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         /* we only decide to swapin, if there is enough young ptes */
 903         if (referenced < HPAGE_PMD_NR/2) {
 904                 trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 0);
 905                 return false;
 906         }
 907         vmf.pte = pte_offset_map(pmd, address);
 908         for (; vmf.address < address + HPAGE_PMD_NR*PAGE_SIZE;
 909                         vmf.pte++, vmf.address += PAGE_SIZE) {
 910                 vmf.orig_pte = *vmf.pte;
 911                 if (!is_swap_pte(vmf.orig_pte))
 912                         continue;
 913                 swapped_in++;
 914                 ret = do_swap_page(&vmf);
 915
 916                 /* do_swap_page returns VM_FAULT_RETRY with released mmap_sem */
 917                 if (ret & VM_FAULT_RETRY) {
 918                         down_read(&mm->mmap_sem);
 919                         if (hugepage_vma_revalidate(mm, address, &vmf.vma)) {
 920                                 /* vma is no longer available, don't continue to swapin */
 921                                 trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 0);
 922                                 return false;
 923                         }
 924                         /* check if the pmd is still valid */
 925                         if (mm_find_pmd(mm, address) != pmd) {
 926                                 trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 0);
 927                                 return false;
 928                         }
 929                 }
 930                 if (ret & VM_FAULT_ERROR) {
 931                         trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 0);
 932                         return false;
 933                 }
 934                 /* pte is unmapped now, we need to map it */
 935                 vmf.pte = pte_offset_map(pmd, vmf.address);
 936         }
 937         vmf.pte--;
 938         pte_unmap(vmf.pte);
 939         trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 1);
 940         return true;
 941 }
 942
 943 static void collapse_huge_page(struct mm_struct *mm,
 944                                    unsigned long address,
 945                                    struct page **hpage,
 946                                    int node, int referenced)
 947 {
 948         pmd_t *pmd, _pmd;
 949         pte_t *pte;
 950         pgtable_t pgtable;
 951         struct page *new_page;
 952         spinlock_t *pmd_ptl, *pte_ptl;
 953         int isolated = 0, result = 0;
 954         struct mem_cgroup *memcg;
 955         struct vm_area_struct *vma;
 956         struct mmu_notifier_range range;
 957         gfp_t gfp;
 958
 959         VM_BUG_ON(address & ~HPAGE_PMD_MASK);
 960
 961         /* Only allocate from the target node */
 962         gfp = alloc_hugepage_khugepaged_gfpmask() | __GFP_THISNODE;
 963
 964         /*
 965          * Before allocating the hugepage, release the mmap_sem read lock.
 966          * The allocation can take potentially a long time if it involves
 967          * sync compaction, and we do not need to hold the mmap_sem during
 968          * that. We will recheck the vma after taking it again in write mode.
 969          */
 970         up_read(&mm->mmap_sem);
 971         new_page = khugepaged_alloc_page(hpage, gfp, node);
 972         if (!new_page) {
 973                 result = SCAN_ALLOC_HUGE_PAGE_FAIL;
 974                 goto out_nolock;
 975         }
 976
 977         if (unlikely(mem_cgroup_try_charge(new_page, mm, gfp, &memcg, true))) {
 978                 result = SCAN_CGROUP_CHARGE_FAIL;
 979                 goto out_nolock;
 980         }
 981
 982         down_read(&mm->mmap_sem);
 983         result = hugepage_vma_revalidate(mm, address, &vma);
 984         if (result) {
 985                 mem_cgroup_cancel_charge(new_page, memcg, true);
 986                 up_read(&mm->mmap_sem);
 987                 goto out_nolock;
 988         }
 989
 990         pmd = mm_find_pmd(mm, address);
 991         if (!pmd) {
 992                 result = SCAN_PMD_NULL;
 993                 mem_cgroup_cancel_charge(new_page, memcg, true);
 994                 up_read(&mm->mmap_sem);
 995                 goto out_nolock;
 996         }
 997
 998         /*
 999          * __collapse_huge_page_swapin always returns with mmap_sem locked.
1000          * If it fails, we release mmap_sem and jump out_nolock.
1001          * Continuing to collapse causes inconsistency.
1002          */
1003         if (!__collapse_huge_page_swapin(mm, vma, address, pmd, referenced)) {
1004                 mem_cgroup_cancel_charge(new_page, memcg, true);
1005                 up_read(&mm->mmap_sem);
1006                 goto out_nolock;
1007         }
1008
1009         up_read(&mm->mmap_sem);
1010         /*
1011          * Prevent all access to pagetables with the exception of
1012          * gup_fast later handled by the ptep_clear_flush and the VM
1013          * handled by the anon_vma lock + PG_lock.
1014          */
1015         down_write(&mm->mmap_sem);
1016         result = SCAN_ANY_PROCESS;
1017         if (!mmget_still_valid(mm))
1018                 goto out;
1019         result = hugepage_vma_revalidate(mm, address, &vma);
1020         if (result)
1021                 goto out;
1022         /* check if the pmd is still valid */
1023         if (mm_find_pmd(mm, address) != pmd)
1024                 goto out;
1025
1026         anon_vma_lock_write(vma->anon_vma);
1027
1028         mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, NULL, mm,
1029                                 address, address + HPAGE_PMD_SIZE);
1030         mmu_notifier_invalidate_range_start(&range);
1031
1032         pte = pte_offset_map(pmd, address);
1033         pte_ptl = pte_lockptr(mm, pmd);
1034
1035         pmd_ptl = pmd_lock(mm, pmd); /* probably unnecessary */
1036         /*
1037          * After this gup_fast can't run anymore. This also removes
1038          * any huge TLB entry from the CPU so we won't allow
1039          * huge and small TLB entries for the same virtual address
1040          * to avoid the risk of CPU bugs in that area.
1041          */
1042         _pmd = pmdp_collapse_flush(vma, address, pmd);
1043         spin_unlock(pmd_ptl);
1044         mmu_notifier_invalidate_range_end(&range);
1045
1046         spin_lock(pte_ptl);
1047         isolated = __collapse_huge_page_isolate(vma, address, pte);
1048         spin_unlock(pte_ptl);
1049
1050         if (unlikely(!isolated)) {
1051                 pte_unmap(pte);
1052                 spin_lock(pmd_ptl);
1053                 BUG_ON(!pmd_none(*pmd));
1054                 /*
1055                  * We can only use set_pmd_at when establishing
1056                  * hugepmds and never for establishing regular pmds that
1057                  * points to regular pagetables. Use pmd_populate for that
1058                  */
1059                 pmd_populate(mm, pmd, pmd_pgtable(_pmd));
1060                 spin_unlock(pmd_ptl);
1061                 anon_vma_unlock_write(vma->anon_vma);
1062                 result = SCAN_FAIL;
1063                 goto out;
1064         }
1065
1066         /*
1067          * All pages are isolated and locked so anon_vma rmap
1068          * can't run anymore.
1069          */
1070         anon_vma_unlock_write(vma->anon_vma);
1071
1072         __collapse_huge_page_copy(pte, new_page, vma, address, pte_ptl);
1073         pte_unmap(pte);
1074         __SetPageUptodate(new_page);
1075         pgtable = pmd_pgtable(_pmd);
1076
1077         _pmd = mk_huge_pmd(new_page, vma->vm_page_prot);
1078         _pmd = maybe_pmd_mkwrite(pmd_mkdirty(_pmd), vma);
1079
1080         /*
1081          * spin_lock() below is not the equivalent of smp_wmb(), so
1082          * this is needed to avoid the copy_huge_page writes to become
1083          * visible after the set_pmd_at() write.
1084          */
1085         smp_wmb();
1086
1087         spin_lock(pmd_ptl);
1088         BUG_ON(!pmd_none(*pmd));
1089         page_add_new_anon_rmap(new_page, vma, address, true);
1090         mem_cgroup_commit_charge(new_page, memcg, false, true);
1091         count_memcg_events(memcg, THP_COLLAPSE_ALLOC, 1);
1092         lru_cache_add_active_or_unevictable(new_page, vma);
1093         pgtable_trans_huge_deposit(mm, pmd, pgtable);
1094         set_pmd_at(mm, address, pmd, _pmd);
1095         update_mmu_cache_pmd(vma, address, pmd);
1096         spin_unlock(pmd_ptl);
1097
1098         *hpage = NULL;
1099
1100         khugepaged_pages_collapsed++;
1101         result = SCAN_SUCCEED;
1102 out_up_write:
1103         up_write(&mm->mmap_sem);
1104 out_nolock:
1105         trace_mm_collapse_huge_page(mm, isolated, result);
1106         return;
1107 out:
1108         mem_cgroup_cancel_charge(new_page, memcg, true);
1109         goto out_up_write;
1110 }
1111
1112 static int khugepaged_scan_pmd(struct mm_struct *mm,
1113                                struct vm_area_struct *vma,
1114                                unsigned long address,
1115                                struct page **hpage)
1116 {
1117         pmd_t *pmd;
1118         pte_t *pte, *_pte;
1119         int ret = 0, none_or_zero = 0, result = 0, referenced = 0;
1120         struct page *page = NULL;
1121         unsigned long _address;
1122         spinlock_t *ptl;
1123         int node = NUMA_NO_NODE, unmapped = 0;
1124         bool writable = false;
1125
1126         VM_BUG_ON(address & ~HPAGE_PMD_MASK);
1127
1128         pmd = mm_find_pmd(mm, address);
1129         if (!pmd) {
1130                 result = SCAN_PMD_NULL;
1131                 goto out;
1132         }
1133
1134         memset(khugepaged_node_load, 0, sizeof(khugepaged_node_load));
1135         pte = pte_offset_map_lock(mm, pmd, address, &ptl);
1136         for (_address = address, _pte = pte; _pte < pte+HPAGE_PMD_NR;
1137              _pte++, _address += PAGE_SIZE) {
1138                 pte_t pteval = *_pte;
1139                 if (is_swap_pte(pteval)) {
1140                         if (++unmapped <= khugepaged_max_ptes_swap) {
1141                                 /*
1142                                  * Always be strict with uffd-wp
1143                                  * enabled swap entries.  Please see
1144                                  * comment below for pte_uffd_wp().
1145                                  */
1146                                 if (pte_swp_uffd_wp(pteval)) {
1147                                         result = SCAN_PTE_UFFD_WP;
1148                                         goto out_unmap;
1149                                 }
1150                                 continue;
1151                         } else {
1152                                 result = SCAN_EXCEED_SWAP_PTE;
1153                                 goto out_unmap;
1154                         }
1155                 }
1156                 if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) {
1157                         if (!userfaultfd_armed(vma) &&
1158                             ++none_or_zero <= khugepaged_max_ptes_none) {
1159                                 continue;
1160                         } else {
1161                                 result = SCAN_EXCEED_NONE_PTE;
1162                                 goto out_unmap;
1163                         }
1164                 }
1165                 if (!pte_present(pteval)) {
1166                         result = SCAN_PTE_NON_PRESENT;
1167                         goto out_unmap;
1168                 }
1169                 if (pte_uffd_wp(pteval)) {
1170                         /*
1171                          * Don't collapse the page if any of the small
1172                          * PTEs are armed with uffd write protection.
1173                          * Here we can also mark the new huge pmd as
1174                          * write protected if any of the small ones is
1175                          * marked but that could bring uknown
1176                          * userfault messages that falls outside of
1177                          * the registered range.  So, just be simple.
1178                          */
1179                         result = SCAN_PTE_UFFD_WP;
1180                         goto out_unmap;
1181                 }
1182                 if (pte_write(pteval))
1183                         writable = true;
1184
1185                 page = vm_normal_page(vma, _address, pteval);
1186                 if (unlikely(!page)) {
1187                         result = SCAN_PAGE_NULL;
1188                         goto out_unmap;
1189                 }
1190
1191                 /* TODO: teach khugepaged to collapse THP mapped with pte */
1192                 if (PageCompound(page)) {
1193                         result = SCAN_PAGE_COMPOUND;
1194                         goto out_unmap;
1195                 }
1196
1197                 /*
1198                  * Record which node the original page is from and save this
1199                  * information to khugepaged_node_load[].
1200                  * Khupaged will allocate hugepage from the node has the max
1201                  * hit record.
1202                  */
1203                 node = page_to_nid(page);
1204                 if (khugepaged_scan_abort(node)) {
1205                         result = SCAN_SCAN_ABORT;
1206                         goto out_unmap;
1207                 }
1208                 khugepaged_node_load[node]++;
1209                 if (!PageLRU(page)) {
1210                         result = SCAN_PAGE_LRU;
1211                         goto out_unmap;
1212                 }
1213                 if (PageLocked(page)) {
1214                         result = SCAN_PAGE_LOCK;
1215                         goto out_unmap;
1216                 }
1217                 if (!PageAnon(page)) {
1218                         result = SCAN_PAGE_ANON;
1219                         goto out_unmap;
1220                 }
1221
1222                 /*
1223                  * cannot use mapcount: can't collapse if there's a gup pin.
1224                  * The page must only be referenced by the scanned process
1225                  * and page swap cache.
1226                  */
1227                 if (page_count(page) != 1 + PageSwapCache(page)) {
1228                         result = SCAN_PAGE_COUNT;
1229                         goto out_unmap;
1230                 }
1231                 if (pte_young(pteval) ||
1232                     page_is_young(page) || PageReferenced(page) ||
1233                     mmu_notifier_test_young(vma->vm_mm, address))
1234                         referenced++;
1235         }
1236         if (writable) {
1237                 if (referenced) {
1238                         result = SCAN_SUCCEED;
1239                         ret = 1;
1240                 } else {
1241                         result = SCAN_LACK_REFERENCED_PAGE;
1242                 }
1243         } else {
1244                 result = SCAN_PAGE_RO;
1245         }
1246 out_unmap:
1247         pte_unmap_unlock(pte, ptl);
1248         if (ret) {
1249                 node = khugepaged_find_target_node();
1250                 /* collapse_huge_page will return with the mmap_sem released */
1251                 collapse_huge_page(mm, address, hpage, node, referenced);
1252         }
1253 out:
1254         trace_mm_khugepaged_scan_pmd(mm, page, writable, referenced,
1255                                      none_or_zero, result, unmapped);
1256         return ret;
1257 }
1258
1259 static void collect_mm_slot(struct mm_slot *mm_slot)
1260 {
1261         struct mm_struct *mm = mm_slot->mm;
1262
1263         lockdep_assert_held(&khugepaged_mm_lock);
1264
1265         if (khugepaged_test_exit(mm)) {
1266                 /* free mm_slot */
1267                 hash_del(&mm_slot->hash);
1268                 list_del(&mm_slot->mm_node);
1269
1270                 /*
1271                  * Not strictly needed because the mm exited already.
1272                  *
1273                  * clear_bit(MMF_VM_HUGEPAGE, &mm->flags);
1274                  */
1275
1276                 /* khugepaged_mm_lock actually not necessary for the below */
1277                 free_mm_slot(mm_slot);
1278                 mmdrop(mm);
1279         }
1280 }
1281
1282 #ifdef CONFIG_SHMEM
1283 /*
1284  * Notify khugepaged that given addr of the mm is pte-mapped THP. Then
1285  * khugepaged should try to collapse the page table.
1286  */
1287 static int khugepaged_add_pte_mapped_thp(struct mm_struct *mm,
1288                                          unsigned long addr)
1289 {
1290         struct mm_slot *mm_slot;
1291
1292         VM_BUG_ON(addr & ~HPAGE_PMD_MASK);
1293
1294         spin_lock(&khugepaged_mm_lock);
1295         mm_slot = get_mm_slot(mm);
1296         if (likely(mm_slot && mm_slot->nr_pte_mapped_thp < MAX_PTE_MAPPED_THP))
1297                 mm_slot->pte_mapped_thp[mm_slot->nr_pte_mapped_thp++] = addr;
1298         spin_unlock(&khugepaged_mm_lock);
1299         return 0;
1300 }
1301
1302 /**
1303  * Try to collapse a pte-mapped THP for mm at address haddr.
1304  *
1305  * This function checks whether all the PTEs in the PMD are pointing to the
1306  * right THP. If so, retract the page table so the THP can refault in with
1307  * as pmd-mapped.
1308  */
1309 void collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr)
1310 {
1311         unsigned long haddr = addr & HPAGE_PMD_MASK;
1312         struct vm_area_struct *vma = find_vma(mm, haddr);
1313         struct page *hpage = NULL;
1314         pte_t *start_pte, *pte;
1315         pmd_t *pmd, _pmd;
1316         spinlock_t *ptl;
1317         int count = 0;
1318         int i;
1319
1320         if (!vma || !vma->vm_file ||
1321             vma->vm_start > haddr || vma->vm_end < haddr + HPAGE_PMD_SIZE)
1322                 return;
1323
1324         /*
1325          * This vm_flags may not have VM_HUGEPAGE if the page was not
1326          * collapsed by this mm. But we can still collapse if the page is
1327          * the valid THP. Add extra VM_HUGEPAGE so hugepage_vma_check()
1328          * will not fail the vma for missing VM_HUGEPAGE
1329          */
1330         if (!hugepage_vma_check(vma, vma->vm_flags | VM_HUGEPAGE))
1331                 return;
1332
1333         pmd = mm_find_pmd(mm, haddr);
1334         if (!pmd)
1335                 return;
1336
1337         start_pte = pte_offset_map_lock(mm, pmd, haddr, &ptl);
1338
1339         /* step 1: check all mapped PTEs are to the right huge page */
1340         for (i = 0, addr = haddr, pte = start_pte;
1341              i < HPAGE_PMD_NR; i++, addr += PAGE_SIZE, pte++) {
1342                 struct page *page;
1343
1344                 /* empty pte, skip */
1345                 if (pte_none(*pte))
1346                         continue;
1347
1348                 /* page swapped out, abort */
1349                 if (!pte_present(*pte))
1350                         goto abort;
1351
1352                 page = vm_normal_page(vma, addr, *pte);
1353
1354                 if (!page || !PageCompound(page))
1355                         goto abort;
1356
1357                 if (!hpage) {
1358                         hpage = compound_head(page);
1359                         /*
1360                          * The mapping of the THP should not change.
1361                          *
1362                          * Note that uprobe, debugger, or MAP_PRIVATE may
1363                          * change the page table, but the new page will
1364                          * not pass PageCompound() check.
1365                          */
1366                         if (WARN_ON(hpage->mapping != vma->vm_file->f_mapping))
1367                                 goto abort;
1368                 }
1369
1370                 /*
1371                  * Confirm the page maps to the correct subpage.
1372                  *
1373                  * Note that uprobe, debugger, or MAP_PRIVATE may change
1374                  * the page table, but the new page will not pass
1375                  * PageCompound() check.
1376                  */
1377                 if (WARN_ON(hpage + i != page))
1378                         goto abort;
1379                 count++;
1380         }
1381
1382         /* step 2: adjust rmap */
1383         for (i = 0, addr = haddr, pte = start_pte;
1384              i < HPAGE_PMD_NR; i++, addr += PAGE_SIZE, pte++) {
1385                 struct page *page;
1386
1387                 if (pte_none(*pte))
1388                         continue;
1389                 page = vm_normal_page(vma, addr, *pte);
1390                 page_remove_rmap(page, false);
1391         }
1392
1393         pte_unmap_unlock(start_pte, ptl);
1394
1395         /* step 3: set proper refcount and mm_counters. */
1396         if (hpage) {
1397                 page_ref_sub(hpage, count);
1398                 add_mm_counter(vma->vm_mm, mm_counter_file(hpage), -count);
1399         }
1400
1401         /* step 4: collapse pmd */
1402         ptl = pmd_lock(vma->vm_mm, pmd);
1403         _pmd = pmdp_collapse_flush(vma, addr, pmd);
1404         spin_unlock(ptl);
1405         mm_dec_nr_ptes(mm);
1406         pte_free(mm, pmd_pgtable(_pmd));
1407         return;
1408
1409 abort:
1410         pte_unmap_unlock(start_pte, ptl);
1411 }
1412
1413 static int khugepaged_collapse_pte_mapped_thps(struct mm_slot *mm_slot)
1414 {
1415         struct mm_struct *mm = mm_slot->mm;
1416         int i;
1417
1418         if (likely(mm_slot->nr_pte_mapped_thp == 0))
1419                 return 0;
1420
1421         if (!down_write_trylock(&mm->mmap_sem))
1422                 return -EBUSY;
1423
1424         if (unlikely(khugepaged_test_exit(mm)))
1425                 goto out;
1426
1427         for (i = 0; i < mm_slot->nr_pte_mapped_thp; i++)
1428                 collapse_pte_mapped_thp(mm, mm_slot->pte_mapped_thp[i]);
1429
1430 out:
1431         mm_slot->nr_pte_mapped_thp = 0;
1432         up_write(&mm->mmap_sem);
1433         return 0;
1434 }
1435
1436 static void retract_page_tables(struct address_space *mapping, pgoff_t pgoff)
1437 {
1438         struct vm_area_struct *vma;
1439         unsigned long addr;
1440         pmd_t *pmd, _pmd;
1441
1442         i_mmap_lock_write(mapping);
1443         vma_interval_tree_foreach(vma, &mapping->i_mmap, pgoff, pgoff) {
1444                 /*
1445                  * Check vma->anon_vma to exclude MAP_PRIVATE mappings that
1446                  * got written to. These VMAs are likely not worth investing
1447                  * down_write(mmap_sem) as PMD-mapping is likely to be split
1448                  * later.
1449                  *
1450                  * Not that vma->anon_vma check is racy: it can be set up after
1451                  * the check but before we took mmap_sem by the fault path.
1452                  * But page lock would prevent establishing any new ptes of the
1453                  * page, so we are safe.
1454                  *
1455                  * An alternative would be drop the check, but check that page
1456                  * table is clear before calling pmdp_collapse_flush() under
1457                  * ptl. It has higher chance to recover THP for the VMA, but
1458                  * has higher cost too.
1459                  */
1460                 if (vma->anon_vma)
1461                         continue;
1462                 addr = vma->vm_start + ((pgoff - vma->vm_pgoff) << PAGE_SHIFT);
1463                 if (addr & ~HPAGE_PMD_MASK)
1464                         continue;
1465                 if (vma->vm_end < addr + HPAGE_PMD_SIZE)
1466                         continue;
1467                 pmd = mm_find_pmd(vma->vm_mm, addr);
1468                 if (!pmd)
1469                         continue;
1470                 /*
1471                  * We need exclusive mmap_sem to retract page table.
1472                  *
1473                  * We use trylock due to lock inversion: we need to acquire
1474                  * mmap_sem while holding page lock. Fault path does it in
1475                  * reverse order. Trylock is a way to avoid deadlock.
1476                  */
1477                 if (down_write_trylock(&vma->vm_mm->mmap_sem)) {
1478                         spinlock_t *ptl = pmd_lock(vma->vm_mm, pmd);
1479                         /* assume page table is clear */
1480                         _pmd = pmdp_collapse_flush(vma, addr, pmd);
1481                         spin_unlock(ptl);
1482                         up_write(&vma->vm_mm->mmap_sem);
1483                         mm_dec_nr_ptes(vma->vm_mm);
1484                         pte_free(vma->vm_mm, pmd_pgtable(_pmd));
1485                 } else {
1486                         /* Try again later */
1487                         khugepaged_add_pte_mapped_thp(vma->vm_mm, addr);
1488                 }
1489         }
1490         i_mmap_unlock_write(mapping);
1491 }
1492
1493 /**
1494  * collapse_file - collapse filemap/tmpfs/shmem pages into huge one.
1495  *
1496  * Basic scheme is simple, details are more complex:
1497  *  - allocate and lock a new huge page;
1498  *  - scan page cache replacing old pages with the new one
1499  *    + swap/gup in pages if necessary;
1500  *    + fill in gaps;
1501  *    + keep old pages around in case rollback is required;
1502  *  - if replacing succeeds:
1503  *    + copy data over;
1504  *    + free old pages;
1505  *    + unlock huge page;
1506  *  - if replacing failed;
1507  *    + put all pages back and unfreeze them;
1508  *    + restore gaps in the page cache;
1509  *    + unlock and free huge page;
1510  */
1511 static void collapse_file(struct mm_struct *mm,
1512                 struct file *file, pgoff_t start,
1513                 struct page **hpage, int node)
1514 {
1515         struct address_space *mapping = file->f_mapping;
1516         gfp_t gfp;
1517         struct page *new_page;
1518         struct mem_cgroup *memcg;
1519         pgoff_t index, end = start + HPAGE_PMD_NR;
1520         LIST_HEAD(pagelist);
1521         XA_STATE_ORDER(xas, &mapping->i_pages, start, HPAGE_PMD_ORDER);
1522         int nr_none = 0, result = SCAN_SUCCEED;
1523         bool is_shmem = shmem_file(file);
1524
1525         VM_BUG_ON(!IS_ENABLED(CONFIG_READ_ONLY_THP_FOR_FS) && !is_shmem);
1526         VM_BUG_ON(start & (HPAGE_PMD_NR - 1));
1527
1528         /* Only allocate from the target node */
1529         gfp = alloc_hugepage_khugepaged_gfpmask() | __GFP_THISNODE;
1530
1531         new_page = khugepaged_alloc_page(hpage, gfp, node);
1532         if (!new_page) {
1533                 result = SCAN_ALLOC_HUGE_PAGE_FAIL;
1534                 goto out;
1535         }
1536
1537         if (unlikely(mem_cgroup_try_charge(new_page, mm, gfp, &memcg, true))) {
1538                 result = SCAN_CGROUP_CHARGE_FAIL;
1539                 goto out;
1540         }
1541
1542         /* This will be less messy when we use multi-index entries */
1543         do {
1544                 xas_lock_irq(&xas);
1545                 xas_create_range(&xas);
1546                 if (!xas_error(&xas))
1547                         break;
1548                 xas_unlock_irq(&xas);
1549                 if (!xas_nomem(&xas, GFP_KERNEL)) {
1550                         mem_cgroup_cancel_charge(new_page, memcg, true);
1551                         result = SCAN_FAIL;
1552                         goto out;
1553                 }
1554         } while (1);
1555
1556         __SetPageLocked(new_page);
1557         if (is_shmem)
1558                 __SetPageSwapBacked(new_page);
1559         new_page->index = start;
1560         new_page->mapping = mapping;
1561
1562         /*
1563          * At this point the new_page is locked and not up-to-date.
1564          * It's safe to insert it into the page cache, because nobody would
1565          * be able to map it or use it in another way until we unlock it.
1566          */
1567
1568         xas_set(&xas, start);
1569         for (index = start; index < end; index++) {
1570                 struct page *page = xas_next(&xas);
1571
1572                 VM_BUG_ON(index != xas.xa_index);
1573                 if (is_shmem) {
1574                         if (!page) {
1575                                 /*
1576                                  * Stop if extent has been truncated or
1577                                  * hole-punched, and is now completely
1578                                  * empty.
1579                                  */
1580                                 if (index == start) {
1581                                         if (!xas_next_entry(&xas, end - 1)) {
1582                                                 result = SCAN_TRUNCATED;
1583                                                 goto xa_locked;
1584                                         }
1585                                         xas_set(&xas, index);
1586                                 }
1587                                 if (!shmem_charge(mapping->host, 1)) {
1588                                         result = SCAN_FAIL;
1589                                         goto xa_locked;
1590                                 }
1591                                 xas_store(&xas, new_page);
1592                                 nr_none++;
1593                                 continue;
1594                         }
1595
1596                         if (xa_is_value(page) || !PageUptodate(page)) {
1597                                 xas_unlock_irq(&xas);
1598                                 /* swap in or instantiate fallocated page */
1599                                 if (shmem_getpage(mapping->host, index, &page,
1600                                                   SGP_NOHUGE)) {
1601                                         result = SCAN_FAIL;
1602                                         goto xa_unlocked;
1603                                 }
1604                         } else if (trylock_page(page)) {
1605                                 get_page(page);
1606                                 xas_unlock_irq(&xas);
1607                         } else {
1608                                 result = SCAN_PAGE_LOCK;
1609                                 goto xa_locked;
1610                         }
1611                 } else {        /* !is_shmem */
1612                         if (!page || xa_is_value(page)) {
1613                                 xas_unlock_irq(&xas);
1614                                 page_cache_sync_readahead(mapping, &file->f_ra,
1615                                                           file, index,
1616                                                           PAGE_SIZE);
1617                                 /* drain pagevecs to help isolate_lru_page() */
1618                                 lru_add_drain();
1619                                 page = find_lock_page(mapping, index);
1620                                 if (unlikely(page == NULL)) {
1621                                         result = SCAN_FAIL;
1622                                         goto xa_unlocked;
1623                                 }
1624                         } else if (PageDirty(page)) {
1625                                 /*
1626                                  * khugepaged only works on read-only fd,
1627                                  * so this page is dirty because it hasn't
1628                                  * been flushed since first write. There
1629                                  * won't be new dirty pages.
1630                                  *
1631                                  * Trigger async flush here and hope the
1632                                  * writeback is done when khugepaged
1633                                  * revisits this page.
1634                                  *
1635                                  * This is a one-off situation. We are not
1636                                  * forcing writeback in loop.
1637                                  */
1638                                 xas_unlock_irq(&xas);
1639                                 filemap_flush(mapping);
1640                                 result = SCAN_FAIL;
1641                                 goto xa_unlocked;
1642                         } else if (trylock_page(page)) {
1643                                 get_page(page);
1644                                 xas_unlock_irq(&xas);
1645                         } else {
1646                                 result = SCAN_PAGE_LOCK;
1647                                 goto xa_locked;
1648                         }
1649                 }
1650
1651                 /*
1652                  * The page must be locked, so we can drop the i_pages lock
1653                  * without racing with truncate.
1654                  */
1655                 VM_BUG_ON_PAGE(!PageLocked(page), page);
1656
1657                 /* make sure the page is up to date */
1658                 if (unlikely(!PageUptodate(page))) {
1659                         result = SCAN_FAIL;
1660                         goto out_unlock;
1661                 }
1662
1663                 /*
1664                  * If file was truncated then extended, or hole-punched, before
1665                  * we locked the first page, then a THP might be there already.
1666                  */
1667                 if (PageTransCompound(page)) {
1668                         result = SCAN_PAGE_COMPOUND;
1669                         goto out_unlock;
1670                 }
1671
1672                 if (page_mapping(page) != mapping) {
1673                         result = SCAN_TRUNCATED;
1674                         goto out_unlock;
1675                 }
1676
1677                 if (!is_shmem && PageDirty(page)) {
1678                         /*
1679                          * khugepaged only works on read-only fd, so this
1680                          * page is dirty because it hasn't been flushed
1681                          * since first write.
1682                          */
1683                         result = SCAN_FAIL;
1684                         goto out_unlock;
1685                 }
1686
1687                 if (isolate_lru_page(page)) {
1688                         result = SCAN_DEL_PAGE_LRU;
1689                         goto out_unlock;
1690                 }
1691
1692                 if (page_has_private(page) &&
1693                     !try_to_release_page(page, GFP_KERNEL)) {
1694                         result = SCAN_PAGE_HAS_PRIVATE;
1695                         putback_lru_page(page);
1696                         goto out_unlock;
1697                 }
1698
1699                 if (page_mapped(page))
1700                         unmap_mapping_pages(mapping, index, 1, false);
1701
1702                 xas_lock_irq(&xas);
1703                 xas_set(&xas, index);
1704
1705                 VM_BUG_ON_PAGE(page != xas_load(&xas), page);
1706                 VM_BUG_ON_PAGE(page_mapped(page), page);
1707
1708                 /*
1709                  * The page is expected to have page_count() == 3:
1710                  *  - we hold a pin on it;
1711                  *  - one reference from page cache;
1712                  *  - one from isolate_lru_page;
1713                  */
1714                 if (!page_ref_freeze(page, 3)) {
1715                         result = SCAN_PAGE_COUNT;
1716                         xas_unlock_irq(&xas);
1717                         putback_lru_page(page);
1718                         goto out_unlock;
1719                 }
1720
1721                 /*
1722                  * Add the page to the list to be able to undo the collapse if
1723                  * something go wrong.
1724                  */
1725                 list_add_tail(&page->lru, &pagelist);
1726
1727                 /* Finally, replace with the new page. */
1728                 xas_store(&xas, new_page);
1729                 continue;
1730 out_unlock:
1731                 unlock_page(page);
1732                 put_page(page);
1733                 goto xa_unlocked;
1734         }
1735
1736         if (is_shmem)
1737                 __inc_node_page_state(new_page, NR_SHMEM_THPS);
1738         else {
1739                 __inc_node_page_state(new_page, NR_FILE_THPS);
1740                 filemap_nr_thps_inc(mapping);
1741         }
1742
1743         if (nr_none) {
1744                 struct zone *zone = page_zone(new_page);
1745
1746                 __mod_node_page_state(zone->zone_pgdat, NR_FILE_PAGES, nr_none);
1747                 if (is_shmem)
1748                         __mod_node_page_state(zone->zone_pgdat,
1749                                               NR_SHMEM, nr_none);
1750         }
1751
1752 xa_locked:
1753         xas_unlock_irq(&xas);
1754 xa_unlocked:
1755
1756         if (result == SCAN_SUCCEED) {
1757                 struct page *page, *tmp;
1758
1759                 /*
1760                  * Replacing old pages with new one has succeeded, now we
1761                  * need to copy the content and free the old pages.
1762                  */
1763                 index = start;
1764                 list_for_each_entry_safe(page, tmp, &pagelist, lru) {
1765                         while (index < page->index) {
1766                                 clear_highpage(new_page + (index % HPAGE_PMD_NR));
1767                                 index++;
1768                         }
1769                         copy_highpage(new_page + (page->index % HPAGE_PMD_NR),
1770                                         page);
1771                         list_del(&page->lru);
1772                         page->mapping = NULL;
1773                         page_ref_unfreeze(page, 1);
1774                         ClearPageActive(page);
1775                         ClearPageUnevictable(page);
1776                         unlock_page(page);
1777                         put_page(page);
1778                         index++;
1779                 }
1780                 while (index < end) {
1781                         clear_highpage(new_page + (index % HPAGE_PMD_NR));
1782                         index++;
1783                 }
1784
1785                 SetPageUptodate(new_page);
1786                 page_ref_add(new_page, HPAGE_PMD_NR - 1);
1787                 mem_cgroup_commit_charge(new_page, memcg, false, true);
1788
1789                 if (is_shmem) {
1790                         set_page_dirty(new_page);
1791                         lru_cache_add_anon(new_page);
1792                 } else {
1793                         lru_cache_add_file(new_page);
1794                 }
1795                 count_memcg_events(memcg, THP_COLLAPSE_ALLOC, 1);
1796
1797                 /*
1798                  * Remove pte page tables, so we can re-fault the page as huge.
1799                  */
1800                 retract_page_tables(mapping, start);
1801                 *hpage = NULL;
1802
1803                 khugepaged_pages_collapsed++;
1804         } else {
1805                 struct page *page;
1806
1807                 /* Something went wrong: roll back page cache changes */
1808                 xas_lock_irq(&xas);
1809                 mapping->nrpages -= nr_none;
1810
1811                 if (is_shmem)
1812                         shmem_uncharge(mapping->host, nr_none);
1813
1814                 xas_set(&xas, start);
1815                 xas_for_each(&xas, page, end - 1) {
1816                         page = list_first_entry_or_null(&pagelist,
1817                                         struct page, lru);
1818                         if (!page || xas.xa_index < page->index) {
1819                                 if (!nr_none)
1820                                         break;
1821                                 nr_none--;
1822                                 /* Put holes back where they were */
1823                                 xas_store(&xas, NULL);
1824                                 continue;
1825                         }
1826
1827                         VM_BUG_ON_PAGE(page->index != xas.xa_index, page);
1828
1829                         /* Unfreeze the page. */
1830                         list_del(&page->lru);
1831                         page_ref_unfreeze(page, 2);
1832                         xas_store(&xas, page);
1833                         xas_pause(&xas);
1834                         xas_unlock_irq(&xas);
1835                         unlock_page(page);
1836                         putback_lru_page(page);
1837                         xas_lock_irq(&xas);
1838                 }
1839                 VM_BUG_ON(nr_none);
1840                 xas_unlock_irq(&xas);
1841
1842                 mem_cgroup_cancel_charge(new_page, memcg, true);
1843                 new_page->mapping = NULL;
1844         }
1845
1846         unlock_page(new_page);
1847 out:
1848         VM_BUG_ON(!list_empty(&pagelist));
1849         /* TODO: tracepoints */
1850 }
1851
1852 static void khugepaged_scan_file(struct mm_struct *mm,
1853                 struct file *file, pgoff_t start, struct page **hpage)
1854 {
1855         struct page *page = NULL;
1856         struct address_space *mapping = file->f_mapping;
1857         XA_STATE(xas, &mapping->i_pages, start);
1858         int present, swap;
1859         int node = NUMA_NO_NODE;
1860         int result = SCAN_SUCCEED;
1861
1862         present = 0;
1863         swap = 0;
1864         memset(khugepaged_node_load, 0, sizeof(khugepaged_node_load));
1865         rcu_read_lock();
1866         xas_for_each(&xas, page, start + HPAGE_PMD_NR - 1) {
1867                 if (xas_retry(&xas, page))
1868                         continue;
1869
1870                 if (xa_is_value(page)) {
1871                         if (++swap > khugepaged_max_ptes_swap) {
1872                                 result = SCAN_EXCEED_SWAP_PTE;
1873                                 break;
1874                         }
1875                         continue;
1876                 }
1877
1878                 if (PageTransCompound(page)) {
1879                         result = SCAN_PAGE_COMPOUND;
1880                         break;
1881                 }
1882
1883                 node = page_to_nid(page);
1884                 if (khugepaged_scan_abort(node)) {
1885                         result = SCAN_SCAN_ABORT;
1886                         break;
1887                 }
1888                 khugepaged_node_load[node]++;
1889
1890                 if (!PageLRU(page)) {
1891                         result = SCAN_PAGE_LRU;
1892                         break;
1893                 }
1894
1895                 if (page_count(page) !=
1896                     1 + page_mapcount(page) + page_has_private(page)) {
1897                         result = SCAN_PAGE_COUNT;
1898                         break;
1899                 }
1900
1901                 /*
1902                  * We probably should check if the page is referenced here, but
1903                  * nobody would transfer pte_young() to PageReferenced() for us.
1904                  * And rmap walk here is just too costly...
1905                  */
1906
1907                 present++;
1908
1909                 if (need_resched()) {
1910                         xas_pause(&xas);
1911                         cond_resched_rcu();
1912                 }
1913         }
1914         rcu_read_unlock();
1915
1916         if (result == SCAN_SUCCEED) {
1917                 if (present < HPAGE_PMD_NR - khugepaged_max_ptes_none) {
1918                         result = SCAN_EXCEED_NONE_PTE;
1919                 } else {
1920                         node = khugepaged_find_target_node();
1921                         collapse_file(mm, file, start, hpage, node);
1922                 }
1923         }
1924
1925         /* TODO: tracepoints */
1926 }
1927 #else
1928 static void khugepaged_scan_file(struct mm_struct *mm,
1929                 struct file *file, pgoff_t start, struct page **hpage)
1930 {
1931         BUILD_BUG();
1932 }
1933
1934 static int khugepaged_collapse_pte_mapped_thps(struct mm_slot *mm_slot)
1935 {
1936         return 0;
1937 }
1938 #endif
1939
1940 static unsigned int khugepaged_scan_mm_slot(unsigned int pages,
1941                                             struct page **hpage)
1942         __releases(&khugepaged_mm_lock)
1943         __acquires(&khugepaged_mm_lock)
1944 {
1945         struct mm_slot *mm_slot;
1946         struct mm_struct *mm;
1947         struct vm_area_struct *vma;
1948         int progress = 0;
1949
1950         VM_BUG_ON(!pages);
1951         lockdep_assert_held(&khugepaged_mm_lock);
1952
1953         if (khugepaged_scan.mm_slot)
1954                 mm_slot = khugepaged_scan.mm_slot;
1955         else {
1956                 mm_slot = list_entry(khugepaged_scan.mm_head.next,
1957                                      struct mm_slot, mm_node);
1958                 khugepaged_scan.address = 0;
1959                 khugepaged_scan.mm_slot = mm_slot;
1960         }
1961         spin_unlock(&khugepaged_mm_lock);
1962         khugepaged_collapse_pte_mapped_thps(mm_slot);
1963
1964         mm = mm_slot->mm;
1965         /*
1966          * Don't wait for semaphore (to avoid long wait times).  Just move to
1967          * the next mm on the list.
1968          */
1969         vma = NULL;
1970         if (unlikely(!down_read_trylock(&mm->mmap_sem)))
1971                 goto breakouterloop_mmap_sem;
1972         if (likely(!khugepaged_test_exit(mm)))
1973                 vma = find_vma(mm, khugepaged_scan.address);
1974
1975         progress++;
1976         for (; vma; vma = vma->vm_next) {
1977                 unsigned long hstart, hend;
1978
1979                 cond_resched();
1980                 if (unlikely(khugepaged_test_exit(mm))) {
1981                         progress++;
1982                         break;
1983                 }
1984                 if (!hugepage_vma_check(vma, vma->vm_flags)) {
1985 skip:
1986                         progress++;
1987                         continue;
1988                 }
1989                 hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK;
1990                 hend = vma->vm_end & HPAGE_PMD_MASK;
1991                 if (hstart >= hend)
1992                         goto skip;
1993                 if (khugepaged_scan.address > hend)
1994                         goto skip;
1995                 if (khugepaged_scan.address < hstart)
1996                         khugepaged_scan.address = hstart;
1997                 VM_BUG_ON(khugepaged_scan.address & ~HPAGE_PMD_MASK);
1998                 if (shmem_file(vma->vm_file) && !shmem_huge_enabled(vma))
1999                         goto skip;
2000
2001                 while (khugepaged_scan.address < hend) {
2002                         int ret;
2003                         cond_resched();
2004                         if (unlikely(khugepaged_test_exit(mm)))
2005                                 goto breakouterloop;
2006
2007                         VM_BUG_ON(khugepaged_scan.address < hstart ||
2008                                   khugepaged_scan.address + HPAGE_PMD_SIZE >
2009                                   hend);
2010                         if (IS_ENABLED(CONFIG_SHMEM) && vma->vm_file) {
2011                                 struct file *file = get_file(vma->vm_file);
2012                                 pgoff_t pgoff = linear_page_index(vma,
2013                                                 khugepaged_scan.address);
2014
2015                                 up_read(&mm->mmap_sem);
2016                                 ret = 1;
2017                                 khugepaged_scan_file(mm, file, pgoff, hpage);
2018                                 fput(file);
2019                         } else {
2020                                 ret = khugepaged_scan_pmd(mm, vma,
2021                                                 khugepaged_scan.address,
2022                                                 hpage);
2023                         }
2024                         /* move to next address */
2025                         khugepaged_scan.address += HPAGE_PMD_SIZE;
2026                         progress += HPAGE_PMD_NR;
2027                         if (ret)
2028                                 /* we released mmap_sem so break loop */
2029                                 goto breakouterloop_mmap_sem;
2030                         if (progress >= pages)
2031                                 goto breakouterloop;
2032                 }
2033         }
2034 breakouterloop:
2035         up_read(&mm->mmap_sem); /* exit_mmap will destroy ptes after this */
2036 breakouterloop_mmap_sem:
2037
2038         spin_lock(&khugepaged_mm_lock);
2039         VM_BUG_ON(khugepaged_scan.mm_slot != mm_slot);
2040         /*
2041          * Release the current mm_slot if this mm is about to die, or
2042          * if we scanned all vmas of this mm.
2043          */
2044         if (khugepaged_test_exit(mm) || !vma) {
2045                 /*
2046                  * Make sure that if mm_users is reaching zero while
2047                  * khugepaged runs here, khugepaged_exit will find
2048                  * mm_slot not pointing to the exiting mm.
2049                  */
2050                 if (mm_slot->mm_node.next != &khugepaged_scan.mm_head) {
2051                         khugepaged_scan.mm_slot = list_entry(
2052                                 mm_slot->mm_node.next,
2053                                 struct mm_slot, mm_node);
2054                         khugepaged_scan.address = 0;
2055                 } else {
2056                         khugepaged_scan.mm_slot = NULL;
2057                         khugepaged_full_scans++;
2058                 }
2059
2060                 collect_mm_slot(mm_slot);
2061         }
2062
2063         return progress;
2064 }
2065
2066 static int khugepaged_has_work(void)
2067 {
2068         return !list_empty(&khugepaged_scan.mm_head) &&
2069                 khugepaged_enabled();
2070 }
2071
2072 static int khugepaged_wait_event(void)
2073 {
2074         return !list_empty(&khugepaged_scan.mm_head) ||
2075                 kthread_should_stop();
2076 }
2077
2078 static void khugepaged_do_scan(void)
2079 {
2080         struct page *hpage = NULL;
2081         unsigned int progress = 0, pass_through_head = 0;
2082         unsigned int pages = khugepaged_pages_to_scan;
2083         bool wait = true;
2084
2085         barrier(); /* write khugepaged_pages_to_scan to local stack */
2086
2087         while (progress < pages) {
2088                 if (!khugepaged_prealloc_page(&hpage, &wait))
2089                         break;
2090
2091                 cond_resched();
2092
2093                 if (unlikely(kthread_should_stop() || try_to_freeze()))
2094                         break;
2095
2096                 spin_lock(&khugepaged_mm_lock);
2097                 if (!khugepaged_scan.mm_slot)
2098                         pass_through_head++;
2099                 if (khugepaged_has_work() &&
2100                     pass_through_head < 2)
2101                         progress += khugepaged_scan_mm_slot(pages - progress,
2102                                                             &hpage);
2103                 else
2104                         progress = pages;
2105                 spin_unlock(&khugepaged_mm_lock);
2106         }
2107
2108         if (!IS_ERR_OR_NULL(hpage))
2109                 put_page(hpage);
2110 }
2111
2112 static bool khugepaged_should_wakeup(void)
2113 {
2114         return kthread_should_stop() ||
2115                time_after_eq(jiffies, khugepaged_sleep_expire);
2116 }
2117
2118 static void khugepaged_wait_work(void)
2119 {
2120         if (khugepaged_has_work()) {
2121                 const unsigned long scan_sleep_jiffies =
2122                         msecs_to_jiffies(khugepaged_scan_sleep_millisecs);
2123
2124                 if (!scan_sleep_jiffies)
2125                         return;
2126
2127                 khugepaged_sleep_expire = jiffies + scan_sleep_jiffies;
2128                 wait_event_freezable_timeout(khugepaged_wait,
2129                                              khugepaged_should_wakeup(),
2130                                              scan_sleep_jiffies);
2131                 return;
2132         }
2133
2134         if (khugepaged_enabled())
2135                 wait_event_freezable(khugepaged_wait, khugepaged_wait_event());
2136 }
2137
2138 static int khugepaged(void *none)
2139 {
2140         struct mm_slot *mm_slot;
2141
2142         set_freezable();
2143         set_user_nice(current, MAX_NICE);
2144
2145         while (!kthread_should_stop()) {
2146                 khugepaged_do_scan();
2147                 khugepaged_wait_work();
2148         }
2149
2150         spin_lock(&khugepaged_mm_lock);
2151         mm_slot = khugepaged_scan.mm_slot;
2152         khugepaged_scan.mm_slot = NULL;
2153         if (mm_slot)
2154                 collect_mm_slot(mm_slot);
2155         spin_unlock(&khugepaged_mm_lock);
2156         return 0;
2157 }
2158
2159 static void set_recommended_min_free_kbytes(void)
2160 {
2161         struct zone *zone;
2162         int nr_zones = 0;
2163         unsigned long recommended_min;
2164
2165         for_each_populated_zone(zone) {
2166                 /*
2167                  * We don't need to worry about fragmentation of
2168                  * ZONE_MOVABLE since it only has movable pages.
2169                  */
2170                 if (zone_idx(zone) > gfp_zone(GFP_USER))
2171                         continue;
2172
2173                 nr_zones++;
2174         }
2175
2176         /* Ensure 2 pageblocks are free to assist fragmentation avoidance */
2177         recommended_min = pageblock_nr_pages * nr_zones * 2;
2178
2179         /*
2180          * Make sure that on average at least two pageblocks are almost free
2181          * of another type, one for a migratetype to fall back to and a
2182          * second to avoid subsequent fallbacks of other types There are 3
2183          * MIGRATE_TYPES we care about.
2184          */
2185         recommended_min += pageblock_nr_pages * nr_zones *
2186                            MIGRATE_PCPTYPES * MIGRATE_PCPTYPES;
2187
2188         /* don't ever allow to reserve more than 5% of the lowmem */
2189         recommended_min = min(recommended_min,
2190                               (unsigned long) nr_free_buffer_pages() / 20);
2191         recommended_min <<= (PAGE_SHIFT-10);
2192
2193         if (recommended_min > min_free_kbytes) {
2194                 if (user_min_free_kbytes >= 0)
2195                         pr_info("raising min_free_kbytes from %d to %lu to help transparent hugepage allocations\n",
2196                                 min_free_kbytes, recommended_min);
2197
2198                 min_free_kbytes = recommended_min;
2199         }
2200         setup_per_zone_wmarks();
2201 }
2202
2203 int start_stop_khugepaged(void)
2204 {
2205         static struct task_struct *khugepaged_thread __read_mostly;
2206         static DEFINE_MUTEX(khugepaged_mutex);
2207         int err = 0;
2208
2209         mutex_lock(&khugepaged_mutex);
2210         if (khugepaged_enabled()) {
2211                 if (!khugepaged_thread)
2212                         khugepaged_thread = kthread_run(khugepaged, NULL,
2213                                                         "khugepaged");
2214                 if (IS_ERR(khugepaged_thread)) {
2215                         pr_err("khugepaged: kthread_run(khugepaged) failed\n");
2216                         err = PTR_ERR(khugepaged_thread);
2217                         khugepaged_thread = NULL;
2218                         goto fail;
2219                 }
2220
2221                 if (!list_empty(&khugepaged_scan.mm_head))
2222                         wake_up_interruptible(&khugepaged_wait);
2223
2224                 set_recommended_min_free_kbytes();
2225         } else if (khugepaged_thread) {
2226                 kthread_stop(khugepaged_thread);
2227                 khugepaged_thread = NULL;
2228         }
2229 fail:
2230         mutex_unlock(&khugepaged_mutex);
2231         return err;
2232 }