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