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                 VM_BUG_ON_PAGE(PageCompound(page), page);
 534                 VM_BUG_ON_PAGE(!PageAnon(page), page);
 535
 536                 /*
 537                  * We can do it before isolate_lru_page because the
 538                  * page can't be freed from under us. NOTE: PG_lock
 539                  * is needed to serialize against split_huge_page
 540                  * when invoked from the VM.
 541                  */
 542                 if (!trylock_page(page)) {
 543                         result = SCAN_PAGE_LOCK;
 544                         goto out;
 545                 }
 546
 547                 /*
 548                  * cannot use mapcount: can't collapse if there's a gup pin.
 549                  * The page must only be referenced by the scanned process
 550                  * and page swap cache.
 551                  */
 552                 if (page_count(page) != 1 + PageSwapCache(page)) {
 553                         unlock_page(page);
 554                         result = SCAN_PAGE_COUNT;
 555                         goto out;
 556                 }
 557                 if (pte_write(pteval)) {
 558                         writable = true;
 559                 } else {
 560                         if (PageSwapCache(page) &&
 561                             !reuse_swap_page(page, NULL)) {
 562                                 unlock_page(page);
 563                                 result = SCAN_SWAP_CACHE_PAGE;
 564                                 goto out;
 565                         }
 566                         /*
 567                          * Page is not in the swap cache. It can be collapsed
 568                          * into a THP.
 569                          */
 570                 }
 571
 572                 /*
 573                  * Isolate the page to avoid collapsing an hugepage
 574                  * currently in use by the VM.
 575                  */
 576                 if (isolate_lru_page(page)) {
 577                         unlock_page(page);
 578                         result = SCAN_DEL_PAGE_LRU;
 579                         goto out;
 580                 }
 581                 inc_node_page_state(page,
 582                                 NR_ISOLATED_ANON + page_is_file_cache(page));
 583                 VM_BUG_ON_PAGE(!PageLocked(page), page);
 584                 VM_BUG_ON_PAGE(PageLRU(page), page);
 585
 586                 /* There should be enough young pte to collapse the page */
 587                 if (pte_young(pteval) ||
 588                     page_is_young(page) || PageReferenced(page) ||
 589                     mmu_notifier_test_young(vma->vm_mm, address))
 590                         referenced++;
 591         }
 592         if (likely(writable)) {
 593                 if (likely(referenced)) {
 594                         result = SCAN_SUCCEED;
 595                         trace_mm_collapse_huge_page_isolate(page, none_or_zero,
 596                                                             referenced, writable, result);
 597                         return 1;
 598                 }
 599         } else {
 600                 result = SCAN_PAGE_RO;
 601         }
 602
 603 out:
 604         release_pte_pages(pte, _pte);
 605         trace_mm_collapse_huge_page_isolate(page, none_or_zero,
 606                                             referenced, writable, result);
 607         return 0;
 608 }
 609
 610 static void __collapse_huge_page_copy(pte_t *pte, struct page *page,
 611                                       struct vm_area_struct *vma,
 612                                       unsigned long address,
 613                                       spinlock_t *ptl)
 614 {
 615         pte_t *_pte;
 616         for (_pte = pte; _pte < pte + HPAGE_PMD_NR;
 617                                 _pte++, page++, address += PAGE_SIZE) {
 618                 pte_t pteval = *_pte;
 619                 struct page *src_page;
 620
 621                 if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) {
 622                         clear_user_highpage(page, address);
 623                         add_mm_counter(vma->vm_mm, MM_ANONPAGES, 1);
 624                         if (is_zero_pfn(pte_pfn(pteval))) {
 625                                 /*
 626                                  * ptl mostly unnecessary.
 627                                  */
 628                                 spin_lock(ptl);
 629                                 /*
 630                                  * paravirt calls inside pte_clear here are
 631                                  * superfluous.
 632                                  */
 633                                 pte_clear(vma->vm_mm, address, _pte);
 634                                 spin_unlock(ptl);
 635                         }
 636                 } else {
 637                         src_page = pte_page(pteval);
 638                         copy_user_highpage(page, src_page, address, vma);
 639                         VM_BUG_ON_PAGE(page_mapcount(src_page) != 1, src_page);
 640                         release_pte_page(src_page);
 641                         /*
 642                          * ptl mostly unnecessary, but preempt has to
 643                          * be disabled to update the per-cpu stats
 644                          * inside page_remove_rmap().
 645                          */
 646                         spin_lock(ptl);
 647                         /*
 648                          * paravirt calls inside pte_clear here are
 649                          * superfluous.
 650                          */
 651                         pte_clear(vma->vm_mm, address, _pte);
 652                         page_remove_rmap(src_page, false);
 653                         spin_unlock(ptl);
 654                         free_page_and_swap_cache(src_page);
 655                 }
 656         }
 657 }
 658
 659 static void khugepaged_alloc_sleep(void)
 660 {
 661         DEFINE_WAIT(wait);
 662
 663         add_wait_queue(&khugepaged_wait, &wait);
 664         freezable_schedule_timeout_interruptible(
 665                 msecs_to_jiffies(khugepaged_alloc_sleep_millisecs));
 666         remove_wait_queue(&khugepaged_wait, &wait);
 667 }
 668
 669 static int khugepaged_node_load[MAX_NUMNODES];
 670
 671 static bool khugepaged_scan_abort(int nid)
 672 {
 673         int i;
 674
 675         /*
 676          * If node_reclaim_mode is disabled, then no extra effort is made to
 677          * allocate memory locally.
 678          */
 679         if (!node_reclaim_mode)
 680                 return false;
 681
 682         /* If there is a count for this node already, it must be acceptable */
 683         if (khugepaged_node_load[nid])
 684                 return false;
 685
 686         for (i = 0; i < MAX_NUMNODES; i++) {
 687                 if (!khugepaged_node_load[i])
 688                         continue;
 689                 if (node_distance(nid, i) > RECLAIM_DISTANCE)
 690                         return true;
 691         }
 692         return false;
 693 }
 694
 695 /* Defrag for khugepaged will enter direct reclaim/compaction if necessary */
 696 static inline gfp_t alloc_hugepage_khugepaged_gfpmask(void)
 697 {
 698         return khugepaged_defrag() ? GFP_TRANSHUGE : GFP_TRANSHUGE_LIGHT;
 699 }
 700
 701 #ifdef CONFIG_NUMA
 702 static int khugepaged_find_target_node(void)
 703 {
 704         static int last_khugepaged_target_node = NUMA_NO_NODE;
 705         int nid, target_node = 0, max_value = 0;
 706
 707         /* find first node with max normal pages hit */
 708         for (nid = 0; nid < MAX_NUMNODES; nid++)
 709                 if (khugepaged_node_load[nid] > max_value) {
 710                         max_value = khugepaged_node_load[nid];
 711                         target_node = nid;
 712                 }
 713
 714         /* do some balance if several nodes have the same hit record */
 715         if (target_node <= last_khugepaged_target_node)
 716                 for (nid = last_khugepaged_target_node + 1; nid < MAX_NUMNODES;
 717                                 nid++)
 718                         if (max_value == khugepaged_node_load[nid]) {
 719                                 target_node = nid;
 720                                 break;
 721                         }
 722
 723         last_khugepaged_target_node = target_node;
 724         return target_node;
 725 }
 726
 727 static bool khugepaged_prealloc_page(struct page **hpage, bool *wait)
 728 {
 729         if (IS_ERR(*hpage)) {
 730                 if (!*wait)
 731                         return false;
 732
 733                 *wait = false;
 734                 *hpage = NULL;
 735                 khugepaged_alloc_sleep();
 736         } else if (*hpage) {
 737                 put_page(*hpage);
 738                 *hpage = NULL;
 739         }
 740
 741         return true;
 742 }
 743
 744 static struct page *
 745 khugepaged_alloc_page(struct page **hpage, gfp_t gfp, int node)
 746 {
 747         VM_BUG_ON_PAGE(*hpage, *hpage);
 748
 749         *hpage = __alloc_pages_node(node, gfp, HPAGE_PMD_ORDER);
 750         if (unlikely(!*hpage)) {
 751                 count_vm_event(THP_COLLAPSE_ALLOC_FAILED);
 752                 *hpage = ERR_PTR(-ENOMEM);
 753                 return NULL;
 754         }
 755
 756         prep_transhuge_page(*hpage);
 757         count_vm_event(THP_COLLAPSE_ALLOC);
 758         return *hpage;
 759 }
 760 #else
 761 static int khugepaged_find_target_node(void)
 762 {
 763         return 0;
 764 }
 765
 766 static inline struct page *alloc_khugepaged_hugepage(void)
 767 {
 768         struct page *page;
 769
 770         page = alloc_pages(alloc_hugepage_khugepaged_gfpmask(),
 771                            HPAGE_PMD_ORDER);
 772         if (page)
 773                 prep_transhuge_page(page);
 774         return page;
 775 }
 776
 777 static struct page *khugepaged_alloc_hugepage(bool *wait)
 778 {
 779         struct page *hpage;
 780
 781         do {
 782                 hpage = alloc_khugepaged_hugepage();
 783                 if (!hpage) {
 784                         count_vm_event(THP_COLLAPSE_ALLOC_FAILED);
 785                         if (!*wait)
 786                                 return NULL;
 787
 788                         *wait = false;
 789                         khugepaged_alloc_sleep();
 790                 } else
 791                         count_vm_event(THP_COLLAPSE_ALLOC);
 792         } while (unlikely(!hpage) && likely(khugepaged_enabled()));
 793
 794         return hpage;
 795 }
 796
 797 static bool khugepaged_prealloc_page(struct page **hpage, bool *wait)
 798 {
 799         if (!*hpage)
 800                 *hpage = khugepaged_alloc_hugepage(wait);
 801
 802         if (unlikely(!*hpage))
 803                 return false;
 804
 805         return true;
 806 }
 807
 808 static struct page *
 809 khugepaged_alloc_page(struct page **hpage, gfp_t gfp, int node)
 810 {
 811         VM_BUG_ON(!*hpage);
 812
 813         return  *hpage;
 814 }
 815 #endif
 816
 817 static bool hugepage_vma_check(struct vm_area_struct *vma)
 818 {
 819         if ((!(vma->vm_flags & VM_HUGEPAGE) && !khugepaged_always()) ||
 820             (vma->vm_flags & VM_NOHUGEPAGE) ||
 821             test_bit(MMF_DISABLE_THP, &vma->vm_mm->flags))
 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         int swapped_in = 0, ret = 0;
 879         struct vm_fault vmf = {
 880                 .vma = vma,
 881                 .address = address,
 882                 .flags = FAULT_FLAG_ALLOW_RETRY,
 883                 .pmd = pmd,
 884                 .pgoff = linear_page_index(vma, address),
 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         vmf.pte = pte_offset_map(pmd, address);
 893         for (; vmf.address < address + HPAGE_PMD_NR*PAGE_SIZE;
 894                         vmf.pte++, vmf.address += PAGE_SIZE) {
 895                 vmf.orig_pte = *vmf.pte;
 896                 if (!is_swap_pte(vmf.orig_pte))
 897                         continue;
 898                 swapped_in++;
 899                 ret = do_swap_page(&vmf);
 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, &vmf.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                                 trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 0);
 912                                 return false;
 913                         }
 914                 }
 915                 if (ret & VM_FAULT_ERROR) {
 916                         trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 0);
 917                         return false;
 918                 }
 919                 /* pte is unmapped now, we need to map it */
 920                 vmf.pte = pte_offset_map(pmd, vmf.address);
 921         }
 922         vmf.pte--;
 923         pte_unmap(vmf.pte);
 924         trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 1);
 925         return true;
 926 }
 927
 928 static void collapse_huge_page(struct mm_struct *mm,
 929                                    unsigned long address,
 930                                    struct page **hpage,
 931                                    int node, int referenced)
 932 {
 933         pmd_t *pmd, _pmd;
 934         pte_t *pte;
 935         pgtable_t pgtable;
 936         struct page *new_page;
 937         spinlock_t *pmd_ptl, *pte_ptl;
 938         int isolated = 0, result = 0;
 939         struct mem_cgroup *memcg;
 940         struct vm_area_struct *vma;
 941         unsigned long mmun_start;       /* For mmu_notifiers */
 942         unsigned long mmun_end;         /* For mmu_notifiers */
 943         gfp_t gfp;
 944
 945         VM_BUG_ON(address & ~HPAGE_PMD_MASK);
 946
 947         /* Only allocate from the target node */
 948         gfp = alloc_hugepage_khugepaged_gfpmask() | __GFP_THISNODE;
 949
 950         /*
 951          * Before allocating the hugepage, release the mmap_sem read lock.
 952          * The allocation can take potentially a long time if it involves
 953          * sync compaction, and we do not need to hold the mmap_sem during
 954          * that. We will recheck the vma after taking it again in write mode.
 955          */
 956         up_read(&mm->mmap_sem);
 957         new_page = khugepaged_alloc_page(hpage, gfp, node);
 958         if (!new_page) {
 959                 result = SCAN_ALLOC_HUGE_PAGE_FAIL;
 960                 goto out_nolock;
 961         }
 962
 963         if (unlikely(mem_cgroup_try_charge(new_page, mm, gfp, &memcg, true))) {
 964                 result = SCAN_CGROUP_CHARGE_FAIL;
 965                 goto out_nolock;
 966         }
 967
 968         down_read(&mm->mmap_sem);
 969         result = hugepage_vma_revalidate(mm, address, &vma);
 970         if (result) {
 971                 mem_cgroup_cancel_charge(new_page, memcg, true);
 972                 up_read(&mm->mmap_sem);
 973                 goto out_nolock;
 974         }
 975
 976         pmd = mm_find_pmd(mm, address);
 977         if (!pmd) {
 978                 result = SCAN_PMD_NULL;
 979                 mem_cgroup_cancel_charge(new_page, memcg, true);
 980                 up_read(&mm->mmap_sem);
 981                 goto out_nolock;
 982         }
 983
 984         /*
 985          * __collapse_huge_page_swapin always returns with mmap_sem locked.
 986          * If it fails, we release mmap_sem and jump out_nolock.
 987          * Continuing to collapse causes inconsistency.
 988          */
 989         if (!__collapse_huge_page_swapin(mm, vma, address, pmd, referenced)) {
 990                 mem_cgroup_cancel_charge(new_page, memcg, true);
 991                 up_read(&mm->mmap_sem);
 992                 goto out_nolock;
 993         }
 994
 995         up_read(&mm->mmap_sem);
 996         /*
 997          * Prevent all access to pagetables with the exception of
 998          * gup_fast later handled by the ptep_clear_flush and the VM
 999          * handled by the anon_vma lock + PG_lock.
1000          */
1001         down_write(&mm->mmap_sem);
1002         result = hugepage_vma_revalidate(mm, address, &vma);
1003         if (result)
1004                 goto out;
1005         /* check if the pmd is still valid */
1006         if (mm_find_pmd(mm, address) != pmd)
1007                 goto out;
1008
1009         anon_vma_lock_write(vma->anon_vma);
1010
1011         pte = pte_offset_map(pmd, address);
1012         pte_ptl = pte_lockptr(mm, pmd);
1013
1014         mmun_start = address;
1015         mmun_end   = address + HPAGE_PMD_SIZE;
1016         mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
1017         pmd_ptl = pmd_lock(mm, pmd); /* probably unnecessary */
1018         /*
1019          * After this gup_fast can't run anymore. This also removes
1020          * any huge TLB entry from the CPU so we won't allow
1021          * huge and small TLB entries for the same virtual address
1022          * to avoid the risk of CPU bugs in that area.
1023          */
1024         _pmd = pmdp_collapse_flush(vma, address, pmd);
1025         spin_unlock(pmd_ptl);
1026         mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
1027
1028         spin_lock(pte_ptl);
1029         isolated = __collapse_huge_page_isolate(vma, address, pte);
1030         spin_unlock(pte_ptl);
1031
1032         if (unlikely(!isolated)) {
1033                 pte_unmap(pte);
1034                 spin_lock(pmd_ptl);
1035                 BUG_ON(!pmd_none(*pmd));
1036                 /*
1037                  * We can only use set_pmd_at when establishing
1038                  * hugepmds and never for establishing regular pmds that
1039                  * points to regular pagetables. Use pmd_populate for that
1040                  */
1041                 pmd_populate(mm, pmd, pmd_pgtable(_pmd));
1042                 spin_unlock(pmd_ptl);
1043                 anon_vma_unlock_write(vma->anon_vma);
1044                 result = SCAN_FAIL;
1045                 goto out;
1046         }
1047
1048         /*
1049          * All pages are isolated and locked so anon_vma rmap
1050          * can't run anymore.
1051          */
1052         anon_vma_unlock_write(vma->anon_vma);
1053
1054         __collapse_huge_page_copy(pte, new_page, vma, address, pte_ptl);
1055         pte_unmap(pte);
1056         __SetPageUptodate(new_page);
1057         pgtable = pmd_pgtable(_pmd);
1058
1059         _pmd = mk_huge_pmd(new_page, vma->vm_page_prot);
1060         _pmd = maybe_pmd_mkwrite(pmd_mkdirty(_pmd), vma);
1061
1062         /*
1063          * spin_lock() below is not the equivalent of smp_wmb(), so
1064          * this is needed to avoid the copy_huge_page writes to become
1065          * visible after the set_pmd_at() write.
1066          */
1067         smp_wmb();
1068
1069         spin_lock(pmd_ptl);
1070         BUG_ON(!pmd_none(*pmd));
1071         page_add_new_anon_rmap(new_page, vma, address, true);
1072         mem_cgroup_commit_charge(new_page, memcg, false, true);
1073         lru_cache_add_active_or_unevictable(new_page, vma);
1074         pgtable_trans_huge_deposit(mm, pmd, pgtable);
1075         set_pmd_at(mm, address, pmd, _pmd);
1076         update_mmu_cache_pmd(vma, address, pmd);
1077         spin_unlock(pmd_ptl);
1078
1079         *hpage = NULL;
1080
1081         khugepaged_pages_collapsed++;
1082         result = SCAN_SUCCEED;
1083 out_up_write:
1084         up_write(&mm->mmap_sem);
1085 out_nolock:
1086         trace_mm_collapse_huge_page(mm, isolated, result);
1087         return;
1088 out:
1089         mem_cgroup_cancel_charge(new_page, memcg, true);
1090         goto out_up_write;
1091 }
1092
1093 static int khugepaged_scan_pmd(struct mm_struct *mm,
1094                                struct vm_area_struct *vma,
1095                                unsigned long address,
1096                                struct page **hpage)
1097 {
1098         pmd_t *pmd;
1099         pte_t *pte, *_pte;
1100         int ret = 0, none_or_zero = 0, result = 0, referenced = 0;
1101         struct page *page = NULL;
1102         unsigned long _address;
1103         spinlock_t *ptl;
1104         int node = NUMA_NO_NODE, unmapped = 0;
1105         bool writable = false;
1106
1107         VM_BUG_ON(address & ~HPAGE_PMD_MASK);
1108
1109         pmd = mm_find_pmd(mm, address);
1110         if (!pmd) {
1111                 result = SCAN_PMD_NULL;
1112                 goto out;
1113         }
1114
1115         memset(khugepaged_node_load, 0, sizeof(khugepaged_node_load));
1116         pte = pte_offset_map_lock(mm, pmd, address, &ptl);
1117         for (_address = address, _pte = pte; _pte < pte+HPAGE_PMD_NR;
1118              _pte++, _address += PAGE_SIZE) {
1119                 pte_t pteval = *_pte;
1120                 if (is_swap_pte(pteval)) {
1121                         if (++unmapped <= khugepaged_max_ptes_swap) {
1122                                 continue;
1123                         } else {
1124                                 result = SCAN_EXCEED_SWAP_PTE;
1125                                 goto out_unmap;
1126                         }
1127                 }
1128                 if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) {
1129                         if (!userfaultfd_armed(vma) &&
1130                             ++none_or_zero <= khugepaged_max_ptes_none) {
1131                                 continue;
1132                         } else {
1133                                 result = SCAN_EXCEED_NONE_PTE;
1134                                 goto out_unmap;
1135                         }
1136                 }
1137                 if (!pte_present(pteval)) {
1138                         result = SCAN_PTE_NON_PRESENT;
1139                         goto out_unmap;
1140                 }
1141                 if (pte_write(pteval))
1142                         writable = true;
1143
1144                 page = vm_normal_page(vma, _address, pteval);
1145                 if (unlikely(!page)) {
1146                         result = SCAN_PAGE_NULL;
1147                         goto out_unmap;
1148                 }
1149
1150                 /* TODO: teach khugepaged to collapse THP mapped with pte */
1151                 if (PageCompound(page)) {
1152                         result = SCAN_PAGE_COMPOUND;
1153                         goto out_unmap;
1154                 }
1155
1156                 /*
1157                  * Record which node the original page is from and save this
1158                  * information to khugepaged_node_load[].
1159                  * Khupaged will allocate hugepage from the node has the max
1160                  * hit record.
1161                  */
1162                 node = page_to_nid(page);
1163                 if (khugepaged_scan_abort(node)) {
1164                         result = SCAN_SCAN_ABORT;
1165                         goto out_unmap;
1166                 }
1167                 khugepaged_node_load[node]++;
1168                 if (!PageLRU(page)) {
1169                         result = SCAN_PAGE_LRU;
1170                         goto out_unmap;
1171                 }
1172                 if (PageLocked(page)) {
1173                         result = SCAN_PAGE_LOCK;
1174                         goto out_unmap;
1175                 }
1176                 if (!PageAnon(page)) {
1177                         result = SCAN_PAGE_ANON;
1178                         goto out_unmap;
1179                 }
1180
1181                 /*
1182                  * cannot use mapcount: can't collapse if there's a gup pin.
1183                  * The page must only be referenced by the scanned process
1184                  * and page swap cache.
1185                  */
1186                 if (page_count(page) != 1 + PageSwapCache(page)) {
1187                         result = SCAN_PAGE_COUNT;
1188                         goto out_unmap;
1189                 }
1190                 if (pte_young(pteval) ||
1191                     page_is_young(page) || PageReferenced(page) ||
1192                     mmu_notifier_test_young(vma->vm_mm, address))
1193                         referenced++;
1194         }
1195         if (writable) {
1196                 if (referenced) {
1197                         result = SCAN_SUCCEED;
1198                         ret = 1;
1199                 } else {
1200                         result = SCAN_LACK_REFERENCED_PAGE;
1201                 }
1202         } else {
1203                 result = SCAN_PAGE_RO;
1204         }
1205 out_unmap:
1206         pte_unmap_unlock(pte, ptl);
1207         if (ret) {
1208                 node = khugepaged_find_target_node();
1209                 /* collapse_huge_page will return with the mmap_sem released */
1210                 collapse_huge_page(mm, address, hpage, node, referenced);
1211         }
1212 out:
1213         trace_mm_khugepaged_scan_pmd(mm, page, writable, referenced,
1214                                      none_or_zero, result, unmapped);
1215         return ret;
1216 }
1217
1218 static void collect_mm_slot(struct mm_slot *mm_slot)
1219 {
1220         struct mm_struct *mm = mm_slot->mm;
1221
1222         VM_BUG_ON(NR_CPUS != 1 && !spin_is_locked(&khugepaged_mm_lock));
1223
1224         if (khugepaged_test_exit(mm)) {
1225                 /* free mm_slot */
1226                 hash_del(&mm_slot->hash);
1227                 list_del(&mm_slot->mm_node);
1228
1229                 /*
1230                  * Not strictly needed because the mm exited already.
1231                  *
1232                  * clear_bit(MMF_VM_HUGEPAGE, &mm->flags);
1233                  */
1234
1235                 /* khugepaged_mm_lock actually not necessary for the below */
1236                 free_mm_slot(mm_slot);
1237                 mmdrop(mm);
1238         }
1239 }
1240
1241 #if defined(CONFIG_SHMEM) && defined(CONFIG_TRANSPARENT_HUGE_PAGECACHE)
1242 static void retract_page_tables(struct address_space *mapping, pgoff_t pgoff)
1243 {
1244         struct vm_area_struct *vma;
1245         unsigned long addr;
1246         pmd_t *pmd, _pmd;
1247
1248         i_mmap_lock_write(mapping);
1249         vma_interval_tree_foreach(vma, &mapping->i_mmap, pgoff, pgoff) {
1250                 /* probably overkill */
1251                 if (vma->anon_vma)
1252                         continue;
1253                 addr = vma->vm_start + ((pgoff - vma->vm_pgoff) << PAGE_SHIFT);
1254                 if (addr & ~HPAGE_PMD_MASK)
1255                         continue;
1256                 if (vma->vm_end < addr + HPAGE_PMD_SIZE)
1257                         continue;
1258                 pmd = mm_find_pmd(vma->vm_mm, addr);
1259                 if (!pmd)
1260                         continue;
1261                 /*
1262                  * We need exclusive mmap_sem to retract page table.
1263                  * If trylock fails we would end up with pte-mapped THP after
1264                  * re-fault. Not ideal, but it's more important to not disturb
1265                  * the system too much.
1266                  */
1267                 if (down_write_trylock(&vma->vm_mm->mmap_sem)) {
1268                         spinlock_t *ptl = pmd_lock(vma->vm_mm, pmd);
1269                         /* assume page table is clear */
1270                         _pmd = pmdp_collapse_flush(vma, addr, pmd);
1271                         spin_unlock(ptl);
1272                         up_write(&vma->vm_mm->mmap_sem);
1273                         mm_dec_nr_ptes(vma->vm_mm);
1274                         pte_free(vma->vm_mm, pmd_pgtable(_pmd));
1275                 }
1276         }
1277         i_mmap_unlock_write(mapping);
1278 }
1279
1280 /**
1281  * collapse_shmem - collapse small tmpfs/shmem pages into huge one.
1282  *
1283  * Basic scheme is simple, details are more complex:
1284  *  - allocate and freeze a new huge page;
1285  *  - scan over radix tree replacing old pages the new one
1286  *    + swap in pages if necessary;
1287  *    + fill in gaps;
1288  *    + keep old pages around in case if rollback is required;
1289  *  - if replacing succeed:
1290  *    + copy data over;
1291  *    + free old pages;
1292  *    + unfreeze huge page;
1293  *  - if replacing failed;
1294  *    + put all pages back and unfreeze them;
1295  *    + restore gaps in the radix-tree;
1296  *    + free huge page;
1297  */
1298 static void collapse_shmem(struct mm_struct *mm,
1299                 struct address_space *mapping, pgoff_t start,
1300                 struct page **hpage, int node)
1301 {
1302         gfp_t gfp;
1303         struct page *page, *new_page, *tmp;
1304         struct mem_cgroup *memcg;
1305         pgoff_t index, end = start + HPAGE_PMD_NR;
1306         LIST_HEAD(pagelist);
1307         struct radix_tree_iter iter;
1308         void **slot;
1309         int nr_none = 0, result = SCAN_SUCCEED;
1310
1311         VM_BUG_ON(start & (HPAGE_PMD_NR - 1));
1312
1313         /* Only allocate from the target node */
1314         gfp = alloc_hugepage_khugepaged_gfpmask() | __GFP_THISNODE;
1315
1316         new_page = khugepaged_alloc_page(hpage, gfp, node);
1317         if (!new_page) {
1318                 result = SCAN_ALLOC_HUGE_PAGE_FAIL;
1319                 goto out;
1320         }
1321
1322         if (unlikely(mem_cgroup_try_charge(new_page, mm, gfp, &memcg, true))) {
1323                 result = SCAN_CGROUP_CHARGE_FAIL;
1324                 goto out;
1325         }
1326
1327         new_page->index = start;
1328         new_page->mapping = mapping;
1329         __SetPageSwapBacked(new_page);
1330         __SetPageLocked(new_page);
1331         BUG_ON(!page_ref_freeze(new_page, 1));
1332
1333
1334         /*
1335          * At this point the new_page is 'frozen' (page_count() is zero), locked
1336          * and not up-to-date. It's safe to insert it into radix tree, because
1337          * nobody would be able to map it or use it in other way until we
1338          * unfreeze it.
1339          */
1340
1341         index = start;
1342         spin_lock_irq(&mapping->tree_lock);
1343         radix_tree_for_each_slot(slot, &mapping->page_tree, &iter, start) {
1344                 int n = min(iter.index, end) - index;
1345
1346                 /*
1347                  * Handle holes in the radix tree: charge it from shmem and
1348                  * insert relevant subpage of new_page into the radix-tree.
1349                  */
1350                 if (n && !shmem_charge(mapping->host, n)) {
1351                         result = SCAN_FAIL;
1352                         break;
1353                 }
1354                 nr_none += n;
1355                 for (; index < min(iter.index, end); index++) {
1356                         radix_tree_insert(&mapping->page_tree, index,
1357                                         new_page + (index % HPAGE_PMD_NR));
1358                 }
1359
1360                 /* We are done. */
1361                 if (index >= end)
1362                         break;
1363
1364                 page = radix_tree_deref_slot_protected(slot,
1365                                 &mapping->tree_lock);
1366                 if (radix_tree_exceptional_entry(page) || !PageUptodate(page)) {
1367                         spin_unlock_irq(&mapping->tree_lock);
1368                         /* swap in or instantiate fallocated page */
1369                         if (shmem_getpage(mapping->host, index, &page,
1370                                                 SGP_NOHUGE)) {
1371                                 result = SCAN_FAIL;
1372                                 goto tree_unlocked;
1373                         }
1374                         spin_lock_irq(&mapping->tree_lock);
1375                 } else if (trylock_page(page)) {
1376                         get_page(page);
1377                 } else {
1378                         result = SCAN_PAGE_LOCK;
1379                         break;
1380                 }
1381
1382                 /*
1383                  * The page must be locked, so we can drop the tree_lock
1384                  * without racing with truncate.
1385                  */
1386                 VM_BUG_ON_PAGE(!PageLocked(page), page);
1387                 VM_BUG_ON_PAGE(!PageUptodate(page), page);
1388                 VM_BUG_ON_PAGE(PageTransCompound(page), page);
1389
1390                 if (page_mapping(page) != mapping) {
1391                         result = SCAN_TRUNCATED;
1392                         goto out_unlock;
1393                 }
1394                 spin_unlock_irq(&mapping->tree_lock);
1395
1396                 if (isolate_lru_page(page)) {
1397                         result = SCAN_DEL_PAGE_LRU;
1398                         goto out_isolate_failed;
1399                 }
1400
1401                 if (page_mapped(page))
1402                         unmap_mapping_pages(mapping, index, 1, false);
1403
1404                 spin_lock_irq(&mapping->tree_lock);
1405
1406                 slot = radix_tree_lookup_slot(&mapping->page_tree, index);
1407                 VM_BUG_ON_PAGE(page != radix_tree_deref_slot_protected(slot,
1408                                         &mapping->tree_lock), page);
1409                 VM_BUG_ON_PAGE(page_mapped(page), page);
1410
1411                 /*
1412                  * The page is expected to have page_count() == 3:
1413                  *  - we hold a pin on it;
1414                  *  - one reference from radix tree;
1415                  *  - one from isolate_lru_page;
1416                  */
1417                 if (!page_ref_freeze(page, 3)) {
1418                         result = SCAN_PAGE_COUNT;
1419                         goto out_lru;
1420                 }
1421
1422                 /*
1423                  * Add the page to the list to be able to undo the collapse if
1424                  * something go wrong.
1425                  */
1426                 list_add_tail(&page->lru, &pagelist);
1427
1428                 /* Finally, replace with the new page. */
1429                 radix_tree_replace_slot(&mapping->page_tree, slot,
1430                                 new_page + (index % HPAGE_PMD_NR));
1431
1432                 slot = radix_tree_iter_resume(slot, &iter);
1433                 index++;
1434                 continue;
1435 out_lru:
1436                 spin_unlock_irq(&mapping->tree_lock);
1437                 putback_lru_page(page);
1438 out_isolate_failed:
1439                 unlock_page(page);
1440                 put_page(page);
1441                 goto tree_unlocked;
1442 out_unlock:
1443                 unlock_page(page);
1444                 put_page(page);
1445                 break;
1446         }
1447
1448         /*
1449          * Handle hole in radix tree at the end of the range.
1450          * This code only triggers if there's nothing in radix tree
1451          * beyond 'end'.
1452          */
1453         if (result == SCAN_SUCCEED && index < end) {
1454                 int n = end - index;
1455
1456                 if (!shmem_charge(mapping->host, n)) {
1457                         result = SCAN_FAIL;
1458                         goto tree_locked;
1459                 }
1460
1461                 for (; index < end; index++) {
1462                         radix_tree_insert(&mapping->page_tree, index,
1463                                         new_page + (index % HPAGE_PMD_NR));
1464                 }
1465                 nr_none += n;
1466         }
1467
1468 tree_locked:
1469         spin_unlock_irq(&mapping->tree_lock);
1470 tree_unlocked:
1471
1472         if (result == SCAN_SUCCEED) {
1473                 unsigned long flags;
1474                 struct zone *zone = page_zone(new_page);
1475
1476                 /*
1477                  * Replacing old pages with new one has succeed, now we need to
1478                  * copy the content and free old pages.
1479                  */
1480                 list_for_each_entry_safe(page, tmp, &pagelist, lru) {
1481                         copy_highpage(new_page + (page->index % HPAGE_PMD_NR),
1482                                         page);
1483                         list_del(&page->lru);
1484                         unlock_page(page);
1485                         page_ref_unfreeze(page, 1);
1486                         page->mapping = NULL;
1487                         ClearPageActive(page);
1488                         ClearPageUnevictable(page);
1489                         put_page(page);
1490                 }
1491
1492                 local_irq_save(flags);
1493                 __inc_node_page_state(new_page, NR_SHMEM_THPS);
1494                 if (nr_none) {
1495                         __mod_node_page_state(zone->zone_pgdat, NR_FILE_PAGES, nr_none);
1496                         __mod_node_page_state(zone->zone_pgdat, NR_SHMEM, nr_none);
1497                 }
1498                 local_irq_restore(flags);
1499
1500                 /*
1501                  * Remove pte page tables, so we can re-faulti
1502                  * the page as huge.
1503                  */
1504                 retract_page_tables(mapping, start);
1505
1506                 /* Everything is ready, let's unfreeze the new_page */
1507                 set_page_dirty(new_page);
1508                 SetPageUptodate(new_page);
1509                 page_ref_unfreeze(new_page, HPAGE_PMD_NR);
1510                 mem_cgroup_commit_charge(new_page, memcg, false, true);
1511                 lru_cache_add_anon(new_page);
1512                 unlock_page(new_page);
1513
1514                 *hpage = NULL;
1515         } else {
1516                 /* Something went wrong: rollback changes to the radix-tree */
1517                 shmem_uncharge(mapping->host, nr_none);
1518                 spin_lock_irq(&mapping->tree_lock);
1519                 radix_tree_for_each_slot(slot, &mapping->page_tree, &iter,
1520                                 start) {
1521                         if (iter.index >= end)
1522                                 break;
1523                         page = list_first_entry_or_null(&pagelist,
1524                                         struct page, lru);
1525                         if (!page || iter.index < page->index) {
1526                                 if (!nr_none)
1527                                         break;
1528                                 nr_none--;
1529                                 /* Put holes back where they were */
1530                                 radix_tree_delete(&mapping->page_tree,
1531                                                   iter.index);
1532                                 continue;
1533                         }
1534
1535                         VM_BUG_ON_PAGE(page->index != iter.index, page);
1536
1537                         /* Unfreeze the page. */
1538                         list_del(&page->lru);
1539                         page_ref_unfreeze(page, 2);
1540                         radix_tree_replace_slot(&mapping->page_tree,
1541                                                 slot, page);
1542                         slot = radix_tree_iter_resume(slot, &iter);
1543                         spin_unlock_irq(&mapping->tree_lock);
1544                         putback_lru_page(page);
1545                         unlock_page(page);
1546                         spin_lock_irq(&mapping->tree_lock);
1547                 }
1548                 VM_BUG_ON(nr_none);
1549                 spin_unlock_irq(&mapping->tree_lock);
1550
1551                 /* Unfreeze new_page, caller would take care about freeing it */
1552                 page_ref_unfreeze(new_page, 1);
1553                 mem_cgroup_cancel_charge(new_page, memcg, true);
1554                 unlock_page(new_page);
1555                 new_page->mapping = NULL;
1556         }
1557 out:
1558         VM_BUG_ON(!list_empty(&pagelist));
1559         /* TODO: tracepoints */
1560 }
1561
1562 static void khugepaged_scan_shmem(struct mm_struct *mm,
1563                 struct address_space *mapping,
1564                 pgoff_t start, struct page **hpage)
1565 {
1566         struct page *page = NULL;
1567         struct radix_tree_iter iter;
1568         void **slot;
1569         int present, swap;
1570         int node = NUMA_NO_NODE;
1571         int result = SCAN_SUCCEED;
1572
1573         present = 0;
1574         swap = 0;
1575         memset(khugepaged_node_load, 0, sizeof(khugepaged_node_load));
1576         rcu_read_lock();
1577         radix_tree_for_each_slot(slot, &mapping->page_tree, &iter, start) {
1578                 if (iter.index >= start + HPAGE_PMD_NR)
1579                         break;
1580
1581                 page = radix_tree_deref_slot(slot);
1582                 if (radix_tree_deref_retry(page)) {
1583                         slot = radix_tree_iter_retry(&iter);
1584                         continue;
1585                 }
1586
1587                 if (radix_tree_exception(page)) {
1588                         if (++swap > khugepaged_max_ptes_swap) {
1589                                 result = SCAN_EXCEED_SWAP_PTE;
1590                                 break;
1591                         }
1592                         continue;
1593                 }
1594
1595                 if (PageTransCompound(page)) {
1596                         result = SCAN_PAGE_COMPOUND;
1597                         break;
1598                 }
1599
1600                 node = page_to_nid(page);
1601                 if (khugepaged_scan_abort(node)) {
1602                         result = SCAN_SCAN_ABORT;
1603                         break;
1604                 }
1605                 khugepaged_node_load[node]++;
1606
1607                 if (!PageLRU(page)) {
1608                         result = SCAN_PAGE_LRU;
1609                         break;
1610                 }
1611
1612                 if (page_count(page) != 1 + page_mapcount(page)) {
1613                         result = SCAN_PAGE_COUNT;
1614                         break;
1615                 }
1616
1617                 /*
1618                  * We probably should check if the page is referenced here, but
1619                  * nobody would transfer pte_young() to PageReferenced() for us.
1620                  * And rmap walk here is just too costly...
1621                  */
1622
1623                 present++;
1624
1625                 if (need_resched()) {
1626                         slot = radix_tree_iter_resume(slot, &iter);
1627                         cond_resched_rcu();
1628                 }
1629         }
1630         rcu_read_unlock();
1631
1632         if (result == SCAN_SUCCEED) {
1633                 if (present < HPAGE_PMD_NR - khugepaged_max_ptes_none) {
1634                         result = SCAN_EXCEED_NONE_PTE;
1635                 } else {
1636                         node = khugepaged_find_target_node();
1637                         collapse_shmem(mm, mapping, start, hpage, node);
1638                 }
1639         }
1640
1641         /* TODO: tracepoints */
1642 }
1643 #else
1644 static void khugepaged_scan_shmem(struct mm_struct *mm,
1645                 struct address_space *mapping,
1646                 pgoff_t start, struct page **hpage)
1647 {
1648         BUILD_BUG();
1649 }
1650 #endif
1651
1652 static unsigned int khugepaged_scan_mm_slot(unsigned int pages,
1653                                             struct page **hpage)
1654         __releases(&khugepaged_mm_lock)
1655         __acquires(&khugepaged_mm_lock)
1656 {
1657         struct mm_slot *mm_slot;
1658         struct mm_struct *mm;
1659         struct vm_area_struct *vma;
1660         int progress = 0;
1661
1662         VM_BUG_ON(!pages);
1663         VM_BUG_ON(NR_CPUS != 1 && !spin_is_locked(&khugepaged_mm_lock));
1664
1665         if (khugepaged_scan.mm_slot)
1666                 mm_slot = khugepaged_scan.mm_slot;
1667         else {
1668                 mm_slot = list_entry(khugepaged_scan.mm_head.next,
1669                                      struct mm_slot, mm_node);
1670                 khugepaged_scan.address = 0;
1671                 khugepaged_scan.mm_slot = mm_slot;
1672         }
1673         spin_unlock(&khugepaged_mm_lock);
1674
1675         mm = mm_slot->mm;
1676         /*
1677          * Don't wait for semaphore (to avoid long wait times).  Just move to
1678          * the next mm on the list.
1679          */
1680         vma = NULL;
1681         if (unlikely(!down_read_trylock(&mm->mmap_sem)))
1682                 goto breakouterloop_mmap_sem;
1683         if (likely(!khugepaged_test_exit(mm)))
1684                 vma = find_vma(mm, khugepaged_scan.address);
1685
1686         progress++;
1687         for (; vma; vma = vma->vm_next) {
1688                 unsigned long hstart, hend;
1689
1690                 cond_resched();
1691                 if (unlikely(khugepaged_test_exit(mm))) {
1692                         progress++;
1693                         break;
1694                 }
1695                 if (!hugepage_vma_check(vma)) {
1696 skip:
1697                         progress++;
1698                         continue;
1699                 }
1700                 hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK;
1701                 hend = vma->vm_end & HPAGE_PMD_MASK;
1702                 if (hstart >= hend)
1703                         goto skip;
1704                 if (khugepaged_scan.address > hend)
1705                         goto skip;
1706                 if (khugepaged_scan.address < hstart)
1707                         khugepaged_scan.address = hstart;
1708                 VM_BUG_ON(khugepaged_scan.address & ~HPAGE_PMD_MASK);
1709
1710                 while (khugepaged_scan.address < hend) {
1711                         int ret;
1712                         cond_resched();
1713                         if (unlikely(khugepaged_test_exit(mm)))
1714                                 goto breakouterloop;
1715
1716                         VM_BUG_ON(khugepaged_scan.address < hstart ||
1717                                   khugepaged_scan.address + HPAGE_PMD_SIZE >
1718                                   hend);
1719                         if (shmem_file(vma->vm_file)) {
1720                                 struct file *file;
1721                                 pgoff_t pgoff = linear_page_index(vma,
1722                                                 khugepaged_scan.address);
1723                                 if (!shmem_huge_enabled(vma))
1724                                         goto skip;
1725                                 file = get_file(vma->vm_file);
1726                                 up_read(&mm->mmap_sem);
1727                                 ret = 1;
1728                                 khugepaged_scan_shmem(mm, file->f_mapping,
1729                                                 pgoff, hpage);
1730                                 fput(file);
1731                         } else {
1732                                 ret = khugepaged_scan_pmd(mm, vma,
1733                                                 khugepaged_scan.address,
1734                                                 hpage);
1735                         }
1736                         /* move to next address */
1737                         khugepaged_scan.address += HPAGE_PMD_SIZE;
1738                         progress += HPAGE_PMD_NR;
1739                         if (ret)
1740                                 /* we released mmap_sem so break loop */
1741                                 goto breakouterloop_mmap_sem;
1742                         if (progress >= pages)
1743                                 goto breakouterloop;
1744                 }
1745         }
1746 breakouterloop:
1747         up_read(&mm->mmap_sem); /* exit_mmap will destroy ptes after this */
1748 breakouterloop_mmap_sem:
1749
1750         spin_lock(&khugepaged_mm_lock);
1751         VM_BUG_ON(khugepaged_scan.mm_slot != mm_slot);
1752         /*
1753          * Release the current mm_slot if this mm is about to die, or
1754          * if we scanned all vmas of this mm.
1755          */
1756         if (khugepaged_test_exit(mm) || !vma) {
1757                 /*
1758                  * Make sure that if mm_users is reaching zero while
1759                  * khugepaged runs here, khugepaged_exit will find
1760                  * mm_slot not pointing to the exiting mm.
1761                  */
1762                 if (mm_slot->mm_node.next != &khugepaged_scan.mm_head) {
1763                         khugepaged_scan.mm_slot = list_entry(
1764                                 mm_slot->mm_node.next,
1765                                 struct mm_slot, mm_node);
1766                         khugepaged_scan.address = 0;
1767                 } else {
1768                         khugepaged_scan.mm_slot = NULL;
1769                         khugepaged_full_scans++;
1770                 }
1771
1772                 collect_mm_slot(mm_slot);
1773         }
1774
1775         return progress;
1776 }
1777
1778 static int khugepaged_has_work(void)
1779 {
1780         return !list_empty(&khugepaged_scan.mm_head) &&
1781                 khugepaged_enabled();
1782 }
1783
1784 static int khugepaged_wait_event(void)
1785 {
1786         return !list_empty(&khugepaged_scan.mm_head) ||
1787                 kthread_should_stop();
1788 }
1789
1790 static void khugepaged_do_scan(void)
1791 {
1792         struct page *hpage = NULL;
1793         unsigned int progress = 0, pass_through_head = 0;
1794         unsigned int pages = khugepaged_pages_to_scan;
1795         bool wait = true;
1796
1797         barrier(); /* write khugepaged_pages_to_scan to local stack */
1798
1799         while (progress < pages) {
1800                 if (!khugepaged_prealloc_page(&hpage, &wait))
1801                         break;
1802
1803                 cond_resched();
1804
1805                 if (unlikely(kthread_should_stop() || try_to_freeze()))
1806                         break;
1807
1808                 spin_lock(&khugepaged_mm_lock);
1809                 if (!khugepaged_scan.mm_slot)
1810                         pass_through_head++;
1811                 if (khugepaged_has_work() &&
1812                     pass_through_head < 2)
1813                         progress += khugepaged_scan_mm_slot(pages - progress,
1814                                                             &hpage);
1815                 else
1816                         progress = pages;
1817                 spin_unlock(&khugepaged_mm_lock);
1818         }
1819
1820         if (!IS_ERR_OR_NULL(hpage))
1821                 put_page(hpage);
1822 }
1823
1824 static bool khugepaged_should_wakeup(void)
1825 {
1826         return kthread_should_stop() ||
1827                time_after_eq(jiffies, khugepaged_sleep_expire);
1828 }
1829
1830 static void khugepaged_wait_work(void)
1831 {
1832         if (khugepaged_has_work()) {
1833                 const unsigned long scan_sleep_jiffies =
1834                         msecs_to_jiffies(khugepaged_scan_sleep_millisecs);
1835
1836                 if (!scan_sleep_jiffies)
1837                         return;
1838
1839                 khugepaged_sleep_expire = jiffies + scan_sleep_jiffies;
1840                 wait_event_freezable_timeout(khugepaged_wait,
1841                                              khugepaged_should_wakeup(),
1842                                              scan_sleep_jiffies);
1843                 return;
1844         }
1845
1846         if (khugepaged_enabled())
1847                 wait_event_freezable(khugepaged_wait, khugepaged_wait_event());
1848 }
1849
1850 static int khugepaged(void *none)
1851 {
1852         struct mm_slot *mm_slot;
1853
1854         set_freezable();
1855         set_user_nice(current, MAX_NICE);
1856
1857         while (!kthread_should_stop()) {
1858                 khugepaged_do_scan();
1859                 khugepaged_wait_work();
1860         }
1861
1862         spin_lock(&khugepaged_mm_lock);
1863         mm_slot = khugepaged_scan.mm_slot;
1864         khugepaged_scan.mm_slot = NULL;
1865         if (mm_slot)
1866                 collect_mm_slot(mm_slot);
1867         spin_unlock(&khugepaged_mm_lock);
1868         return 0;
1869 }
1870
1871 static void set_recommended_min_free_kbytes(void)
1872 {
1873         struct zone *zone;
1874         int nr_zones = 0;
1875         unsigned long recommended_min;
1876
1877         for_each_populated_zone(zone)
1878                 nr_zones++;
1879
1880         /* Ensure 2 pageblocks are free to assist fragmentation avoidance */
1881         recommended_min = pageblock_nr_pages * nr_zones * 2;
1882
1883         /*
1884          * Make sure that on average at least two pageblocks are almost free
1885          * of another type, one for a migratetype to fall back to and a
1886          * second to avoid subsequent fallbacks of other types There are 3
1887          * MIGRATE_TYPES we care about.
1888          */
1889         recommended_min += pageblock_nr_pages * nr_zones *
1890                            MIGRATE_PCPTYPES * MIGRATE_PCPTYPES;
1891
1892         /* don't ever allow to reserve more than 5% of the lowmem */
1893         recommended_min = min(recommended_min,
1894                               (unsigned long) nr_free_buffer_pages() / 20);
1895         recommended_min <<= (PAGE_SHIFT-10);
1896
1897         if (recommended_min > min_free_kbytes) {
1898                 if (user_min_free_kbytes >= 0)
1899                         pr_info("raising min_free_kbytes from %d to %lu to help transparent hugepage allocations\n",
1900                                 min_free_kbytes, recommended_min);
1901
1902                 min_free_kbytes = recommended_min;
1903         }
1904         setup_per_zone_wmarks();
1905 }
1906
1907 int start_stop_khugepaged(void)
1908 {
1909         static struct task_struct *khugepaged_thread __read_mostly;
1910         static DEFINE_MUTEX(khugepaged_mutex);
1911         int err = 0;
1912
1913         mutex_lock(&khugepaged_mutex);
1914         if (khugepaged_enabled()) {
1915                 if (!khugepaged_thread)
1916                         khugepaged_thread = kthread_run(khugepaged, NULL,
1917                                                         "khugepaged");
1918                 if (IS_ERR(khugepaged_thread)) {
1919                         pr_err("khugepaged: kthread_run(khugepaged) failed\n");
1920                         err = PTR_ERR(khugepaged_thread);
1921                         khugepaged_thread = NULL;
1922                         goto fail;
1923                 }
1924
1925                 if (!list_empty(&khugepaged_scan.mm_head))
1926                         wake_up_interruptible(&khugepaged_wait);
1927
1928                 set_recommended_min_free_kbytes();
1929         } else if (khugepaged_thread) {
1930                 kthread_stop(khugepaged_thread);
1931                 khugepaged_thread = NULL;
1932         }
1933 fail:
1934         mutex_unlock(&khugepaged_mutex);
1935         return err;
1936 }