page);
 664                         release_pte_page(src_page);
 665                         /*
 666                          * ptl mostly unnecessary, but preempt has to
 667                          * be disabled to update the per-cpu stats
 668                          * inside page_remove_rmap().
 669                          */
 670                         spin_lock(ptl);
 671                         /*
 672                          * paravirt calls inside pte_clear here are
 673                          * superfluous.
 674                          */
 675                         pte_clear(vma->vm_mm, address, _pte);
 676                         page_remove_rmap(src_page, false);
 677                         spin_unlock(ptl);
 678                         free_page_and_swap_cache(src_page);
 679                 }
 680         }
 681 }
 682
 683 static void khugepaged_alloc_sleep(void)
 684 {
 685         DEFINE_WAIT(wait);
 686
 687         add_wait_queue(&khugepaged_wait, &wait);
 688         freezable_schedule_timeout_interruptible(
 689                 msecs_to_jiffies(khugepaged_alloc_sleep_millisecs));
 690         remove_wait_queue(&khugepaged_wait, &wait);
 691 }
 692
 693 static int khugepaged_node_load[MAX_NUMNODES];
 694
 695 static bool khugepaged_scan_abort(int nid)
 696 {
 697         int i;
 698
 699         /*
 700          * If node_reclaim_mode is disabled, then no extra effort is made to
 701          * allocate memory locally.
 702          */
 703         if (!node_reclaim_mode)
 704                 return false;
 705
 706         /* If there is a count for this node already, it must be acceptable */
 707         if (khugepaged_node_load[nid])
 708                 return false;
 709
 710         for (i = 0; i < MAX_NUMNODES; i++) {
 711                 if (!khugepaged_node_load[i])
 712                         continue;
 713                 if (node_distance(nid, i) > RECLAIM_DISTANCE)
 714                         return true;
 715         }
 716         return false;
 717 }
 718
 719 /* Defrag for khugepaged will enter direct reclaim/compaction if necessary */
 720 static inline gfp_t alloc_hugepage_khugepaged_gfpmask(void)
 721 {
 722         return khugepaged_defrag() ? GFP_TRANSHUGE : GFP_TRANSHUGE_LIGHT;
 723 }
 724
 725 #ifdef CONFIG_NUMA
 726 static int khugepaged_find_target_node(void)
 727 {
 728         static int last_khugepaged_target_node = NUMA_NO_NODE;
 729         int nid, target_node = 0, max_value = 0;
 730
 731         /* find first node with max normal pages hit */
 732         for (nid = 0; nid < MAX_NUMNODES; nid++)
 733                 if (khugepaged_node_load[nid] > max_value) {
 734                         max_value = khugepaged_node_load[nid];
 735                         target_node = nid;
 736                 }
 737
 738         /* do some balance if several nodes have the same hit record */
 739         if (target_node <= last_khugepaged_target_node)
 740                 for (nid = last_khugepaged_target_node + 1; nid < MAX_NUMNODES;
 741                                 nid++)
 742                         if (max_value == khugepaged_node_load[nid]) {
 743                                 target_node = nid;
 744                                 break;
 745                         }
 746
 747         last_khugepaged_target_node = target_node;
 748         return target_node;
 749 }
 750
 751 static bool khugepaged_prealloc_page(struct page **hpage, bool *wait)
 752 {
 753         if (IS_ERR(*hpage)) {
 754                 if (!*wait)
 755                         return false;
 756
 757                 *wait = false;
 758                 *hpage = NULL;
 759                 khugepaged_alloc_sleep();
 760         } else if (*hpage) {
 761                 put_page(*hpage);
 762                 *hpage = NULL;
 763         }
 764
 765         return true;
 766 }
 767
 768 static struct page *
 769 khugepaged_alloc_page(struct page **hpage, gfp_t gfp, int node)
 770 {
 771         VM_BUG_ON_PAGE(*hpage, *hpage);
 772
 773         *hpage = __alloc_pages_node(node, gfp, HPAGE_PMD_ORDER);
 774         if (unlikely(!*hpage)) {
 775                 count_vm_event(THP_COLLAPSE_ALLOC_FAILED);
 776                 *hpage = ERR_PTR(-ENOMEM);
 777                 return NULL;
 778         }
 779
 780         prep_transhuge_page(*hpage);
 781         count_vm_event(THP_COLLAPSE_ALLOC);
 782         return *hpage;
 783 }
 784 #else
 785 static int khugepaged_find_target_node(void)
 786 {
 787         return 0;
 788 }
 789
 790 static inline struct page *alloc_khugepaged_hugepage(void)
 791 {
 792         struct page *page;
 793
 794         page = alloc_pages(alloc_hugepage_khugepaged_gfpmask(),
 795                            HPAGE_PMD_ORDER);
 796         if (page)
 797                 prep_transhuge_page(page);
 798         return page;
 799 }
 800
 801 static struct page *khugepaged_alloc_hugepage(bool *wait)
 802 {
 803         struct page *hpage;
 804
 805         do {
 806                 hpage = alloc_khugepaged_hugepage();
 807                 if (!hpage) {
 808                         count_vm_event(THP_COLLAPSE_ALLOC_FAILED);
 809                         if (!*wait)
 810                                 return NULL;
 811
 812                         *wait = false;
 813                         khugepaged_alloc_sleep();
 814                 } else
 815                         count_vm_event(THP_COLLAPSE_ALLOC);
 816         } while (unlikely(!hpage) && likely(khugepaged_enabled()));
 817
 818         return hpage;
 819 }
 820
 821 static bool khugepaged_prealloc_page(struct page **hpage, bool *wait)
 822 {
 823         if (!*hpage)
 824                 *hpage = khugepaged_alloc_hugepage(wait);
 825
 826         if (unlikely(!*hpage))
 827                 return false;
 828
 829         return true;
 830 }
 831
 832 static struct page *
 833 khugepaged_alloc_page(struct page **hpage, gfp_t gfp, int node)
 834 {
 835         VM_BUG_ON(!*hpage);
 836
 837         return  *hpage;
 838 }
 839 #endif
 840
 841 /*
 842  * If mmap_sem temporarily dropped, revalidate vma
 843  * before taking mmap_sem.
 844  * Return 0 if succeeds, otherwise return none-zero
 845  * value (scan code).
 846  */
 847
 848 static int hugepage_vma_revalidate(struct mm_struct *mm, unsigned long address,
 849                 struct vm_area_struct **vmap)
 850 {
 851         struct vm_area_struct *vma;
 852         unsigned long hstart, hend;
 853
 854         if (unlikely(khugepaged_test_exit(mm)))
 855                 return SCAN_ANY_PROCESS;
 856
 857         *vmap = vma = find_vma(mm, address);
 858         if (!vma)
 859                 return SCAN_VMA_NULL;
 860
 861         hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK;
 862         hend = vma->vm_end & HPAGE_PMD_MASK;
 863         if (address < hstart || address + HPAGE_PMD_SIZE > hend)
 864                 return SCAN_ADDRESS_RANGE;
 865         if (!hugepage_vma_check(vma, vma->vm_flags))
 866                 return SCAN_VMA_CHECK;
 867         return 0;
 868 }
 869
 870 /*
 871  * Bring missing pages in from swap, to complete THP collapse.
 872  * Only done if khugepaged_scan_pmd believes it is worthwhile.
 873  *
 874  * Called and returns without pte mapped or spinlocks held,
 875  * but with mmap_sem held to protect against vma changes.
 876  */
 877
 878 static bool __collapse_huge_page_swapin(struct mm_struct *mm,
 879                                         struct vm_area_struct *vma,
 880                                         unsigned long address, pmd_t *pmd,
 881                                         int referenced)
 882 {
 883         int swapped_in = 0;
 884         vm_fault_t ret = 0;
 885         struct vm_fault vmf = {
 886                 .vma = vma,
 887                 .address = address,
 888                 .flags = FAULT_FLAG_ALLOW_RETRY,
 889                 .pmd = pmd,
 890                 .pgoff = linear_page_index(vma, address),
 891         };
 892
 893         /* we only decide to swapin, if there is enough young ptes */
 894         if (referenced < HPAGE_PMD_NR/2) {
 895                 trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 0);
 896                 return false;
 897         }
 898         vmf.pte = pte_offset_map(pmd, address);
 899         for (; vmf.address < address + HPAGE_PMD_NR*PAGE_SIZE;
 900                         vmf.pte++, vmf.address += PAGE_SIZE) {
 901                 vmf.orig_pte = *vmf.pte;
 902                 if (!is_swap_pte(vmf.orig_pte))
 903                         continue;
 904                 swapped_in++;
 905                 ret = do_swap_page(&vmf);
 906
 907                 /* do_swap_page returns VM_FAULT_RETRY with released mmap_sem */
 908                 if (ret & VM_FAULT_RETRY) {
 909                         down_read(&mm->mmap_sem);
 910                         if (hugepage_vma_revalidate(mm, address, &vmf.vma)) {
 911                                 /* vma is no longer available, don't continue to swapin */
 912                                 trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 0);
 913                                 return false;
 914                         }
 915                         /* check if the pmd is still valid */
 916                         if (mm_find_pmd(mm, address) != pmd) {
 917                                 trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 0);
 918                                 return false;
 919                         }
 920                 }
 921                 if (ret & VM_FAULT_ERROR) {
 922                         trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 0);
 923                         return false;
 924                 }
 925                 /* pte is unmapped now, we need to map it */
 926                 vmf.pte = pte_offset_map(pmd, vmf.address);
 927         }
 928         vmf.pte--;
 929         pte_unmap(vmf.pte);
 930         trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 1);
 931         return true;
 932 }
 933
 934 static void collapse_huge_page(struct mm_struct *mm,
 935                                    unsigned long address,
 936                                    struct page **hpage,
 937                                    int node, int referenced)
 938 {
 939         pmd_t *pmd, _pmd;
 940         pte_t *pte;
 941         pgtable_t pgtable;
 942         struct page *new_page;
 943         spinlock_t *pmd_ptl, *pte_ptl;
 944         int isolated = 0, result = 0;
 945         struct mem_cgroup *memcg;
 946         struct vm_area_struct *vma;
 947         struct mmu_notifier_range range;
 948         gfp_t gfp;
 949
 950         VM_BUG_ON(address & ~HPAGE_PMD_MASK);
 951
 952         /* Only allocate from the target node */
 953         gfp = alloc_hugepage_khugepaged_gfpmask() | __GFP_THISNODE;
 954
 955         /*
 956          * Before allocating the hugepage, release the mmap_sem read lock.
 957          * The allocation can take potentially a long time if it involves
 958          * sync compaction, and we do not need to hold the mmap_sem during
 959          * that. We will recheck the vma after taking it again in write mode.
 960          */
 961         up_read(&mm->mmap_sem);
 962         new_page = khugepaged_alloc_page(hpage, gfp, node);
 963         if (!new_page) {
 964                 result = SCAN_ALLOC_HUGE_PAGE_FAIL;
 965                 goto out_nolock;
 966         }
 967
 968         if (unlikely(mem_cgroup_try_charge(new_page, mm, gfp, &memcg, true))) {
 969                 result = SCAN_CGROUP_CHARGE_FAIL;
 970                 goto out_nolock;
 971         }
 972
 973         down_read(&mm->mmap_sem);
 974         result = hugepage_vma_revalidate(mm, address, &vma);
 975         if (result) {
 976                 mem_cgroup_cancel_charge(new_page, memcg, true);
 977                 up_read(&mm->mmap_sem);
 978                 goto out_nolock;
 979         }
 980
 981         pmd = mm_find_pmd(mm, address);
 982         if (!pmd) {
 983                 result = SCAN_PMD_NULL;
 984                 mem_cgroup_cancel_charge(new_page, memcg, true);
 985                 up_read(&mm->mmap_sem);
 986                 goto out_nolock;
 987         }
 988
 989         /*
 990          * __collapse_huge_page_swapin always returns with mmap_sem locked.
 991          * If it fails, we release mmap_sem and jump out_nolock.
 992          * Continuing to collapse causes inconsistency.
 993          */
 994         if (!__collapse_huge_page_swapin(mm, vma, address, pmd, referenced)) {
 995                 mem_cgroup_cancel_charge(new_page, memcg, true);
 996                 up_read(&mm->mmap_sem);
 997                 goto out_nolock;
 998         }
 999
1000         up_read(&mm->mmap_sem);
1001         /*
1002          * Prevent all access to pagetables with the exception of
1003          * gup_fast later handled by the ptep_clear_flush and the VM
1004          * handled by the anon_vma lock + PG_lock.
1005          */
1006         down_write(&mm->mmap_sem);
1007         result = SCAN_ANY_PROCESS;
1008         if (!mmget_still_valid(mm))
1009                 goto out;
1010         result = hugepage_vma_revalidate(mm, address, &vma);
1011         if (result)
1012                 goto out;
1013         /* check if the pmd is still valid */
1014         if (mm_find_pmd(mm, address) != pmd)
1015                 goto out;
1016
1017         anon_vma_lock_write(vma->anon_vma);
1018
1019         pte = pte_offset_map(pmd, address);
1020         pte_ptl = pte_lockptr(mm, pmd);
1021
1022         mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, NULL, mm,
1023                                 address, address + HPAGE_PMD_SIZE);
1024         mmu_notifier_invalidate_range_start(&range);
1025         pmd_ptl = pmd_lock(mm, pmd); /* probably unnecessary */
1026         /*
1027          * After this gup_fast can't run anymore. This also removes
1028          * any huge TLB entry from the CPU so we won't allow
1029          * huge and small TLB entries for the same virtual address
1030          * to avoid the risk of CPU bugs in that area.
1031          */
1032         _pmd = pmdp_collapse_flush(vma, address, pmd);
1033         spin_unlock(pmd_ptl);
1034         mmu_notifier_invalidate_range_end(&range);
1035
1036         spin_lock(pte_ptl);
1037         isolated = __collapse_huge_page_isolate(vma, address, pte);
1038         spin_unlock(pte_ptl);
1039
1040         if (unlikely(!isolated)) {
1041                 pte_unmap(pte);
1042                 spin_lock(pmd_ptl);
1043                 BUG_ON(!pmd_none(*pmd));
1044                 /*
1045                  * We can only use set_pmd_at when establishing
1046                  * hugepmds and never for establishing regular pmds that
1047                  * points to regular pagetables. Use pmd_populate for that
1048                  */
1049                 pmd_populate(mm, pmd, pmd_pgtable(_pmd));
1050                 spin_unlock(pmd_ptl);
1051                 anon_vma_unlock_write(vma->anon_vma);
1052                 result = SCAN_FAIL;
1053                 goto out;
1054         }
1055
1056         /*
1057          * All pages are isolated and locked so anon_vma rmap
1058          * can't run anymore.
1059          */
1060         anon_vma_unlock_write(vma->anon_vma);
1061
1062         __collapse_huge_page_copy(pte, new_page, vma, address, pte_ptl);
1063         pte_unmap(pte);
1064         __SetPageUptodate(new_page);
1065         pgtable = pmd_pgtable(_pmd);
1066
1067         _pmd = mk_huge_pmd(new_page, vma->vm_page_prot);
1068         _pmd = maybe_pmd_mkwrite(pmd_mkdirty(_pmd), vma);
1069
1070         /*
1071          * spin_lock() below is not the equivalent of smp_wmb(), so
1072          * this is needed to avoid the copy_huge_page writes to become
1073          * visible after the set_pmd_at() write.
1074          */
1075         smp_wmb();
1076
1077         spin_lock(pmd_ptl);
1078         BUG_ON(!pmd_none(*pmd));
1079         page_add_new_anon_rmap(new_page, vma, address, true);
1080         mem_cgroup_commit_charge(new_page, memcg, false, true);
1081         count_memcg_events(memcg, THP_COLLAPSE_ALLOC, 1);
1082         lru_cache_add_active_or_unevictable(new_page, vma);
1083         pgtable_trans_huge_deposit(mm, pmd, pgtable);
1084         set_pmd_at(mm, address, pmd, _pmd);
1085         update_mmu_cache_pmd(vma, address, pmd);
1086         spin_unlock(pmd_ptl);
1087
1088         *hpage = NULL;
1089
1090         khugepaged_pages_collapsed++;
1091         result = SCAN_SUCCEED;
1092 out_up_write:
1093         up_write(&mm->mmap_sem);
1094 out_nolock:
1095         trace_mm_collapse_huge_page(mm, isolated, result);
1096         return;
1097 out:
1098         mem_cgroup_cancel_charge(new_page, memcg, true);
1099         goto out_up_write;
1100 }
1101
1102 static int khugepaged_scan_pmd(struct mm_struct *mm,
1103                                struct vm_area_struct *vma,
1104                                unsigned long address,
1105                                struct page **hpage)
1106 {
1107         pmd_t *pmd;
1108         pte_t *pte, *_pte;
1109         int ret = 0, none_or_zero = 0, result = 0, referenced = 0;
1110         struct page *page = NULL;
1111         unsigned long _address;
1112         spinlock_t *ptl;
1113         int node = NUMA_NO_NODE, unmapped = 0;
1114         bool writable = false;
1115
1116         VM_BUG_ON(address & ~HPAGE_PMD_MASK);
1117
1118         pmd = mm_find_pmd(mm, address);
1119         if (!pmd) {
1120                 result = SCAN_PMD_NULL;
1121                 goto out;
1122         }
1123
1124         memset(khugepaged_node_load, 0, sizeof(khugepaged_node_load));
1125         pte = pte_offset_map_lock(mm, pmd, address, &ptl);
1126         for (_address = address, _pte = pte; _pte < pte+HPAGE_PMD_NR;
1127              _pte++, _address += PAGE_SIZE) {
1128                 pte_t pteval = *_pte;
1129                 if (is_swap_pte(pteval)) {
1130                         if (++unmapped <= khugepaged_max_ptes_swap) {
1131                                 continue;
1132                         } else {
1133                                 result = SCAN_EXCEED_SWAP_PTE;
1134                                 goto out_unmap;
1135                         }
1136                 }
1137                 if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) {
1138                         if (!userfaultfd_armed(vma) &&
1139                             ++none_or_zero <= khugepaged_max_ptes_none) {
1140                                 continue;
1141                         } else {
1142                                 result = SCAN_EXCEED_NONE_PTE;
1143                                 goto out_unmap;
1144                         }
1145                 }
1146                 if (!pte_present(pteval)) {
1147                         result = SCAN_PTE_NON_PRESENT;
1148                         goto out_unmap;
1149                 }
1150                 if (pte_write(pteval))
1151                         writable = true;
1152
1153                 page = vm_normal_page(vma, _address, pteval);
1154                 if (unlikely(!page)) {
1155                         result = SCAN_PAGE_NULL;
1156                         goto out_unmap;
1157                 }
1158
1159                 /* TODO: teach khugepaged to collapse THP mapped with pte */
1160                 if (PageCompound(page)) {
1161                         result = SCAN_PAGE_COMPOUND;
1162                         goto out_unmap;
1163                 }
1164
1165                 /*
1166                  * Record which node the original page is from and save this
1167                  * information to khugepaged_node_load[].
1168                  * Khupaged will allocate hugepage from the node has the max
1169                  * hit record.
1170                  */
1171                 node = page_to_nid(page);
1172                 if (khugepaged_scan_abort(node)) {
1173                         result = SCAN_SCAN_ABORT;
1174                         goto out_unmap;
1175                 }
1176                 khugepaged_node_load[node]++;
1177                 if (!PageLRU(page)) {
1178                         result = SCAN_PAGE_LRU;
1179                         goto out_unmap;
1180                 }
1181                 if (PageLocked(page)) {
1182                         result = SCAN_PAGE_LOCK;
1183                         goto out_unmap;
1184                 }
1185                 if (!PageAnon(page)) {
1186                         result = SCAN_PAGE_ANON;
1187                         goto out_unmap;
1188                 }
1189
1190                 /*
1191                  * cannot use mapcount: can't collapse if there's a gup pin.
1192                  * The page must only be referenced by the scanned process
1193                  * and page swap cache.
1194                  */
1195                 if (page_count(page) != 1 + PageSwapCache(page)) {
1196                         result = SCAN_PAGE_COUNT;
1197                         goto out_unmap;
1198                 }
1199                 if (pte_young(pteval) ||
1200                     page_is_young(page) || PageReferenced(page) ||
1201                     mmu_notifier_test_young(vma->vm_mm, address))
1202                         referenced++;
1203         }
1204         if (writable) {
1205                 if (referenced) {
1206                         result = SCAN_SUCCEED;
1207                         ret = 1;
1208                 } else {
1209                         result = SCAN_LACK_REFERENCED_PAGE;
1210                 }
1211         } else {
1212                 result = SCAN_PAGE_RO;
1213         }
1214 out_unmap:
1215         pte_unmap_unlock(pte, ptl);
1216         if (ret) {
1217                 node = khugepaged_find_target_node();
1218                 /* collapse_huge_page will return with the mmap_sem released */
1219                 collapse_huge_page(mm, address, hpage, node, referenced);
1220         }
1221 out:
1222         trace_mm_khugepaged_scan_pmd(mm, page, writable, referenced,
1223                                      none_or_zero, result, unmapped);
1224         return ret;
1225 }
1226
1227 static void collect_mm_slot(struct mm_slot *mm_slot)
1228 {
1229         struct mm_struct *mm = mm_slot->mm;
1230
1231         lockdep_assert_held(&khugepaged_mm_lock);
1232
1233         if (khugepaged_test_exit(mm)) {
1234                 /* free mm_slot */
1235                 hash_del(&mm_slot->hash);
1236                 list_del(&mm_slot->mm_node);
1237
1238                 /*
1239                  * Not strictly needed because the mm exited already.
1240                  *
1241                  * clear_bit(MMF_VM_HUGEPAGE, &mm->flags);
1242                  */
1243
1244                 /* khugepaged_mm_lock actually not necessary for the below */
1245                 free_mm_slot(mm_slot);
1246                 mmdrop(mm);
1247         }
1248 }
1249
1250 #if defined(CONFIG_SHMEM) && defined(CONFIG_TRANSPARENT_HUGE_PAGECACHE)
1251 static void retract_page_tables(struct address_space *mapping, pgoff_t pgoff)
1252 {
1253         struct vm_area_struct *vma;
1254         unsigned long addr;
1255         pmd_t *pmd, _pmd;
1256
1257         i_mmap_lock_write(mapping);
1258         vma_interval_tree_foreach(vma, &mapping->i_mmap, pgoff, pgoff) {
1259                 /* probably overkill */
1260                 if (vma->anon_vma)
1261                         continue;
1262                 addr = vma->vm_start + ((pgoff - vma->vm_pgoff) << PAGE_SHIFT);
1263                 if (addr & ~HPAGE_PMD_MASK)
1264                         continue;
1265                 if (vma->vm_end < addr + HPAGE_PMD_SIZE)
1266                         continue;
1267                 pmd = mm_find_pmd(vma->vm_mm, addr);
1268                 if (!pmd)
1269                         continue;
1270                 /*
1271                  * We need exclusive mmap_sem to retract page table.
1272                  * If trylock fails we would end up with pte-mapped THP after
1273                  * re-fault. Not ideal, but it's more important to not disturb
1274                  * the system too much.
1275                  */
1276                 if (down_write_trylock(&vma->vm_mm->mmap_sem)) {
1277                         spinlock_t *ptl = pmd_lock(vma->vm_mm, pmd);
1278                         /* assume page table is clear */
1279                         _pmd = pmdp_collapse_flush(vma, addr, pmd);
1280                         spin_unlock(ptl);
1281                         up_write(&vma->vm_mm->mmap_sem);
1282                         mm_dec_nr_ptes(vma->vm_mm);
1283                         pte_free(vma->vm_mm, pmd_pgtable(_pmd));
1284                 }
1285         }
1286         i_mmap_unlock_write(mapping);
1287 }
1288
1289 /**
1290  * collapse_shmem - collapse small tmpfs/shmem pages into huge one.
1291  *
1292  * Basic scheme is simple, details are more complex:
1293  *  - allocate and lock a new huge page;
1294  *  - scan page cache replacing old pages with the new one
1295  *    + swap in pages if necessary;
1296  *    + fill in gaps;
1297  *    + keep old pages around in case rollback is required;
1298  *  - if replacing succeeds:
1299  *    + copy data over;
1300  *    + free old pages;
1301  *    + unlock huge page;
1302  *  - if replacing failed;
1303  *    + put all pages back and unfreeze them;
1304  *    + restore gaps in the page cache;
1305  *    + unlock and free huge page;
1306  */
1307 static void collapse_shmem(struct mm_struct *mm,
1308                 struct address_space *mapping, pgoff_t start,
1309                 struct page **hpage, int node)
1310 {
1311         gfp_t gfp;
1312         struct page *new_page;
1313         struct mem_cgroup *memcg;
1314         pgoff_t index, end = start + HPAGE_PMD_NR;
1315         LIST_HEAD(pagelist);
1316         XA_STATE_ORDER(xas, &mapping->i_pages, start, HPAGE_PMD_ORDER);
1317         int nr_none = 0, result = SCAN_SUCCEED;
1318
1319         VM_BUG_ON(start & (HPAGE_PMD_NR - 1));
1320
1321         /* Only allocate from the target node */
1322         gfp = alloc_hugepage_khugepaged_gfpmask() | __GFP_THISNODE;
1323
1324         new_page = khugepaged_alloc_page(hpage, gfp, node);
1325         if (!new_page) {
1326                 result = SCAN_ALLOC_HUGE_PAGE_FAIL;
1327                 goto out;
1328         }
1329
1330         if (unlikely(mem_cgroup_try_charge(new_page, mm, gfp, &memcg, true))) {
1331                 result = SCAN_CGROUP_CHARGE_FAIL;
1332                 goto out;
1333         }
1334
1335         /* This will be less messy when we use multi-index entries */
1336         do {
1337                 xas_lock_irq(&xas);
1338                 xas_create_range(&xas);
1339                 if (!xas_error(&xas))
1340                         break;
1341                 xas_unlock_irq(&xas);
1342                 if (!xas_nomem(&xas, GFP_KERNEL)) {
1343                         mem_cgroup_cancel_charge(new_page, memcg, true);
1344                         result = SCAN_FAIL;
1345                         goto out;
1346                 }
1347         } while (1);
1348
1349         __SetPageLocked(new_page);
1350         __SetPageSwapBacked(new_page);
1351         new_page->index = start;
1352         new_page->mapping = mapping;
1353
1354         /*
1355          * At this point the new_page is locked and not up-to-date.
1356          * It's safe to insert it into the page cache, because nobody would
1357          * be able to map it or use it in another way until we unlock it.
1358          */
1359
1360         xas_set(&xas, start);
1361         for (index = start; index < end; index++) {
1362                 struct page *page = xas_next(&xas);
1363
1364                 VM_BUG_ON(index != xas.xa_index);
1365                 if (!page) {
1366                         /*
1367                          * Stop if extent has been truncated or hole-punched,
1368                          * and is now completely empty.
1369                          */
1370                         if (index == start) {
1371                                 if (!xas_next_entry(&xas, end - 1)) {
1372                                         result = SCAN_TRUNCATED;
1373                                         goto xa_locked;
1374                                 }
1375                                 xas_set(&xas, index);
1376                         }
1377                         if (!shmem_charge(mapping->host, 1)) {
1378                                 result = SCAN_FAIL;
1379                                 goto xa_locked;
1380                         }
1381                         xas_store(&xas, new_page + (index % HPAGE_PMD_NR));
1382                         nr_none++;
1383                         continue;
1384                 }
1385
1386                 if (xa_is_value(page) || !PageUptodate(page)) {
1387                         xas_unlock_irq(&xas);
1388                         /* swap in or instantiate fallocated page */
1389                         if (shmem_getpage(mapping->host, index, &page,
1390                                                 SGP_NOHUGE)) {
1391                                 result = SCAN_FAIL;
1392                                 goto xa_unlocked;
1393                         }
1394                 } else if (trylock_page(page)) {
1395                         get_page(page);
1396                         xas_unlock_irq(&xas);
1397                 } else {
1398                         result = SCAN_PAGE_LOCK;
1399                         goto xa_locked;
1400                 }
1401
1402                 /*
1403                  * The page must be locked, so we can drop the i_pages lock
1404                  * without racing with truncate.
1405                  */
1406                 VM_BUG_ON_PAGE(!PageLocked(page), page);
1407                 VM_BUG_ON_PAGE(!PageUptodate(page), page);
1408
1409                 /*
1410                  * If file was truncated then extended, or hole-punched, before
1411                  * we locked the first page, then a THP might be there already.
1412                  */
1413                 if (PageTransCompound(page)) {
1414                         result = SCAN_PAGE_COMPOUND;
1415                         goto out_unlock;
1416                 }
1417
1418                 if (page_mapping(page) != mapping) {
1419                         result = SCAN_TRUNCATED;
1420                         goto out_unlock;
1421                 }
1422
1423                 if (isolate_lru_page(page)) {
1424                         result = SCAN_DEL_PAGE_LRU;
1425                         goto out_unlock;
1426                 }
1427
1428                 if (page_mapped(page))
1429                         unmap_mapping_pages(mapping, index, 1, false);
1430
1431                 xas_lock_irq(&xas);
1432                 xas_set(&xas, index);
1433
1434                 VM_BUG_ON_PAGE(page != xas_load(&xas), page);
1435                 VM_BUG_ON_PAGE(page_mapped(page), page);
1436
1437                 /*
1438                  * The page is expected to have page_count() == 3:
1439                  *  - we hold a pin on it;
1440                  *  - one reference from page cache;
1441                  *  - one from isolate_lru_page;
1442                  */
1443                 if (!page_ref_freeze(page, 3)) {
1444                         result = SCAN_PAGE_COUNT;
1445                         xas_unlock_irq(&xas);
1446                         putback_lru_page(page);
1447                         goto out_unlock;
1448                 }
1449
1450                 /*
1451                  * Add the page to the list to be able to undo the collapse if
1452                  * something go wrong.
1453                  */
1454                 list_add_tail(&page->lru, &pagelist);
1455
1456                 /* Finally, replace with the new page. */
1457                 xas_store(&xas, new_page + (index % HPAGE_PMD_NR));
1458                 continue;
1459 out_unlock:
1460                 unlock_page(page);
1461                 put_page(page);
1462                 goto xa_unlocked;
1463         }
1464
1465         __inc_node_page_state(new_page, NR_SHMEM_THPS);
1466         if (nr_none) {
1467                 struct zone *zone = page_zone(new_page);
1468
1469                 __mod_node_page_state(zone->zone_pgdat, NR_FILE_PAGES, nr_none);
1470                 __mod_node_page_state(zone->zone_pgdat, NR_SHMEM, nr_none);
1471         }
1472
1473 xa_locked:
1474         xas_unlock_irq(&xas);
1475 xa_unlocked:
1476
1477         if (result == SCAN_SUCCEED) {
1478                 struct page *page, *tmp;
1479
1480                 /*
1481                  * Replacing old pages with new one has succeeded, now we
1482                  * need to copy the content and free the old pages.
1483                  */
1484                 index = start;
1485                 list_for_each_entry_safe(page, tmp, &pagelist, lru) {
1486                         while (index < page->index) {
1487                                 clear_highpage(new_page + (index % HPAGE_PMD_NR));
1488                                 index++;
1489                         }
1490                         copy_highpage(new_page + (page->index % HPAGE_PMD_NR),
1491                                         page);
1492                         list_del(&page->lru);
1493                         page->mapping = NULL;
1494                         page_ref_unfreeze(page, 1);
1495                         ClearPageActive(page);
1496                         ClearPageUnevictable(page);
1497                         unlock_page(page);
1498                         put_page(page);
1499                         index++;
1500                 }
1501                 while (index < end) {
1502                         clear_highpage(new_page + (index % HPAGE_PMD_NR));
1503                         index++;
1504                 }
1505
1506                 SetPageUptodate(new_page);
1507                 page_ref_add(new_page, HPAGE_PMD_NR - 1);
1508                 set_page_dirty(new_page);
1509                 mem_cgroup_commit_charge(new_page, memcg, false, true);
1510                 count_memcg_events(memcg, THP_COLLAPSE_ALLOC, 1);
1511                 lru_cache_add_anon(new_page);
1512
1513                 /*
1514                  * Remove pte page tables, so we can re-fault the page as huge.
1515                  */
1516                 retract_page_tables(mapping, start);
1517                 *hpage = NULL;
1518
1519                 khugepaged_pages_collapsed++;
1520         } else {
1521                 struct page *page;
1522
1523                 /* Something went wrong: roll back page cache changes */
1524                 xas_lock_irq(&xas);
1525                 mapping->nrpages -= nr_none;
1526                 shmem_uncharge(mapping->host, nr_none);
1527
1528                 xas_set(&xas, start);
1529                 xas_for_each(&xas, page, end - 1) {
1530                         page = list_first_entry_or_null(&pagelist,
1531                                         struct page, lru);
1532                         if (!page || xas.xa_index < page->index) {
1533                                 if (!nr_none)
1534                                         break;
1535                                 nr_none--;
1536                                 /* Put holes back where they were */
1537                                 xas_store(&xas, NULL);
1538                                 continue;
1539                         }
1540
1541                         VM_BUG_ON_PAGE(page->index != xas.xa_index, page);
1542
1543                         /* Unfreeze the page. */
1544                         list_del(&page->lru);
1545                         page_ref_unfreeze(page, 2);
1546                         xas_store(&xas, page);
1547                         xas_pause(&xas);
1548                         xas_unlock_irq(&xas);
1549                         unlock_page(page);
1550                         putback_lru_page(page);
1551                         xas_lock_irq(&xas);
1552                 }
1553                 VM_BUG_ON(nr_none);
1554                 xas_unlock_irq(&xas);
1555
1556                 mem_cgroup_cancel_charge(new_page, memcg, true);
1557                 new_page->mapping = NULL;
1558         }
1559
1560         unlock_page(new_page);
1561 out:
1562         VM_BUG_ON(!list_empty(&pagelist));
1563         /* TODO: tracepoints */
1564 }
1565
1566 static void khugepaged_scan_shmem(struct mm_struct *mm,
1567                 struct address_space *mapping,
1568                 pgoff_t start, struct page **hpage)
1569 {
1570         struct page *page = NULL;
1571         XA_STATE(xas, &mapping->i_pages, start);
1572         int present, swap;
1573         int node = NUMA_NO_NODE;
1574         int result = SCAN_SUCCEED;
1575
1576         present = 0;
1577         swap = 0;
1578         memset(khugepaged_node_load, 0, sizeof(khugepaged_node_load));
1579         rcu_read_lock();
1580         xas_for_each(&xas, page, start + HPAGE_PMD_NR - 1) {
1581                 if (xas_retry(&xas, page))
1582                         continue;
1583
1584                 if (xa_is_value(page)) {
1585                         if (++swap > khugepaged_max_ptes_swap) {
1586                                 result = SCAN_EXCEED_SWAP_PTE;
1587                                 break;
1588                         }
1589                         continue;
1590                 }
1591
1592                 if (PageTransCompound(page)) {
1593                         result = SCAN_PAGE_COMPOUND;
1594                         break;
1595                 }
1596
1597                 node = page_to_nid(page);
1598                 if (khugepaged_scan_abort(node)) {
1599                         result = SCAN_SCAN_ABORT;
1600                         break;
1601                 }
1602                 khugepaged_node_load[node]++;
1603
1604                 if (!PageLRU(page)) {
1605                         result = SCAN_PAGE_LRU;
1606                         break;
1607                 }
1608
1609                 if (page_count(page) != 1 + page_mapcount(page)) {
1610                         result = SCAN_PAGE_COUNT;
1611                         break;
1612                 }
1613
1614                 /*
1615                  * We probably should check if the page is referenced here, but
1616                  * nobody would transfer pte_young() to PageReferenced() for us.
1617                  * And rmap walk here is just too costly...
1618                  */
1619
1620                 present++;
1621
1622                 if (need_resched()) {
1623                         xas_pause(&xas);
1624                         cond_resched_rcu();
1625                 }
1626         }
1627         rcu_read_unlock();
1628
1629         if (result == SCAN_SUCCEED) {
1630                 if (present < HPAGE_PMD_NR - khugepaged_max_ptes_none) {
1631                         result = SCAN_EXCEED_NONE_PTE;
1632                 } else {
1633                         node = khugepaged_find_target_node();
1634                         collapse_shmem(mm, mapping, start, hpage, node);
1635                 }
1636         }
1637
1638         /* TODO: tracepoints */
1639 }
1640 #else
1641 static void khugepaged_scan_shmem(struct mm_struct *mm,
1642                 struct address_space *mapping,
1643                 pgoff_t start, struct page **hpage)
1644 {
1645         BUILD_BUG();
1646 }
1647 #endif
1648
1649 static unsigned int khugepaged_scan_mm_slot(unsigned int pages,
1650                                             struct page **hpage)
1651         __releases(&khugepaged_mm_lock)
1652         __acquires(&khugepaged_mm_lock)
1653 {
1654         struct mm_slot *mm_slot;
1655         struct mm_struct *mm;
1656         struct vm_area_struct *vma;
1657         int progress = 0;
1658
1659         VM_BUG_ON(!pages);
1660         lockdep_assert_held(&khugepaged_mm_lock);
1661
1662         if (khugepaged_scan.mm_slot)
1663                 mm_slot = khugepaged_scan.mm_slot;
1664         else {
1665                 mm_slot = list_entry(khugepaged_scan.mm_head.next,
1666                                      struct mm_slot, mm_node);
1667                 khugepaged_scan.address = 0;
1668                 khugepaged_scan.mm_slot = mm_slot;
1669         }
1670         spin_unlock(&khugepaged_mm_lock);
1671
1672         mm = mm_slot->mm;
1673         /*
1674          * Don't wait for semaphore (to avoid long wait times).  Just move to
1675          * the next mm on the list.
1676          */
1677         vma = NULL;
1678         if (unlikely(!down_read_trylock(&mm->mmap_sem)))
1679                 goto breakouterloop_mmap_sem;
1680         if (likely(!khugepaged_test_exit(mm)))
1681                 vma = find_vma(mm, khugepaged_scan.address);
1682
1683         progress++;
1684         for (; vma; vma = vma->vm_next) {
1685                 unsigned long hstart, hend;
1686
1687                 cond_resched();
1688                 if (unlikely(khugepaged_test_exit(mm))) {
1689                         progress++;
1690                         break;
1691                 }
1692                 if (!hugepage_vma_check(vma, vma->vm_flags)) {
1693 skip:
1694                         progress++;
1695                         continue;
1696                 }
1697                 hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK;
1698                 hend = vma->vm_end & HPAGE_PMD_MASK;
1699                 if (hstart >= hend)
1700                         goto skip;
1701                 if (khugepaged_scan.address > hend)
1702                         goto skip;
1703                 if (khugepaged_scan.address < hstart)
1704                         khugepaged_scan.address = hstart;
1705                 VM_BUG_ON(khugepaged_scan.address & ~HPAGE_PMD_MASK);
1706
1707                 while (khugepaged_scan.address < hend) {
1708                         int ret;
1709                         cond_resched();
1710                         if (unlikely(khugepaged_test_exit(mm)))
1711                                 goto breakouterloop;
1712
1713                         VM_BUG_ON(khugepaged_scan.address < hstart ||
1714                                   khugepaged_scan.address + HPAGE_PMD_SIZE >
1715                                   hend);
1716                         if (shmem_file(vma->vm_file)) {
1717                                 struct file *file;
1718                                 pgoff_t pgoff = linear_page_index(vma,
1719                                                 khugepaged_scan.address);
1720                                 if (!shmem_huge_enabled(vma))
1721                                         goto skip;
1722                                 file = get_file(vma->vm_file);
1723                                 up_read(&mm->mmap_sem);
1724                                 ret = 1;
1725                                 khugepaged_scan_shmem(mm, file->f_mapping,
1726                                                 pgoff, hpage);
1727                                 fput(file);
1728                         } else {
1729                                 ret = khugepaged_scan_pmd(mm, vma,
1730                                                 khugepaged_scan.address,
1731                                                 hpage);
1732                         }
1733                         /* move to next address */
1734                         khugepaged_scan.address += HPAGE_PMD_SIZE;
1735                         progress += HPAGE_PMD_NR;
1736                         if (ret)
1737                                 /* we released mmap_sem so break loop */
1738                                 goto breakouterloop_mmap_sem;
1739                         if (progress >= pages)
1740                                 goto breakouterloop;
1741                 }
1742         }
1743 breakouterloop:
1744         up_read(&mm->mmap_sem); /* exit_mmap will destroy ptes after this */
1745 breakouterloop_mmap_sem:
1746
1747         spin_lock(&khugepaged_mm_lock);
1748         VM_BUG_ON(khugepaged_scan.mm_slot != mm_slot);
1749         /*
1750          * Release the current mm_slot if this mm is about to die, or
1751          * if we scanned all vmas of this mm.
1752          */
1753         if (khugepaged_test_exit(mm) || !vma) {
1754                 /*
1755                  * Make sure that if mm_users is reaching zero while
1756                  * khugepaged runs here, khugepaged_exit will find
1757                  * mm_slot not pointing to the exiting mm.
1758                  */
1759                 if (mm_slot->mm_node.next != &khugepaged_scan.mm_head) {
1760                         khugepaged_scan.mm_slot = list_entry(
1761                                 mm_slot->mm_node.next,
1762                                 struct mm_slot, mm_node);
1763                         khugepaged_scan.address = 0;
1764                 } else {
1765                         khugepaged_scan.mm_slot = NULL;
1766                         khugepaged_full_scans++;
1767                 }
1768
1769                 collect_mm_slot(mm_slot);
1770         }
1771
1772         return progress;
1773 }
1774
1775 static int khugepaged_has_work(void)
1776 {
1777         return !list_empty(&khugepaged_scan.mm_head) &&
1778                 khugepaged_enabled();
1779 }
1780
1781 static int khugepaged_wait_event(void)
1782 {
1783         return !list_empty(&khugepaged_scan.mm_head) ||
1784                 kthread_should_stop();
1785 }
1786
1787 static void khugepaged_do_scan(void)
1788 {
1789         struct page *hpage = NULL;
1790         unsigned int progress = 0, pass_through_head = 0;
1791         unsigned int pages = khugepaged_pages_to_scan;
1792         bool wait = true;
1793
1794         barrier(); /* write khugepaged_pages_to_scan to local stack */
1795
1796         while (progress < pages) {
1797                 if (!khugepaged_prealloc_page(&hpage, &wait))
1798                         break;
1799
1800                 cond_resched();
1801
1802                 if (unlikely(kthread_should_stop() || try_to_freeze()))
1803                         break;
1804
1805                 spin_lock(&khugepaged_mm_lock);
1806                 if (!khugepaged_scan.mm_slot)
1807                         pass_through_head++;
1808                 if (khugepaged_has_work() &&
1809                     pass_through_head < 2)
1810                         progress += khugepaged_scan_mm_slot(pages - progress,
1811                                                             &hpage);
1812                 else
1813                         progress = pages;
1814                 spin_unlock(&khugepaged_mm_lock);
1815         }
1816
1817         if (!IS_ERR_OR_NULL(hpage))
1818                 put_page(hpage);
1819 }
1820
1821 static bool khugepaged_should_wakeup(void)
1822 {
1823         return kthread_should_stop() ||
1824                time_after_eq(jiffies, khugepaged_sleep_expire);
1825 }
1826
1827 static void khugepaged_wait_work(void)
1828 {
1829         if (khugepaged_has_work()) {
1830                 const unsigned long scan_sleep_jiffies =
1831                         msecs_to_jiffies(khugepaged_scan_sleep_millisecs);
1832
1833                 if (!scan_sleep_jiffies)
1834                         return;
1835
1836                 khugepaged_sleep_expire = jiffies + scan_sleep_jiffies;
1837                 wait_event_freezable_timeout(khugepaged_wait,
1838                                              khugepaged_should_wakeup(),
1839                                              scan_sleep_jiffies);
1840                 return;
1841         }
1842
1843         if (khugepaged_enabled())
1844                 wait_event_freezable(khugepaged_wait, khugepaged_wait_event());
1845 }
1846
1847 static int khugepaged(void *none)
1848 {
1849         struct mm_slot *mm_slot;
1850
1851         set_freezable();
1852         set_user_nice(current, MAX_NICE);
1853
1854         while (!kthread_should_stop()) {
1855                 khugepaged_do_scan();
1856                 khugepaged_wait_work();
1857         }
1858
1859         spin_lock(&khugepaged_mm_lock);
1860         mm_slot = khugepaged_scan.mm_slot;
1861         khugepaged_scan.mm_slot = NULL;
1862         if (mm_slot)
1863                 collect_mm_slot(mm_slot);
1864         spin_unlock(&khugepaged_mm_lock);
1865         return 0;
1866 }
1867
1868 static void set_recommended_min_free_kbytes(void)
1869 {
1870         struct zone *zone;
1871         int nr_zones = 0;
1872         unsigned long recommended_min;
1873
1874         for_each_populated_zone(zone) {
1875                 /*
1876                  * We don't need to worry about fragmentation of
1877                  * ZONE_MOVABLE since it only has movable pages.
1878                  */
1879                 if (zone_idx(zone) > gfp_zone(GFP_USER))
1880                         continue;
1881
1882                 nr_zones++;
1883         }
1884
1885         /* Ensure 2 pageblocks are free to assist fragmentation avoidance */
1886         recommended_min = pageblock_nr_pages * nr_zones * 2;
1887
1888         /*
1889          * Make sure that on average at least two pageblocks are almost free
1890          * of another type, one for a migratetype to fall back to and a
1891          * second to avoid subsequent fallbacks of other types There are 3
1892          * MIGRATE_TYPES we care about.
1893          */
1894         recommended_min += pageblock_nr_pages * nr_zones *
1895                            MIGRATE_PCPTYPES * MIGRATE_PCPTYPES;
1896
1897         /* don't ever allow to reserve more than 5% of the lowmem */
1898         recommended_min = min(recommended_min,
1899                               (unsigned long) nr_free_buffer_pages() / 20);
1900         recommended_min <<= (PAGE_SHIFT-10);
1901
1902         if (recommended_min > min_free_kbytes) {
1903                 if (user_min_free_kbytes >= 0)
1904                         pr_info("raising min_free_kbytes from %d to %lu to help transparent hugepage allocations\n",
1905                                 min_free_kbytes, recommended_min);
1906
1907                 min_free_kbytes = recommended_min;
1908         }
1909         setup_per_zone_wmarks();
1910 }
1911
1912 int start_stop_khugepaged(void)
1913 {
1914         static struct task_struct *khugepaged_thread __read_mostly;
1915         static DEFINE_MUTEX(khugepaged_mutex);
1916         int err = 0;
1917
1918         mutex_lock(&khugepaged_mutex);
1919         if (khugepaged_enabled()) {
1920                 if (!khugepaged_thread)
1921                         khugepaged_thread = kthread_run(khugepaged, NULL,
1922                                                         "khugepaged");
1923                 if (IS_ERR(khugepaged_thread)) {
1924                         pr_err("khugepaged: kthread_run(khugepaged) failed\n");
1925                         err = PTR_ERR(khugepaged_thread);
1926                         khugepaged_thread = NULL;
1927                         goto fail;
1928                 }
1929
1930                 if (!list_empty(&khugepaged_scan.mm_head))
1931                         wake_up_interruptible(&khugepaged_wait);
1932
1933                 set_recommended_min_free_kbytes();
1934         } else if (khugepaged_thread) {
1935                 kthread_stop(khugepaged_thread);
1936                 khugepaged_thread = NULL;
1937         }
1938 fail:
1939         mutex_unlock(&khugepaged_mutex);
1940         return err;
1941 }