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_PTE_UFFD_WP,
  33         SCAN_PAGE_RO,
  34         SCAN_LACK_REFERENCED_PAGE,
  35         SCAN_PAGE_NULL,
  36         SCAN_SCAN_ABORT,
  37         SCAN_PAGE_COUNT,
  38         SCAN_PAGE_LRU,
  39         SCAN_PAGE_LOCK,
  40         SCAN_PAGE_ANON,
  41         SCAN_PAGE_COMPOUND,
  42         SCAN_ANY_PROCESS,
  43         SCAN_VMA_NULL,
  44         SCAN_VMA_CHECK,
  45         SCAN_ADDRESS_RANGE,
  46         SCAN_SWAP_CACHE_PAGE,
  47         SCAN_DEL_PAGE_LRU,
  48         SCAN_ALLOC_HUGE_PAGE_FAIL,
  49         SCAN_CGROUP_CHARGE_FAIL,
  50         SCAN_EXCEED_SWAP_PTE,
  51         SCAN_TRUNCATED,
  52         SCAN_PAGE_HAS_PRIVATE,
  53 };
  54
  55 #define CREATE_TRACE_POINTS
  56 #include <trace/events/huge_memory.h>
  57
  58 /* default scan 8*512 pte (or vmas) every 30 second */
  59 static unsigned int khugepaged_pages_to_scan __read_mostly;
  60 static unsigned int khugepaged_pages_collapsed;
  61 static unsigned int khugepaged_full_scans;
  62 static unsigned int khugepaged_scan_sleep_millisecs __read_mostly = 10000;
  63 /* during fragmentation poll the hugepage allocator once every minute */
  64 static unsigned int khugepaged_alloc_sleep_millisecs __read_mostly = 60000;
  65 static unsigned long khugepaged_sleep_expire;
  66 static DEFINE_SPINLOCK(khugepaged_mm_lock);
  67 static DECLARE_WAIT_QUEUE_HEAD(khugepaged_wait);
  68 /*
  69  * default collapse hugepages if there is at least one pte mapped like
  70  * it would have happened if the vma was large enough during page
  71  * fault.
  72  */
  73 static unsigned int khugepaged_max_ptes_none __read_mostly;
  74 static unsigned int khugepaged_max_ptes_swap __read_mostly;
  75
  76 #define MM_SLOTS_HASH_BITS 10
  77 static __read_mostly DEFINE_HASHTABLE(mm_slots_hash, MM_SLOTS_HASH_BITS);
  78
  79 static struct kmem_cache *mm_slot_cache __read_mostly;
  80
  81 #define MAX_PTE_MAPPED_THP 8
  82
  83 /**
  84  * struct mm_slot - hash lookup from mm to mm_slot
  85  * @hash: hash collision list
  86  * @mm_node: khugepaged scan list headed in khugepaged_scan.mm_head
  87  * @mm: the mm that this information is valid for
  88  */
  89 struct mm_slot {
  90         struct hlist_node hash;
  91         struct list_head mm_node;
  92         struct mm_struct *mm;
  93
  94         /* pte-mapped THP in this mm */
  95         int nr_pte_mapped_thp;
  96         unsigned long pte_mapped_thp[MAX_PTE_MAPPED_THP];
  97 };
  98
  99 /**
 100  * struct khugepaged_scan - cursor for scanning
 101  * @mm_head: the head of the mm list to scan
 102  * @mm_slot: the current mm_slot we are scanning
 103  * @address: the next address inside that to be scanned
 104  *
 105  * There is only the one khugepaged_scan instance of this cursor structure.
 106  */
 107 struct khugepaged_scan {
 108         struct list_head mm_head;
 109         struct mm_slot *mm_slot;
 110         unsigned long address;
 111 };
 112
 113 static struct khugepaged_scan khugepaged_scan = {
 114         .mm_head = LIST_HEAD_INIT(khugepaged_scan.mm_head),
 115 };
 116
 117 #ifdef CONFIG_SYSFS
 118 static ssize_t scan_sleep_millisecs_show(struct kobject *kobj,
 119                                          struct kobj_attribute *attr,
 120                                          char *buf)
 121 {
 122         return sprintf(buf, "%u\n", khugepaged_scan_sleep_millisecs);
 123 }
 124
 125 static ssize_t scan_sleep_millisecs_store(struct kobject *kobj,
 126                                           struct kobj_attribute *attr,
 127                                           const char *buf, size_t count)
 128 {
 129         unsigned long msecs;
 130         int err;
 131
 132         err = kstrtoul(buf, 10, &msecs);
 133         if (err || msecs > UINT_MAX)
 134                 return -EINVAL;
 135
 136         khugepaged_scan_sleep_millisecs = msecs;
 137         khugepaged_sleep_expire = 0;
 138         wake_up_interruptible(&khugepaged_wait);
 139
 140         return count;
 141 }
 142 static struct kobj_attribute scan_sleep_millisecs_attr =
 143         __ATTR(scan_sleep_millisecs, 0644, scan_sleep_millisecs_show,
 144                scan_sleep_millisecs_store);
 145
 146 static ssize_t alloc_sleep_millisecs_show(struct kobject *kobj,
 147                                           struct kobj_attribute *attr,
 148                                           char *buf)
 149 {
 150         return sprintf(buf, "%u\n", khugepaged_alloc_sleep_millisecs);
 151 }
 152
 153 static ssize_t alloc_sleep_millisecs_store(struct kobject *kobj,
 154                                            struct kobj_attribute *attr,
 155                                            const char *buf, size_t count)
 156 {
 157         unsigned long msecs;
 158         int err;
 159
 160         err = kstrtoul(buf, 10, &msecs);
 161         if (err || msecs > UINT_MAX)
 162                 return -EINVAL;
 163
 164         khugepaged_alloc_sleep_millisecs = msecs;
 165         khugepaged_sleep_expire = 0;
 166         wake_up_interruptible(&khugepaged_wait);
 167
 168         return count;
 169 }
 170 static struct kobj_attribute alloc_sleep_millisecs_attr =
 171         __ATTR(alloc_sleep_millisecs, 0644, alloc_sleep_millisecs_show,
 172                alloc_sleep_millisecs_store);
 173
 174 static ssize_t pages_to_scan_show(struct kobject *kobj,
 175                                   struct kobj_attribute *attr,
 176                                   char *buf)
 177 {
 178         return sprintf(buf, "%u\n", khugepaged_pages_to_scan);
 179 }
 180 static ssize_t pages_to_scan_store(struct kobject *kobj,
 181                                    struct kobj_attribute *attr,
 182                                    const char *buf, size_t count)
 183 {
 184         int err;
 185         unsigned long pages;
 186
 187         err = kstrtoul(buf, 10, &pages);
 188         if (err || !pages || pages > UINT_MAX)
 189                 return -EINVAL;
 190
 191         khugepaged_pages_to_scan = pages;
 192
 193         return count;
 194 }
 195 static struct kobj_attribute pages_to_scan_attr =
 196         __ATTR(pages_to_scan, 0644, pages_to_scan_show,
 197                pages_to_scan_store);
 198
 199 static ssize_t pages_collapsed_show(struct kobject *kobj,
 200                                     struct kobj_attribute *attr,
 201                                     char *buf)
 202 {
 203         return sprintf(buf, "%u\n", khugepaged_pages_collapsed);
 204 }
 205 static struct kobj_attribute pages_collapsed_attr =
 206         __ATTR_RO(pages_collapsed);
 207
 208 static ssize_t full_scans_show(struct kobject *kobj,
 209                                struct kobj_attribute *attr,
 210                                char *buf)
 211 {
 212         return sprintf(buf, "%u\n", khugepaged_full_scans);
 213 }
 214 static struct kobj_attribute full_scans_attr =
 215         __ATTR_RO(full_scans);
 216
 217 static ssize_t khugepaged_defrag_show(struct kobject *kobj,
 218                                       struct kobj_attribute *attr, char *buf)
 219 {
 220         return single_hugepage_flag_show(kobj, attr, buf,
 221                                 TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG);
 222 }
 223 static ssize_t khugepaged_defrag_store(struct kobject *kobj,
 224                                        struct kobj_attribute *attr,
 225                                        const char *buf, size_t count)
 226 {
 227         return single_hugepage_flag_store(kobj, attr, buf, count,
 228                                  TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG);
 229 }
 230 static struct kobj_attribute khugepaged_defrag_attr =
 231         __ATTR(defrag, 0644, khugepaged_defrag_show,
 232                khugepaged_defrag_store);
 233
 234 /*
 235  * max_ptes_none controls if khugepaged should collapse hugepages over
 236  * any unmapped ptes in turn potentially increasing the memory
 237  * footprint of the vmas. When max_ptes_none is 0 khugepaged will not
 238  * reduce the available free memory in the system as it
 239  * runs. Increasing max_ptes_none will instead potentially reduce the
 240  * free memory in the system during the khugepaged scan.
 241  */
 242 static ssize_t khugepaged_max_ptes_none_show(struct kobject *kobj,
 243                                              struct kobj_attribute *attr,
 244                                              char *buf)
 245 {
 246         return sprintf(buf, "%u\n", khugepaged_max_ptes_none);
 247 }
 248 static ssize_t khugepaged_max_ptes_none_store(struct kobject *kobj,
 249                                               struct kobj_attribute *attr,
 250                                               const char *buf, size_t count)
 251 {
 252         int err;
 253         unsigned long max_ptes_none;
 254
 255         err = kstrtoul(buf, 10, &max_ptes_none);
 256         if (err || max_ptes_none > HPAGE_PMD_NR-1)
 257                 return -EINVAL;
 258
 259         khugepaged_max_ptes_none = max_ptes_none;
 260
 261         return count;
 262 }
 263 static struct kobj_attribute khugepaged_max_ptes_none_attr =
 264         __ATTR(max_ptes_none, 0644, khugepaged_max_ptes_none_show,
 265                khugepaged_max_ptes_none_store);
 266
 267 static ssize_t khugepaged_max_ptes_swap_show(struct kobject *kobj,
 268                                              struct kobj_attribute *attr,
 269                                              char *buf)
 270 {
 271         return sprintf(buf, "%u\n", khugepaged_max_ptes_swap);
 272 }
 273
 274 static ssize_t khugepaged_max_ptes_swap_store(struct kobject *kobj,
 275                                               struct kobj_attribute *attr,
 276                                               const char *buf, size_t count)
 277 {
 278         int err;
 279         unsigned long max_ptes_swap;
 280
 281         err  = kstrtoul(buf, 10, &max_ptes_swap);
 282         if (err || max_ptes_swap > HPAGE_PMD_NR-1)
 283                 return -EINVAL;
 284
 285         khugepaged_max_ptes_swap = max_ptes_swap;
 286
 287         return count;
 288 }
 289
 290 static struct kobj_attribute khugepaged_max_ptes_swap_attr =
 291         __ATTR(max_ptes_swap, 0644, khugepaged_max_ptes_swap_show,
 292                khugepaged_max_ptes_swap_store);
 293
 294 static struct attribute *khugepaged_attr[] = {
 295         &khugepaged_defrag_attr.attr,
 296         &khugepaged_max_ptes_none_attr.attr,
 297         &pages_to_scan_attr.attr,
 298         &pages_collapsed_attr.attr,
 299         &full_scans_attr.attr,
 300         &scan_sleep_millisecs_attr.attr,
 301         &alloc_sleep_millisecs_attr.attr,
 302         &khugepaged_max_ptes_swap_attr.attr,
 303         NULL,
 304 };
 305
 306 struct attribute_group khugepaged_attr_group = {
 307         .attrs = khugepaged_attr,
 308         .name = "khugepaged",
 309 };
 310 #endif /* CONFIG_SYSFS */
 311
 312 int hugepage_madvise(struct vm_area_struct *vma,
 313                      unsigned long *vm_flags, int advice)
 314 {
 315         switch (advice) {
 316         case MADV_HUGEPAGE:
 317 #ifdef CONFIG_S390
 318                 /*
 319                  * qemu blindly sets MADV_HUGEPAGE on all allocations, but s390
 320                  * can't handle this properly after s390_enable_sie, so we simply
 321                  * ignore the madvise to prevent qemu from causing a SIGSEGV.
 322                  */
 323                 if (mm_has_pgste(vma->vm_mm))
 324                         return 0;
 325 #endif
 326                 *vm_flags &= ~VM_NOHUGEPAGE;
 327                 *vm_flags |= VM_HUGEPAGE;
 328                 /*
 329                  * If the vma become good for khugepaged to scan,
 330                  * register it here without waiting a page fault that
 331                  * may not happen any time soon.
 332                  */
 333                 if (!(*vm_flags & VM_NO_KHUGEPAGED) &&
 334                                 khugepaged_enter_vma_merge(vma, *vm_flags))
 335                         return -ENOMEM;
 336                 break;
 337         case MADV_NOHUGEPAGE:
 338                 *vm_flags &= ~VM_HUGEPAGE;
 339                 *vm_flags |= VM_NOHUGEPAGE;
 340                 /*
 341                  * Setting VM_NOHUGEPAGE will prevent khugepaged from scanning
 342                  * this vma even if we leave the mm registered in khugepaged if
 343                  * it got registered before VM_NOHUGEPAGE was set.
 344                  */
 345                 break;
 346         }
 347
 348         return 0;
 349 }
 350
 351 int __init khugepaged_init(void)
 352 {
 353         mm_slot_cache = kmem_cache_create("khugepaged_mm_slot",
 354                                           sizeof(struct mm_slot),
 355                                           __alignof__(struct mm_slot), 0, NULL);
 356         if (!mm_slot_cache)
 357                 return -ENOMEM;
 358
 359         khugepaged_pages_to_scan = HPAGE_PMD_NR * 8;
 360         khugepaged_max_ptes_none = HPAGE_PMD_NR - 1;
 361         khugepaged_max_ptes_swap = HPAGE_PMD_NR / 8;
 362
 363         return 0;
 364 }
 365
 366 void __init khugepaged_destroy(void)
 367 {
 368         kmem_cache_destroy(mm_slot_cache);
 369 }
 370
 371 static inline struct mm_slot *alloc_mm_slot(void)
 372 {
 373         if (!mm_slot_cache)     /* initialization failed */
 374                 return NULL;
 375         return kmem_cache_zalloc(mm_slot_cache, GFP_KERNEL);
 376 }
 377
 378 static inline void free_mm_slot(struct mm_slot *mm_slot)
 379 {
 380         kmem_cache_free(mm_slot_cache, mm_slot);
 381 }
 382
 383 static struct mm_slot *get_mm_slot(struct mm_struct *mm)
 384 {
 385         struct mm_slot *mm_slot;
 386
 387         hash_for_each_possible(mm_slots_hash, mm_slot, hash, (unsigned long)mm)
 388                 if (mm == mm_slot->mm)
 389                         return mm_slot;
 390
 391         return NULL;
 392 }
 393
 394 static void insert_to_mm_slots_hash(struct mm_struct *mm,
 395                                     struct mm_slot *mm_slot)
 396 {
 397         mm_slot->mm = mm;
 398         hash_add(mm_slots_hash, &mm_slot->hash, (long)mm);
 399 }
 400
 401 static inline int khugepaged_test_exit(struct mm_struct *mm)
 402 {
 403         return atomic_read(&mm->mm_users) == 0;
 404 }
 405
 406 static bool hugepage_vma_check(struct vm_area_struct *vma,
 407                                unsigned long vm_flags)
 408 {
 409         if ((!(vm_flags & VM_HUGEPAGE) && !khugepaged_always()) ||
 410             (vm_flags & VM_NOHUGEPAGE) ||
 411             test_bit(MMF_DISABLE_THP, &vma->vm_mm->flags))
 412                 return false;
 413
 414         if (shmem_file(vma->vm_file) ||
 415             (IS_ENABLED(CONFIG_READ_ONLY_THP_FOR_FS) &&
 416              vma->vm_file &&
 417              (vm_flags & VM_DENYWRITE))) {
 418                 return IS_ALIGNED((vma->vm_start >> PAGE_SHIFT) - vma->vm_pgoff,
 419                                 HPAGE_PMD_NR);
 420         }
 421         if (!vma->anon_vma || vma->vm_ops)
 422                 return false;
 423         if (vma_is_temporary_stack(vma))
 424                 return false;
 425         return !(vm_flags & VM_NO_KHUGEPAGED);
 426 }
 427
 428 int __khugepaged_enter(struct mm_struct *mm)
 429 {
 430         struct mm_slot *mm_slot;
 431         int wakeup;
 432
 433         mm_slot = alloc_mm_slot();
 434         if (!mm_slot)
 435                 return -ENOMEM;
 436
 437         /* __khugepaged_exit() must not run from under us */
 438         VM_BUG_ON_MM(khugepaged_test_exit(mm), mm);
 439         if (unlikely(test_and_set_bit(MMF_VM_HUGEPAGE, &mm->flags))) {
 440                 free_mm_slot(mm_slot);
 441                 return 0;
 442         }
 443
 444         spin_lock(&khugepaged_mm_lock);
 445         insert_to_mm_slots_hash(mm, mm_slot);
 446         /*
 447          * Insert just behind the scanning cursor, to let the area settle
 448          * down a little.
 449          */
 450         wakeup = list_empty(&khugepaged_scan.mm_head);
 451         list_add_tail(&mm_slot->mm_node, &khugepaged_scan.mm_head);
 452         spin_unlock(&khugepaged_mm_lock);
 453
 454         mmgrab(mm);
 455         if (wakeup)
 456                 wake_up_interruptible(&khugepaged_wait);
 457
 458         return 0;
 459 }
 460
 461 int khugepaged_enter_vma_merge(struct vm_area_struct *vma,
 462                                unsigned long vm_flags)
 463 {
 464         unsigned long hstart, hend;
 465
 466         /*
 467          * khugepaged only supports read-only files for non-shmem files.
 468          * khugepaged does not yet work on special mappings. And
 469          * file-private shmem THP is not supported.
 470          */
 471         if (!hugepage_vma_check(vma, vm_flags))
 472                 return 0;
 473
 474         hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK;
 475         hend = vma->vm_end & HPAGE_PMD_MASK;
 476         if (hstart < hend)
 477                 return khugepaged_enter(vma, vm_flags);
 478         return 0;
 479 }
 480
 481 void __khugepaged_exit(struct mm_struct *mm)
 482 {
 483         struct mm_slot *mm_slot;
 484         int free = 0;
 485
 486         spin_lock(&khugepaged_mm_lock);
 487         mm_slot = get_mm_slot(mm);
 488         if (mm_slot && khugepaged_scan.mm_slot != mm_slot) {
 489                 hash_del(&mm_slot->hash);
 490                 list_del(&mm_slot->mm_node);
 491                 free = 1;
 492         }
 493         spin_unlock(&khugepaged_mm_lock);
 494
 495         if (free) {
 496                 clear_bit(MMF_VM_HUGEPAGE, &mm->flags);
 497                 free_mm_slot(mm_slot);
 498                 mmdrop(mm);
 499         } else if (mm_slot) {
 500                 /*
 501                  * This is required to serialize against
 502                  * khugepaged_test_exit() (which is guaranteed to run
 503                  * under mmap sem read mode). Stop here (after we
 504                  * return all pagetables will be destroyed) until
 505                  * khugepaged has finished working on the pagetables
 506                  * under the mmap_sem.
 507                  */
 508                 down_write(&mm->mmap_sem);
 509                 up_write(&mm->mmap_sem);
 510         }
 511 }
 512
 513 static void release_pte_page(struct page *page)
 514 {
 515         dec_node_page_state(page, NR_ISOLATED_ANON + page_is_file_lru(page));
 516         unlock_page(page);
 517         putback_lru_page(page);
 518 }
 519
 520 static void release_pte_pages(pte_t *pte, pte_t *_pte)
 521 {
 522         while (--_pte >= pte) {
 523                 pte_t pteval = *_pte;
 524                 if (!pte_none(pteval) && !is_zero_pfn(pte_pfn(pteval)))
 525                         release_pte_page(pte_page(pteval));
 526         }
 527 }
 528
 529 static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
 530                                         unsigned long address,
 531                                         pte_t *pte)
 532 {
 533         struct page *page = NULL;
 534         pte_t *_pte;
 535         int none_or_zero = 0, result = 0, referenced = 0;
 536         bool writable = false;
 537
 538         for (_pte = pte; _pte < pte+HPAGE_PMD_NR;
 539              _pte++, address += PAGE_SIZE) {
 540                 pte_t pteval = *_pte;
 541                 if (pte_none(pteval) || (pte_present(pteval) &&
 542                                 is_zero_pfn(pte_pfn(pteval)))) {
 543                         if (!userfaultfd_armed(vma) &&
 544                             ++none_or_zero <= khugepaged_max_ptes_none) {
 545                                 continue;
 546                         } else {
 547                                 result = SCAN_EXCEED_NONE_PTE;
 548                                 goto out;
 549                         }
 550                 }
 551                 if (!pte_present(pteval)) {
 552                         result = SCAN_PTE_NON_PRESENT;
 553                         goto out;
 554                 }
 555                 page = vm_normal_page(vma, address, pteval);
 556                 if (unlikely(!page)) {
 557                         result = SCAN_PAGE_NULL;
 558                         goto out;
 559                 }
 560
 561                 /* TODO: teach khugepaged to collapse THP mapped with pte */
 562                 if (PageCompound(page)) {
 563                         result = SCAN_PAGE_COMPOUND;
 564                         goto out;
 565                 }
 566
 567                 VM_BUG_ON_PAGE(!PageAnon(page), page);
 568
 569                 /*
 570                  * We can do it before isolate_lru_page because the
 571                  * page can't be freed from under us. NOTE: PG_lock
 572                  * is needed to serialize against split_huge_page
 573                  * when invoked from the VM.
 574                  */
 575                 if (!trylock_page(page)) {
 576                         result = SCAN_PAGE_LOCK;
 577                         goto out;
 578                 }
 579
 580                 /*
 581                  * cannot use mapcount: can't collapse if there's a gup pin.
 582                  * The page must only be referenced by the scanned process
 583                  * and page swap cache.
 584                  */
 585                 if (page_count(page) != 1 + PageSwapCache(page)) {
 586                         unlock_page(page);
 587                         result = SCAN_PAGE_COUNT;
 588                         goto out;
 589                 }
 590                 if (pte_write(pteval)) {
 591                         writable = true;
 592                 } else {
 593                         if (PageSwapCache(page) &&
 594                             !reuse_swap_page(page, NULL)) {
 595                                 unlock_page(page);
 596                                 result = SCAN_SWAP_CACHE_PAGE;
 597                                 goto out;
 598                         }
 599                         /*
 600                          * Page is not in the swap cache. It can be collapsed
 601                          * into a THP.
 602                          */
 603                 }
 604
 605                 /*
 606                  * Isolate the page to avoid collapsing an hugepage
 607                  * currently in use by the VM.
 608                  */
 609                 if (isolate_lru_page(page)) {
 610                         unlock_page(page);
 611                         result = SCAN_DEL_PAGE_LRU;
 612                         goto out;
 613                 }
 614                 inc_node_page_state(page,
 615                                 NR_ISOLATED_ANON + page_is_file_lru(page));
 616                 VM_BUG_ON_PAGE(!PageLocked(page), page);
 617                 VM_BUG_ON_PAGE(PageLRU(page), page);
 618
 619                 /* There should be enough young pte to collapse the page */
 620                 if (pte_young(pteval) ||
 621                     page_is_young(page) || PageReferenced(page) ||
 622                     mmu_notifier_test_young(vma->vm_mm, address))
 623                         referenced++;
 624         }
 625         if (likely(writable)) {
 626                 if (likely(referenced)) {
 627                         result = SCAN_SUCCEED;
 628                         trace_mm_collapse_huge_page_isolate(page, none_or_zero,
 629                                                             referenced, writable, result);
 630                         return 1;
 631                 }
 632         } else {
 633                 result = SCAN_PAGE_RO;
 634         }
 635
 636 out:
 637         release_pte_pages(pte, _pte);
 638         trace_mm_collapse_huge_page_isolate(page, none_or_zero,
 639                                             referenced, writable, result);
 640         return 0;
 641 }
 642
 643 static void __collapse_huge_page_copy(pte_t *pte, struct page *page,
 644                                       struct vm_area_struct *vma,
 645                                       unsigned long address,
 646                                       spinlock_t *ptl)
 647 {
 648         pte_t *_pte;
 649         for (_pte = pte; _pte < pte + HPAGE_PMD_NR;
 650                                 _pte++, page++, address += PAGE_SIZE) {
 651                 pte_t pteval = *_pte;
 652                 struct page *src_page;
 653
 654                 if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) {
 655                         clear_user_highpage(page, address);
 656                         add_mm_counter(vma->vm_mm, MM_ANONPAGES, 1);
 657                         if (is_zero_pfn(pte_pfn(pteval))) {
 658                                 /*
 659                                  * ptl mostly unnecessary.
 660                                  */
 661                                 spin_lock(ptl);
 662                                 /*
 663                                  * paravirt calls inside pte_clear here are
 664                                  * superfluous.
 665                                  */
 666                                 pte_clear(vma->vm_mm, address, _pte);
 667                                 spin_unlock(ptl);
 668                         }
 669                 } else {
 670                         src_page = pte_page(pteval);
 671                         copy_user_highpage(page, src_page, address, vma);
 672                         VM_BUG_ON_PAGE(page_mapcount(src_page) != 1, src_page);
 673                         release_pte_page(src_page);
 674                         /*
 675                          * ptl mostly unnecessary, but preempt has to
 676                          * be disabled to update the per-cpu stats
 677                          * inside page_remove_rmap().
 678                          */
 679                         spin_lock(ptl);
 680                         /*
 681                          * paravirt calls inside pte_clear here are
 682                          * superfluous.
 683                          */
 684                         pte_clear(vma->vm_mm, address, _pte);
 685                         page_remove_rmap(src_page, false);
 686                         spin_unlock(ptl);
 687                         free_page_and_swap_cache(src_page);
 688                 }
 689         }
 690 }
 691
 692 static void khugepaged_alloc_sleep(void)
 693 {
 694         DEFINE_WAIT(wait);
 695
 696         add_wait_queue(&khugepaged_wait, &wait);
 697         freezable_schedule_timeout_interruptible(
 698                 msecs_to_jiffies(khugepaged_alloc_sleep_millisecs));
 699         remove_wait_queue(&khugepaged_wait, &wait);
 700 }
 701
 702 static int khugepaged_node_load[MAX_NUMNODES];
 703
 704 static bool khugepaged_scan_abort(int nid)
 705 {
 706         int i;
 707
 708         /*
 709          * If node_reclaim_mode is disabled, then no extra effort is made to
 710          * allocate memory locally.
 711          */
 712         if (!node_reclaim_mode)
 713                 return false;
 714
 715         /* If there is a count for this node already, it must be acceptable */
 716         if (khugepaged_node_load[nid])
 717                 return false;
 718
 719         for (i = 0; i < MAX_NUMNODES; i++) {
 720                 if (!khugepaged_node_load[i])
 721                         continue;
 722                 if (node_distance(nid, i) > node_reclaim_distance)
 723                         return true;
 724         }
 725         return false;
 726 }
 727
 728 /* Defrag for khugepaged will enter direct reclaim/compaction if necessary */
 729 static inline gfp_t alloc_hugepage_khugepaged_gfpmask(void)
 730 {
 731         return khugepaged_defrag() ? GFP_TRANSHUGE : GFP_TRANSHUGE_LIGHT;
 732 }
 733
 734 #ifdef CONFIG_NUMA
 735 static int khugepaged_find_target_node(void)
 736 {
 737         static int last_khugepaged_target_node = NUMA_NO_NODE;
 738         int nid, target_node = 0, max_value = 0;
 739
 740         /* find first node with max normal pages hit */
 741         for (nid = 0; nid < MAX_NUMNODES; nid++)
 742                 if (khugepaged_node_load[nid] > max_value) {
 743                         max_value = khugepaged_node_load[nid];
 744                         target_node = nid;
 745                 }
 746
 747         /* do some balance if several nodes have the same hit record */
 748         if (target_node <= last_khugepaged_target_node)
 749                 for (nid = last_khugepaged_target_node + 1; nid < MAX_NUMNODES;
 750                                 nid++)
 751                         if (max_value == khugepaged_node_load[nid]) {
 752                                 target_node = nid;
 753                                 break;
 754                         }
 755
 756         last_khugepaged_target_node = target_node;
 757         return target_node;
 758 }
 759
 760 static bool khugepaged_prealloc_page(struct page **hpage, bool *wait)
 761 {
 762         if (IS_ERR(*hpage)) {
 763                 if (!*wait)
 764                         return false;
 765
 766                 *wait = false;
 767                 *hpage = NULL;
 768                 khugepaged_alloc_sleep();
 769         } else if (*hpage) {
 770                 put_page(*hpage);
 771                 *hpage = NULL;
 772         }
 773
 774         return true;
 775 }
 776
 777 static struct page *
 778 khugepaged_alloc_page(struct page **hpage, gfp_t gfp, int node)
 779 {
 780         VM_BUG_ON_PAGE(*hpage, *hpage);
 781
 782         *hpage = __alloc_pages_node(node, gfp, HPAGE_PMD_ORDER);
 783         if (unlikely(!*hpage)) {
 784                 count_vm_event(THP_COLLAPSE_ALLOC_FAILED);
 785                 *hpage = ERR_PTR(-ENOMEM);
 786                 return NULL;
 787         }
 788
 789         prep_transhuge_page(*hpage);
 790         count_vm_event(THP_COLLAPSE_ALLOC);
 791         return *hpage;
 792 }
 793 #else
 794 static int khugepaged_find_target_node(void)
 795 {
 796         return 0;
 797 }
 798
 799 static inline struct page *alloc_khugepaged_hugepage(void)
 800 {
 801         struct page *page;
 802
 803         page = alloc_pages(alloc_hugepage_khugepaged_gfpmask(),
 804                            HPAGE_PMD_ORDER);
 805         if (page)
 806                 prep_transhuge_page(page);
 807         return page;
 808 }
 809
 810 static struct page *khugepaged_alloc_hugepage(bool *wait)
 811 {
 812         struct page *hpage;
 813
 814         do {
 815                 hpage = alloc_khugepaged_hugepage();
 816                 if (!hpage) {
 817                         count_vm_event(THP_COLLAPSE_ALLOC_FAILED);
 818                         if (!*wait)
 819                                 return NULL;
 820
 821                         *wait = false;
 822                         khugepaged_alloc_sleep();
 823                 } else
 824                         count_vm_event(THP_COLLAPSE_ALLOC);
 825         } while (unlikely(!hpage) && likely(khugepaged_enabled()));
 826
 827         return hpage;
 828 }
 829
 830 static bool khugepaged_prealloc_page(struct page **hpage, bool *wait)
 831 {
 832         if (!*hpage)
 833                 *hpage = khugepaged_alloc_hugepage(wait);
 834
 835         if (unlikely(!*hpage))
 836                 return false;
 837
 838         return true;
 839 }
 840
 841 static struct page *
 842 khugepaged_alloc_page(struct page **hpage, gfp_t gfp, int node)
 843 {
 844         VM_BUG_ON(!*hpage);
 845
 846         return  *hpage;
 847 }
 848 #endif
 849
 850 /*
 851  * If mmap_sem temporarily dropped, revalidate vma
 852  * before taking mmap_sem.
 853  * Return 0 if succeeds, otherwise return none-zero
 854  * value (scan code).
 855  */
 856
 857 static int hugepage_vma_revalidate(struct mm_struct *mm, unsigned long address,
 858                 struct vm_area_struct **vmap)
 859 {
 860         struct vm_area_struct *vma;
 861         unsigned long hstart, hend;
 862
 863         if (unlikely(khugepaged_test_exit(mm)))
 864                 return SCAN_ANY_PROCESS;
 865
 866         *vmap = vma = find_vma(mm, address);
 867         if (!vma)
 868                 return SCAN_VMA_NULL;
 869
 870         hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK;
 871         hend = vma->vm_end & HPAGE_PMD_MASK;
 872         if (address < hstart || address + HPAGE_PMD_SIZE > hend)
 873                 return SCAN_ADDRESS_RANGE;
 874         if (!hugepage_vma_check(vma, vma->vm_flags))
 875                 return SCAN_VMA_CHECK;
 876         return 0;
 877 }
 878
 879 /*
 880  * Bring missing pages in from swap, to complete THP collapse.
 881  * Only done if khugepaged_scan_pmd believes it is worthwhile.
 882  *
 883  * Called and returns without pte mapped or spinlocks held,
 884  * but with mmap_sem held to protect against vma changes.
 885  */
 886
 887 static bool __collapse_huge_page_swapin(struct mm_struct *mm,
 888                                         struct vm_area_struct *vma,
 889                                         unsigned long address, pmd_t *pmd,
 890                                         int referenced)
 891 {
 892         int swapped_in = 0;
 893         vm_fault_t ret = 0;
 894         struct vm_fault vmf = {
 895                 .vma = vma,
 896                 .address = address,
 897                 .flags = FAULT_FLAG_ALLOW_RETRY,
 898                 .pmd = pmd,
 899                 .pgoff = linear_page_index(vma, address),
 900         };
 901
 902         vmf.pte = pte_offset_map(pmd, address);
 903         for (; vmf.address < address + HPAGE_PMD_NR*PAGE_SIZE;
 904                         vmf.pte++, vmf.address += PAGE_SIZE) {
 905                 vmf.orig_pte = *vmf.pte;
 906                 if (!is_swap_pte(vmf.orig_pte))
 907                         continue;
 908                 swapped_in++;
 909                 ret = do_swap_page(&vmf);
 910
 911                 /* do_swap_page returns VM_FAULT_RETRY with released mmap_sem */
 912                 if (ret & VM_FAULT_RETRY) {
 913                         down_read(&mm->mmap_sem);
 914                         if (hugepage_vma_revalidate(mm, address, &vmf.vma)) {
 915                                 /* vma is no longer available, don't continue to swapin */
 916                                 trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 0);
 917                                 return false;
 918                         }
 919                         /* check if the pmd is still valid */
 920                         if (mm_find_pmd(mm, address) != pmd) {
 921                                 trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 0);
 922                                 return false;
 923                         }
 924                 }
 925                 if (ret & VM_FAULT_ERROR) {
 926                         trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 0);
 927                         return false;
 928                 }
 929                 /* pte is unmapped now, we need to map it */
 930                 vmf.pte = pte_offset_map(pmd, vmf.address);
 931         }
 932         vmf.pte--;
 933         pte_unmap(vmf.pte);
 934         trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 1);
 935         return true;
 936 }
 937
 938 static void collapse_huge_page(struct mm_struct *mm,
 939                                    unsigned long address,
 940                                    struct page **hpage,
 941                                    int node, int referenced, int unmapped)
 942 {
 943         pmd_t *pmd, _pmd;
 944         pte_t *pte;
 945         pgtable_t pgtable;
 946         struct page *new_page;
 947         spinlock_t *pmd_ptl, *pte_ptl;
 948         int isolated = 0, result = 0;
 949         struct mem_cgroup *memcg;
 950         struct vm_area_struct *vma;
 951         struct mmu_notifier_range range;
 952         gfp_t gfp;
 953
 954         VM_BUG_ON(address & ~HPAGE_PMD_MASK);
 955
 956         /* Only allocate from the target node */
 957         gfp = alloc_hugepage_khugepaged_gfpmask() | __GFP_THISNODE;
 958
 959         /*
 960          * Before allocating the hugepage, release the mmap_sem read lock.
 961          * The allocation can take potentially a long time if it involves
 962          * sync compaction, and we do not need to hold the mmap_sem during
 963          * that. We will recheck the vma after taking it again in write mode.
 964          */
 965         up_read(&mm->mmap_sem);
 966         new_page = khugepaged_alloc_page(hpage, gfp, node);
 967         if (!new_page) {
 968                 result = SCAN_ALLOC_HUGE_PAGE_FAIL;
 969                 goto out_nolock;
 970         }
 971
 972         if (unlikely(mem_cgroup_try_charge(new_page, mm, gfp, &memcg, true))) {
 973                 result = SCAN_CGROUP_CHARGE_FAIL;
 974                 goto out_nolock;
 975         }
 976
 977         down_read(&mm->mmap_sem);
 978         result = hugepage_vma_revalidate(mm, address, &vma);
 979         if (result) {
 980                 mem_cgroup_cancel_charge(new_page, memcg, true);
 981                 up_read(&mm->mmap_sem);
 982                 goto out_nolock;
 983         }
 984
 985         pmd = mm_find_pmd(mm, address);
 986         if (!pmd) {
 987                 result = SCAN_PMD_NULL;
 988                 mem_cgroup_cancel_charge(new_page, memcg, true);
 989                 up_read(&mm->mmap_sem);
 990                 goto out_nolock;
 991         }
 992
 993         /*
 994          * __collapse_huge_page_swapin always returns with mmap_sem locked.
 995          * If it fails, we release mmap_sem and jump out_nolock.
 996          * Continuing to collapse causes inconsistency.
 997          */
 998         if (unmapped && !__collapse_huge_page_swapin(mm, vma, address,
 999                                                      pmd, referenced)) {
1000                 mem_cgroup_cancel_charge(new_page, memcg, true);
1001                 up_read(&mm->mmap_sem);
1002                 goto out_nolock;
1003         }
1004
1005         up_read(&mm->mmap_sem);
1006         /*
1007          * Prevent all access to pagetables with the exception of
1008          * gup_fast later handled by the ptep_clear_flush and the VM
1009          * handled by the anon_vma lock + PG_lock.
1010          */
1011         down_write(&mm->mmap_sem);
1012         result = SCAN_ANY_PROCESS;
1013         if (!mmget_still_valid(mm))
1014                 goto out;
1015         result = hugepage_vma_revalidate(mm, address, &vma);
1016         if (result)
1017                 goto out;
1018         /* check if the pmd is still valid */
1019         if (mm_find_pmd(mm, address) != pmd)
1020                 goto out;
1021
1022         anon_vma_lock_write(vma->anon_vma);
1023
1024         mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, NULL, mm,
1025                                 address, address + HPAGE_PMD_SIZE);
1026         mmu_notifier_invalidate_range_start(&range);
1027
1028         pte = pte_offset_map(pmd, address);
1029         pte_ptl = pte_lockptr(mm, pmd);
1030
1031         pmd_ptl = pmd_lock(mm, pmd); /* probably unnecessary */
1032         /*
1033          * After this gup_fast can't run anymore. This also removes
1034          * any huge TLB entry from the CPU so we won't allow
1035          * huge and small TLB entries for the same virtual address
1036          * to avoid the risk of CPU bugs in that area.
1037          */
1038         _pmd = pmdp_collapse_flush(vma, address, pmd);
1039         spin_unlock(pmd_ptl);
1040         mmu_notifier_invalidate_range_end(&range);
1041
1042         spin_lock(pte_ptl);
1043         isolated = __collapse_huge_page_isolate(vma, address, pte);
1044         spin_unlock(pte_ptl);
1045
1046         if (unlikely(!isolated)) {
1047                 pte_unmap(pte);
1048                 spin_lock(pmd_ptl);
1049                 BUG_ON(!pmd_none(*pmd));
1050                 /*
1051                  * We can only use set_pmd_at when establishing
1052                  * hugepmds and never for establishing regular pmds that
1053                  * points to regular pagetables. Use pmd_populate for that
1054                  */
1055                 pmd_populate(mm, pmd, pmd_pgtable(_pmd));
1056                 spin_unlock(pmd_ptl);
1057                 anon_vma_unlock_write(vma->anon_vma);
1058                 result = SCAN_FAIL;
1059                 goto out;
1060         }
1061
1062         /*
1063          * All pages are isolated and locked so anon_vma rmap
1064          * can't run anymore.
1065          */
1066         anon_vma_unlock_write(vma->anon_vma);
1067
1068         __collapse_huge_page_copy(pte, new_page, vma, address, pte_ptl);
1069         pte_unmap(pte);
1070         __SetPageUptodate(new_page);
1071         pgtable = pmd_pgtable(_pmd);
1072
1073         _pmd = mk_huge_pmd(new_page, vma->vm_page_prot);
1074         _pmd = maybe_pmd_mkwrite(pmd_mkdirty(_pmd), vma);
1075
1076         /*
1077          * spin_lock() below is not the equivalent of smp_wmb(), so
1078          * this is needed to avoid the copy_huge_page writes to become
1079          * visible after the set_pmd_at() write.
1080          */
1081         smp_wmb();
1082
1083         spin_lock(pmd_ptl);
1084         BUG_ON(!pmd_none(*pmd));
1085         page_add_new_anon_rmap(new_page, vma, address, true);
1086         mem_cgroup_commit_charge(new_page, memcg, false, true);
1087         count_memcg_events(memcg, THP_COLLAPSE_ALLOC, 1);
1088         lru_cache_add_active_or_unevictable(new_page, vma);
1089         pgtable_trans_huge_deposit(mm, pmd, pgtable);
1090         set_pmd_at(mm, address, pmd, _pmd);
1091         update_mmu_cache_pmd(vma, address, pmd);
1092         spin_unlock(pmd_ptl);
1093
1094         *hpage = NULL;
1095
1096         khugepaged_pages_collapsed++;
1097         result = SCAN_SUCCEED;
1098 out_up_write:
1099         up_write(&mm->mmap_sem);
1100 out_nolock:
1101         trace_mm_collapse_huge_page(mm, isolated, result);
1102         return;
1103 out:
1104         mem_cgroup_cancel_charge(new_page, memcg, true);
1105         goto out_up_write;
1106 }
1107
1108 static int khugepaged_scan_pmd(struct mm_struct *mm,
1109                                struct vm_area_struct *vma,
1110                                unsigned long address,
1111                                struct page **hpage)
1112 {
1113         pmd_t *pmd;
1114         pte_t *pte, *_pte;
1115         int ret = 0, none_or_zero = 0, result = 0, referenced = 0;
1116         struct page *page = NULL;
1117         unsigned long _address;
1118         spinlock_t *ptl;
1119         int node = NUMA_NO_NODE, unmapped = 0;
1120         bool writable = false;
1121
1122         VM_BUG_ON(address & ~HPAGE_PMD_MASK);
1123
1124         pmd = mm_find_pmd(mm, address);
1125         if (!pmd) {
1126                 result = SCAN_PMD_NULL;
1127                 goto out;
1128         }
1129
1130         memset(khugepaged_node_load, 0, sizeof(khugepaged_node_load));
1131         pte = pte_offset_map_lock(mm, pmd, address, &ptl);
1132         for (_address = address, _pte = pte; _pte < pte+HPAGE_PMD_NR;
1133              _pte++, _address += PAGE_SIZE) {
1134                 pte_t pteval = *_pte;
1135                 if (is_swap_pte(pteval)) {
1136                         if (++unmapped <= khugepaged_max_ptes_swap) {
1137                                 /*
1138                                  * Always be strict with uffd-wp
1139                                  * enabled swap entries.  Please see
1140                                  * comment below for pte_uffd_wp().
1141                                  */
1142                                 if (pte_swp_uffd_wp(pteval)) {
1143                                         result = SCAN_PTE_UFFD_WP;
1144                                         goto out_unmap;
1145                                 }
1146                                 continue;
1147                         } else {
1148                                 result = SCAN_EXCEED_SWAP_PTE;
1149                                 goto out_unmap;
1150                         }
1151                 }
1152                 if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) {
1153                         if (!userfaultfd_armed(vma) &&
1154                             ++none_or_zero <= khugepaged_max_ptes_none) {
1155                                 continue;
1156                         } else {
1157                                 result = SCAN_EXCEED_NONE_PTE;
1158                                 goto out_unmap;
1159                         }
1160                 }
1161                 if (!pte_present(pteval)) {
1162                         result = SCAN_PTE_NON_PRESENT;
1163                         goto out_unmap;
1164                 }
1165                 if (pte_uffd_wp(pteval)) {
1166                         /*
1167                          * Don't collapse the page if any of the small
1168                          * PTEs are armed with uffd write protection.
1169                          * Here we can also mark the new huge pmd as
1170                          * write protected if any of the small ones is
1171                          * marked but that could bring uknown
1172                          * userfault messages that falls outside of
1173                          * the registered range.  So, just be simple.
1174                          */
1175                         result = SCAN_PTE_UFFD_WP;
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                 result = SCAN_PAGE_RO;
1234         } else if (!referenced || (unmapped && referenced < HPAGE_PMD_NR/2)) {
1235                 result = SCAN_LACK_REFERENCED_PAGE;
1236         } else {
1237                 result = SCAN_SUCCEED;
1238                 ret = 1;
1239         }
1240 out_unmap:
1241         pte_unmap_unlock(pte, ptl);
1242         if (ret) {
1243                 node = khugepaged_find_target_node();
1244                 /* collapse_huge_page will return with the mmap_sem released */
1245                 collapse_huge_page(mm, address, hpage, node,
1246                                 referenced, unmapped);
1247         }
1248 out:
1249         trace_mm_khugepaged_scan_pmd(mm, page, writable, referenced,
1250                                      none_or_zero, result, unmapped);
1251         return ret;
1252 }
1253
1254 static void collect_mm_slot(struct mm_slot *mm_slot)
1255 {
1256         struct mm_struct *mm = mm_slot->mm;
1257
1258         lockdep_assert_held(&khugepaged_mm_lock);
1259
1260         if (khugepaged_test_exit(mm)) {
1261                 /* free mm_slot */
1262                 hash_del(&mm_slot->hash);
1263                 list_del(&mm_slot->mm_node);
1264
1265                 /*
1266                  * Not strictly needed because the mm exited already.
1267                  *
1268                  * clear_bit(MMF_VM_HUGEPAGE, &mm->flags);
1269                  */
1270
1271                 /* khugepaged_mm_lock actually not necessary for the below */
1272                 free_mm_slot(mm_slot);
1273                 mmdrop(mm);
1274         }
1275 }
1276
1277 #ifdef CONFIG_SHMEM
1278 /*
1279  * Notify khugepaged that given addr of the mm is pte-mapped THP. Then
1280  * khugepaged should try to collapse the page table.
1281  */
1282 static int khugepaged_add_pte_mapped_thp(struct mm_struct *mm,
1283                                          unsigned long addr)
1284 {
1285         struct mm_slot *mm_slot;
1286
1287         VM_BUG_ON(addr & ~HPAGE_PMD_MASK);
1288
1289         spin_lock(&khugepaged_mm_lock);
1290         mm_slot = get_mm_slot(mm);
1291         if (likely(mm_slot && mm_slot->nr_pte_mapped_thp < MAX_PTE_MAPPED_THP))
1292                 mm_slot->pte_mapped_thp[mm_slot->nr_pte_mapped_thp++] = addr;
1293         spin_unlock(&khugepaged_mm_lock);
1294         return 0;
1295 }
1296
1297 /**
1298  * Try to collapse a pte-mapped THP for mm at address haddr.
1299  *
1300  * This function checks whether all the PTEs in the PMD are pointing to the
1301  * right THP. If so, retract the page table so the THP can refault in with
1302  * as pmd-mapped.
1303  */
1304 void collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr)
1305 {
1306         unsigned long haddr = addr & HPAGE_PMD_MASK;
1307         struct vm_area_struct *vma = find_vma(mm, haddr);
1308         struct page *hpage = NULL;
1309         pte_t *start_pte, *pte;
1310         pmd_t *pmd, _pmd;
1311         spinlock_t *ptl;
1312         int count = 0;
1313         int i;
1314
1315         if (!vma || !vma->vm_file ||
1316             vma->vm_start > haddr || vma->vm_end < haddr + HPAGE_PMD_SIZE)
1317                 return;
1318
1319         /*
1320          * This vm_flags may not have VM_HUGEPAGE if the page was not
1321          * collapsed by this mm. But we can still collapse if the page is
1322          * the valid THP. Add extra VM_HUGEPAGE so hugepage_vma_check()
1323          * will not fail the vma for missing VM_HUGEPAGE
1324          */
1325         if (!hugepage_vma_check(vma, vma->vm_flags | VM_HUGEPAGE))
1326                 return;
1327
1328         pmd = mm_find_pmd(mm, haddr);
1329         if (!pmd)
1330                 return;
1331
1332         start_pte = pte_offset_map_lock(mm, pmd, haddr, &ptl);
1333
1334         /* step 1: check all mapped PTEs are to the right huge page */
1335         for (i = 0, addr = haddr, pte = start_pte;
1336              i < HPAGE_PMD_NR; i++, addr += PAGE_SIZE, pte++) {
1337                 struct page *page;
1338
1339                 /* empty pte, skip */
1340                 if (pte_none(*pte))
1341                         continue;
1342
1343                 /* page swapped out, abort */
1344                 if (!pte_present(*pte))
1345                         goto abort;
1346
1347                 page = vm_normal_page(vma, addr, *pte);
1348
1349                 if (!page || !PageCompound(page))
1350                         goto abort;
1351
1352                 if (!hpage) {
1353                         hpage = compound_head(page);
1354                         /*
1355                          * The mapping of the THP should not change.
1356                          *
1357                          * Note that uprobe, debugger, or MAP_PRIVATE may
1358                          * change the page table, but the new page will
1359                          * not pass PageCompound() check.
1360                          */
1361                         if (WARN_ON(hpage->mapping != vma->vm_file->f_mapping))
1362                                 goto abort;
1363                 }
1364
1365                 /*
1366                  * Confirm the page maps to the correct subpage.
1367                  *
1368                  * Note that uprobe, debugger, or MAP_PRIVATE may change
1369                  * the page table, but the new page will not pass
1370                  * PageCompound() check.
1371                  */
1372                 if (WARN_ON(hpage + i != page))
1373                         goto abort;
1374                 count++;
1375         }
1376
1377         /* step 2: adjust rmap */
1378         for (i = 0, addr = haddr, pte = start_pte;
1379              i < HPAGE_PMD_NR; i++, addr += PAGE_SIZE, pte++) {
1380                 struct page *page;
1381
1382                 if (pte_none(*pte))
1383                         continue;
1384                 page = vm_normal_page(vma, addr, *pte);
1385                 page_remove_rmap(page, false);
1386         }
1387
1388         pte_unmap_unlock(start_pte, ptl);
1389
1390         /* step 3: set proper refcount and mm_counters. */
1391         if (hpage) {
1392                 page_ref_sub(hpage, count);
1393                 add_mm_counter(vma->vm_mm, mm_counter_file(hpage), -count);
1394         }
1395
1396         /* step 4: collapse pmd */
1397         ptl = pmd_lock(vma->vm_mm, pmd);
1398         _pmd = pmdp_collapse_flush(vma, addr, pmd);
1399         spin_unlock(ptl);
1400         mm_dec_nr_ptes(mm);
1401         pte_free(mm, pmd_pgtable(_pmd));
1402         return;
1403
1404 abort:
1405         pte_unmap_unlock(start_pte, ptl);
1406 }
1407
1408 static int khugepaged_collapse_pte_mapped_thps(struct mm_slot *mm_slot)
1409 {
1410         struct mm_struct *mm = mm_slot->mm;
1411         int i;
1412
1413         if (likely(mm_slot->nr_pte_mapped_thp == 0))
1414                 return 0;
1415
1416         if (!down_write_trylock(&mm->mmap_sem))
1417                 return -EBUSY;
1418
1419         if (unlikely(khugepaged_test_exit(mm)))
1420                 goto out;
1421
1422         for (i = 0; i < mm_slot->nr_pte_mapped_thp; i++)
1423                 collapse_pte_mapped_thp(mm, mm_slot->pte_mapped_thp[i]);
1424
1425 out:
1426         mm_slot->nr_pte_mapped_thp = 0;
1427         up_write(&mm->mmap_sem);
1428         return 0;
1429 }
1430
1431 static void retract_page_tables(struct address_space *mapping, pgoff_t pgoff)
1432 {
1433         struct vm_area_struct *vma;
1434         unsigned long addr;
1435         pmd_t *pmd, _pmd;
1436
1437         i_mmap_lock_write(mapping);
1438         vma_interval_tree_foreach(vma, &mapping->i_mmap, pgoff, pgoff) {
1439                 /*
1440                  * Check vma->anon_vma to exclude MAP_PRIVATE mappings that
1441                  * got written to. These VMAs are likely not worth investing
1442                  * down_write(mmap_sem) as PMD-mapping is likely to be split
1443                  * later.
1444                  *
1445                  * Not that vma->anon_vma check is racy: it can be set up after
1446                  * the check but before we took mmap_sem by the fault path.
1447                  * But page lock would prevent establishing any new ptes of the
1448                  * page, so we are safe.
1449                  *
1450                  * An alternative would be drop the check, but check that page
1451                  * table is clear before calling pmdp_collapse_flush() under
1452                  * ptl. It has higher chance to recover THP for the VMA, but
1453                  * has higher cost too.
1454                  */
1455                 if (vma->anon_vma)
1456                         continue;
1457                 addr = vma->vm_start + ((pgoff - vma->vm_pgoff) << PAGE_SHIFT);
1458                 if (addr & ~HPAGE_PMD_MASK)
1459                         continue;
1460                 if (vma->vm_end < addr + HPAGE_PMD_SIZE)
1461                         continue;
1462                 pmd = mm_find_pmd(vma->vm_mm, addr);
1463                 if (!pmd)
1464                         continue;
1465                 /*
1466                  * We need exclusive mmap_sem to retract page table.
1467                  *
1468                  * We use trylock due to lock inversion: we need to acquire
1469                  * mmap_sem while holding page lock. Fault path does it in
1470                  * reverse order. Trylock is a way to avoid deadlock.
1471                  */
1472                 if (down_write_trylock(&vma->vm_mm->mmap_sem)) {
1473                         spinlock_t *ptl = pmd_lock(vma->vm_mm, pmd);
1474                         /* assume page table is clear */
1475                         _pmd = pmdp_collapse_flush(vma, addr, pmd);
1476                         spin_unlock(ptl);
1477                         up_write(&vma->vm_mm->mmap_sem);
1478                         mm_dec_nr_ptes(vma->vm_mm);
1479                         pte_free(vma->vm_mm, pmd_pgtable(_pmd));
1480                 } else {
1481                         /* Try again later */
1482                         khugepaged_add_pte_mapped_thp(vma->vm_mm, addr);
1483                 }
1484         }
1485         i_mmap_unlock_write(mapping);
1486 }
1487
1488 /**
1489  * collapse_file - collapse filemap/tmpfs/shmem pages into huge one.
1490  *
1491  * Basic scheme is simple, details are more complex:
1492  *  - allocate and lock a new huge page;
1493  *  - scan page cache replacing old pages with the new one
1494  *    + swap/gup in pages if necessary;
1495  *    + fill in gaps;
1496  *    + keep old pages around in case rollback is required;
1497  *  - if replacing succeeds:
1498  *    + copy data over;
1499  *    + free old pages;
1500  *    + unlock huge page;
1501  *  - if replacing failed;
1502  *    + put all pages back and unfreeze them;
1503  *    + restore gaps in the page cache;
1504  *    + unlock and free huge page;
1505  */
1506 static void collapse_file(struct mm_struct *mm,
1507                 struct file *file, pgoff_t start,
1508                 struct page **hpage, int node)
1509 {
1510         struct address_space *mapping = file->f_mapping;
1511         gfp_t gfp;
1512         struct page *new_page;
1513         struct mem_cgroup *memcg;
1514         pgoff_t index, end = start + HPAGE_PMD_NR;
1515         LIST_HEAD(pagelist);
1516         XA_STATE_ORDER(xas, &mapping->i_pages, start, HPAGE_PMD_ORDER);
1517         int nr_none = 0, result = SCAN_SUCCEED;
1518         bool is_shmem = shmem_file(file);
1519
1520         VM_BUG_ON(!IS_ENABLED(CONFIG_READ_ONLY_THP_FOR_FS) && !is_shmem);
1521         VM_BUG_ON(start & (HPAGE_PMD_NR - 1));
1522
1523         /* Only allocate from the target node */
1524         gfp = alloc_hugepage_khugepaged_gfpmask() | __GFP_THISNODE;
1525
1526         new_page = khugepaged_alloc_page(hpage, gfp, node);
1527         if (!new_page) {
1528                 result = SCAN_ALLOC_HUGE_PAGE_FAIL;
1529                 goto out;
1530         }
1531
1532         if (unlikely(mem_cgroup_try_charge(new_page, mm, gfp, &memcg, true))) {
1533                 result = SCAN_CGROUP_CHARGE_FAIL;
1534                 goto out;
1535         }
1536
1537         /* This will be less messy when we use multi-index entries */
1538         do {
1539                 xas_lock_irq(&xas);
1540                 xas_create_range(&xas);
1541                 if (!xas_error(&xas))
1542                         break;
1543                 xas_unlock_irq(&xas);
1544                 if (!xas_nomem(&xas, GFP_KERNEL)) {
1545                         mem_cgroup_cancel_charge(new_page, memcg, true);
1546                         result = SCAN_FAIL;
1547                         goto out;
1548                 }
1549         } while (1);
1550
1551         __SetPageLocked(new_page);
1552         if (is_shmem)
1553                 __SetPageSwapBacked(new_page);
1554         new_page->index = start;
1555         new_page->mapping = mapping;
1556
1557         /*
1558          * At this point the new_page is locked and not up-to-date.
1559          * It's safe to insert it into the page cache, because nobody would
1560          * be able to map it or use it in another way until we unlock it.
1561          */
1562
1563         xas_set(&xas, start);
1564         for (index = start; index < end; index++) {
1565                 struct page *page = xas_next(&xas);
1566
1567                 VM_BUG_ON(index != xas.xa_index);
1568                 if (is_shmem) {
1569                         if (!page) {
1570                                 /*
1571                                  * Stop if extent has been truncated or
1572                                  * hole-punched, and is now completely
1573                                  * empty.
1574                                  */
1575                                 if (index == start) {
1576                                         if (!xas_next_entry(&xas, end - 1)) {
1577                                                 result = SCAN_TRUNCATED;
1578                                                 goto xa_locked;
1579                                         }
1580                                         xas_set(&xas, index);
1581                                 }
1582                                 if (!shmem_charge(mapping->host, 1)) {
1583                                         result = SCAN_FAIL;
1584                                         goto xa_locked;
1585                                 }
1586                                 xas_store(&xas, new_page);
1587                                 nr_none++;
1588                                 continue;
1589                         }
1590
1591                         if (xa_is_value(page) || !PageUptodate(page)) {
1592                                 xas_unlock_irq(&xas);
1593                                 /* swap in or instantiate fallocated page */
1594                                 if (shmem_getpage(mapping->host, index, &page,
1595                                                   SGP_NOHUGE)) {
1596                                         result = SCAN_FAIL;
1597                                         goto xa_unlocked;
1598                                 }
1599                         } else if (trylock_page(page)) {
1600                                 get_page(page);
1601                                 xas_unlock_irq(&xas);
1602                         } else {
1603                                 result = SCAN_PAGE_LOCK;
1604                                 goto xa_locked;
1605                         }
1606                 } else {        /* !is_shmem */
1607                         if (!page || xa_is_value(page)) {
1608                                 xas_unlock_irq(&xas);
1609                                 page_cache_sync_readahead(mapping, &file->f_ra,
1610                                                           file, index,
1611                                                           PAGE_SIZE);
1612                                 /* drain pagevecs to help isolate_lru_page() */
1613                                 lru_add_drain();
1614                                 page = find_lock_page(mapping, index);
1615                                 if (unlikely(page == NULL)) {
1616                                         result = SCAN_FAIL;
1617                                         goto xa_unlocked;
1618                                 }
1619                         } else if (PageDirty(page)) {
1620                                 /*
1621                                  * khugepaged only works on read-only fd,
1622                                  * so this page is dirty because it hasn't
1623                                  * been flushed since first write. There
1624                                  * won't be new dirty pages.
1625                                  *
1626                                  * Trigger async flush here and hope the
1627                                  * writeback is done when khugepaged
1628                                  * revisits this page.
1629                                  *
1630                                  * This is a one-off situation. We are not
1631                                  * forcing writeback in loop.
1632                                  */
1633                                 xas_unlock_irq(&xas);
1634                                 filemap_flush(mapping);
1635                                 result = SCAN_FAIL;
1636                                 goto xa_unlocked;
1637                         } else if (trylock_page(page)) {
1638                                 get_page(page);
1639                                 xas_unlock_irq(&xas);
1640                         } else {
1641                                 result = SCAN_PAGE_LOCK;
1642                                 goto xa_locked;
1643                         }
1644                 }
1645
1646                 /*
1647                  * The page must be locked, so we can drop the i_pages lock
1648                  * without racing with truncate.
1649                  */
1650                 VM_BUG_ON_PAGE(!PageLocked(page), page);
1651
1652                 /* make sure the page is up to date */
1653                 if (unlikely(!PageUptodate(page))) {
1654                         result = SCAN_FAIL;
1655                         goto out_unlock;
1656                 }
1657
1658                 /*
1659                  * If file was truncated then extended, or hole-punched, before
1660                  * we locked the first page, then a THP might be there already.
1661                  */
1662                 if (PageTransCompound(page)) {
1663                         result = SCAN_PAGE_COMPOUND;
1664                         goto out_unlock;
1665                 }
1666
1667                 if (page_mapping(page) != mapping) {
1668                         result = SCAN_TRUNCATED;
1669                         goto out_unlock;
1670                 }
1671
1672                 if (!is_shmem && PageDirty(page)) {
1673                         /*
1674                          * khugepaged only works on read-only fd, so this
1675                          * page is dirty because it hasn't been flushed
1676                          * since first write.
1677                          */
1678                         result = SCAN_FAIL;
1679                         goto out_unlock;
1680                 }
1681
1682                 if (isolate_lru_page(page)) {
1683                         result = SCAN_DEL_PAGE_LRU;
1684                         goto out_unlock;
1685                 }
1686
1687                 if (page_has_private(page) &&
1688                     !try_to_release_page(page, GFP_KERNEL)) {
1689                         result = SCAN_PAGE_HAS_PRIVATE;
1690                         putback_lru_page(page);
1691                         goto out_unlock;
1692                 }
1693
1694                 if (page_mapped(page))
1695                         unmap_mapping_pages(mapping, index, 1, false);
1696
1697                 xas_lock_irq(&xas);
1698                 xas_set(&xas, index);
1699
1700                 VM_BUG_ON_PAGE(page != xas_load(&xas), page);
1701                 VM_BUG_ON_PAGE(page_mapped(page), page);
1702
1703                 /*
1704                  * The page is expected to have page_count() == 3:
1705                  *  - we hold a pin on it;
1706                  *  - one reference from page cache;
1707                  *  - one from isolate_lru_page;
1708                  */
1709                 if (!page_ref_freeze(page, 3)) {
1710                         result = SCAN_PAGE_COUNT;
1711                         xas_unlock_irq(&xas);
1712                         putback_lru_page(page);
1713                         goto out_unlock;
1714                 }
1715
1716                 /*
1717                  * Add the page to the list to be able to undo the collapse if
1718                  * something go wrong.
1719                  */
1720                 list_add_tail(&page->lru, &pagelist);
1721
1722                 /* Finally, replace with the new page. */
1723                 xas_store(&xas, new_page);
1724                 continue;
1725 out_unlock:
1726                 unlock_page(page);
1727                 put_page(page);
1728                 goto xa_unlocked;
1729         }
1730
1731         if (is_shmem)
1732                 __inc_node_page_state(new_page, NR_SHMEM_THPS);
1733         else {
1734                 __inc_node_page_state(new_page, NR_FILE_THPS);
1735                 filemap_nr_thps_inc(mapping);
1736         }
1737
1738         if (nr_none) {
1739                 struct zone *zone = page_zone(new_page);
1740
1741                 __mod_node_page_state(zone->zone_pgdat, NR_FILE_PAGES, nr_none);
1742                 if (is_shmem)
1743                         __mod_node_page_state(zone->zone_pgdat,
1744                                               NR_SHMEM, nr_none);
1745         }
1746
1747 xa_locked:
1748         xas_unlock_irq(&xas);
1749 xa_unlocked:
1750
1751         if (result == SCAN_SUCCEED) {
1752                 struct page *page, *tmp;
1753
1754                 /*
1755                  * Replacing old pages with new one has succeeded, now we
1756                  * need to copy the content and free the old pages.
1757                  */
1758                 index = start;
1759                 list_for_each_entry_safe(page, tmp, &pagelist, lru) {
1760                         while (index < page->index) {
1761                                 clear_highpage(new_page + (index % HPAGE_PMD_NR));
1762                                 index++;
1763                         }
1764                         copy_highpage(new_page + (page->index % HPAGE_PMD_NR),
1765                                         page);
1766                         list_del(&page->lru);
1767                         page->mapping = NULL;
1768                         page_ref_unfreeze(page, 1);
1769                         ClearPageActive(page);
1770                         ClearPageUnevictable(page);
1771                         unlock_page(page);
1772                         put_page(page);
1773                         index++;
1774                 }
1775                 while (index < end) {
1776                         clear_highpage(new_page + (index % HPAGE_PMD_NR));
1777                         index++;
1778                 }
1779
1780                 SetPageUptodate(new_page);
1781                 page_ref_add(new_page, HPAGE_PMD_NR - 1);
1782                 mem_cgroup_commit_charge(new_page, memcg, false, true);
1783
1784                 if (is_shmem) {
1785                         set_page_dirty(new_page);
1786                         lru_cache_add_anon(new_page);
1787                 } else {
1788                         lru_cache_add_file(new_page);
1789                 }
1790                 count_memcg_events(memcg, THP_COLLAPSE_ALLOC, 1);
1791
1792                 /*
1793                  * Remove pte page tables, so we can re-fault the page as huge.
1794                  */
1795                 retract_page_tables(mapping, start);
1796                 *hpage = NULL;
1797
1798                 khugepaged_pages_collapsed++;
1799         } else {
1800                 struct page *page;
1801
1802                 /* Something went wrong: roll back page cache changes */
1803                 xas_lock_irq(&xas);
1804                 mapping->nrpages -= nr_none;
1805
1806                 if (is_shmem)
1807                         shmem_uncharge(mapping->host, nr_none);
1808
1809                 xas_set(&xas, start);
1810                 xas_for_each(&xas, page, end - 1) {
1811                         page = list_first_entry_or_null(&pagelist,
1812                                         struct page, lru);
1813                         if (!page || xas.xa_index < page->index) {
1814                                 if (!nr_none)
1815                                         break;
1816                                 nr_none--;
1817                                 /* Put holes back where they were */
1818                                 xas_store(&xas, NULL);
1819                                 continue;
1820                         }
1821
1822                         VM_BUG_ON_PAGE(page->index != xas.xa_index, page);
1823
1824                         /* Unfreeze the page. */
1825                         list_del(&page->lru);
1826                         page_ref_unfreeze(page, 2);
1827                         xas_store(&xas, page);
1828                         xas_pause(&xas);
1829                         xas_unlock_irq(&xas);
1830                         unlock_page(page);
1831                         putback_lru_page(page);
1832                         xas_lock_irq(&xas);
1833                 }
1834                 VM_BUG_ON(nr_none);
1835                 xas_unlock_irq(&xas);
1836
1837                 mem_cgroup_cancel_charge(new_page, memcg, true);
1838                 new_page->mapping = NULL;
1839         }
1840
1841         unlock_page(new_page);
1842 out:
1843         VM_BUG_ON(!list_empty(&pagelist));
1844         /* TODO: tracepoints */
1845 }
1846
1847 static void khugepaged_scan_file(struct mm_struct *mm,
1848                 struct file *file, pgoff_t start, struct page **hpage)
1849 {
1850         struct page *page = NULL;
1851         struct address_space *mapping = file->f_mapping;
1852         XA_STATE(xas, &mapping->i_pages, start);
1853         int present, swap;
1854         int node = NUMA_NO_NODE;
1855         int result = SCAN_SUCCEED;
1856
1857         present = 0;
1858         swap = 0;
1859         memset(khugepaged_node_load, 0, sizeof(khugepaged_node_load));
1860         rcu_read_lock();
1861         xas_for_each(&xas, page, start + HPAGE_PMD_NR - 1) {
1862                 if (xas_retry(&xas, page))
1863                         continue;
1864
1865                 if (xa_is_value(page)) {
1866                         if (++swap > khugepaged_max_ptes_swap) {
1867                                 result = SCAN_EXCEED_SWAP_PTE;
1868                                 break;
1869                         }
1870                         continue;
1871                 }
1872
1873                 if (PageTransCompound(page)) {
1874                         result = SCAN_PAGE_COMPOUND;
1875                         break;
1876                 }
1877
1878                 node = page_to_nid(page);
1879                 if (khugepaged_scan_abort(node)) {
1880                         result = SCAN_SCAN_ABORT;
1881                         break;
1882                 }
1883                 khugepaged_node_load[node]++;
1884
1885                 if (!PageLRU(page)) {
1886                         result = SCAN_PAGE_LRU;
1887                         break;
1888                 }
1889
1890                 if (page_count(page) !=
1891                     1 + page_mapcount(page) + page_has_private(page)) {
1892                         result = SCAN_PAGE_COUNT;
1893                         break;
1894                 }
1895
1896                 /*
1897                  * We probably should check if the page is referenced here, but
1898                  * nobody would transfer pte_young() to PageReferenced() for us.
1899                  * And rmap walk here is just too costly...
1900                  */
1901
1902                 present++;
1903
1904                 if (need_resched()) {
1905                         xas_pause(&xas);
1906                         cond_resched_rcu();
1907                 }
1908         }
1909         rcu_read_unlock();
1910
1911         if (result == SCAN_SUCCEED) {
1912                 if (present < HPAGE_PMD_NR - khugepaged_max_ptes_none) {
1913                         result = SCAN_EXCEED_NONE_PTE;
1914                 } else {
1915                         node = khugepaged_find_target_node();
1916                         collapse_file(mm, file, start, hpage, node);
1917                 }
1918         }
1919
1920         /* TODO: tracepoints */
1921 }
1922 #else
1923 static void khugepaged_scan_file(struct mm_struct *mm,
1924                 struct file *file, pgoff_t start, struct page **hpage)
1925 {
1926         BUILD_BUG();
1927 }
1928
1929 static int khugepaged_collapse_pte_mapped_thps(struct mm_slot *mm_slot)
1930 {
1931         return 0;
1932 }
1933 #endif
1934
1935 static unsigned int khugepaged_scan_mm_slot(unsigned int pages,
1936                                             struct page **hpage)
1937         __releases(&khugepaged_mm_lock)
1938         __acquires(&khugepaged_mm_lock)
1939 {
1940         struct mm_slot *mm_slot;
1941         struct mm_struct *mm;
1942         struct vm_area_struct *vma;
1943         int progress = 0;
1944
1945         VM_BUG_ON(!pages);
1946         lockdep_assert_held(&khugepaged_mm_lock);
1947
1948         if (khugepaged_scan.mm_slot)
1949                 mm_slot = khugepaged_scan.mm_slot;
1950         else {
1951                 mm_slot = list_entry(khugepaged_scan.mm_head.next,
1952                                      struct mm_slot, mm_node);
1953                 khugepaged_scan.address = 0;
1954                 khugepaged_scan.mm_slot = mm_slot;
1955         }
1956         spin_unlock(&khugepaged_mm_lock);
1957         khugepaged_collapse_pte_mapped_thps(mm_slot);
1958
1959         mm = mm_slot->mm;
1960         /*
1961          * Don't wait for semaphore (to avoid long wait times).  Just move to
1962          * the next mm on the list.
1963          */
1964         vma = NULL;
1965         if (unlikely(!down_read_trylock(&mm->mmap_sem)))
1966                 goto breakouterloop_mmap_sem;
1967         if (likely(!khugepaged_test_exit(mm)))
1968                 vma = find_vma(mm, khugepaged_scan.address);
1969
1970         progress++;
1971         for (; vma; vma = vma->vm_next) {
1972                 unsigned long hstart, hend;
1973
1974                 cond_resched();
1975                 if (unlikely(khugepaged_test_exit(mm))) {
1976                         progress++;
1977                         break;
1978                 }
1979                 if (!hugepage_vma_check(vma, vma->vm_flags)) {
1980 skip:
1981                         progress++;
1982                         continue;
1983                 }
1984                 hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK;
1985                 hend = vma->vm_end & HPAGE_PMD_MASK;
1986                 if (hstart >= hend)
1987                         goto skip;
1988                 if (khugepaged_scan.address > hend)
1989                         goto skip;
1990                 if (khugepaged_scan.address < hstart)
1991                         khugepaged_scan.address = hstart;
1992                 VM_BUG_ON(khugepaged_scan.address & ~HPAGE_PMD_MASK);
1993                 if (shmem_file(vma->vm_file) && !shmem_huge_enabled(vma))
1994                         goto skip;
1995
1996                 while (khugepaged_scan.address < hend) {
1997                         int ret;
1998                         cond_resched();
1999                         if (unlikely(khugepaged_test_exit(mm)))
2000                                 goto breakouterloop;
2001
2002                         VM_BUG_ON(khugepaged_scan.address < hstart ||
2003                                   khugepaged_scan.address + HPAGE_PMD_SIZE >
2004                                   hend);
2005                         if (IS_ENABLED(CONFIG_SHMEM) && vma->vm_file) {
2006                                 struct file *file = get_file(vma->vm_file);
2007                                 pgoff_t pgoff = linear_page_index(vma,
2008                                                 khugepaged_scan.address);
2009
2010                                 up_read(&mm->mmap_sem);
2011                                 ret = 1;
2012                                 khugepaged_scan_file(mm, file, pgoff, hpage);
2013                                 fput(file);
2014                         } else {
2015                                 ret = khugepaged_scan_pmd(mm, vma,
2016                                                 khugepaged_scan.address,
2017                                                 hpage);
2018                         }
2019                         /* move to next address */
2020                         khugepaged_scan.address += HPAGE_PMD_SIZE;
2021                         progress += HPAGE_PMD_NR;
2022                         if (ret)
2023                                 /* we released mmap_sem so break loop */
2024                                 goto breakouterloop_mmap_sem;
2025                         if (progress >= pages)
2026                                 goto breakouterloop;
2027                 }
2028         }
2029 breakouterloop:
2030         up_read(&mm->mmap_sem); /* exit_mmap will destroy ptes after this */
2031 breakouterloop_mmap_sem:
2032
2033         spin_lock(&khugepaged_mm_lock);
2034         VM_BUG_ON(khugepaged_scan.mm_slot != mm_slot);
2035         /*
2036          * Release the current mm_slot if this mm is about to die, or
2037          * if we scanned all vmas of this mm.
2038          */
2039         if (khugepaged_test_exit(mm) || !vma) {
2040                 /*
2041                  * Make sure that if mm_users is reaching zero while
2042                  * khugepaged runs here, khugepaged_exit will find
2043                  * mm_slot not pointing to the exiting mm.
2044                  */
2045                 if (mm_slot->mm_node.next != &khugepaged_scan.mm_head) {
2046                         khugepaged_scan.mm_slot = list_entry(
2047                                 mm_slot->mm_node.next,
2048                                 struct mm_slot, mm_node);
2049                         khugepaged_scan.address = 0;
2050                 } else {
2051                         khugepaged_scan.mm_slot = NULL;
2052                         khugepaged_full_scans++;
2053                 }
2054
2055                 collect_mm_slot(mm_slot);
2056         }
2057
2058         return progress;
2059 }
2060
2061 static int khugepaged_has_work(void)
2062 {
2063         return !list_empty(&khugepaged_scan.mm_head) &&
2064                 khugepaged_enabled();
2065 }
2066
2067 static int khugepaged_wait_event(void)
2068 {
2069         return !list_empty(&khugepaged_scan.mm_head) ||
2070                 kthread_should_stop();
2071 }
2072
2073 static void khugepaged_do_scan(void)
2074 {
2075         struct page *hpage = NULL;
2076         unsigned int progress = 0, pass_through_head = 0;
2077         unsigned int pages = khugepaged_pages_to_scan;
2078         bool wait = true;
2079
2080         barrier(); /* write khugepaged_pages_to_scan to local stack */
2081
2082         lru_add_drain_all();
2083
2084         while (progress < pages) {
2085                 if (!khugepaged_prealloc_page(&hpage, &wait))
2086                         break;
2087
2088                 cond_resched();
2089
2090                 if (unlikely(kthread_should_stop() || try_to_freeze()))
2091                         break;
2092
2093                 spin_lock(&khugepaged_mm_lock);
2094                 if (!khugepaged_scan.mm_slot)
2095                         pass_through_head++;
2096                 if (khugepaged_has_work() &&
2097                     pass_through_head < 2)
2098                         progress += khugepaged_scan_mm_slot(pages - progress,
2099                                                             &hpage);
2100                 else
2101                         progress = pages;
2102                 spin_unlock(&khugepaged_mm_lock);
2103         }
2104
2105         if (!IS_ERR_OR_NULL(hpage))
2106                 put_page(hpage);
2107 }
2108
2109 static bool khugepaged_should_wakeup(void)
2110 {
2111         return kthread_should_stop() ||
2112                time_after_eq(jiffies, khugepaged_sleep_expire);
2113 }
2114
2115 static void khugepaged_wait_work(void)
2116 {
2117         if (khugepaged_has_work()) {
2118                 const unsigned long scan_sleep_jiffies =
2119                         msecs_to_jiffies(khugepaged_scan_sleep_millisecs);
2120
2121                 if (!scan_sleep_jiffies)
2122                         return;
2123
2124                 khugepaged_sleep_expire = jiffies + scan_sleep_jiffies;
2125                 wait_event_freezable_timeout(khugepaged_wait,
2126                                              khugepaged_should_wakeup(),
2127                                              scan_sleep_jiffies);
2128                 return;
2129         }
2130
2131         if (khugepaged_enabled())
2132                 wait_event_freezable(khugepaged_wait, khugepaged_wait_event());
2133 }
2134
2135 static int khugepaged(void *none)
2136 {
2137         struct mm_slot *mm_slot;
2138
2139         set_freezable();
2140         set_user_nice(current, MAX_NICE);
2141
2142         while (!kthread_should_stop()) {
2143                 khugepaged_do_scan();
2144                 khugepaged_wait_work();
2145         }
2146
2147         spin_lock(&khugepaged_mm_lock);
2148         mm_slot = khugepaged_scan.mm_slot;
2149         khugepaged_scan.mm_slot = NULL;
2150         if (mm_slot)
2151                 collect_mm_slot(mm_slot);
2152         spin_unlock(&khugepaged_mm_lock);
2153         return 0;
2154 }
2155
2156 static void set_recommended_min_free_kbytes(void)
2157 {
2158         struct zone *zone;
2159         int nr_zones = 0;
2160         unsigned long recommended_min;
2161
2162         for_each_populated_zone(zone) {
2163                 /*
2164                  * We don't need to worry about fragmentation of
2165                  * ZONE_MOVABLE since it only has movable pages.
2166                  */
2167                 if (zone_idx(zone) > gfp_zone(GFP_USER))
2168                         continue;
2169
2170                 nr_zones++;
2171         }
2172
2173         /* Ensure 2 pageblocks are free to assist fragmentation avoidance */
2174         recommended_min = pageblock_nr_pages * nr_zones * 2;
2175
2176         /*
2177          * Make sure that on average at least two pageblocks are almost free
2178          * of another type, one for a migratetype to fall back to and a
2179          * second to avoid subsequent fallbacks of other types There are 3
2180          * MIGRATE_TYPES we care about.
2181          */
2182         recommended_min += pageblock_nr_pages * nr_zones *
2183                            MIGRATE_PCPTYPES * MIGRATE_PCPTYPES;
2184
2185         /* don't ever allow to reserve more than 5% of the lowmem */
2186         recommended_min = min(recommended_min,
2187                               (unsigned long) nr_free_buffer_pages() / 20);
2188         recommended_min <<= (PAGE_SHIFT-10);
2189
2190         if (recommended_min > min_free_kbytes) {
2191                 if (user_min_free_kbytes >= 0)
2192                         pr_info("raising min_free_kbytes from %d to %lu to help transparent hugepage allocations\n",
2193                                 min_free_kbytes, recommended_min);
2194
2195                 min_free_kbytes = recommended_min;
2196         }
2197         setup_per_zone_wmarks();
2198 }
2199
2200 int start_stop_khugepaged(void)
2201 {
2202         static struct task_struct *khugepaged_thread __read_mostly;
2203         static DEFINE_MUTEX(khugepaged_mutex);
2204         int err = 0;
2205
2206         mutex_lock(&khugepaged_mutex);
2207         if (khugepaged_enabled()) {
2208                 if (!khugepaged_thread)
2209                         khugepaged_thread = kthread_run(khugepaged, NULL,
2210                                                         "khugepaged");
2211                 if (IS_ERR(khugepaged_thread)) {
2212                         pr_err("khugepaged: kthread_run(khugepaged) failed\n");
2213                         err = PTR_ERR(khugepaged_thread);
2214                         khugepaged_thread = NULL;
2215                         goto fail;
2216                 }
2217
2218                 if (!list_empty(&khugepaged_scan.mm_head))
2219                         wake_up_interruptible(&khugepaged_wait);
2220
2221                 set_recommended_min_free_kbytes();
2222         } else if (khugepaged_thread) {
2223                 kthread_stop(khugepaged_thread);
2224                 khugepaged_thread = NULL;
2225         }
2226 fail:
2227         mutex_unlock(&khugepaged_mutex);
2228         return err;
2229 }