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 int __khugepaged_enter(struct mm_struct *mm)
 401 {
 402         struct mm_slot *mm_slot;
 403         int wakeup;
 404
 405         mm_slot = alloc_mm_slot();
 406         if (!mm_slot)
 407                 return -ENOMEM;
 408
 409         /* __khugepaged_exit() must not run from under us */
 410         VM_BUG_ON_MM(khugepaged_test_exit(mm), mm);
 411         if (unlikely(test_and_set_bit(MMF_VM_HUGEPAGE, &mm->flags))) {
 412                 free_mm_slot(mm_slot);
 413                 return 0;
 414         }
 415
 416         spin_lock(&khugepaged_mm_lock);
 417         insert_to_mm_slots_hash(mm, mm_slot);
 418         /*
 419          * Insert just behind the scanning cursor, to let the area settle
 420          * down a little.
 421          */
 422         wakeup = list_empty(&khugepaged_scan.mm_head);
 423         list_add_tail(&mm_slot->mm_node, &khugepaged_scan.mm_head);
 424         spin_unlock(&khugepaged_mm_lock);
 425
 426         mmgrab(mm);
 427         if (wakeup)
 428                 wake_up_interruptible(&khugepaged_wait);
 429
 430         return 0;
 431 }
 432
 433 int khugepaged_enter_vma_merge(struct vm_area_struct *vma,
 434                                unsigned long vm_flags)
 435 {
 436         unsigned long hstart, hend;
 437         if (!vma->anon_vma)
 438                 /*
 439                  * Not yet faulted in so we will register later in the
 440                  * page fault if needed.
 441                  */
 442                 return 0;
 443         if (vma->vm_ops || (vm_flags & VM_NO_KHUGEPAGED))
 444                 /* khugepaged not yet working on file or special mappings */
 445                 return 0;
 446         hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK;
 447         hend = vma->vm_end & HPAGE_PMD_MASK;
 448         if (hstart < hend)
 449                 return khugepaged_enter(vma, vm_flags);
 450         return 0;
 451 }
 452
 453 void __khugepaged_exit(struct mm_struct *mm)
 454 {
 455         struct mm_slot *mm_slot;
 456         int free = 0;
 457
 458         spin_lock(&khugepaged_mm_lock);
 459         mm_slot = get_mm_slot(mm);
 460         if (mm_slot && khugepaged_scan.mm_slot != mm_slot) {
 461                 hash_del(&mm_slot->hash);
 462                 list_del(&mm_slot->mm_node);
 463                 free = 1;
 464         }
 465         spin_unlock(&khugepaged_mm_lock);
 466
 467         if (free) {
 468                 clear_bit(MMF_VM_HUGEPAGE, &mm->flags);
 469                 free_mm_slot(mm_slot);
 470                 mmdrop(mm);
 471         } else if (mm_slot) {
 472                 /*
 473                  * This is required to serialize against
 474                  * khugepaged_test_exit() (which is guaranteed to run
 475                  * under mmap sem read mode). Stop here (after we
 476                  * return all pagetables will be destroyed) until
 477                  * khugepaged has finished working on the pagetables
 478                  * under the mmap_sem.
 479                  */
 480                 down_write(&mm->mmap_sem);
 481                 up_write(&mm->mmap_sem);
 482         }
 483 }
 484
 485 static void release_pte_page(struct page *page)
 486 {
 487         dec_node_page_state(page, NR_ISOLATED_ANON + page_is_file_cache(page));
 488         unlock_page(page);
 489         putback_lru_page(page);
 490 }
 491
 492 static void release_pte_pages(pte_t *pte, pte_t *_pte)
 493 {
 494         while (--_pte >= pte) {
 495                 pte_t pteval = *_pte;
 496                 if (!pte_none(pteval) && !is_zero_pfn(pte_pfn(pteval)))
 497                         release_pte_page(pte_page(pteval));
 498         }
 499 }
 500
 501 static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
 502                                         unsigned long address,
 503                                         pte_t *pte)
 504 {
 505         struct page *page = NULL;
 506         pte_t *_pte;
 507         int none_or_zero = 0, result = 0, referenced = 0;
 508         bool writable = false;
 509
 510         for (_pte = pte; _pte < pte+HPAGE_PMD_NR;
 511              _pte++, address += PAGE_SIZE) {
 512                 pte_t pteval = *_pte;
 513                 if (pte_none(pteval) || (pte_present(pteval) &&
 514                                 is_zero_pfn(pte_pfn(pteval)))) {
 515                         if (!userfaultfd_armed(vma) &&
 516                             ++none_or_zero <= khugepaged_max_ptes_none) {
 517                                 continue;
 518                         } else {
 519                                 result = SCAN_EXCEED_NONE_PTE;
 520                                 goto out;
 521                         }
 522                 }
 523                 if (!pte_present(pteval)) {
 524                         result = SCAN_PTE_NON_PRESENT;
 525                         goto out;
 526                 }
 527                 page = vm_normal_page(vma, address, pteval);
 528                 if (unlikely(!page)) {
 529                         result = SCAN_PAGE_NULL;
 530                         goto out;
 531                 }
 532
 533                 /* TODO: teach khugepaged to collapse THP mapped with pte */
 534                 if (PageCompound(page)) {
 535                         result = SCAN_PAGE_COMPOUND;
 536                         goto out;
 537                 }
 538
 539                 VM_BUG_ON_PAGE(!PageAnon(page), page);
 540
 541                 /*
 542                  * We can do it before isolate_lru_page because the
 543                  * page can't be freed from under us. NOTE: PG_lock
 544                  * is needed to serialize against split_huge_page
 545                  * when invoked from the VM.
 546                  */
 547                 if (!trylock_page(page)) {
 548                         result = SCAN_PAGE_LOCK;
 549                         goto out;
 550                 }
 551
 552                 /*
 553                  * cannot use mapcount: can't collapse if there's a gup pin.
 554                  * The page must only be referenced by the scanned process
 555                  * and page swap cache.
 556                  */
 557                 if (page_count(page) != 1 + PageSwapCache(page)) {
 558                         unlock_page(page);
 559                         result = SCAN_PAGE_COUNT;
 560                         goto out;
 561                 }
 562                 if (pte_write(pteval)) {
 563                         writable = true;
 564                 } else {
 565                         if (PageSwapCache(page) &&
 566                             !reuse_swap_page(page, NULL)) {
 567                                 unlock_page(page);
 568                                 result = SCAN_SWAP_CACHE_PAGE;
 569                                 goto out;
 570                         }
 571                         /*
 572                          * Page is not in the swap cache. It can be collapsed
 573                          * into a THP.
 574                          */
 575                 }
 576
 577                 /*
 578                  * Isolate the page to avoid collapsing an hugepage
 579                  * currently in use by the VM.
 580                  */
 581                 if (isolate_lru_page(page)) {
 582                         unlock_page(page);
 583                         result = SCAN_DEL_PAGE_LRU;
 584                         goto out;
 585                 }
 586                 inc_node_page_state(page,
 587                                 NR_ISOLATED_ANON + page_is_file_cache(page));
 588                 VM_BUG_ON_PAGE(!PageLocked(page), page);
 589                 VM_BUG_ON_PAGE(PageLRU(page), page);
 590
 591                 /* There should be enough young pte to collapse the page */
 592                 if (pte_young(pteval) ||
 593                     page_is_young(page) || PageReferenced(page) ||
 594                     mmu_notifier_test_young(vma->vm_mm, address))
 595                         referenced++;
 596         }
 597         if (likely(writable)) {
 598                 if (likely(referenced)) {
 599                         result = SCAN_SUCCEED;
 600                         trace_mm_collapse_huge_page_isolate(page, none_or_zero,
 601                                                             referenced, writable, result);
 602                         return 1;
 603                 }
 604         } else {
 605                 result = SCAN_PAGE_RO;
 606         }
 607
 608 out:
 609         release_pte_pages(pte, _pte);
 610         trace_mm_collapse_huge_page_isolate(page, none_or_zero,
 611                                             referenced, writable, result);
 612         return 0;
 613 }
 614
 615 static void __collapse_huge_page_copy(pte_t *pte, struct page *page,
 616                                       struct vm_area_struct *vma,
 617                                       unsigned long address,
 618                                       spinlock_t *ptl)
 619 {
 620         pte_t *_pte;
 621         for (_pte = pte; _pte < pte + HPAGE_PMD_NR;
 622                                 _pte++, page++, address += PAGE_SIZE) {
 623                 pte_t pteval = *_pte;
 624                 struct page *src_page;
 625
 626                 if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) {
 627                         clear_user_highpage(page, address);
 628                         add_mm_counter(vma->vm_mm, MM_ANONPAGES, 1);
 629                         if (is_zero_pfn(pte_pfn(pteval))) {
 630                                 /*
 631                                  * ptl mostly unnecessary.
 632                                  */
 633                                 spin_lock(ptl);
 634                                 /*
 635                                  * paravirt calls inside pte_clear here are
 636                                  * superfluous.
 637                                  */
 638                                 pte_clear(vma->vm_mm, address, _pte);
 639                                 spin_unlock(ptl);
 640                         }
 641                 } else {
 642                         src_page = pte_page(pteval);
 643                         copy_user_highpage(page, src_page, address, vma);
 644                         VM_BUG_ON_PAGE(page_mapcount(src_page) != 1, src_page);
 645                         release_pte_page(src_page);
 646                         /*
 647                          * ptl mostly unnecessary, but preempt has to
 648                          * be disabled to update the per-cpu stats
 649                          * inside page_remove_rmap().
 650                          */
 651                         spin_lock(ptl);
 652                         /*
 653                          * paravirt calls inside pte_clear here are
 654                          * superfluous.
 655                          */
 656                         pte_clear(vma->vm_mm, address, _pte);
 657                         page_remove_rmap(src_page, false);
 658                         spin_unlock(ptl);
 659                         free_page_and_swap_cache(src_page);
 660                 }
 661         }
 662 }
 663
 664 static void khugepaged_alloc_sleep(void)
 665 {
 666         DEFINE_WAIT(wait);
 667
 668         add_wait_queue(&khugepaged_wait, &wait);
 669         freezable_schedule_timeout_interruptible(
 670                 msecs_to_jiffies(khugepaged_alloc_sleep_millisecs));
 671         remove_wait_queue(&khugepaged_wait, &wait);
 672 }
 673
 674 static int khugepaged_node_load[MAX_NUMNODES];
 675
 676 static bool khugepaged_scan_abort(int nid)
 677 {
 678         int i;
 679
 680         /*
 681          * If node_reclaim_mode is disabled, then no extra effort is made to
 682          * allocate memory locally.
 683          */
 684         if (!node_reclaim_mode)
 685                 return false;
 686
 687         /* If there is a count for this node already, it must be acceptable */
 688         if (khugepaged_node_load[nid])
 689                 return false;
 690
 691         for (i = 0; i < MAX_NUMNODES; i++) {
 692                 if (!khugepaged_node_load[i])
 693                         continue;
 694                 if (node_distance(nid, i) > RECLAIM_DISTANCE)
 695                         return true;
 696         }
 697         return false;
 698 }
 699
 700 /* Defrag for khugepaged will enter direct reclaim/compaction if necessary */
 701 static inline gfp_t alloc_hugepage_khugepaged_gfpmask(void)
 702 {
 703         return khugepaged_defrag() ? GFP_TRANSHUGE : GFP_TRANSHUGE_LIGHT;
 704 }
 705
 706 #ifdef CONFIG_NUMA
 707 static int khugepaged_find_target_node(void)
 708 {
 709         static int last_khugepaged_target_node = NUMA_NO_NODE;
 710         int nid, target_node = 0, max_value = 0;
 711
 712         /* find first node with max normal pages hit */
 713         for (nid = 0; nid < MAX_NUMNODES; nid++)
 714                 if (khugepaged_node_load[nid] > max_value) {
 715                         max_value = khugepaged_node_load[nid];
 716                         target_node = nid;
 717                 }
 718
 719         /* do some balance if several nodes have the same hit record */
 720         if (target_node <= last_khugepaged_target_node)
 721                 for (nid = last_khugepaged_target_node + 1; nid < MAX_NUMNODES;
 722                                 nid++)
 723                         if (max_value == khugepaged_node_load[nid]) {
 724                                 target_node = nid;
 725                                 break;
 726                         }
 727
 728         last_khugepaged_target_node = target_node;
 729         return target_node;
 730 }
 731
 732 static bool khugepaged_prealloc_page(struct page **hpage, bool *wait)
 733 {
 734         if (IS_ERR(*hpage)) {
 735                 if (!*wait)
 736                         return false;
 737
 738                 *wait = false;
 739                 *hpage = NULL;
 740                 khugepaged_alloc_sleep();
 741         } else if (*hpage) {
 742                 put_page(*hpage);
 743                 *hpage = NULL;
 744         }
 745
 746         return true;
 747 }
 748
 749 static struct page *
 750 khugepaged_alloc_page(struct page **hpage, gfp_t gfp, int node)
 751 {
 752         VM_BUG_ON_PAGE(*hpage, *hpage);
 753
 754         *hpage = __alloc_pages_node(node, gfp, HPAGE_PMD_ORDER);
 755         if (unlikely(!*hpage)) {
 756                 count_vm_event(THP_COLLAPSE_ALLOC_FAILED);
 757                 *hpage = ERR_PTR(-ENOMEM);
 758                 return NULL;
 759         }
 760
 761         prep_transhuge_page(*hpage);
 762         count_vm_event(THP_COLLAPSE_ALLOC);
 763         return *hpage;
 764 }
 765 #else
 766 static int khugepaged_find_target_node(void)
 767 {
 768         return 0;
 769 }
 770
 771 static inline struct page *alloc_khugepaged_hugepage(void)
 772 {
 773         struct page *page;
 774
 775         page = alloc_pages(alloc_hugepage_khugepaged_gfpmask(),
 776                            HPAGE_PMD_ORDER);
 777         if (page)
 778                 prep_transhuge_page(page);
 779         return page;
 780 }
 781
 782 static struct page *khugepaged_alloc_hugepage(bool *wait)
 783 {
 784         struct page *hpage;
 785
 786         do {
 787                 hpage = alloc_khugepaged_hugepage();
 788                 if (!hpage) {
 789                         count_vm_event(THP_COLLAPSE_ALLOC_FAILED);
 790                         if (!*wait)
 791                                 return NULL;
 792
 793                         *wait = false;
 794                         khugepaged_alloc_sleep();
 795                 } else
 796                         count_vm_event(THP_COLLAPSE_ALLOC);
 797         } while (unlikely(!hpage) && likely(khugepaged_enabled()));
 798
 799         return hpage;
 800 }
 801
 802 static bool khugepaged_prealloc_page(struct page **hpage, bool *wait)
 803 {
 804         if (!*hpage)
 805                 *hpage = khugepaged_alloc_hugepage(wait);
 806
 807         if (unlikely(!*hpage))
 808                 return false;
 809
 810         return true;
 811 }
 812
 813 static struct page *
 814 khugepaged_alloc_page(struct page **hpage, gfp_t gfp, int node)
 815 {
 816         VM_BUG_ON(!*hpage);
 817
 818         return  *hpage;
 819 }
 820 #endif
 821
 822 static bool hugepage_vma_check(struct vm_area_struct *vma)
 823 {
 824         if ((!(vma->vm_flags & VM_HUGEPAGE) && !khugepaged_always()) ||
 825             (vma->vm_flags & VM_NOHUGEPAGE) ||
 826             test_bit(MMF_DISABLE_THP, &vma->vm_mm->flags))
 827                 return false;
 828         if (shmem_file(vma->vm_file)) {
 829                 if (!IS_ENABLED(CONFIG_TRANSPARENT_HUGE_PAGECACHE))
 830                         return false;
 831                 return IS_ALIGNED((vma->vm_start >> PAGE_SHIFT) - vma->vm_pgoff,
 832                                 HPAGE_PMD_NR);
 833         }
 834         if (!vma->anon_vma || vma->vm_ops)
 835                 return false;
 836         if (is_vma_temporary_stack(vma))
 837                 return false;
 838         return !(vma->vm_flags & VM_NO_KHUGEPAGED);
 839 }
 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))
 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, ret = 0;
 884         struct vm_fault vmf = {
 885                 .vma = vma,
 886                 .address = address,
 887                 .flags = FAULT_FLAG_ALLOW_RETRY,
 888                 .pmd = pmd,
 889                 .pgoff = linear_page_index(vma, address),
 890         };
 891
 892         /* we only decide to swapin, if there is enough young ptes */
 893         if (referenced < HPAGE_PMD_NR/2) {
 894                 trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 0);
 895                 return false;
 896         }
 897         vmf.pte = pte_offset_map(pmd, address);
 898         for (; vmf.address < address + HPAGE_PMD_NR*PAGE_SIZE;
 899                         vmf.pte++, vmf.address += PAGE_SIZE) {
 900                 vmf.orig_pte = *vmf.pte;
 901                 if (!is_swap_pte(vmf.orig_pte))
 902                         continue;
 903                 swapped_in++;
 904                 ret = do_swap_page(&vmf);
 905
 906                 /* do_swap_page returns VM_FAULT_RETRY with released mmap_sem */
 907                 if (ret & VM_FAULT_RETRY) {
 908                         down_read(&mm->mmap_sem);
 909                         if (hugepage_vma_revalidate(mm, address, &vmf.vma)) {
 910                                 /* vma is no longer available, don't continue to swapin */
 911                                 trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 0);
 912                                 return false;
 913                         }
 914                         /* check if the pmd is still valid */
 915                         if (mm_find_pmd(mm, address) != pmd) {
 916                                 trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 0);
 917                                 return false;
 918                         }
 919                 }
 920                 if (ret & VM_FAULT_ERROR) {
 921                         trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 0);
 922                         return false;
 923                 }
 924                 /* pte is unmapped now, we need to map it */
 925                 vmf.pte = pte_offset_map(pmd, vmf.address);
 926         }
 927         vmf.pte--;
 928         pte_unmap(vmf.pte);
 929         trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 1);
 930         return true;
 931 }
 932
 933 static void collapse_huge_page(struct mm_struct *mm,
 934                                    unsigned long address,
 935                                    struct page **hpage,
 936                                    int node, int referenced)
 937 {
 938         pmd_t *pmd, _pmd;
 939         pte_t *pte;
 940         pgtable_t pgtable;
 941         struct page *new_page;
 942         spinlock_t *pmd_ptl, *pte_ptl;
 943         int isolated = 0, result = 0;
 944         struct mem_cgroup *memcg;
 945         struct vm_area_struct *vma;
 946         unsigned long mmun_start;       /* For mmu_notifiers */
 947         unsigned long mmun_end;         /* For mmu_notifiers */
 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         /* Do not oom kill for khugepaged charges */
 969         if (unlikely(mem_cgroup_try_charge(new_page, mm, gfp | __GFP_NORETRY,
 970                                            &memcg, true))) {
 971                 result = SCAN_CGROUP_CHARGE_FAIL;
 972                 goto out_nolock;
 973         }
 974
 975         down_read(&mm->mmap_sem);
 976         result = hugepage_vma_revalidate(mm, address, &vma);
 977         if (result) {
 978                 mem_cgroup_cancel_charge(new_page, memcg, true);
 979                 up_read(&mm->mmap_sem);
 980                 goto out_nolock;
 981         }
 982
 983         pmd = mm_find_pmd(mm, address);
 984         if (!pmd) {
 985                 result = SCAN_PMD_NULL;
 986                 mem_cgroup_cancel_charge(new_page, memcg, true);
 987                 up_read(&mm->mmap_sem);
 988                 goto out_nolock;
 989         }
 990
 991         /*
 992          * __collapse_huge_page_swapin always returns with mmap_sem locked.
 993          * If it fails, we release mmap_sem and jump out_nolock.
 994          * Continuing to collapse causes inconsistency.
 995          */
 996         if (!__collapse_huge_page_swapin(mm, vma, address, pmd, referenced)) {
 997                 mem_cgroup_cancel_charge(new_page, memcg, true);
 998                 up_read(&mm->mmap_sem);
 999                 goto out_nolock;
1000         }
1001
1002         up_read(&mm->mmap_sem);
1003         /*
1004          * Prevent all access to pagetables with the exception of
1005          * gup_fast later handled by the ptep_clear_flush and the VM
1006          * handled by the anon_vma lock + PG_lock.
1007          */
1008         down_write(&mm->mmap_sem);
1009         result = hugepage_vma_revalidate(mm, address, &vma);
1010         if (result)
1011                 goto out;
1012         /* check if the pmd is still valid */
1013         if (mm_find_pmd(mm, address) != pmd)
1014                 goto out;
1015
1016         anon_vma_lock_write(vma->anon_vma);
1017
1018         pte = pte_offset_map(pmd, address);
1019         pte_ptl = pte_lockptr(mm, pmd);
1020
1021         mmun_start = address;
1022         mmun_end   = address + HPAGE_PMD_SIZE;
1023         mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
1024         pmd_ptl = pmd_lock(mm, pmd); /* probably unnecessary */
1025         /*
1026          * After this gup_fast can't run anymore. This also removes
1027          * any huge TLB entry from the CPU so we won't allow
1028          * huge and small TLB entries for the same virtual address
1029          * to avoid the risk of CPU bugs in that area.
1030          */
1031         _pmd = pmdp_collapse_flush(vma, address, pmd);
1032         spin_unlock(pmd_ptl);
1033         mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
1034
1035         spin_lock(pte_ptl);
1036         isolated = __collapse_huge_page_isolate(vma, address, pte);
1037         spin_unlock(pte_ptl);
1038
1039         if (unlikely(!isolated)) {
1040                 pte_unmap(pte);
1041                 spin_lock(pmd_ptl);
1042                 BUG_ON(!pmd_none(*pmd));
1043                 /*
1044                  * We can only use set_pmd_at when establishing
1045                  * hugepmds and never for establishing regular pmds that
1046                  * points to regular pagetables. Use pmd_populate for that
1047                  */
1048                 pmd_populate(mm, pmd, pmd_pgtable(_pmd));
1049                 spin_unlock(pmd_ptl);
1050                 anon_vma_unlock_write(vma->anon_vma);
1051                 result = SCAN_FAIL;
1052                 goto out;
1053         }
1054
1055         /*
1056          * All pages are isolated and locked so anon_vma rmap
1057          * can't run anymore.
1058          */
1059         anon_vma_unlock_write(vma->anon_vma);
1060
1061         __collapse_huge_page_copy(pte, new_page, vma, address, pte_ptl);
1062         pte_unmap(pte);
1063         __SetPageUptodate(new_page);
1064         pgtable = pmd_pgtable(_pmd);
1065
1066         _pmd = mk_huge_pmd(new_page, vma->vm_page_prot);
1067         _pmd = maybe_pmd_mkwrite(pmd_mkdirty(_pmd), vma);
1068
1069         /*
1070          * spin_lock() below is not the equivalent of smp_wmb(), so
1071          * this is needed to avoid the copy_huge_page writes to become
1072          * visible after the set_pmd_at() write.
1073          */
1074         smp_wmb();
1075
1076         spin_lock(pmd_ptl);
1077         BUG_ON(!pmd_none(*pmd));
1078         page_add_new_anon_rmap(new_page, vma, address, true);
1079         mem_cgroup_commit_charge(new_page, memcg, false, true);
1080         lru_cache_add_active_or_unevictable(new_page, vma);
1081         pgtable_trans_huge_deposit(mm, pmd, pgtable);
1082         set_pmd_at(mm, address, pmd, _pmd);
1083         update_mmu_cache_pmd(vma, address, pmd);
1084         spin_unlock(pmd_ptl);
1085
1086         *hpage = NULL;
1087
1088         khugepaged_pages_collapsed++;
1089         result = SCAN_SUCCEED;
1090 out_up_write:
1091         up_write(&mm->mmap_sem);
1092 out_nolock:
1093         trace_mm_collapse_huge_page(mm, isolated, result);
1094         return;
1095 out:
1096         mem_cgroup_cancel_charge(new_page, memcg, true);
1097         goto out_up_write;
1098 }
1099
1100 static int khugepaged_scan_pmd(struct mm_struct *mm,
1101                                struct vm_area_struct *vma,
1102                                unsigned long address,
1103                                struct page **hpage)
1104 {
1105         pmd_t *pmd;
1106         pte_t *pte, *_pte;
1107         int ret = 0, none_or_zero = 0, result = 0, referenced = 0;
1108         struct page *page = NULL;
1109         unsigned long _address;
1110         spinlock_t *ptl;
1111         int node = NUMA_NO_NODE, unmapped = 0;
1112         bool writable = false;
1113
1114         VM_BUG_ON(address & ~HPAGE_PMD_MASK);
1115
1116         pmd = mm_find_pmd(mm, address);
1117         if (!pmd) {
1118                 result = SCAN_PMD_NULL;
1119                 goto out;
1120         }
1121
1122         memset(khugepaged_node_load, 0, sizeof(khugepaged_node_load));
1123         pte = pte_offset_map_lock(mm, pmd, address, &ptl);
1124         for (_address = address, _pte = pte; _pte < pte+HPAGE_PMD_NR;
1125              _pte++, _address += PAGE_SIZE) {
1126                 pte_t pteval = *_pte;
1127                 if (is_swap_pte(pteval)) {
1128                         if (++unmapped <= khugepaged_max_ptes_swap) {
1129                                 continue;
1130                         } else {
1131                                 result = SCAN_EXCEED_SWAP_PTE;
1132                                 goto out_unmap;
1133                         }
1134                 }
1135                 if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) {
1136                         if (!userfaultfd_armed(vma) &&
1137                             ++none_or_zero <= khugepaged_max_ptes_none) {
1138                                 continue;
1139                         } else {
1140                                 result = SCAN_EXCEED_NONE_PTE;
1141                                 goto out_unmap;
1142                         }
1143                 }
1144                 if (!pte_present(pteval)) {
1145                         result = SCAN_PTE_NON_PRESENT;
1146                         goto out_unmap;
1147                 }
1148                 if (pte_write(pteval))
1149                         writable = true;
1150
1151                 page = vm_normal_page(vma, _address, pteval);
1152                 if (unlikely(!page)) {
1153                         result = SCAN_PAGE_NULL;
1154                         goto out_unmap;
1155                 }
1156
1157                 /* TODO: teach khugepaged to collapse THP mapped with pte */
1158                 if (PageCompound(page)) {
1159                         result = SCAN_PAGE_COMPOUND;
1160                         goto out_unmap;
1161                 }
1162
1163                 /*
1164                  * Record which node the original page is from and save this
1165                  * information to khugepaged_node_load[].
1166                  * Khupaged will allocate hugepage from the node has the max
1167                  * hit record.
1168                  */
1169                 node = page_to_nid(page);
1170                 if (khugepaged_scan_abort(node)) {
1171                         result = SCAN_SCAN_ABORT;
1172                         goto out_unmap;
1173                 }
1174                 khugepaged_node_load[node]++;
1175                 if (!PageLRU(page)) {
1176                         result = SCAN_PAGE_LRU;
1177                         goto out_unmap;
1178                 }
1179                 if (PageLocked(page)) {
1180                         result = SCAN_PAGE_LOCK;
1181                         goto out_unmap;
1182                 }
1183                 if (!PageAnon(page)) {
1184                         result = SCAN_PAGE_ANON;
1185                         goto out_unmap;
1186                 }
1187
1188                 /*
1189                  * cannot use mapcount: can't collapse if there's a gup pin.
1190                  * The page must only be referenced by the scanned process
1191                  * and page swap cache.
1192                  */
1193                 if (page_count(page) != 1 + PageSwapCache(page)) {
1194                         result = SCAN_PAGE_COUNT;
1195                         goto out_unmap;
1196                 }
1197                 if (pte_young(pteval) ||
1198                     page_is_young(page) || PageReferenced(page) ||
1199                     mmu_notifier_test_young(vma->vm_mm, address))
1200                         referenced++;
1201         }
1202         if (writable) {
1203                 if (referenced) {
1204                         result = SCAN_SUCCEED;
1205                         ret = 1;
1206                 } else {
1207                         result = SCAN_LACK_REFERENCED_PAGE;
1208                 }
1209         } else {
1210                 result = SCAN_PAGE_RO;
1211         }
1212 out_unmap:
1213         pte_unmap_unlock(pte, ptl);
1214         if (ret) {
1215                 node = khugepaged_find_target_node();
1216                 /* collapse_huge_page will return with the mmap_sem released */
1217                 collapse_huge_page(mm, address, hpage, node, referenced);
1218         }
1219 out:
1220         trace_mm_khugepaged_scan_pmd(mm, page, writable, referenced,
1221                                      none_or_zero, result, unmapped);
1222         return ret;
1223 }
1224
1225 static void collect_mm_slot(struct mm_slot *mm_slot)
1226 {
1227         struct mm_struct *mm = mm_slot->mm;
1228
1229         VM_BUG_ON(NR_CPUS != 1 && !spin_is_locked(&khugepaged_mm_lock));
1230
1231         if (khugepaged_test_exit(mm)) {
1232                 /* free mm_slot */
1233                 hash_del(&mm_slot->hash);
1234                 list_del(&mm_slot->mm_node);
1235
1236                 /*
1237                  * Not strictly needed because the mm exited already.
1238                  *
1239                  * clear_bit(MMF_VM_HUGEPAGE, &mm->flags);
1240                  */
1241
1242                 /* khugepaged_mm_lock actually not necessary for the below */
1243                 free_mm_slot(mm_slot);
1244                 mmdrop(mm);
1245         }
1246 }
1247
1248 #if defined(CONFIG_SHMEM) && defined(CONFIG_TRANSPARENT_HUGE_PAGECACHE)
1249 static void retract_page_tables(struct address_space *mapping, pgoff_t pgoff)
1250 {
1251         struct vm_area_struct *vma;
1252         unsigned long addr;
1253         pmd_t *pmd, _pmd;
1254
1255         i_mmap_lock_write(mapping);
1256         vma_interval_tree_foreach(vma, &mapping->i_mmap, pgoff, pgoff) {
1257                 /* probably overkill */
1258                 if (vma->anon_vma)
1259                         continue;
1260                 addr = vma->vm_start + ((pgoff - vma->vm_pgoff) << PAGE_SHIFT);
1261                 if (addr & ~HPAGE_PMD_MASK)
1262                         continue;
1263                 if (vma->vm_end < addr + HPAGE_PMD_SIZE)
1264                         continue;
1265                 pmd = mm_find_pmd(vma->vm_mm, addr);
1266                 if (!pmd)
1267                         continue;
1268                 /*
1269                  * We need exclusive mmap_sem to retract page table.
1270                  * If trylock fails we would end up with pte-mapped THP after
1271                  * re-fault. Not ideal, but it's more important to not disturb
1272                  * the system too much.
1273                  */
1274                 if (down_write_trylock(&vma->vm_mm->mmap_sem)) {
1275                         spinlock_t *ptl = pmd_lock(vma->vm_mm, pmd);
1276                         /* assume page table is clear */
1277                         _pmd = pmdp_collapse_flush(vma, addr, pmd);
1278                         spin_unlock(ptl);
1279                         up_write(&vma->vm_mm->mmap_sem);
1280                         mm_dec_nr_ptes(vma->vm_mm);
1281                         pte_free(vma->vm_mm, pmd_pgtable(_pmd));
1282                 }
1283         }
1284         i_mmap_unlock_write(mapping);
1285 }
1286
1287 /**
1288  * collapse_shmem - collapse small tmpfs/shmem pages into huge one.
1289  *
1290  * Basic scheme is simple, details are more complex:
1291  *  - allocate and freeze a new huge page;
1292  *  - scan over radix tree replacing old pages the new one
1293  *    + swap in pages if necessary;
1294  *    + fill in gaps;
1295  *    + keep old pages around in case if rollback is required;
1296  *  - if replacing succeed:
1297  *    + copy data over;
1298  *    + free old pages;
1299  *    + unfreeze huge page;
1300  *  - if replacing failed;
1301  *    + put all pages back and unfreeze them;
1302  *    + restore gaps in the radix-tree;
1303  *    + free huge page;
1304  */
1305 static void collapse_shmem(struct mm_struct *mm,
1306                 struct address_space *mapping, pgoff_t start,
1307                 struct page **hpage, int node)
1308 {
1309         gfp_t gfp;
1310         struct page *page, *new_page, *tmp;
1311         struct mem_cgroup *memcg;
1312         pgoff_t index, end = start + HPAGE_PMD_NR;
1313         LIST_HEAD(pagelist);
1314         struct radix_tree_iter iter;
1315         void **slot;
1316         int nr_none = 0, result = SCAN_SUCCEED;
1317
1318         VM_BUG_ON(start & (HPAGE_PMD_NR - 1));
1319
1320         /* Only allocate from the target node */
1321         gfp = alloc_hugepage_khugepaged_gfpmask() | __GFP_THISNODE;
1322
1323         new_page = khugepaged_alloc_page(hpage, gfp, node);
1324         if (!new_page) {
1325                 result = SCAN_ALLOC_HUGE_PAGE_FAIL;
1326                 goto out;
1327         }
1328
1329         /* Do not oom kill for khugepaged charges */
1330         if (unlikely(mem_cgroup_try_charge(new_page, mm, gfp | __GFP_NORETRY,
1331                                            &memcg, true))) {
1332                 result = SCAN_CGROUP_CHARGE_FAIL;
1333                 goto out;
1334         }
1335
1336         new_page->index = start;
1337         new_page->mapping = mapping;
1338         __SetPageSwapBacked(new_page);
1339         __SetPageLocked(new_page);
1340         BUG_ON(!page_ref_freeze(new_page, 1));
1341
1342
1343         /*
1344          * At this point the new_page is 'frozen' (page_count() is zero), locked
1345          * and not up-to-date. It's safe to insert it into radix tree, because
1346          * nobody would be able to map it or use it in other way until we
1347          * unfreeze it.
1348          */
1349
1350         index = start;
1351         spin_lock_irq(&mapping->tree_lock);
1352         radix_tree_for_each_slot(slot, &mapping->page_tree, &iter, start) {
1353                 int n = min(iter.index, end) - index;
1354
1355                 /*
1356                  * Handle holes in the radix tree: charge it from shmem and
1357                  * insert relevant subpage of new_page into the radix-tree.
1358                  */
1359                 if (n && !shmem_charge(mapping->host, n)) {
1360                         result = SCAN_FAIL;
1361                         break;
1362                 }
1363                 nr_none += n;
1364                 for (; index < min(iter.index, end); index++) {
1365                         radix_tree_insert(&mapping->page_tree, index,
1366                                         new_page + (index % HPAGE_PMD_NR));
1367                 }
1368
1369                 /* We are done. */
1370                 if (index >= end)
1371                         break;
1372
1373                 page = radix_tree_deref_slot_protected(slot,
1374                                 &mapping->tree_lock);
1375                 if (radix_tree_exceptional_entry(page) || !PageUptodate(page)) {
1376                         spin_unlock_irq(&mapping->tree_lock);
1377                         /* swap in or instantiate fallocated page */
1378                         if (shmem_getpage(mapping->host, index, &page,
1379                                                 SGP_NOHUGE)) {
1380                                 result = SCAN_FAIL;
1381                                 goto tree_unlocked;
1382                         }
1383                         spin_lock_irq(&mapping->tree_lock);
1384                 } else if (trylock_page(page)) {
1385                         get_page(page);
1386                 } else {
1387                         result = SCAN_PAGE_LOCK;
1388                         break;
1389                 }
1390
1391                 /*
1392                  * The page must be locked, so we can drop the tree_lock
1393                  * without racing with truncate.
1394                  */
1395                 VM_BUG_ON_PAGE(!PageLocked(page), page);
1396                 VM_BUG_ON_PAGE(!PageUptodate(page), page);
1397                 VM_BUG_ON_PAGE(PageTransCompound(page), page);
1398
1399                 if (page_mapping(page) != mapping) {
1400                         result = SCAN_TRUNCATED;
1401                         goto out_unlock;
1402                 }
1403                 spin_unlock_irq(&mapping->tree_lock);
1404
1405                 if (isolate_lru_page(page)) {
1406                         result = SCAN_DEL_PAGE_LRU;
1407                         goto out_isolate_failed;
1408                 }
1409
1410                 if (page_mapped(page))
1411                         unmap_mapping_pages(mapping, index, 1, false);
1412
1413                 spin_lock_irq(&mapping->tree_lock);
1414
1415                 slot = radix_tree_lookup_slot(&mapping->page_tree, index);
1416                 VM_BUG_ON_PAGE(page != radix_tree_deref_slot_protected(slot,
1417                                         &mapping->tree_lock), page);
1418                 VM_BUG_ON_PAGE(page_mapped(page), page);
1419
1420                 /*
1421                  * The page is expected to have page_count() == 3:
1422                  *  - we hold a pin on it;
1423                  *  - one reference from radix tree;
1424                  *  - one from isolate_lru_page;
1425                  */
1426                 if (!page_ref_freeze(page, 3)) {
1427                         result = SCAN_PAGE_COUNT;
1428                         goto out_lru;
1429                 }
1430
1431                 /*
1432                  * Add the page to the list to be able to undo the collapse if
1433                  * something go wrong.
1434                  */
1435                 list_add_tail(&page->lru, &pagelist);
1436
1437                 /* Finally, replace with the new page. */
1438                 radix_tree_replace_slot(&mapping->page_tree, slot,
1439                                 new_page + (index % HPAGE_PMD_NR));
1440
1441                 slot = radix_tree_iter_resume(slot, &iter);
1442                 index++;
1443                 continue;
1444 out_lru:
1445                 spin_unlock_irq(&mapping->tree_lock);
1446                 putback_lru_page(page);
1447 out_isolate_failed:
1448                 unlock_page(page);
1449                 put_page(page);
1450                 goto tree_unlocked;
1451 out_unlock:
1452                 unlock_page(page);
1453                 put_page(page);
1454                 break;
1455         }
1456
1457         /*
1458          * Handle hole in radix tree at the end of the range.
1459          * This code only triggers if there's nothing in radix tree
1460          * beyond 'end'.
1461          */
1462         if (result == SCAN_SUCCEED && index < end) {
1463                 int n = end - index;
1464
1465                 if (!shmem_charge(mapping->host, n)) {
1466                         result = SCAN_FAIL;
1467                         goto tree_locked;
1468                 }
1469
1470                 for (; index < end; index++) {
1471                         radix_tree_insert(&mapping->page_tree, index,
1472                                         new_page + (index % HPAGE_PMD_NR));
1473                 }
1474                 nr_none += n;
1475         }
1476
1477 tree_locked:
1478         spin_unlock_irq(&mapping->tree_lock);
1479 tree_unlocked:
1480
1481         if (result == SCAN_SUCCEED) {
1482                 unsigned long flags;
1483                 struct zone *zone = page_zone(new_page);
1484
1485                 /*
1486                  * Replacing old pages with new one has succeed, now we need to
1487                  * copy the content and free old pages.
1488                  */
1489                 list_for_each_entry_safe(page, tmp, &pagelist, lru) {
1490                         copy_highpage(new_page + (page->index % HPAGE_PMD_NR),
1491                                         page);
1492                         list_del(&page->lru);
1493                         unlock_page(page);
1494                         page_ref_unfreeze(page, 1);
1495                         page->mapping = NULL;
1496                         ClearPageActive(page);
1497                         ClearPageUnevictable(page);
1498                         put_page(page);
1499                 }
1500
1501                 local_irq_save(flags);
1502                 __inc_node_page_state(new_page, NR_SHMEM_THPS);
1503                 if (nr_none) {
1504                         __mod_node_page_state(zone->zone_pgdat, NR_FILE_PAGES, nr_none);
1505                         __mod_node_page_state(zone->zone_pgdat, NR_SHMEM, nr_none);
1506                 }
1507                 local_irq_restore(flags);
1508
1509                 /*
1510                  * Remove pte page tables, so we can re-faulti
1511                  * the page as huge.
1512                  */
1513                 retract_page_tables(mapping, start);
1514
1515                 /* Everything is ready, let's unfreeze the new_page */
1516                 set_page_dirty(new_page);
1517                 SetPageUptodate(new_page);
1518                 page_ref_unfreeze(new_page, HPAGE_PMD_NR);
1519                 mem_cgroup_commit_charge(new_page, memcg, false, true);
1520                 lru_cache_add_anon(new_page);
1521                 unlock_page(new_page);
1522
1523                 *hpage = NULL;
1524         } else {
1525                 /* Something went wrong: rollback changes to the radix-tree */
1526                 shmem_uncharge(mapping->host, nr_none);
1527                 spin_lock_irq(&mapping->tree_lock);
1528                 radix_tree_for_each_slot(slot, &mapping->page_tree, &iter,
1529                                 start) {
1530                         if (iter.index >= end)
1531                                 break;
1532                         page = list_first_entry_or_null(&pagelist,
1533                                         struct page, lru);
1534                         if (!page || iter.index < page->index) {
1535                                 if (!nr_none)
1536                                         break;
1537                                 nr_none--;
1538                                 /* Put holes back where they were */
1539                                 radix_tree_delete(&mapping->page_tree,
1540                                                   iter.index);
1541                                 continue;
1542                         }
1543
1544                         VM_BUG_ON_PAGE(page->index != iter.index, page);
1545
1546                         /* Unfreeze the page. */
1547                         list_del(&page->lru);
1548                         page_ref_unfreeze(page, 2);
1549                         radix_tree_replace_slot(&mapping->page_tree,
1550                                                 slot, page);
1551                         slot = radix_tree_iter_resume(slot, &iter);
1552                         spin_unlock_irq(&mapping->tree_lock);
1553                         putback_lru_page(page);
1554                         unlock_page(page);
1555                         spin_lock_irq(&mapping->tree_lock);
1556                 }
1557                 VM_BUG_ON(nr_none);
1558                 spin_unlock_irq(&mapping->tree_lock);
1559
1560                 /* Unfreeze new_page, caller would take care about freeing it */
1561                 page_ref_unfreeze(new_page, 1);
1562                 mem_cgroup_cancel_charge(new_page, memcg, true);
1563                 unlock_page(new_page);
1564                 new_page->mapping = NULL;
1565         }
1566 out:
1567         VM_BUG_ON(!list_empty(&pagelist));
1568         /* TODO: tracepoints */
1569 }
1570
1571 static void khugepaged_scan_shmem(struct mm_struct *mm,
1572                 struct address_space *mapping,
1573                 pgoff_t start, struct page **hpage)
1574 {
1575         struct page *page = NULL;
1576         struct radix_tree_iter iter;
1577         void **slot;
1578         int present, swap;
1579         int node = NUMA_NO_NODE;
1580         int result = SCAN_SUCCEED;
1581
1582         present = 0;
1583         swap = 0;
1584         memset(khugepaged_node_load, 0, sizeof(khugepaged_node_load));
1585         rcu_read_lock();
1586         radix_tree_for_each_slot(slot, &mapping->page_tree, &iter, start) {
1587                 if (iter.index >= start + HPAGE_PMD_NR)
1588                         break;
1589
1590                 page = radix_tree_deref_slot(slot);
1591                 if (radix_tree_deref_retry(page)) {
1592                         slot = radix_tree_iter_retry(&iter);
1593                         continue;
1594                 }
1595
1596                 if (radix_tree_exception(page)) {
1597                         if (++swap > khugepaged_max_ptes_swap) {
1598                                 result = SCAN_EXCEED_SWAP_PTE;
1599                                 break;
1600                         }
1601                         continue;
1602                 }
1603
1604                 if (PageTransCompound(page)) {
1605                         result = SCAN_PAGE_COMPOUND;
1606                         break;
1607                 }
1608
1609                 node = page_to_nid(page);
1610                 if (khugepaged_scan_abort(node)) {
1611                         result = SCAN_SCAN_ABORT;
1612                         break;
1613                 }
1614                 khugepaged_node_load[node]++;
1615
1616                 if (!PageLRU(page)) {
1617                         result = SCAN_PAGE_LRU;
1618                         break;
1619                 }
1620
1621                 if (page_count(page) != 1 + page_mapcount(page)) {
1622                         result = SCAN_PAGE_COUNT;
1623                         break;
1624                 }
1625
1626                 /*
1627                  * We probably should check if the page is referenced here, but
1628                  * nobody would transfer pte_young() to PageReferenced() for us.
1629                  * And rmap walk here is just too costly...
1630                  */
1631
1632                 present++;
1633
1634                 if (need_resched()) {
1635                         slot = radix_tree_iter_resume(slot, &iter);
1636                         cond_resched_rcu();
1637                 }
1638         }
1639         rcu_read_unlock();
1640
1641         if (result == SCAN_SUCCEED) {
1642                 if (present < HPAGE_PMD_NR - khugepaged_max_ptes_none) {
1643                         result = SCAN_EXCEED_NONE_PTE;
1644                 } else {
1645                         node = khugepaged_find_target_node();
1646                         collapse_shmem(mm, mapping, start, hpage, node);
1647                 }
1648         }
1649
1650         /* TODO: tracepoints */
1651 }
1652 #else
1653 static void khugepaged_scan_shmem(struct mm_struct *mm,
1654                 struct address_space *mapping,
1655                 pgoff_t start, struct page **hpage)
1656 {
1657         BUILD_BUG();
1658 }
1659 #endif
1660
1661 static unsigned int khugepaged_scan_mm_slot(unsigned int pages,
1662                                             struct page **hpage)
1663         __releases(&khugepaged_mm_lock)
1664         __acquires(&khugepaged_mm_lock)
1665 {
1666         struct mm_slot *mm_slot;
1667         struct mm_struct *mm;
1668         struct vm_area_struct *vma;
1669         int progress = 0;
1670
1671         VM_BUG_ON(!pages);
1672         VM_BUG_ON(NR_CPUS != 1 && !spin_is_locked(&khugepaged_mm_lock));
1673
1674         if (khugepaged_scan.mm_slot)
1675                 mm_slot = khugepaged_scan.mm_slot;
1676         else {
1677                 mm_slot = list_entry(khugepaged_scan.mm_head.next,
1678                                      struct mm_slot, mm_node);
1679                 khugepaged_scan.address = 0;
1680                 khugepaged_scan.mm_slot = mm_slot;
1681         }
1682         spin_unlock(&khugepaged_mm_lock);
1683
1684         mm = mm_slot->mm;
1685         /*
1686          * Don't wait for semaphore (to avoid long wait times).  Just move to
1687          * the next mm on the list.
1688          */
1689         vma = NULL;
1690         if (unlikely(!down_read_trylock(&mm->mmap_sem)))
1691                 goto breakouterloop_mmap_sem;
1692         if (likely(!khugepaged_test_exit(mm)))
1693                 vma = find_vma(mm, khugepaged_scan.address);
1694
1695         progress++;
1696         for (; vma; vma = vma->vm_next) {
1697                 unsigned long hstart, hend;
1698
1699                 cond_resched();
1700                 if (unlikely(khugepaged_test_exit(mm))) {
1701                         progress++;
1702                         break;
1703                 }
1704                 if (!hugepage_vma_check(vma)) {
1705 skip:
1706                         progress++;
1707                         continue;
1708                 }
1709                 hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK;
1710                 hend = vma->vm_end & HPAGE_PMD_MASK;
1711                 if (hstart >= hend)
1712                         goto skip;
1713                 if (khugepaged_scan.address > hend)
1714                         goto skip;
1715                 if (khugepaged_scan.address < hstart)
1716                         khugepaged_scan.address = hstart;
1717                 VM_BUG_ON(khugepaged_scan.address & ~HPAGE_PMD_MASK);
1718
1719                 while (khugepaged_scan.address < hend) {
1720                         int ret;
1721                         cond_resched();
1722                         if (unlikely(khugepaged_test_exit(mm)))
1723                                 goto breakouterloop;
1724
1725                         VM_BUG_ON(khugepaged_scan.address < hstart ||
1726                                   khugepaged_scan.address + HPAGE_PMD_SIZE >
1727                                   hend);
1728                         if (shmem_file(vma->vm_file)) {
1729                                 struct file *file;
1730                                 pgoff_t pgoff = linear_page_index(vma,
1731                                                 khugepaged_scan.address);
1732                                 if (!shmem_huge_enabled(vma))
1733                                         goto skip;
1734                                 file = get_file(vma->vm_file);
1735                                 up_read(&mm->mmap_sem);
1736                                 ret = 1;
1737                                 khugepaged_scan_shmem(mm, file->f_mapping,
1738                                                 pgoff, hpage);
1739                                 fput(file);
1740                         } else {
1741                                 ret = khugepaged_scan_pmd(mm, vma,
1742                                                 khugepaged_scan.address,
1743                                                 hpage);
1744                         }
1745                         /* move to next address */
1746                         khugepaged_scan.address += HPAGE_PMD_SIZE;
1747                         progress += HPAGE_PMD_NR;
1748                         if (ret)
1749                                 /* we released mmap_sem so break loop */
1750                                 goto breakouterloop_mmap_sem;
1751                         if (progress >= pages)
1752                                 goto breakouterloop;
1753                 }
1754         }
1755 breakouterloop:
1756         up_read(&mm->mmap_sem); /* exit_mmap will destroy ptes after this */
1757 breakouterloop_mmap_sem:
1758
1759         spin_lock(&khugepaged_mm_lock);
1760         VM_BUG_ON(khugepaged_scan.mm_slot != mm_slot);
1761         /*
1762          * Release the current mm_slot if this mm is about to die, or
1763          * if we scanned all vmas of this mm.
1764          */
1765         if (khugepaged_test_exit(mm) || !vma) {
1766                 /*
1767                  * Make sure that if mm_users is reaching zero while
1768                  * khugepaged runs here, khugepaged_exit will find
1769                  * mm_slot not pointing to the exiting mm.
1770                  */
1771                 if (mm_slot->mm_node.next != &khugepaged_scan.mm_head) {
1772                         khugepaged_scan.mm_slot = list_entry(
1773                                 mm_slot->mm_node.next,
1774                                 struct mm_slot, mm_node);
1775                         khugepaged_scan.address = 0;
1776                 } else {
1777                         khugepaged_scan.mm_slot = NULL;
1778                         khugepaged_full_scans++;
1779                 }
1780
1781                 collect_mm_slot(mm_slot);
1782         }
1783
1784         return progress;
1785 }
1786
1787 static int khugepaged_has_work(void)
1788 {
1789         return !list_empty(&khugepaged_scan.mm_head) &&
1790                 khugepaged_enabled();
1791 }
1792
1793 static int khugepaged_wait_event(void)
1794 {
1795         return !list_empty(&khugepaged_scan.mm_head) ||
1796                 kthread_should_stop();
1797 }
1798
1799 static void khugepaged_do_scan(void)
1800 {
1801         struct page *hpage = NULL;
1802         unsigned int progress = 0, pass_through_head = 0;
1803         unsigned int pages = khugepaged_pages_to_scan;
1804         bool wait = true;
1805
1806         barrier(); /* write khugepaged_pages_to_scan to local stack */
1807
1808         while (progress < pages) {
1809                 if (!khugepaged_prealloc_page(&hpage, &wait))
1810                         break;
1811
1812                 cond_resched();
1813
1814                 if (unlikely(kthread_should_stop() || try_to_freeze()))
1815                         break;
1816
1817                 spin_lock(&khugepaged_mm_lock);
1818                 if (!khugepaged_scan.mm_slot)
1819                         pass_through_head++;
1820                 if (khugepaged_has_work() &&
1821                     pass_through_head < 2)
1822                         progress += khugepaged_scan_mm_slot(pages - progress,
1823                                                             &hpage);
1824                 else
1825                         progress = pages;
1826                 spin_unlock(&khugepaged_mm_lock);
1827         }
1828
1829         if (!IS_ERR_OR_NULL(hpage))
1830                 put_page(hpage);
1831 }
1832
1833 static bool khugepaged_should_wakeup(void)
1834 {
1835         return kthread_should_stop() ||
1836                time_after_eq(jiffies, khugepaged_sleep_expire);
1837 }
1838
1839 static void khugepaged_wait_work(void)
1840 {
1841         if (khugepaged_has_work()) {
1842                 const unsigned long scan_sleep_jiffies =
1843                         msecs_to_jiffies(khugepaged_scan_sleep_millisecs);
1844
1845                 if (!scan_sleep_jiffies)
1846                         return;
1847
1848                 khugepaged_sleep_expire = jiffies + scan_sleep_jiffies;
1849                 wait_event_freezable_timeout(khugepaged_wait,
1850                                              khugepaged_should_wakeup(),
1851                                              scan_sleep_jiffies);
1852                 return;
1853         }
1854
1855         if (khugepaged_enabled())
1856                 wait_event_freezable(khugepaged_wait, khugepaged_wait_event());
1857 }
1858
1859 static int khugepaged(void *none)
1860 {
1861         struct mm_slot *mm_slot;
1862
1863         set_freezable();
1864         set_user_nice(current, MAX_NICE);
1865
1866         while (!kthread_should_stop()) {
1867                 khugepaged_do_scan();
1868                 khugepaged_wait_work();
1869         }
1870
1871         spin_lock(&khugepaged_mm_lock);
1872         mm_slot = khugepaged_scan.mm_slot;
1873         khugepaged_scan.mm_slot = NULL;
1874         if (mm_slot)
1875                 collect_mm_slot(mm_slot);
1876         spin_unlock(&khugepaged_mm_lock);
1877         return 0;
1878 }
1879
1880 static void set_recommended_min_free_kbytes(void)
1881 {
1882         struct zone *zone;
1883         int nr_zones = 0;
1884         unsigned long recommended_min;
1885
1886         for_each_populated_zone(zone)
1887                 nr_zones++;
1888
1889         /* Ensure 2 pageblocks are free to assist fragmentation avoidance */
1890         recommended_min = pageblock_nr_pages * nr_zones * 2;
1891
1892         /*
1893          * Make sure that on average at least two pageblocks are almost free
1894          * of another type, one for a migratetype to fall back to and a
1895          * second to avoid subsequent fallbacks of other types There are 3
1896          * MIGRATE_TYPES we care about.
1897          */
1898         recommended_min += pageblock_nr_pages * nr_zones *
1899                            MIGRATE_PCPTYPES * MIGRATE_PCPTYPES;
1900
1901         /* don't ever allow to reserve more than 5% of the lowmem */
1902         recommended_min = min(recommended_min,
1903                               (unsigned long) nr_free_buffer_pages() / 20);
1904         recommended_min <<= (PAGE_SHIFT-10);
1905
1906         if (recommended_min > min_free_kbytes) {
1907                 if (user_min_free_kbytes >= 0)
1908                         pr_info("raising min_free_kbytes from %d to %lu to help transparent hugepage allocations\n",
1909                                 min_free_kbytes, recommended_min);
1910
1911                 min_free_kbytes = recommended_min;
1912         }
1913         setup_per_zone_wmarks();
1914 }
1915
1916 int start_stop_khugepaged(void)
1917 {
1918         static struct task_struct *khugepaged_thread __read_mostly;
1919         static DEFINE_MUTEX(khugepaged_mutex);
1920         int err = 0;
1921
1922         mutex_lock(&khugepaged_mutex);
1923         if (khugepaged_enabled()) {
1924                 if (!khugepaged_thread)
1925                         khugepaged_thread = kthread_run(khugepaged, NULL,
1926                                                         "khugepaged");
1927                 if (IS_ERR(khugepaged_thread)) {
1928                         pr_err("khugepaged: kthread_run(khugepaged) failed\n");
1929                         err = PTR_ERR(khugepaged_thread);
1930                         khugepaged_thread = NULL;
1931                         goto fail;
1932                 }
1933
1934                 if (!list_empty(&khugepaged_scan.mm_head))
1935                         wake_up_interruptible(&khugepaged_wait);
1936
1937                 set_recommended_min_free_kbytes();
1938         } else if (khugepaged_thread) {
1939                 kthread_stop(khugepaged_thread);
1940                 khugepaged_thread = NULL;
1941         }
1942 fail:
1943         mutex_unlock(&khugepaged_mutex);
1944         return err;
1945 }