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         SCAN_PAGE_HAS_PRIVATE,
  52 };
  53
  54 #define CREATE_TRACE_POINTS
  55 #include <trace/events/huge_memory.h>
  56
  57 static struct task_struct *khugepaged_thread __read_mostly;
  58 static DEFINE_MUTEX(khugepaged_mutex);
  59
  60 /* default scan 8*512 pte (or vmas) every 30 second */
  61 static unsigned int khugepaged_pages_to_scan __read_mostly;
  62 static unsigned int khugepaged_pages_collapsed;
  63 static unsigned int khugepaged_full_scans;
  64 static unsigned int khugepaged_scan_sleep_millisecs __read_mostly = 10000;
  65 /* during fragmentation poll the hugepage allocator once every minute */
  66 static unsigned int khugepaged_alloc_sleep_millisecs __read_mostly = 60000;
  67 static unsigned long khugepaged_sleep_expire;
  68 static DEFINE_SPINLOCK(khugepaged_mm_lock);
  69 static DECLARE_WAIT_QUEUE_HEAD(khugepaged_wait);
  70 /*
  71  * default collapse hugepages if there is at least one pte mapped like
  72  * it would have happened if the vma was large enough during page
  73  * fault.
  74  */
  75 static unsigned int khugepaged_max_ptes_none __read_mostly;
  76 static unsigned int khugepaged_max_ptes_swap __read_mostly;
  77
  78 #define MM_SLOTS_HASH_BITS 10
  79 static __read_mostly DEFINE_HASHTABLE(mm_slots_hash, MM_SLOTS_HASH_BITS);
  80
  81 static struct kmem_cache *mm_slot_cache __read_mostly;
  82
  83 #define MAX_PTE_MAPPED_THP 8
  84
  85 /**
  86  * struct mm_slot - hash lookup from mm to mm_slot
  87  * @hash: hash collision list
  88  * @mm_node: khugepaged scan list headed in khugepaged_scan.mm_head
  89  * @mm: the mm that this information is valid for
  90  */
  91 struct mm_slot {
  92         struct hlist_node hash;
  93         struct list_head mm_node;
  94         struct mm_struct *mm;
  95
  96         /* pte-mapped THP in this mm */
  97         int nr_pte_mapped_thp;
  98         unsigned long pte_mapped_thp[MAX_PTE_MAPPED_THP];
  99 };
 100
 101 /**
 102  * struct khugepaged_scan - cursor for scanning
 103  * @mm_head: the head of the mm list to scan
 104  * @mm_slot: the current mm_slot we are scanning
 105  * @address: the next address inside that to be scanned
 106  *
 107  * There is only the one khugepaged_scan instance of this cursor structure.
 108  */
 109 struct khugepaged_scan {
 110         struct list_head mm_head;
 111         struct mm_slot *mm_slot;
 112         unsigned long address;
 113 };
 114
 115 static struct khugepaged_scan khugepaged_scan = {
 116         .mm_head = LIST_HEAD_INIT(khugepaged_scan.mm_head),
 117 };
 118
 119 #ifdef CONFIG_SYSFS
 120 static ssize_t scan_sleep_millisecs_show(struct kobject *kobj,
 121                                          struct kobj_attribute *attr,
 122                                          char *buf)
 123 {
 124         return sprintf(buf, "%u\n", khugepaged_scan_sleep_millisecs);
 125 }
 126
 127 static ssize_t scan_sleep_millisecs_store(struct kobject *kobj,
 128                                           struct kobj_attribute *attr,
 129                                           const char *buf, size_t count)
 130 {
 131         unsigned long msecs;
 132         int err;
 133
 134         err = kstrtoul(buf, 10, &msecs);
 135         if (err || msecs > UINT_MAX)
 136                 return -EINVAL;
 137
 138         khugepaged_scan_sleep_millisecs = msecs;
 139         khugepaged_sleep_expire = 0;
 140         wake_up_interruptible(&khugepaged_wait);
 141
 142         return count;
 143 }
 144 static struct kobj_attribute scan_sleep_millisecs_attr =
 145         __ATTR(scan_sleep_millisecs, 0644, scan_sleep_millisecs_show,
 146                scan_sleep_millisecs_store);
 147
 148 static ssize_t alloc_sleep_millisecs_show(struct kobject *kobj,
 149                                           struct kobj_attribute *attr,
 150                                           char *buf)
 151 {
 152         return sprintf(buf, "%u\n", khugepaged_alloc_sleep_millisecs);
 153 }
 154
 155 static ssize_t alloc_sleep_millisecs_store(struct kobject *kobj,
 156                                            struct kobj_attribute *attr,
 157                                            const char *buf, size_t count)
 158 {
 159         unsigned long msecs;
 160         int err;
 161
 162         err = kstrtoul(buf, 10, &msecs);
 163         if (err || msecs > UINT_MAX)
 164                 return -EINVAL;
 165
 166         khugepaged_alloc_sleep_millisecs = msecs;
 167         khugepaged_sleep_expire = 0;
 168         wake_up_interruptible(&khugepaged_wait);
 169
 170         return count;
 171 }
 172 static struct kobj_attribute alloc_sleep_millisecs_attr =
 173         __ATTR(alloc_sleep_millisecs, 0644, alloc_sleep_millisecs_show,
 174                alloc_sleep_millisecs_store);
 175
 176 static ssize_t pages_to_scan_show(struct kobject *kobj,
 177                                   struct kobj_attribute *attr,
 178                                   char *buf)
 179 {
 180         return sprintf(buf, "%u\n", khugepaged_pages_to_scan);
 181 }
 182 static ssize_t pages_to_scan_store(struct kobject *kobj,
 183                                    struct kobj_attribute *attr,
 184                                    const char *buf, size_t count)
 185 {
 186         int err;
 187         unsigned long pages;
 188
 189         err = kstrtoul(buf, 10, &pages);
 190         if (err || !pages || pages > UINT_MAX)
 191                 return -EINVAL;
 192
 193         khugepaged_pages_to_scan = pages;
 194
 195         return count;
 196 }
 197 static struct kobj_attribute pages_to_scan_attr =
 198         __ATTR(pages_to_scan, 0644, pages_to_scan_show,
 199                pages_to_scan_store);
 200
 201 static ssize_t pages_collapsed_show(struct kobject *kobj,
 202                                     struct kobj_attribute *attr,
 203                                     char *buf)
 204 {
 205         return sprintf(buf, "%u\n", khugepaged_pages_collapsed);
 206 }
 207 static struct kobj_attribute pages_collapsed_attr =
 208         __ATTR_RO(pages_collapsed);
 209
 210 static ssize_t full_scans_show(struct kobject *kobj,
 211                                struct kobj_attribute *attr,
 212                                char *buf)
 213 {
 214         return sprintf(buf, "%u\n", khugepaged_full_scans);
 215 }
 216 static struct kobj_attribute full_scans_attr =
 217         __ATTR_RO(full_scans);
 218
 219 static ssize_t khugepaged_defrag_show(struct kobject *kobj,
 220                                       struct kobj_attribute *attr, char *buf)
 221 {
 222         return single_hugepage_flag_show(kobj, attr, buf,
 223                                 TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG);
 224 }
 225 static ssize_t khugepaged_defrag_store(struct kobject *kobj,
 226                                        struct kobj_attribute *attr,
 227                                        const char *buf, size_t count)
 228 {
 229         return single_hugepage_flag_store(kobj, attr, buf, count,
 230                                  TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG);
 231 }
 232 static struct kobj_attribute khugepaged_defrag_attr =
 233         __ATTR(defrag, 0644, khugepaged_defrag_show,
 234                khugepaged_defrag_store);
 235
 236 /*
 237  * max_ptes_none controls if khugepaged should collapse hugepages over
 238  * any unmapped ptes in turn potentially increasing the memory
 239  * footprint of the vmas. When max_ptes_none is 0 khugepaged will not
 240  * reduce the available free memory in the system as it
 241  * runs. Increasing max_ptes_none will instead potentially reduce the
 242  * free memory in the system during the khugepaged scan.
 243  */
 244 static ssize_t khugepaged_max_ptes_none_show(struct kobject *kobj,
 245                                              struct kobj_attribute *attr,
 246                                              char *buf)
 247 {
 248         return sprintf(buf, "%u\n", khugepaged_max_ptes_none);
 249 }
 250 static ssize_t khugepaged_max_ptes_none_store(struct kobject *kobj,
 251                                               struct kobj_attribute *attr,
 252                                               const char *buf, size_t count)
 253 {
 254         int err;
 255         unsigned long max_ptes_none;
 256
 257         err = kstrtoul(buf, 10, &max_ptes_none);
 258         if (err || max_ptes_none > HPAGE_PMD_NR-1)
 259                 return -EINVAL;
 260
 261         khugepaged_max_ptes_none = max_ptes_none;
 262
 263         return count;
 264 }
 265 static struct kobj_attribute khugepaged_max_ptes_none_attr =
 266         __ATTR(max_ptes_none, 0644, khugepaged_max_ptes_none_show,
 267                khugepaged_max_ptes_none_store);
 268
 269 static ssize_t khugepaged_max_ptes_swap_show(struct kobject *kobj,
 270                                              struct kobj_attribute *attr,
 271                                              char *buf)
 272 {
 273         return sprintf(buf, "%u\n", khugepaged_max_ptes_swap);
 274 }
 275
 276 static ssize_t khugepaged_max_ptes_swap_store(struct kobject *kobj,
 277                                               struct kobj_attribute *attr,
 278                                               const char *buf, size_t count)
 279 {
 280         int err;
 281         unsigned long max_ptes_swap;
 282
 283         err  = kstrtoul(buf, 10, &max_ptes_swap);
 284         if (err || max_ptes_swap > HPAGE_PMD_NR-1)
 285                 return -EINVAL;
 286
 287         khugepaged_max_ptes_swap = max_ptes_swap;
 288
 289         return count;
 290 }
 291
 292 static struct kobj_attribute khugepaged_max_ptes_swap_attr =
 293         __ATTR(max_ptes_swap, 0644, khugepaged_max_ptes_swap_show,
 294                khugepaged_max_ptes_swap_store);
 295
 296 static struct attribute *khugepaged_attr[] = {
 297         &khugepaged_defrag_attr.attr,
 298         &khugepaged_max_ptes_none_attr.attr,
 299         &pages_to_scan_attr.attr,
 300         &pages_collapsed_attr.attr,
 301         &full_scans_attr.attr,
 302         &scan_sleep_millisecs_attr.attr,
 303         &alloc_sleep_millisecs_attr.attr,
 304         &khugepaged_max_ptes_swap_attr.attr,
 305         NULL,
 306 };
 307
 308 struct attribute_group khugepaged_attr_group = {
 309         .attrs = khugepaged_attr,
 310         .name = "khugepaged",
 311 };
 312 #endif /* CONFIG_SYSFS */
 313
 314 #define VM_NO_KHUGEPAGED (VM_SPECIAL | VM_HUGETLB)
 315
 316 int hugepage_madvise(struct vm_area_struct *vma,
 317                      unsigned long *vm_flags, int advice)
 318 {
 319         switch (advice) {
 320         case MADV_HUGEPAGE:
 321 #ifdef CONFIG_S390
 322                 /*
 323                  * qemu blindly sets MADV_HUGEPAGE on all allocations, but s390
 324                  * can't handle this properly after s390_enable_sie, so we simply
 325                  * ignore the madvise to prevent qemu from causing a SIGSEGV.
 326                  */
 327                 if (mm_has_pgste(vma->vm_mm))
 328                         return 0;
 329 #endif
 330                 *vm_flags &= ~VM_NOHUGEPAGE;
 331                 *vm_flags |= VM_HUGEPAGE;
 332                 /*
 333                  * If the vma become good for khugepaged to scan,
 334                  * register it here without waiting a page fault that
 335                  * may not happen any time soon.
 336                  */
 337                 if (!(*vm_flags & VM_NO_KHUGEPAGED) &&
 338                                 khugepaged_enter_vma_merge(vma, *vm_flags))
 339                         return -ENOMEM;
 340                 break;
 341         case MADV_NOHUGEPAGE:
 342                 *vm_flags &= ~VM_HUGEPAGE;
 343                 *vm_flags |= VM_NOHUGEPAGE;
 344                 /*
 345                  * Setting VM_NOHUGEPAGE will prevent khugepaged from scanning
 346                  * this vma even if we leave the mm registered in khugepaged if
 347                  * it got registered before VM_NOHUGEPAGE was set.
 348                  */
 349                 break;
 350         }
 351
 352         return 0;
 353 }
 354
 355 int __init khugepaged_init(void)
 356 {
 357         mm_slot_cache = kmem_cache_create("khugepaged_mm_slot",
 358                                           sizeof(struct mm_slot),
 359                                           __alignof__(struct mm_slot), 0, NULL);
 360         if (!mm_slot_cache)
 361                 return -ENOMEM;
 362
 363         khugepaged_pages_to_scan = HPAGE_PMD_NR * 8;
 364         khugepaged_max_ptes_none = HPAGE_PMD_NR - 1;
 365         khugepaged_max_ptes_swap = HPAGE_PMD_NR / 8;
 366
 367         return 0;
 368 }
 369
 370 void __init khugepaged_destroy(void)
 371 {
 372         kmem_cache_destroy(mm_slot_cache);
 373 }
 374
 375 static inline struct mm_slot *alloc_mm_slot(void)
 376 {
 377         if (!mm_slot_cache)     /* initialization failed */
 378                 return NULL;
 379         return kmem_cache_zalloc(mm_slot_cache, GFP_KERNEL);
 380 }
 381
 382 static inline void free_mm_slot(struct mm_slot *mm_slot)
 383 {
 384         kmem_cache_free(mm_slot_cache, mm_slot);
 385 }
 386
 387 static struct mm_slot *get_mm_slot(struct mm_struct *mm)
 388 {
 389         struct mm_slot *mm_slot;
 390
 391         hash_for_each_possible(mm_slots_hash, mm_slot, hash, (unsigned long)mm)
 392                 if (mm == mm_slot->mm)
 393                         return mm_slot;
 394
 395         return NULL;
 396 }
 397
 398 static void insert_to_mm_slots_hash(struct mm_struct *mm,
 399                                     struct mm_slot *mm_slot)
 400 {
 401         mm_slot->mm = mm;
 402         hash_add(mm_slots_hash, &mm_slot->hash, (long)mm);
 403 }
 404
 405 static inline int khugepaged_test_exit(struct mm_struct *mm)
 406 {
 407         return atomic_read(&mm->mm_users) == 0 || !mmget_still_valid(mm);
 408 }
 409
 410 static bool hugepage_vma_check(struct vm_area_struct *vma,
 411                                unsigned long vm_flags)
 412 {
 413         if ((!(vm_flags & VM_HUGEPAGE) && !khugepaged_always()) ||
 414             (vm_flags & VM_NOHUGEPAGE) ||
 415             test_bit(MMF_DISABLE_THP, &vma->vm_mm->flags))
 416                 return false;
 417
 418         if (shmem_file(vma->vm_file) ||
 419             (IS_ENABLED(CONFIG_READ_ONLY_THP_FOR_FS) &&
 420              vma->vm_file &&
 421              (vm_flags & VM_DENYWRITE))) {
 422                 if (!IS_ENABLED(CONFIG_TRANSPARENT_HUGE_PAGECACHE))
 423                         return false;
 424                 return IS_ALIGNED((vma->vm_start >> PAGE_SHIFT) - vma->vm_pgoff,
 425                                 HPAGE_PMD_NR);
 426         }
 427         if (!vma->anon_vma || vma->vm_ops)
 428                 return false;
 429         if (is_vma_temporary_stack(vma))
 430                 return false;
 431         return !(vm_flags & VM_NO_KHUGEPAGED);
 432 }
 433
 434 int __khugepaged_enter(struct mm_struct *mm)
 435 {
 436         struct mm_slot *mm_slot;
 437         int wakeup;
 438
 439         mm_slot = alloc_mm_slot();
 440         if (!mm_slot)
 441                 return -ENOMEM;
 442
 443         /* __khugepaged_exit() must not run from under us */
 444         VM_BUG_ON_MM(atomic_read(&mm->mm_users) == 0, mm);
 445         if (unlikely(test_and_set_bit(MMF_VM_HUGEPAGE, &mm->flags))) {
 446                 free_mm_slot(mm_slot);
 447                 return 0;
 448         }
 449
 450         spin_lock(&khugepaged_mm_lock);
 451         insert_to_mm_slots_hash(mm, mm_slot);
 452         /*
 453          * Insert just behind the scanning cursor, to let the area settle
 454          * down a little.
 455          */
 456         wakeup = list_empty(&khugepaged_scan.mm_head);
 457         list_add_tail(&mm_slot->mm_node, &khugepaged_scan.mm_head);
 458         spin_unlock(&khugepaged_mm_lock);
 459
 460         mmgrab(mm);
 461         if (wakeup)
 462                 wake_up_interruptible(&khugepaged_wait);
 463
 464         return 0;
 465 }
 466
 467 int khugepaged_enter_vma_merge(struct vm_area_struct *vma,
 468                                unsigned long vm_flags)
 469 {
 470         unsigned long hstart, hend;
 471
 472         /*
 473          * khugepaged only supports read-only files for non-shmem files.
 474          * khugepaged does not yet work on special mappings. And
 475          * file-private shmem THP is not supported.
 476          */
 477         if (!hugepage_vma_check(vma, vm_flags))
 478                 return 0;
 479
 480         hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK;
 481         hend = vma->vm_end & HPAGE_PMD_MASK;
 482         if (hstart < hend)
 483                 return khugepaged_enter(vma, vm_flags);
 484         return 0;
 485 }
 486
 487 void __khugepaged_exit(struct mm_struct *mm)
 488 {
 489         struct mm_slot *mm_slot;
 490         int free = 0;
 491
 492         spin_lock(&khugepaged_mm_lock);
 493         mm_slot = get_mm_slot(mm);
 494         if (mm_slot && khugepaged_scan.mm_slot != mm_slot) {
 495                 hash_del(&mm_slot->hash);
 496                 list_del(&mm_slot->mm_node);
 497                 free = 1;
 498         }
 499         spin_unlock(&khugepaged_mm_lock);
 500
 501         if (free) {
 502                 clear_bit(MMF_VM_HUGEPAGE, &mm->flags);
 503                 free_mm_slot(mm_slot);
 504                 mmdrop(mm);
 505         } else if (mm_slot) {
 506                 /*
 507                  * This is required to serialize against
 508                  * khugepaged_test_exit() (which is guaranteed to run
 509                  * under mmap sem read mode). Stop here (after we
 510                  * return all pagetables will be destroyed) until
 511                  * khugepaged has finished working on the pagetables
 512                  * under the mmap_sem.
 513                  */
 514                 down_write(&mm->mmap_sem);
 515                 up_write(&mm->mmap_sem);
 516         }
 517 }
 518
 519 static void release_pte_page(struct page *page)
 520 {
 521         dec_node_page_state(page, NR_ISOLATED_ANON + page_is_file_cache(page));
 522         unlock_page(page);
 523         putback_lru_page(page);
 524 }
 525
 526 static void release_pte_pages(pte_t *pte, pte_t *_pte)
 527 {
 528         while (--_pte >= pte) {
 529                 pte_t pteval = *_pte;
 530                 if (!pte_none(pteval) && !is_zero_pfn(pte_pfn(pteval)))
 531                         release_pte_page(pte_page(pteval));
 532         }
 533 }
 534
 535 static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
 536                                         unsigned long address,
 537                                         pte_t *pte)
 538 {
 539         struct page *page = NULL;
 540         pte_t *_pte;
 541         int none_or_zero = 0, result = 0, referenced = 0;
 542         bool writable = false;
 543
 544         for (_pte = pte; _pte < pte+HPAGE_PMD_NR;
 545              _pte++, address += PAGE_SIZE) {
 546                 pte_t pteval = *_pte;
 547                 if (pte_none(pteval) || (pte_present(pteval) &&
 548                                 is_zero_pfn(pte_pfn(pteval)))) {
 549                         if (!userfaultfd_armed(vma) &&
 550                             ++none_or_zero <= khugepaged_max_ptes_none) {
 551                                 continue;
 552                         } else {
 553                                 result = SCAN_EXCEED_NONE_PTE;
 554                                 goto out;
 555                         }
 556                 }
 557                 if (!pte_present(pteval)) {
 558                         result = SCAN_PTE_NON_PRESENT;
 559                         goto out;
 560                 }
 561                 page = vm_normal_page(vma, address, pteval);
 562                 if (unlikely(!page)) {
 563                         result = SCAN_PAGE_NULL;
 564                         goto out;
 565                 }
 566
 567                 /* TODO: teach khugepaged to collapse THP mapped with pte */
 568                 if (PageCompound(page)) {
 569                         result = SCAN_PAGE_COMPOUND;
 570                         goto out;
 571                 }
 572
 573                 VM_BUG_ON_PAGE(!PageAnon(page), page);
 574
 575                 /*
 576                  * We can do it before isolate_lru_page because the
 577                  * page can't be freed from under us. NOTE: PG_lock
 578                  * is needed to serialize against split_huge_page
 579                  * when invoked from the VM.
 580                  */
 581                 if (!trylock_page(page)) {
 582                         result = SCAN_PAGE_LOCK;
 583                         goto out;
 584                 }
 585
 586                 /*
 587                  * cannot use mapcount: can't collapse if there's a gup pin.
 588                  * The page must only be referenced by the scanned process
 589                  * and page swap cache.
 590                  */
 591                 if (page_count(page) != 1 + PageSwapCache(page)) {
 592                         unlock_page(page);
 593                         result = SCAN_PAGE_COUNT;
 594                         goto out;
 595                 }
 596                 if (pte_write(pteval)) {
 597                         writable = true;
 598                 } else {
 599                         if (PageSwapCache(page) &&
 600                             !reuse_swap_page(page, NULL)) {
 601                                 unlock_page(page);
 602                                 result = SCAN_SWAP_CACHE_PAGE;
 603                                 goto out;
 604                         }
 605                         /*
 606                          * Page is not in the swap cache. It can be collapsed
 607                          * into a THP.
 608                          */
 609                 }
 610
 611                 /*
 612                  * Isolate the page to avoid collapsing an hugepage
 613                  * currently in use by the VM.
 614                  */
 615                 if (isolate_lru_page(page)) {
 616                         unlock_page(page);
 617                         result = SCAN_DEL_PAGE_LRU;
 618                         goto out;
 619                 }
 620                 inc_node_page_state(page,
 621                                 NR_ISOLATED_ANON + page_is_file_cache(page));
 622                 VM_BUG_ON_PAGE(!PageLocked(page), page);
 623                 VM_BUG_ON_PAGE(PageLRU(page), page);
 624
 625                 /* There should be enough young pte to collapse the page */
 626                 if (pte_young(pteval) ||
 627                     page_is_young(page) || PageReferenced(page) ||
 628                     mmu_notifier_test_young(vma->vm_mm, address))
 629                         referenced++;
 630         }
 631
 632         if (unlikely(!writable)) {
 633                 result = SCAN_PAGE_RO;
 634         } else if (unlikely(!referenced)) {
 635                 result = SCAN_LACK_REFERENCED_PAGE;
 636         } else {
 637                 result = SCAN_SUCCEED;
 638                 trace_mm_collapse_huge_page_isolate(page, none_or_zero,
 639                                                     referenced, writable, result);
 640                 return 1;
 641         }
 642 out:
 643         release_pte_pages(pte, _pte);
 644         trace_mm_collapse_huge_page_isolate(page, none_or_zero,
 645                                             referenced, writable, result);
 646         return 0;
 647 }
 648
 649 static void __collapse_huge_page_copy(pte_t *pte, struct page *page,
 650                                       struct vm_area_struct *vma,
 651                                       unsigned long address,
 652                                       spinlock_t *ptl)
 653 {
 654         pte_t *_pte;
 655         for (_pte = pte; _pte < pte + HPAGE_PMD_NR;
 656                                 _pte++, page++, address += PAGE_SIZE) {
 657                 pte_t pteval = *_pte;
 658                 struct page *src_page;
 659
 660                 if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) {
 661                         clear_user_highpage(page, address);
 662                         add_mm_counter(vma->vm_mm, MM_ANONPAGES, 1);
 663                         if (is_zero_pfn(pte_pfn(pteval))) {
 664                                 /*
 665                                  * ptl mostly unnecessary.
 666                                  */
 667                                 spin_lock(ptl);
 668                                 /*
 669                                  * paravirt calls inside pte_clear here are
 670                                  * superfluous.
 671                                  */
 672                                 pte_clear(vma->vm_mm, address, _pte);
 673                                 spin_unlock(ptl);
 674                         }
 675                 } else {
 676                         src_page = pte_page(pteval);
 677                         copy_user_highpage(page, src_page, address, vma);
 678                         VM_BUG_ON_PAGE(page_mapcount(src_page) != 1, src_page);
 679                         release_pte_page(src_page);
 680                         /*
 681                          * ptl mostly unnecessary, but preempt has to
 682                          * be disabled to update the per-cpu stats
 683                          * inside page_remove_rmap().
 684                          */
 685                         spin_lock(ptl);
 686                         /*
 687                          * paravirt calls inside pte_clear here are
 688                          * superfluous.
 689                          */
 690                         pte_clear(vma->vm_mm, address, _pte);
 691                         page_remove_rmap(src_page, false);
 692                         spin_unlock(ptl);
 693                         free_page_and_swap_cache(src_page);
 694                 }
 695         }
 696 }
 697
 698 static void khugepaged_alloc_sleep(void)
 699 {
 700         DEFINE_WAIT(wait);
 701
 702         add_wait_queue(&khugepaged_wait, &wait);
 703         freezable_schedule_timeout_interruptible(
 704                 msecs_to_jiffies(khugepaged_alloc_sleep_millisecs));
 705         remove_wait_queue(&khugepaged_wait, &wait);
 706 }
 707
 708 static int khugepaged_node_load[MAX_NUMNODES];
 709
 710 static bool khugepaged_scan_abort(int nid)
 711 {
 712         int i;
 713
 714         /*
 715          * If node_reclaim_mode is disabled, then no extra effort is made to
 716          * allocate memory locally.
 717          */
 718         if (!node_reclaim_mode)
 719                 return false;
 720
 721         /* If there is a count for this node already, it must be acceptable */
 722         if (khugepaged_node_load[nid])
 723                 return false;
 724
 725         for (i = 0; i < MAX_NUMNODES; i++) {
 726                 if (!khugepaged_node_load[i])
 727                         continue;
 728                 if (node_distance(nid, i) > node_reclaim_distance)
 729                         return true;
 730         }
 731         return false;
 732 }
 733
 734 /* Defrag for khugepaged will enter direct reclaim/compaction if necessary */
 735 static inline gfp_t alloc_hugepage_khugepaged_gfpmask(void)
 736 {
 737         return khugepaged_defrag() ? GFP_TRANSHUGE : GFP_TRANSHUGE_LIGHT;
 738 }
 739
 740 #ifdef CONFIG_NUMA
 741 static int khugepaged_find_target_node(void)
 742 {
 743         static int last_khugepaged_target_node = NUMA_NO_NODE;
 744         int nid, target_node = 0, max_value = 0;
 745
 746         /* find first node with max normal pages hit */
 747         for (nid = 0; nid < MAX_NUMNODES; nid++)
 748                 if (khugepaged_node_load[nid] > max_value) {
 749                         max_value = khugepaged_node_load[nid];
 750                         target_node = nid;
 751                 }
 752
 753         /* do some balance if several nodes have the same hit record */
 754         if (target_node <= last_khugepaged_target_node)
 755                 for (nid = last_khugepaged_target_node + 1; nid < MAX_NUMNODES;
 756                                 nid++)
 757                         if (max_value == khugepaged_node_load[nid]) {
 758                                 target_node = nid;
 759                                 break;
 760                         }
 761
 762         last_khugepaged_target_node = target_node;
 763         return target_node;
 764 }
 765
 766 static bool khugepaged_prealloc_page(struct page **hpage, bool *wait)
 767 {
 768         if (IS_ERR(*hpage)) {
 769                 if (!*wait)
 770                         return false;
 771
 772                 *wait = false;
 773                 *hpage = NULL;
 774                 khugepaged_alloc_sleep();
 775         } else if (*hpage) {
 776                 put_page(*hpage);
 777                 *hpage = NULL;
 778         }
 779
 780         return true;
 781 }
 782
 783 static struct page *
 784 khugepaged_alloc_page(struct page **hpage, gfp_t gfp, int node)
 785 {
 786         VM_BUG_ON_PAGE(*hpage, *hpage);
 787
 788         *hpage = __alloc_pages_node(node, gfp, HPAGE_PMD_ORDER);
 789         if (unlikely(!*hpage)) {
 790                 count_vm_event(THP_COLLAPSE_ALLOC_FAILED);
 791                 *hpage = ERR_PTR(-ENOMEM);
 792                 return NULL;
 793         }
 794
 795         prep_transhuge_page(*hpage);
 796         count_vm_event(THP_COLLAPSE_ALLOC);
 797         return *hpage;
 798 }
 799 #else
 800 static int khugepaged_find_target_node(void)
 801 {
 802         return 0;
 803 }
 804
 805 static inline struct page *alloc_khugepaged_hugepage(void)
 806 {
 807         struct page *page;
 808
 809         page = alloc_pages(alloc_hugepage_khugepaged_gfpmask(),
 810                            HPAGE_PMD_ORDER);
 811         if (page)
 812                 prep_transhuge_page(page);
 813         return page;
 814 }
 815
 816 static struct page *khugepaged_alloc_hugepage(bool *wait)
 817 {
 818         struct page *hpage;
 819
 820         do {
 821                 hpage = alloc_khugepaged_hugepage();
 822                 if (!hpage) {
 823                         count_vm_event(THP_COLLAPSE_ALLOC_FAILED);
 824                         if (!*wait)
 825                                 return NULL;
 826
 827                         *wait = false;
 828                         khugepaged_alloc_sleep();
 829                 } else
 830                         count_vm_event(THP_COLLAPSE_ALLOC);
 831         } while (unlikely(!hpage) && likely(khugepaged_enabled()));
 832
 833         return hpage;
 834 }
 835
 836 static bool khugepaged_prealloc_page(struct page **hpage, bool *wait)
 837 {
 838         /*
 839          * If the hpage allocated earlier was briefly exposed in page cache
 840          * before collapse_file() failed, it is possible that racing lookups
 841          * have not yet completed, and would then be unpleasantly surprised by
 842          * finding the hpage reused for the same mapping at a different offset.
 843          * Just release the previous allocation if there is any danger of that.
 844          */
 845         if (*hpage && page_count(*hpage) > 1) {
 846                 put_page(*hpage);
 847                 *hpage = NULL;
 848         }
 849
 850         if (!*hpage)
 851                 *hpage = khugepaged_alloc_hugepage(wait);
 852
 853         if (unlikely(!*hpage))
 854                 return false;
 855
 856         return true;
 857 }
 858
 859 static struct page *
 860 khugepaged_alloc_page(struct page **hpage, gfp_t gfp, int node)
 861 {
 862         VM_BUG_ON(!*hpage);
 863
 864         return  *hpage;
 865 }
 866 #endif
 867
 868 /*
 869  * If mmap_sem temporarily dropped, revalidate vma
 870  * before taking mmap_sem.
 871  * Return 0 if succeeds, otherwise return none-zero
 872  * value (scan code).
 873  */
 874
 875 static int hugepage_vma_revalidate(struct mm_struct *mm, unsigned long address,
 876                 struct vm_area_struct **vmap)
 877 {
 878         struct vm_area_struct *vma;
 879         unsigned long hstart, hend;
 880
 881         if (unlikely(khugepaged_test_exit(mm)))
 882                 return SCAN_ANY_PROCESS;
 883
 884         *vmap = vma = find_vma(mm, address);
 885         if (!vma)
 886                 return SCAN_VMA_NULL;
 887
 888         hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK;
 889         hend = vma->vm_end & HPAGE_PMD_MASK;
 890         if (address < hstart || address + HPAGE_PMD_SIZE > hend)
 891                 return SCAN_ADDRESS_RANGE;
 892         if (!hugepage_vma_check(vma, vma->vm_flags))
 893                 return SCAN_VMA_CHECK;
 894         /* Anon VMA expected */
 895         if (!vma->anon_vma || vma->vm_ops)
 896                 return SCAN_VMA_CHECK;
 897         return 0;
 898 }
 899
 900 /*
 901  * Bring missing pages in from swap, to complete THP collapse.
 902  * Only done if khugepaged_scan_pmd believes it is worthwhile.
 903  *
 904  * Called and returns without pte mapped or spinlocks held,
 905  * but with mmap_sem held to protect against vma changes.
 906  */
 907
 908 static bool __collapse_huge_page_swapin(struct mm_struct *mm,
 909                                         struct vm_area_struct *vma,
 910                                         unsigned long address, pmd_t *pmd,
 911                                         int referenced)
 912 {
 913         int swapped_in = 0;
 914         vm_fault_t ret = 0;
 915         struct vm_fault vmf = {
 916                 .vma = vma,
 917                 .address = address,
 918                 .flags = FAULT_FLAG_ALLOW_RETRY,
 919                 .pmd = pmd,
 920                 .pgoff = linear_page_index(vma, address),
 921         };
 922
 923         /* we only decide to swapin, if there is enough young ptes */
 924         if (referenced < HPAGE_PMD_NR/2) {
 925                 trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 0);
 926                 return false;
 927         }
 928         vmf.pte = pte_offset_map(pmd, address);
 929         for (; vmf.address < address + HPAGE_PMD_NR*PAGE_SIZE;
 930                         vmf.pte++, vmf.address += PAGE_SIZE) {
 931                 vmf.orig_pte = *vmf.pte;
 932                 if (!is_swap_pte(vmf.orig_pte))
 933                         continue;
 934                 swapped_in++;
 935                 ret = do_swap_page(&vmf);
 936
 937                 /* do_swap_page returns VM_FAULT_RETRY with released mmap_sem */
 938                 if (ret & VM_FAULT_RETRY) {
 939                         down_read(&mm->mmap_sem);
 940                         if (hugepage_vma_revalidate(mm, address, &vmf.vma)) {
 941                                 /* vma is no longer available, don't continue to swapin */
 942                                 trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 0);
 943                                 return false;
 944                         }
 945                         /* check if the pmd is still valid */
 946                         if (mm_find_pmd(mm, address) != pmd) {
 947                                 trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 0);
 948                                 return false;
 949                         }
 950                 }
 951                 if (ret & VM_FAULT_ERROR) {
 952                         trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 0);
 953                         return false;
 954                 }
 955                 /* pte is unmapped now, we need to map it */
 956                 vmf.pte = pte_offset_map(pmd, vmf.address);
 957         }
 958         vmf.pte--;
 959         pte_unmap(vmf.pte);
 960         trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 1);
 961         return true;
 962 }
 963
 964 static void collapse_huge_page(struct mm_struct *mm,
 965                                    unsigned long address,
 966                                    struct page **hpage,
 967                                    int node, int referenced)
 968 {
 969         pmd_t *pmd, _pmd;
 970         pte_t *pte;
 971         pgtable_t pgtable;
 972         struct page *new_page;
 973         spinlock_t *pmd_ptl, *pte_ptl;
 974         int isolated = 0, result = 0;
 975         struct mem_cgroup *memcg;
 976         struct vm_area_struct *vma;
 977         struct mmu_notifier_range range;
 978         gfp_t gfp;
 979
 980         VM_BUG_ON(address & ~HPAGE_PMD_MASK);
 981
 982         /* Only allocate from the target node */
 983         gfp = alloc_hugepage_khugepaged_gfpmask() | __GFP_THISNODE;
 984
 985         /*
 986          * Before allocating the hugepage, release the mmap_sem read lock.
 987          * The allocation can take potentially a long time if it involves
 988          * sync compaction, and we do not need to hold the mmap_sem during
 989          * that. We will recheck the vma after taking it again in write mode.
 990          */
 991         up_read(&mm->mmap_sem);
 992         new_page = khugepaged_alloc_page(hpage, gfp, node);
 993         if (!new_page) {
 994                 result = SCAN_ALLOC_HUGE_PAGE_FAIL;
 995                 goto out_nolock;
 996         }
 997
 998         if (unlikely(mem_cgroup_try_charge(new_page, mm, gfp, &memcg, true))) {
 999                 result = SCAN_CGROUP_CHARGE_FAIL;
1000                 goto out_nolock;
1001         }
1002
1003         down_read(&mm->mmap_sem);
1004         result = hugepage_vma_revalidate(mm, address, &vma);
1005         if (result) {
1006                 mem_cgroup_cancel_charge(new_page, memcg, true);
1007                 up_read(&mm->mmap_sem);
1008                 goto out_nolock;
1009         }
1010
1011         pmd = mm_find_pmd(mm, address);
1012         if (!pmd) {
1013                 result = SCAN_PMD_NULL;
1014                 mem_cgroup_cancel_charge(new_page, memcg, true);
1015                 up_read(&mm->mmap_sem);
1016                 goto out_nolock;
1017         }
1018
1019         /*
1020          * __collapse_huge_page_swapin always returns with mmap_sem locked.
1021          * If it fails, we release mmap_sem and jump out_nolock.
1022          * Continuing to collapse causes inconsistency.
1023          */
1024         if (!__collapse_huge_page_swapin(mm, vma, address, pmd, referenced)) {
1025                 mem_cgroup_cancel_charge(new_page, memcg, true);
1026                 up_read(&mm->mmap_sem);
1027                 goto out_nolock;
1028         }
1029
1030         up_read(&mm->mmap_sem);
1031         /*
1032          * Prevent all access to pagetables with the exception of
1033          * gup_fast later handled by the ptep_clear_flush and the VM
1034          * handled by the anon_vma lock + PG_lock.
1035          */
1036         down_write(&mm->mmap_sem);
1037         result = hugepage_vma_revalidate(mm, address, &vma);
1038         if (result)
1039                 goto out;
1040         /* check if the pmd is still valid */
1041         if (mm_find_pmd(mm, address) != pmd)
1042                 goto out;
1043
1044         anon_vma_lock_write(vma->anon_vma);
1045
1046         mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, NULL, mm,
1047                                 address, address + HPAGE_PMD_SIZE);
1048         mmu_notifier_invalidate_range_start(&range);
1049
1050         pte = pte_offset_map(pmd, address);
1051         pte_ptl = pte_lockptr(mm, pmd);
1052
1053         pmd_ptl = pmd_lock(mm, pmd); /* probably unnecessary */
1054         /*
1055          * After this gup_fast can't run anymore. This also removes
1056          * any huge TLB entry from the CPU so we won't allow
1057          * huge and small TLB entries for the same virtual address
1058          * to avoid the risk of CPU bugs in that area.
1059          */
1060         _pmd = pmdp_collapse_flush(vma, address, pmd);
1061         spin_unlock(pmd_ptl);
1062         mmu_notifier_invalidate_range_end(&range);
1063
1064         spin_lock(pte_ptl);
1065         isolated = __collapse_huge_page_isolate(vma, address, pte);
1066         spin_unlock(pte_ptl);
1067
1068         if (unlikely(!isolated)) {
1069                 pte_unmap(pte);
1070                 spin_lock(pmd_ptl);
1071                 BUG_ON(!pmd_none(*pmd));
1072                 /*
1073                  * We can only use set_pmd_at when establishing
1074                  * hugepmds and never for establishing regular pmds that
1075                  * points to regular pagetables. Use pmd_populate for that
1076                  */
1077                 pmd_populate(mm, pmd, pmd_pgtable(_pmd));
1078                 spin_unlock(pmd_ptl);
1079                 anon_vma_unlock_write(vma->anon_vma);
1080                 result = SCAN_FAIL;
1081                 goto out;
1082         }
1083
1084         /*
1085          * All pages are isolated and locked so anon_vma rmap
1086          * can't run anymore.
1087          */
1088         anon_vma_unlock_write(vma->anon_vma);
1089
1090         __collapse_huge_page_copy(pte, new_page, vma, address, pte_ptl);
1091         pte_unmap(pte);
1092         __SetPageUptodate(new_page);
1093         pgtable = pmd_pgtable(_pmd);
1094
1095         _pmd = mk_huge_pmd(new_page, vma->vm_page_prot);
1096         _pmd = maybe_pmd_mkwrite(pmd_mkdirty(_pmd), vma);
1097
1098         /*
1099          * spin_lock() below is not the equivalent of smp_wmb(), so
1100          * this is needed to avoid the copy_huge_page writes to become
1101          * visible after the set_pmd_at() write.
1102          */
1103         smp_wmb();
1104
1105         spin_lock(pmd_ptl);
1106         BUG_ON(!pmd_none(*pmd));
1107         page_add_new_anon_rmap(new_page, vma, address, true);
1108         mem_cgroup_commit_charge(new_page, memcg, false, true);
1109         count_memcg_events(memcg, THP_COLLAPSE_ALLOC, 1);
1110         lru_cache_add_active_or_unevictable(new_page, vma);
1111         pgtable_trans_huge_deposit(mm, pmd, pgtable);
1112         set_pmd_at(mm, address, pmd, _pmd);
1113         update_mmu_cache_pmd(vma, address, pmd);
1114         spin_unlock(pmd_ptl);
1115
1116         *hpage = NULL;
1117
1118         khugepaged_pages_collapsed++;
1119         result = SCAN_SUCCEED;
1120 out_up_write:
1121         up_write(&mm->mmap_sem);
1122 out_nolock:
1123         trace_mm_collapse_huge_page(mm, isolated, result);
1124         return;
1125 out:
1126         mem_cgroup_cancel_charge(new_page, memcg, true);
1127         goto out_up_write;
1128 }
1129
1130 static int khugepaged_scan_pmd(struct mm_struct *mm,
1131                                struct vm_area_struct *vma,
1132                                unsigned long address,
1133                                struct page **hpage)
1134 {
1135         pmd_t *pmd;
1136         pte_t *pte, *_pte;
1137         int ret = 0, none_or_zero = 0, result = 0, referenced = 0;
1138         struct page *page = NULL;
1139         unsigned long _address;
1140         spinlock_t *ptl;
1141         int node = NUMA_NO_NODE, unmapped = 0;
1142         bool writable = false;
1143
1144         VM_BUG_ON(address & ~HPAGE_PMD_MASK);
1145
1146         pmd = mm_find_pmd(mm, address);
1147         if (!pmd) {
1148                 result = SCAN_PMD_NULL;
1149                 goto out;
1150         }
1151
1152         memset(khugepaged_node_load, 0, sizeof(khugepaged_node_load));
1153         pte = pte_offset_map_lock(mm, pmd, address, &ptl);
1154         for (_address = address, _pte = pte; _pte < pte+HPAGE_PMD_NR;
1155              _pte++, _address += PAGE_SIZE) {
1156                 pte_t pteval = *_pte;
1157                 if (is_swap_pte(pteval)) {
1158                         if (++unmapped <= khugepaged_max_ptes_swap) {
1159                                 continue;
1160                         } else {
1161                                 result = SCAN_EXCEED_SWAP_PTE;
1162                                 goto out_unmap;
1163                         }
1164                 }
1165                 if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) {
1166                         if (!userfaultfd_armed(vma) &&
1167                             ++none_or_zero <= khugepaged_max_ptes_none) {
1168                                 continue;
1169                         } else {
1170                                 result = SCAN_EXCEED_NONE_PTE;
1171                                 goto out_unmap;
1172                         }
1173                 }
1174                 if (!pte_present(pteval)) {
1175                         result = SCAN_PTE_NON_PRESENT;
1176                         goto out_unmap;
1177                 }
1178                 if (pte_write(pteval))
1179                         writable = true;
1180
1181                 page = vm_normal_page(vma, _address, pteval);
1182                 if (unlikely(!page)) {
1183                         result = SCAN_PAGE_NULL;
1184                         goto out_unmap;
1185                 }
1186
1187                 /* TODO: teach khugepaged to collapse THP mapped with pte */
1188                 if (PageCompound(page)) {
1189                         result = SCAN_PAGE_COMPOUND;
1190                         goto out_unmap;
1191                 }
1192
1193                 /*
1194                  * Record which node the original page is from and save this
1195                  * information to khugepaged_node_load[].
1196                  * Khupaged will allocate hugepage from the node has the max
1197                  * hit record.
1198                  */
1199                 node = page_to_nid(page);
1200                 if (khugepaged_scan_abort(node)) {
1201                         result = SCAN_SCAN_ABORT;
1202                         goto out_unmap;
1203                 }
1204                 khugepaged_node_load[node]++;
1205                 if (!PageLRU(page)) {
1206                         result = SCAN_PAGE_LRU;
1207                         goto out_unmap;
1208                 }
1209                 if (PageLocked(page)) {
1210                         result = SCAN_PAGE_LOCK;
1211                         goto out_unmap;
1212                 }
1213                 if (!PageAnon(page)) {
1214                         result = SCAN_PAGE_ANON;
1215                         goto out_unmap;
1216                 }
1217
1218                 /*
1219                  * cannot use mapcount: can't collapse if there's a gup pin.
1220                  * The page must only be referenced by the scanned process
1221                  * and page swap cache.
1222                  */
1223                 if (page_count(page) != 1 + PageSwapCache(page)) {
1224                         result = SCAN_PAGE_COUNT;
1225                         goto out_unmap;
1226                 }
1227                 if (pte_young(pteval) ||
1228                     page_is_young(page) || PageReferenced(page) ||
1229                     mmu_notifier_test_young(vma->vm_mm, address))
1230                         referenced++;
1231         }
1232         if (writable) {
1233                 if (referenced) {
1234                         result = SCAN_SUCCEED;
1235                         ret = 1;
1236                 } else {
1237                         result = SCAN_LACK_REFERENCED_PAGE;
1238                 }
1239         } else {
1240                 result = SCAN_PAGE_RO;
1241         }
1242 out_unmap:
1243         pte_unmap_unlock(pte, ptl);
1244         if (ret) {
1245                 node = khugepaged_find_target_node();
1246                 /* collapse_huge_page will return with the mmap_sem released */
1247                 collapse_huge_page(mm, address, hpage, node, referenced);
1248         }
1249 out:
1250         trace_mm_khugepaged_scan_pmd(mm, page, writable, referenced,
1251                                      none_or_zero, result, unmapped);
1252         return ret;
1253 }
1254
1255 static void collect_mm_slot(struct mm_slot *mm_slot)
1256 {
1257         struct mm_struct *mm = mm_slot->mm;
1258
1259         lockdep_assert_held(&khugepaged_mm_lock);
1260
1261         if (khugepaged_test_exit(mm)) {
1262                 /* free mm_slot */
1263                 hash_del(&mm_slot->hash);
1264                 list_del(&mm_slot->mm_node);
1265
1266                 /*
1267                  * Not strictly needed because the mm exited already.
1268                  *
1269                  * clear_bit(MMF_VM_HUGEPAGE, &mm->flags);
1270                  */
1271
1272                 /* khugepaged_mm_lock actually not necessary for the below */
1273                 free_mm_slot(mm_slot);
1274                 mmdrop(mm);
1275         }
1276 }
1277
1278 #if defined(CONFIG_SHMEM) && defined(CONFIG_TRANSPARENT_HUGE_PAGECACHE)
1279 /*
1280  * Notify khugepaged that given addr of the mm is pte-mapped THP. Then
1281  * khugepaged should try to collapse the page table.
1282  */
1283 static int khugepaged_add_pte_mapped_thp(struct mm_struct *mm,
1284                                          unsigned long addr)
1285 {
1286         struct mm_slot *mm_slot;
1287
1288         VM_BUG_ON(addr & ~HPAGE_PMD_MASK);
1289
1290         spin_lock(&khugepaged_mm_lock);
1291         mm_slot = get_mm_slot(mm);
1292         if (likely(mm_slot && mm_slot->nr_pte_mapped_thp < MAX_PTE_MAPPED_THP))
1293                 mm_slot->pte_mapped_thp[mm_slot->nr_pte_mapped_thp++] = addr;
1294         spin_unlock(&khugepaged_mm_lock);
1295         return 0;
1296 }
1297
1298 /**
1299  * Try to collapse a pte-mapped THP for mm at address haddr.
1300  *
1301  * This function checks whether all the PTEs in the PMD are pointing to the
1302  * right THP. If so, retract the page table so the THP can refault in with
1303  * as pmd-mapped.
1304  */
1305 void collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr)
1306 {
1307         unsigned long haddr = addr & HPAGE_PMD_MASK;
1308         struct vm_area_struct *vma = find_vma(mm, haddr);
1309         struct page *hpage;
1310         pte_t *start_pte, *pte;
1311         pmd_t *pmd, _pmd;
1312         spinlock_t *ptl;
1313         int count = 0;
1314         int i;
1315
1316         if (!vma || !vma->vm_file ||
1317             vma->vm_start > haddr || vma->vm_end < haddr + HPAGE_PMD_SIZE)
1318                 return;
1319
1320         /*
1321          * This vm_flags may not have VM_HUGEPAGE if the page was not
1322          * collapsed by this mm. But we can still collapse if the page is
1323          * the valid THP. Add extra VM_HUGEPAGE so hugepage_vma_check()
1324          * will not fail the vma for missing VM_HUGEPAGE
1325          */
1326         if (!hugepage_vma_check(vma, vma->vm_flags | VM_HUGEPAGE))
1327                 return;
1328
1329         hpage = find_lock_page(vma->vm_file->f_mapping,
1330                                linear_page_index(vma, haddr));
1331         if (!hpage)
1332                 return;
1333
1334         if (!PageHead(hpage))
1335                 goto drop_hpage;
1336
1337         pmd = mm_find_pmd(mm, haddr);
1338         if (!pmd)
1339                 goto drop_hpage;
1340
1341         start_pte = pte_offset_map_lock(mm, pmd, haddr, &ptl);
1342
1343         /* step 1: check all mapped PTEs are to the right huge page */
1344         for (i = 0, addr = haddr, pte = start_pte;
1345              i < HPAGE_PMD_NR; i++, addr += PAGE_SIZE, pte++) {
1346                 struct page *page;
1347
1348                 /* empty pte, skip */
1349                 if (pte_none(*pte))
1350                         continue;
1351
1352                 /* page swapped out, abort */
1353                 if (!pte_present(*pte))
1354                         goto abort;
1355
1356                 page = vm_normal_page(vma, addr, *pte);
1357
1358                 /*
1359                  * Note that uprobe, debugger, or MAP_PRIVATE may change the
1360                  * page table, but the new page will not be a subpage of hpage.
1361                  */
1362                 if (hpage + i != page)
1363                         goto abort;
1364                 count++;
1365         }
1366
1367         /* step 2: adjust rmap */
1368         for (i = 0, addr = haddr, pte = start_pte;
1369              i < HPAGE_PMD_NR; i++, addr += PAGE_SIZE, pte++) {
1370                 struct page *page;
1371
1372                 if (pte_none(*pte))
1373                         continue;
1374                 page = vm_normal_page(vma, addr, *pte);
1375                 page_remove_rmap(page, false);
1376         }
1377
1378         pte_unmap_unlock(start_pte, ptl);
1379
1380         /* step 3: set proper refcount and mm_counters. */
1381         if (count) {
1382                 page_ref_sub(hpage, count);
1383                 add_mm_counter(vma->vm_mm, mm_counter_file(hpage), -count);
1384         }
1385
1386         /* step 4: collapse pmd */
1387         ptl = pmd_lock(vma->vm_mm, pmd);
1388         _pmd = pmdp_collapse_flush(vma, haddr, pmd);
1389         spin_unlock(ptl);
1390         mm_dec_nr_ptes(mm);
1391         pte_free(mm, pmd_pgtable(_pmd));
1392
1393 drop_hpage:
1394         unlock_page(hpage);
1395         put_page(hpage);
1396         return;
1397
1398 abort:
1399         pte_unmap_unlock(start_pte, ptl);
1400         goto drop_hpage;
1401 }
1402
1403 static int khugepaged_collapse_pte_mapped_thps(struct mm_slot *mm_slot)
1404 {
1405         struct mm_struct *mm = mm_slot->mm;
1406         int i;
1407
1408         if (likely(mm_slot->nr_pte_mapped_thp == 0))
1409                 return 0;
1410
1411         if (!down_write_trylock(&mm->mmap_sem))
1412                 return -EBUSY;
1413
1414         if (unlikely(khugepaged_test_exit(mm)))
1415                 goto out;
1416
1417         for (i = 0; i < mm_slot->nr_pte_mapped_thp; i++)
1418                 collapse_pte_mapped_thp(mm, mm_slot->pte_mapped_thp[i]);
1419
1420 out:
1421         mm_slot->nr_pte_mapped_thp = 0;
1422         up_write(&mm->mmap_sem);
1423         return 0;
1424 }
1425
1426 static void retract_page_tables(struct address_space *mapping, pgoff_t pgoff)
1427 {
1428         struct vm_area_struct *vma;
1429         struct mm_struct *mm;
1430         unsigned long addr;
1431         pmd_t *pmd, _pmd;
1432
1433         i_mmap_lock_write(mapping);
1434         vma_interval_tree_foreach(vma, &mapping->i_mmap, pgoff, pgoff) {
1435                 /*
1436                  * Check vma->anon_vma to exclude MAP_PRIVATE mappings that
1437                  * got written to. These VMAs are likely not worth investing
1438                  * down_write(mmap_sem) as PMD-mapping is likely to be split
1439                  * later.
1440                  *
1441                  * Not that vma->anon_vma check is racy: it can be set up after
1442                  * the check but before we took mmap_sem by the fault path.
1443                  * But page lock would prevent establishing any new ptes of the
1444                  * page, so we are safe.
1445                  *
1446                  * An alternative would be drop the check, but check that page
1447                  * table is clear before calling pmdp_collapse_flush() under
1448                  * ptl. It has higher chance to recover THP for the VMA, but
1449                  * has higher cost too.
1450                  */
1451                 if (vma->anon_vma)
1452                         continue;
1453                 addr = vma->vm_start + ((pgoff - vma->vm_pgoff) << PAGE_SHIFT);
1454                 if (addr & ~HPAGE_PMD_MASK)
1455                         continue;
1456                 if (vma->vm_end < addr + HPAGE_PMD_SIZE)
1457                         continue;
1458                 mm = vma->vm_mm;
1459                 pmd = mm_find_pmd(mm, addr);
1460                 if (!pmd)
1461                         continue;
1462                 /*
1463                  * We need exclusive mmap_sem to retract page table.
1464                  *
1465                  * We use trylock due to lock inversion: we need to acquire
1466                  * mmap_sem while holding page lock. Fault path does it in
1467                  * reverse order. Trylock is a way to avoid deadlock.
1468                  */
1469                 if (down_write_trylock(&mm->mmap_sem)) {
1470                         if (!khugepaged_test_exit(mm)) {
1471                                 spinlock_t *ptl = pmd_lock(mm, pmd);
1472                                 /* assume page table is clear */
1473                                 _pmd = pmdp_collapse_flush(vma, addr, pmd);
1474                                 spin_unlock(ptl);
1475                                 mm_dec_nr_ptes(mm);
1476                                 pte_free(mm, pmd_pgtable(_pmd));
1477                         }
1478                         up_write(&mm->mmap_sem);
1479                 } else {
1480                         /* Try again later */
1481                         khugepaged_add_pte_mapped_thp(mm, addr);
1482                 }
1483         }
1484         i_mmap_unlock_write(mapping);
1485 }
1486
1487 /**
1488  * collapse_file - collapse filemap/tmpfs/shmem pages into huge one.
1489  *
1490  * Basic scheme is simple, details are more complex:
1491  *  - allocate and lock a new huge page;
1492  *  - scan page cache replacing old pages with the new one
1493  *    + swap/gup in pages if necessary;
1494  *    + fill in gaps;
1495  *    + keep old pages around in case rollback is required;
1496  *  - if replacing succeeds:
1497  *    + copy data over;
1498  *    + free old pages;
1499  *    + unlock huge page;
1500  *  - if replacing failed;
1501  *    + put all pages back and unfreeze them;
1502  *    + restore gaps in the page cache;
1503  *    + unlock and free huge page;
1504  */
1505 static void collapse_file(struct mm_struct *mm,
1506                 struct file *file, pgoff_t start,
1507                 struct page **hpage, int node)
1508 {
1509         struct address_space *mapping = file->f_mapping;
1510         gfp_t gfp;
1511         struct page *new_page;
1512         struct mem_cgroup *memcg;
1513         pgoff_t index, end = start + HPAGE_PMD_NR;
1514         LIST_HEAD(pagelist);
1515         XA_STATE_ORDER(xas, &mapping->i_pages, start, HPAGE_PMD_ORDER);
1516         int nr_none = 0, result = SCAN_SUCCEED;
1517         bool is_shmem = shmem_file(file);
1518
1519         VM_BUG_ON(!IS_ENABLED(CONFIG_READ_ONLY_THP_FOR_FS) && !is_shmem);
1520         VM_BUG_ON(start & (HPAGE_PMD_NR - 1));
1521
1522         /* Only allocate from the target node */
1523         gfp = alloc_hugepage_khugepaged_gfpmask() | __GFP_THISNODE;
1524
1525         new_page = khugepaged_alloc_page(hpage, gfp, node);
1526         if (!new_page) {
1527                 result = SCAN_ALLOC_HUGE_PAGE_FAIL;
1528                 goto out;
1529         }
1530
1531         if (unlikely(mem_cgroup_try_charge(new_page, mm, gfp, &memcg, true))) {
1532                 result = SCAN_CGROUP_CHARGE_FAIL;
1533                 goto out;
1534         }
1535
1536         /* This will be less messy when we use multi-index entries */
1537         do {
1538                 xas_lock_irq(&xas);
1539                 xas_create_range(&xas);
1540                 if (!xas_error(&xas))
1541                         break;
1542                 xas_unlock_irq(&xas);
1543                 if (!xas_nomem(&xas, GFP_KERNEL)) {
1544                         mem_cgroup_cancel_charge(new_page, memcg, true);
1545                         result = SCAN_FAIL;
1546                         goto out;
1547                 }
1548         } while (1);
1549
1550         __SetPageLocked(new_page);
1551         if (is_shmem)
1552                 __SetPageSwapBacked(new_page);
1553         new_page->index = start;
1554         new_page->mapping = mapping;
1555
1556         /*
1557          * At this point the new_page is locked and not up-to-date.
1558          * It's safe to insert it into the page cache, because nobody would
1559          * be able to map it or use it in another way until we unlock it.
1560          */
1561
1562         xas_set(&xas, start);
1563         for (index = start; index < end; index++) {
1564                 struct page *page = xas_next(&xas);
1565
1566                 VM_BUG_ON(index != xas.xa_index);
1567                 if (is_shmem) {
1568                         if (!page) {
1569                                 /*
1570                                  * Stop if extent has been truncated or
1571                                  * hole-punched, and is now completely
1572                                  * empty.
1573                                  */
1574                                 if (index == start) {
1575                                         if (!xas_next_entry(&xas, end - 1)) {
1576                                                 result = SCAN_TRUNCATED;
1577                                                 goto xa_locked;
1578                                         }
1579                                         xas_set(&xas, index);
1580                                 }
1581                                 if (!shmem_charge(mapping->host, 1)) {
1582                                         result = SCAN_FAIL;
1583                                         goto xa_locked;
1584                                 }
1585                                 xas_store(&xas, new_page);
1586                                 nr_none++;
1587                                 continue;
1588                         }
1589
1590                         if (xa_is_value(page) || !PageUptodate(page)) {
1591                                 xas_unlock_irq(&xas);
1592                                 /* swap in or instantiate fallocated page */
1593                                 if (shmem_getpage(mapping->host, index, &page,
1594                                                   SGP_NOHUGE)) {
1595                                         result = SCAN_FAIL;
1596                                         goto xa_unlocked;
1597                                 }
1598                         } else if (trylock_page(page)) {
1599                                 get_page(page);
1600                                 xas_unlock_irq(&xas);
1601                         } else {
1602                                 result = SCAN_PAGE_LOCK;
1603                                 goto xa_locked;
1604                         }
1605                 } else {        /* !is_shmem */
1606                         if (!page || xa_is_value(page)) {
1607                                 xas_unlock_irq(&xas);
1608                                 page_cache_sync_readahead(mapping, &file->f_ra,
1609                                                           file, index,
1610                                                           end - index);
1611                                 /* drain pagevecs to help isolate_lru_page() */
1612                                 lru_add_drain();
1613                                 page = find_lock_page(mapping, index);
1614                                 if (unlikely(page == NULL)) {
1615                                         result = SCAN_FAIL;
1616                                         goto xa_unlocked;
1617                                 }
1618                         } else if (trylock_page(page)) {
1619                                 get_page(page);
1620                                 xas_unlock_irq(&xas);
1621                         } else {
1622                                 result = SCAN_PAGE_LOCK;
1623                                 goto xa_locked;
1624                         }
1625                 }
1626
1627                 /*
1628                  * The page must be locked, so we can drop the i_pages lock
1629                  * without racing with truncate.
1630                  */
1631                 VM_BUG_ON_PAGE(!PageLocked(page), page);
1632
1633                 /* make sure the page is up to date */
1634                 if (unlikely(!PageUptodate(page))) {
1635                         result = SCAN_FAIL;
1636                         goto out_unlock;
1637                 }
1638
1639                 /*
1640                  * If file was truncated then extended, or hole-punched, before
1641                  * we locked the first page, then a THP might be there already.
1642                  */
1643                 if (PageTransCompound(page)) {
1644                         result = SCAN_PAGE_COMPOUND;
1645                         goto out_unlock;
1646                 }
1647
1648                 if (page_mapping(page) != mapping) {
1649                         result = SCAN_TRUNCATED;
1650                         goto out_unlock;
1651                 }
1652
1653                 if (!is_shmem && PageDirty(page)) {
1654                         /*
1655                          * khugepaged only works on read-only fd, so this
1656                          * page is dirty because it hasn't been flushed
1657                          * since first write.
1658                          */
1659                         result = SCAN_FAIL;
1660                         goto out_unlock;
1661                 }
1662
1663                 if (isolate_lru_page(page)) {
1664                         result = SCAN_DEL_PAGE_LRU;
1665                         goto out_unlock;
1666                 }
1667
1668                 if (page_has_private(page) &&
1669                     !try_to_release_page(page, GFP_KERNEL)) {
1670                         result = SCAN_PAGE_HAS_PRIVATE;
1671                         putback_lru_page(page);
1672                         goto out_unlock;
1673                 }
1674
1675                 if (page_mapped(page))
1676                         unmap_mapping_pages(mapping, index, 1, false);
1677
1678                 xas_lock_irq(&xas);
1679                 xas_set(&xas, index);
1680
1681                 VM_BUG_ON_PAGE(page != xas_load(&xas), page);
1682                 VM_BUG_ON_PAGE(page_mapped(page), page);
1683
1684                 /*
1685                  * The page is expected to have page_count() == 3:
1686                  *  - we hold a pin on it;
1687                  *  - one reference from page cache;
1688                  *  - one from isolate_lru_page;
1689                  */
1690                 if (!page_ref_freeze(page, 3)) {
1691                         result = SCAN_PAGE_COUNT;
1692                         xas_unlock_irq(&xas);
1693                         putback_lru_page(page);
1694                         goto out_unlock;
1695                 }
1696
1697                 /*
1698                  * Add the page to the list to be able to undo the collapse if
1699                  * something go wrong.
1700                  */
1701                 list_add_tail(&page->lru, &pagelist);
1702
1703                 /* Finally, replace with the new page. */
1704                 xas_store(&xas, new_page);
1705                 continue;
1706 out_unlock:
1707                 unlock_page(page);
1708                 put_page(page);
1709                 goto xa_unlocked;
1710         }
1711
1712         if (is_shmem)
1713                 __inc_node_page_state(new_page, NR_SHMEM_THPS);
1714         else {
1715                 __inc_node_page_state(new_page, NR_FILE_THPS);
1716                 filemap_nr_thps_inc(mapping);
1717         }
1718
1719         if (nr_none) {
1720                 struct zone *zone = page_zone(new_page);
1721
1722                 __mod_node_page_state(zone->zone_pgdat, NR_FILE_PAGES, nr_none);
1723                 if (is_shmem)
1724                         __mod_node_page_state(zone->zone_pgdat,
1725                                               NR_SHMEM, nr_none);
1726         }
1727
1728 xa_locked:
1729         xas_unlock_irq(&xas);
1730 xa_unlocked:
1731
1732         if (result == SCAN_SUCCEED) {
1733                 struct page *page, *tmp;
1734
1735                 /*
1736                  * Replacing old pages with new one has succeeded, now we
1737                  * need to copy the content and free the old pages.
1738                  */
1739                 index = start;
1740                 list_for_each_entry_safe(page, tmp, &pagelist, lru) {
1741                         while (index < page->index) {
1742                                 clear_highpage(new_page + (index % HPAGE_PMD_NR));
1743                                 index++;
1744                         }
1745                         copy_highpage(new_page + (page->index % HPAGE_PMD_NR),
1746                                         page);
1747                         list_del(&page->lru);
1748                         page->mapping = NULL;
1749                         page_ref_unfreeze(page, 1);
1750                         ClearPageActive(page);
1751                         ClearPageUnevictable(page);
1752                         unlock_page(page);
1753                         put_page(page);
1754                         index++;
1755                 }
1756                 while (index < end) {
1757                         clear_highpage(new_page + (index % HPAGE_PMD_NR));
1758                         index++;
1759                 }
1760
1761                 SetPageUptodate(new_page);
1762                 page_ref_add(new_page, HPAGE_PMD_NR - 1);
1763                 mem_cgroup_commit_charge(new_page, memcg, false, true);
1764
1765                 if (is_shmem) {
1766                         set_page_dirty(new_page);
1767                         lru_cache_add_anon(new_page);
1768                 } else {
1769                         lru_cache_add_file(new_page);
1770                 }
1771                 count_memcg_events(memcg, THP_COLLAPSE_ALLOC, 1);
1772
1773                 /*
1774                  * Remove pte page tables, so we can re-fault the page as huge.
1775                  */
1776                 retract_page_tables(mapping, start);
1777                 *hpage = NULL;
1778
1779                 khugepaged_pages_collapsed++;
1780         } else {
1781                 struct page *page;
1782
1783                 /* Something went wrong: roll back page cache changes */
1784                 xas_lock_irq(&xas);
1785                 mapping->nrpages -= nr_none;
1786
1787                 if (is_shmem)
1788                         shmem_uncharge(mapping->host, nr_none);
1789
1790                 xas_set(&xas, start);
1791                 xas_for_each(&xas, page, end - 1) {
1792                         page = list_first_entry_or_null(&pagelist,
1793                                         struct page, lru);
1794                         if (!page || xas.xa_index < page->index) {
1795                                 if (!nr_none)
1796                                         break;
1797                                 nr_none--;
1798                                 /* Put holes back where they were */
1799                                 xas_store(&xas, NULL);
1800                                 continue;
1801                         }
1802
1803                         VM_BUG_ON_PAGE(page->index != xas.xa_index, page);
1804
1805                         /* Unfreeze the page. */
1806                         list_del(&page->lru);
1807                         page_ref_unfreeze(page, 2);
1808                         xas_store(&xas, page);
1809                         xas_pause(&xas);
1810                         xas_unlock_irq(&xas);
1811                         unlock_page(page);
1812                         putback_lru_page(page);
1813                         xas_lock_irq(&xas);
1814                 }
1815                 VM_BUG_ON(nr_none);
1816                 xas_unlock_irq(&xas);
1817
1818                 mem_cgroup_cancel_charge(new_page, memcg, true);
1819                 new_page->mapping = NULL;
1820         }
1821
1822         unlock_page(new_page);
1823 out:
1824         VM_BUG_ON(!list_empty(&pagelist));
1825         /* TODO: tracepoints */
1826 }
1827
1828 static void khugepaged_scan_file(struct mm_struct *mm,
1829                 struct file *file, pgoff_t start, struct page **hpage)
1830 {
1831         struct page *page = NULL;
1832         struct address_space *mapping = file->f_mapping;
1833         XA_STATE(xas, &mapping->i_pages, start);
1834         int present, swap;
1835         int node = NUMA_NO_NODE;
1836         int result = SCAN_SUCCEED;
1837
1838         present = 0;
1839         swap = 0;
1840         memset(khugepaged_node_load, 0, sizeof(khugepaged_node_load));
1841         rcu_read_lock();
1842         xas_for_each(&xas, page, start + HPAGE_PMD_NR - 1) {
1843                 if (xas_retry(&xas, page))
1844                         continue;
1845
1846                 if (xa_is_value(page)) {
1847                         if (++swap > khugepaged_max_ptes_swap) {
1848                                 result = SCAN_EXCEED_SWAP_PTE;
1849                                 break;
1850                         }
1851                         continue;
1852                 }
1853
1854                 if (PageTransCompound(page)) {
1855                         result = SCAN_PAGE_COMPOUND;
1856                         break;
1857                 }
1858
1859                 node = page_to_nid(page);
1860                 if (khugepaged_scan_abort(node)) {
1861                         result = SCAN_SCAN_ABORT;
1862                         break;
1863                 }
1864                 khugepaged_node_load[node]++;
1865
1866                 if (!PageLRU(page)) {
1867                         result = SCAN_PAGE_LRU;
1868                         break;
1869                 }
1870
1871                 if (page_count(page) !=
1872                     1 + page_mapcount(page) + page_has_private(page)) {
1873                         result = SCAN_PAGE_COUNT;
1874                         break;
1875                 }
1876
1877                 /*
1878                  * We probably should check if the page is referenced here, but
1879                  * nobody would transfer pte_young() to PageReferenced() for us.
1880                  * And rmap walk here is just too costly...
1881                  */
1882
1883                 present++;
1884
1885                 if (need_resched()) {
1886                         xas_pause(&xas);
1887                         cond_resched_rcu();
1888                 }
1889         }
1890         rcu_read_unlock();
1891
1892         if (result == SCAN_SUCCEED) {
1893                 if (present < HPAGE_PMD_NR - khugepaged_max_ptes_none) {
1894                         result = SCAN_EXCEED_NONE_PTE;
1895                 } else {
1896                         node = khugepaged_find_target_node();
1897                         collapse_file(mm, file, start, hpage, node);
1898                 }
1899         }
1900
1901         /* TODO: tracepoints */
1902 }
1903 #else
1904 static void khugepaged_scan_file(struct mm_struct *mm,
1905                 struct file *file, pgoff_t start, struct page **hpage)
1906 {
1907         BUILD_BUG();
1908 }
1909
1910 static int khugepaged_collapse_pte_mapped_thps(struct mm_slot *mm_slot)
1911 {
1912         return 0;
1913 }
1914 #endif
1915
1916 static unsigned int khugepaged_scan_mm_slot(unsigned int pages,
1917                                             struct page **hpage)
1918         __releases(&khugepaged_mm_lock)
1919         __acquires(&khugepaged_mm_lock)
1920 {
1921         struct mm_slot *mm_slot;
1922         struct mm_struct *mm;
1923         struct vm_area_struct *vma;
1924         int progress = 0;
1925
1926         VM_BUG_ON(!pages);
1927         lockdep_assert_held(&khugepaged_mm_lock);
1928
1929         if (khugepaged_scan.mm_slot)
1930                 mm_slot = khugepaged_scan.mm_slot;
1931         else {
1932                 mm_slot = list_entry(khugepaged_scan.mm_head.next,
1933                                      struct mm_slot, mm_node);
1934                 khugepaged_scan.address = 0;
1935                 khugepaged_scan.mm_slot = mm_slot;
1936         }
1937         spin_unlock(&khugepaged_mm_lock);
1938         khugepaged_collapse_pte_mapped_thps(mm_slot);
1939
1940         mm = mm_slot->mm;
1941         /*
1942          * Don't wait for semaphore (to avoid long wait times).  Just move to
1943          * the next mm on the list.
1944          */
1945         vma = NULL;
1946         if (unlikely(!down_read_trylock(&mm->mmap_sem)))
1947                 goto breakouterloop_mmap_sem;
1948         if (likely(!khugepaged_test_exit(mm)))
1949                 vma = find_vma(mm, khugepaged_scan.address);
1950
1951         progress++;
1952         for (; vma; vma = vma->vm_next) {
1953                 unsigned long hstart, hend;
1954
1955                 cond_resched();
1956                 if (unlikely(khugepaged_test_exit(mm))) {
1957                         progress++;
1958                         break;
1959                 }
1960                 if (!hugepage_vma_check(vma, vma->vm_flags)) {
1961 skip:
1962                         progress++;
1963                         continue;
1964                 }
1965                 hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK;
1966                 hend = vma->vm_end & HPAGE_PMD_MASK;
1967                 if (hstart >= hend)
1968                         goto skip;
1969                 if (khugepaged_scan.address > hend)
1970                         goto skip;
1971                 if (khugepaged_scan.address < hstart)
1972                         khugepaged_scan.address = hstart;
1973                 VM_BUG_ON(khugepaged_scan.address & ~HPAGE_PMD_MASK);
1974
1975                 while (khugepaged_scan.address < hend) {
1976                         int ret;
1977                         cond_resched();
1978                         if (unlikely(khugepaged_test_exit(mm)))
1979                                 goto breakouterloop;
1980
1981                         VM_BUG_ON(khugepaged_scan.address < hstart ||
1982                                   khugepaged_scan.address + HPAGE_PMD_SIZE >
1983                                   hend);
1984                         if (IS_ENABLED(CONFIG_SHMEM) && vma->vm_file) {
1985                                 struct file *file;
1986                                 pgoff_t pgoff = linear_page_index(vma,
1987                                                 khugepaged_scan.address);
1988
1989                                 if (shmem_file(vma->vm_file)
1990                                     && !shmem_huge_enabled(vma))
1991                                         goto skip;
1992                                 file = get_file(vma->vm_file);
1993                                 up_read(&mm->mmap_sem);
1994                                 ret = 1;
1995                                 khugepaged_scan_file(mm, file, pgoff, hpage);
1996                                 fput(file);
1997                         } else {
1998                                 ret = khugepaged_scan_pmd(mm, vma,
1999                                                 khugepaged_scan.address,
2000                                                 hpage);
2001                         }
2002                         /* move to next address */
2003                         khugepaged_scan.address += HPAGE_PMD_SIZE;
2004                         progress += HPAGE_PMD_NR;
2005                         if (ret)
2006                                 /* we released mmap_sem so break loop */
2007                                 goto breakouterloop_mmap_sem;
2008                         if (progress >= pages)
2009                                 goto breakouterloop;
2010                 }
2011         }
2012 breakouterloop:
2013         up_read(&mm->mmap_sem); /* exit_mmap will destroy ptes after this */
2014 breakouterloop_mmap_sem:
2015
2016         spin_lock(&khugepaged_mm_lock);
2017         VM_BUG_ON(khugepaged_scan.mm_slot != mm_slot);
2018         /*
2019          * Release the current mm_slot if this mm is about to die, or
2020          * if we scanned all vmas of this mm.
2021          */
2022         if (khugepaged_test_exit(mm) || !vma) {
2023                 /*
2024                  * Make sure that if mm_users is reaching zero while
2025                  * khugepaged runs here, khugepaged_exit will find
2026                  * mm_slot not pointing to the exiting mm.
2027                  */
2028                 if (mm_slot->mm_node.next != &khugepaged_scan.mm_head) {
2029                         khugepaged_scan.mm_slot = list_entry(
2030                                 mm_slot->mm_node.next,
2031                                 struct mm_slot, mm_node);
2032                         khugepaged_scan.address = 0;
2033                 } else {
2034                         khugepaged_scan.mm_slot = NULL;
2035                         khugepaged_full_scans++;
2036                 }
2037
2038                 collect_mm_slot(mm_slot);
2039         }
2040
2041         return progress;
2042 }
2043
2044 static int khugepaged_has_work(void)
2045 {
2046         return !list_empty(&khugepaged_scan.mm_head) &&
2047                 khugepaged_enabled();
2048 }
2049
2050 static int khugepaged_wait_event(void)
2051 {
2052         return !list_empty(&khugepaged_scan.mm_head) ||
2053                 kthread_should_stop();
2054 }
2055
2056 static void khugepaged_do_scan(void)
2057 {
2058         struct page *hpage = NULL;
2059         unsigned int progress = 0, pass_through_head = 0;
2060         unsigned int pages = khugepaged_pages_to_scan;
2061         bool wait = true;
2062
2063         barrier(); /* write khugepaged_pages_to_scan to local stack */
2064
2065         while (progress < pages) {
2066                 if (!khugepaged_prealloc_page(&hpage, &wait))
2067                         break;
2068
2069                 cond_resched();
2070
2071                 if (unlikely(kthread_should_stop() || try_to_freeze()))
2072                         break;
2073
2074                 spin_lock(&khugepaged_mm_lock);
2075                 if (!khugepaged_scan.mm_slot)
2076                         pass_through_head++;
2077                 if (khugepaged_has_work() &&
2078                     pass_through_head < 2)
2079                         progress += khugepaged_scan_mm_slot(pages - progress,
2080                                                             &hpage);
2081                 else
2082                         progress = pages;
2083                 spin_unlock(&khugepaged_mm_lock);
2084         }
2085
2086         if (!IS_ERR_OR_NULL(hpage))
2087                 put_page(hpage);
2088 }
2089
2090 static bool khugepaged_should_wakeup(void)
2091 {
2092         return kthread_should_stop() ||
2093                time_after_eq(jiffies, khugepaged_sleep_expire);
2094 }
2095
2096 static void khugepaged_wait_work(void)
2097 {
2098         if (khugepaged_has_work()) {
2099                 const unsigned long scan_sleep_jiffies =
2100                         msecs_to_jiffies(khugepaged_scan_sleep_millisecs);
2101
2102                 if (!scan_sleep_jiffies)
2103                         return;
2104
2105                 khugepaged_sleep_expire = jiffies + scan_sleep_jiffies;
2106                 wait_event_freezable_timeout(khugepaged_wait,
2107                                              khugepaged_should_wakeup(),
2108                                              scan_sleep_jiffies);
2109                 return;
2110         }
2111
2112         if (khugepaged_enabled())
2113                 wait_event_freezable(khugepaged_wait, khugepaged_wait_event());
2114 }
2115
2116 static int khugepaged(void *none)
2117 {
2118         struct mm_slot *mm_slot;
2119
2120         set_freezable();
2121         set_user_nice(current, MAX_NICE);
2122
2123         while (!kthread_should_stop()) {
2124                 khugepaged_do_scan();
2125                 khugepaged_wait_work();
2126         }
2127
2128         spin_lock(&khugepaged_mm_lock);
2129         mm_slot = khugepaged_scan.mm_slot;
2130         khugepaged_scan.mm_slot = NULL;
2131         if (mm_slot)
2132                 collect_mm_slot(mm_slot);
2133         spin_unlock(&khugepaged_mm_lock);
2134         return 0;
2135 }
2136
2137 static void set_recommended_min_free_kbytes(void)
2138 {
2139         struct zone *zone;
2140         int nr_zones = 0;
2141         unsigned long recommended_min;
2142
2143         for_each_populated_zone(zone) {
2144                 /*
2145                  * We don't need to worry about fragmentation of
2146                  * ZONE_MOVABLE since it only has movable pages.
2147                  */
2148                 if (zone_idx(zone) > gfp_zone(GFP_USER))
2149                         continue;
2150
2151                 nr_zones++;
2152         }
2153
2154         /* Ensure 2 pageblocks are free to assist fragmentation avoidance */
2155         recommended_min = pageblock_nr_pages * nr_zones * 2;
2156
2157         /*
2158          * Make sure that on average at least two pageblocks are almost free
2159          * of another type, one for a migratetype to fall back to and a
2160          * second to avoid subsequent fallbacks of other types There are 3
2161          * MIGRATE_TYPES we care about.
2162          */
2163         recommended_min += pageblock_nr_pages * nr_zones *
2164                            MIGRATE_PCPTYPES * MIGRATE_PCPTYPES;
2165
2166         /* don't ever allow to reserve more than 5% of the lowmem */
2167         recommended_min = min(recommended_min,
2168                               (unsigned long) nr_free_buffer_pages() / 20);
2169         recommended_min <<= (PAGE_SHIFT-10);
2170
2171         if (recommended_min > min_free_kbytes) {
2172                 if (user_min_free_kbytes >= 0)
2173                         pr_info("raising min_free_kbytes from %d to %lu to help transparent hugepage allocations\n",
2174                                 min_free_kbytes, recommended_min);
2175
2176                 min_free_kbytes = recommended_min;
2177         }
2178         setup_per_zone_wmarks();
2179 }
2180
2181 int start_stop_khugepaged(void)
2182 {
2183         int err = 0;
2184
2185         mutex_lock(&khugepaged_mutex);
2186         if (khugepaged_enabled()) {
2187                 if (!khugepaged_thread)
2188                         khugepaged_thread = kthread_run(khugepaged, NULL,
2189                                                         "khugepaged");
2190                 if (IS_ERR(khugepaged_thread)) {
2191                         pr_err("khugepaged: kthread_run(khugepaged) failed\n");
2192                         err = PTR_ERR(khugepaged_thread);
2193                         khugepaged_thread = NULL;
2194                         goto fail;
2195                 }
2196
2197                 if (!list_empty(&khugepaged_scan.mm_head))
2198                         wake_up_interruptible(&khugepaged_wait);
2199
2200                 set_recommended_min_free_kbytes();
2201         } else if (khugepaged_thread) {
2202                 kthread_stop(khugepaged_thread);
2203                 khugepaged_thread = NULL;
2204         }
2205 fail:
2206         mutex_unlock(&khugepaged_mutex);
2207         return err;
2208 }
2209
2210 void khugepaged_min_free_kbytes_update(void)
2211 {
2212         mutex_lock(&khugepaged_mutex);
2213         if (khugepaged_enabled() && khugepaged_thread)
2214                 set_recommended_min_free_kbytes();
2215         mutex_unlock(&khugepaged_mutex);
2216 }