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_EXCEED_SWAP_PTE,
  32         SCAN_EXCEED_SHARED_PTE,
  33         SCAN_PTE_NON_PRESENT,
  34         SCAN_PTE_UFFD_WP,
  35         SCAN_PAGE_RO,
  36         SCAN_LACK_REFERENCED_PAGE,
  37         SCAN_PAGE_NULL,
  38         SCAN_SCAN_ABORT,
  39         SCAN_PAGE_COUNT,
  40         SCAN_PAGE_LRU,
  41         SCAN_PAGE_LOCK,
  42         SCAN_PAGE_ANON,
  43         SCAN_PAGE_COMPOUND,
  44         SCAN_ANY_PROCESS,
  45         SCAN_VMA_NULL,
  46         SCAN_VMA_CHECK,
  47         SCAN_ADDRESS_RANGE,
  48         SCAN_SWAP_CACHE_PAGE,
  49         SCAN_DEL_PAGE_LRU,
  50         SCAN_ALLOC_HUGE_PAGE_FAIL,
  51         SCAN_CGROUP_CHARGE_FAIL,
  52         SCAN_TRUNCATED,
  53         SCAN_PAGE_HAS_PRIVATE,
  54 };
  55
  56 #define CREATE_TRACE_POINTS
  57 #include <trace/events/huge_memory.h>
  58
  59 static struct task_struct *khugepaged_thread __read_mostly;
  60 static DEFINE_MUTEX(khugepaged_mutex);
  61
  62 /* default scan 8*512 pte (or vmas) every 30 second */
  63 static unsigned int khugepaged_pages_to_scan __read_mostly;
  64 static unsigned int khugepaged_pages_collapsed;
  65 static unsigned int khugepaged_full_scans;
  66 static unsigned int khugepaged_scan_sleep_millisecs __read_mostly = 10000;
  67 /* during fragmentation poll the hugepage allocator once every minute */
  68 static unsigned int khugepaged_alloc_sleep_millisecs __read_mostly = 60000;
  69 static unsigned long khugepaged_sleep_expire;
  70 static DEFINE_SPINLOCK(khugepaged_mm_lock);
  71 static DECLARE_WAIT_QUEUE_HEAD(khugepaged_wait);
  72 /*
  73  * default collapse hugepages if there is at least one pte mapped like
  74  * it would have happened if the vma was large enough during page
  75  * fault.
  76  */
  77 static unsigned int khugepaged_max_ptes_none __read_mostly;
  78 static unsigned int khugepaged_max_ptes_swap __read_mostly;
  79 static unsigned int khugepaged_max_ptes_shared __read_mostly;
  80
  81 #define MM_SLOTS_HASH_BITS 10
  82 static __read_mostly DEFINE_HASHTABLE(mm_slots_hash, MM_SLOTS_HASH_BITS);
  83
  84 static struct kmem_cache *mm_slot_cache __read_mostly;
  85
  86 #define MAX_PTE_MAPPED_THP 8
  87
  88 /**
  89  * struct mm_slot - hash lookup from mm to mm_slot
  90  * @hash: hash collision list
  91  * @mm_node: khugepaged scan list headed in khugepaged_scan.mm_head
  92  * @mm: the mm that this information is valid for
  93  */
  94 struct mm_slot {
  95         struct hlist_node hash;
  96         struct list_head mm_node;
  97         struct mm_struct *mm;
  98
  99         /* pte-mapped THP in this mm */
 100         int nr_pte_mapped_thp;
 101         unsigned long pte_mapped_thp[MAX_PTE_MAPPED_THP];
 102 };
 103
 104 /**
 105  * struct khugepaged_scan - cursor for scanning
 106  * @mm_head: the head of the mm list to scan
 107  * @mm_slot: the current mm_slot we are scanning
 108  * @address: the next address inside that to be scanned
 109  *
 110  * There is only the one khugepaged_scan instance of this cursor structure.
 111  */
 112 struct khugepaged_scan {
 113         struct list_head mm_head;
 114         struct mm_slot *mm_slot;
 115         unsigned long address;
 116 };
 117
 118 static struct khugepaged_scan khugepaged_scan = {
 119         .mm_head = LIST_HEAD_INIT(khugepaged_scan.mm_head),
 120 };
 121
 122 #ifdef CONFIG_SYSFS
 123 static ssize_t scan_sleep_millisecs_show(struct kobject *kobj,
 124                                          struct kobj_attribute *attr,
 125                                          char *buf)
 126 {
 127         return sprintf(buf, "%u\n", khugepaged_scan_sleep_millisecs);
 128 }
 129
 130 static ssize_t scan_sleep_millisecs_store(struct kobject *kobj,
 131                                           struct kobj_attribute *attr,
 132                                           const char *buf, size_t count)
 133 {
 134         unsigned long msecs;
 135         int err;
 136
 137         err = kstrtoul(buf, 10, &msecs);
 138         if (err || msecs > UINT_MAX)
 139                 return -EINVAL;
 140
 141         khugepaged_scan_sleep_millisecs = msecs;
 142         khugepaged_sleep_expire = 0;
 143         wake_up_interruptible(&khugepaged_wait);
 144
 145         return count;
 146 }
 147 static struct kobj_attribute scan_sleep_millisecs_attr =
 148         __ATTR(scan_sleep_millisecs, 0644, scan_sleep_millisecs_show,
 149                scan_sleep_millisecs_store);
 150
 151 static ssize_t alloc_sleep_millisecs_show(struct kobject *kobj,
 152                                           struct kobj_attribute *attr,
 153                                           char *buf)
 154 {
 155         return sprintf(buf, "%u\n", khugepaged_alloc_sleep_millisecs);
 156 }
 157
 158 static ssize_t alloc_sleep_millisecs_store(struct kobject *kobj,
 159                                            struct kobj_attribute *attr,
 160                                            const char *buf, size_t count)
 161 {
 162         unsigned long msecs;
 163         int err;
 164
 165         err = kstrtoul(buf, 10, &msecs);
 166         if (err || msecs > UINT_MAX)
 167                 return -EINVAL;
 168
 169         khugepaged_alloc_sleep_millisecs = msecs;
 170         khugepaged_sleep_expire = 0;
 171         wake_up_interruptible(&khugepaged_wait);
 172
 173         return count;
 174 }
 175 static struct kobj_attribute alloc_sleep_millisecs_attr =
 176         __ATTR(alloc_sleep_millisecs, 0644, alloc_sleep_millisecs_show,
 177                alloc_sleep_millisecs_store);
 178
 179 static ssize_t pages_to_scan_show(struct kobject *kobj,
 180                                   struct kobj_attribute *attr,
 181                                   char *buf)
 182 {
 183         return sprintf(buf, "%u\n", khugepaged_pages_to_scan);
 184 }
 185 static ssize_t pages_to_scan_store(struct kobject *kobj,
 186                                    struct kobj_attribute *attr,
 187                                    const char *buf, size_t count)
 188 {
 189         int err;
 190         unsigned long pages;
 191
 192         err = kstrtoul(buf, 10, &pages);
 193         if (err || !pages || pages > UINT_MAX)
 194                 return -EINVAL;
 195
 196         khugepaged_pages_to_scan = pages;
 197
 198         return count;
 199 }
 200 static struct kobj_attribute pages_to_scan_attr =
 201         __ATTR(pages_to_scan, 0644, pages_to_scan_show,
 202                pages_to_scan_store);
 203
 204 static ssize_t pages_collapsed_show(struct kobject *kobj,
 205                                     struct kobj_attribute *attr,
 206                                     char *buf)
 207 {
 208         return sprintf(buf, "%u\n", khugepaged_pages_collapsed);
 209 }
 210 static struct kobj_attribute pages_collapsed_attr =
 211         __ATTR_RO(pages_collapsed);
 212
 213 static ssize_t full_scans_show(struct kobject *kobj,
 214                                struct kobj_attribute *attr,
 215                                char *buf)
 216 {
 217         return sprintf(buf, "%u\n", khugepaged_full_scans);
 218 }
 219 static struct kobj_attribute full_scans_attr =
 220         __ATTR_RO(full_scans);
 221
 222 static ssize_t khugepaged_defrag_show(struct kobject *kobj,
 223                                       struct kobj_attribute *attr, char *buf)
 224 {
 225         return single_hugepage_flag_show(kobj, attr, buf,
 226                                 TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG);
 227 }
 228 static ssize_t khugepaged_defrag_store(struct kobject *kobj,
 229                                        struct kobj_attribute *attr,
 230                                        const char *buf, size_t count)
 231 {
 232         return single_hugepage_flag_store(kobj, attr, buf, count,
 233                                  TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG);
 234 }
 235 static struct kobj_attribute khugepaged_defrag_attr =
 236         __ATTR(defrag, 0644, khugepaged_defrag_show,
 237                khugepaged_defrag_store);
 238
 239 /*
 240  * max_ptes_none controls if khugepaged should collapse hugepages over
 241  * any unmapped ptes in turn potentially increasing the memory
 242  * footprint of the vmas. When max_ptes_none is 0 khugepaged will not
 243  * reduce the available free memory in the system as it
 244  * runs. Increasing max_ptes_none will instead potentially reduce the
 245  * free memory in the system during the khugepaged scan.
 246  */
 247 static ssize_t khugepaged_max_ptes_none_show(struct kobject *kobj,
 248                                              struct kobj_attribute *attr,
 249                                              char *buf)
 250 {
 251         return sprintf(buf, "%u\n", khugepaged_max_ptes_none);
 252 }
 253 static ssize_t khugepaged_max_ptes_none_store(struct kobject *kobj,
 254                                               struct kobj_attribute *attr,
 255                                               const char *buf, size_t count)
 256 {
 257         int err;
 258         unsigned long max_ptes_none;
 259
 260         err = kstrtoul(buf, 10, &max_ptes_none);
 261         if (err || max_ptes_none > HPAGE_PMD_NR-1)
 262                 return -EINVAL;
 263
 264         khugepaged_max_ptes_none = max_ptes_none;
 265
 266         return count;
 267 }
 268 static struct kobj_attribute khugepaged_max_ptes_none_attr =
 269         __ATTR(max_ptes_none, 0644, khugepaged_max_ptes_none_show,
 270                khugepaged_max_ptes_none_store);
 271
 272 static ssize_t khugepaged_max_ptes_swap_show(struct kobject *kobj,
 273                                              struct kobj_attribute *attr,
 274                                              char *buf)
 275 {
 276         return sprintf(buf, "%u\n", khugepaged_max_ptes_swap);
 277 }
 278
 279 static ssize_t khugepaged_max_ptes_swap_store(struct kobject *kobj,
 280                                               struct kobj_attribute *attr,
 281                                               const char *buf, size_t count)
 282 {
 283         int err;
 284         unsigned long max_ptes_swap;
 285
 286         err  = kstrtoul(buf, 10, &max_ptes_swap);
 287         if (err || max_ptes_swap > HPAGE_PMD_NR-1)
 288                 return -EINVAL;
 289
 290         khugepaged_max_ptes_swap = max_ptes_swap;
 291
 292         return count;
 293 }
 294
 295 static struct kobj_attribute khugepaged_max_ptes_swap_attr =
 296         __ATTR(max_ptes_swap, 0644, khugepaged_max_ptes_swap_show,
 297                khugepaged_max_ptes_swap_store);
 298
 299 static ssize_t khugepaged_max_ptes_shared_show(struct kobject *kobj,
 300                                              struct kobj_attribute *attr,
 301                                              char *buf)
 302 {
 303         return sprintf(buf, "%u\n", khugepaged_max_ptes_shared);
 304 }
 305
 306 static ssize_t khugepaged_max_ptes_shared_store(struct kobject *kobj,
 307                                               struct kobj_attribute *attr,
 308                                               const char *buf, size_t count)
 309 {
 310         int err;
 311         unsigned long max_ptes_shared;
 312
 313         err  = kstrtoul(buf, 10, &max_ptes_shared);
 314         if (err || max_ptes_shared > HPAGE_PMD_NR-1)
 315                 return -EINVAL;
 316
 317         khugepaged_max_ptes_shared = max_ptes_shared;
 318
 319         return count;
 320 }
 321
 322 static struct kobj_attribute khugepaged_max_ptes_shared_attr =
 323         __ATTR(max_ptes_shared, 0644, khugepaged_max_ptes_shared_show,
 324                khugepaged_max_ptes_shared_store);
 325
 326 static struct attribute *khugepaged_attr[] = {
 327         &khugepaged_defrag_attr.attr,
 328         &khugepaged_max_ptes_none_attr.attr,
 329         &khugepaged_max_ptes_swap_attr.attr,
 330         &khugepaged_max_ptes_shared_attr.attr,
 331         &pages_to_scan_attr.attr,
 332         &pages_collapsed_attr.attr,
 333         &full_scans_attr.attr,
 334         &scan_sleep_millisecs_attr.attr,
 335         &alloc_sleep_millisecs_attr.attr,
 336         NULL,
 337 };
 338
 339 struct attribute_group khugepaged_attr_group = {
 340         .attrs = khugepaged_attr,
 341         .name = "khugepaged",
 342 };
 343 #endif /* CONFIG_SYSFS */
 344
 345 int hugepage_madvise(struct vm_area_struct *vma,
 346                      unsigned long *vm_flags, int advice)
 347 {
 348         switch (advice) {
 349         case MADV_HUGEPAGE:
 350 #ifdef CONFIG_S390
 351                 /*
 352                  * qemu blindly sets MADV_HUGEPAGE on all allocations, but s390
 353                  * can't handle this properly after s390_enable_sie, so we simply
 354                  * ignore the madvise to prevent qemu from causing a SIGSEGV.
 355                  */
 356                 if (mm_has_pgste(vma->vm_mm))
 357                         return 0;
 358 #endif
 359                 *vm_flags &= ~VM_NOHUGEPAGE;
 360                 *vm_flags |= VM_HUGEPAGE;
 361                 /*
 362                  * If the vma become good for khugepaged to scan,
 363                  * register it here without waiting a page fault that
 364                  * may not happen any time soon.
 365                  */
 366                 if (!(*vm_flags & VM_NO_KHUGEPAGED) &&
 367                                 khugepaged_enter_vma_merge(vma, *vm_flags))
 368                         return -ENOMEM;
 369                 break;
 370         case MADV_NOHUGEPAGE:
 371                 *vm_flags &= ~VM_HUGEPAGE;
 372                 *vm_flags |= VM_NOHUGEPAGE;
 373                 /*
 374                  * Setting VM_NOHUGEPAGE will prevent khugepaged from scanning
 375                  * this vma even if we leave the mm registered in khugepaged if
 376                  * it got registered before VM_NOHUGEPAGE was set.
 377                  */
 378                 break;
 379         }
 380
 381         return 0;
 382 }
 383
 384 int __init khugepaged_init(void)
 385 {
 386         mm_slot_cache = kmem_cache_create("khugepaged_mm_slot",
 387                                           sizeof(struct mm_slot),
 388                                           __alignof__(struct mm_slot), 0, NULL);
 389         if (!mm_slot_cache)
 390                 return -ENOMEM;
 391
 392         khugepaged_pages_to_scan = HPAGE_PMD_NR * 8;
 393         khugepaged_max_ptes_none = HPAGE_PMD_NR - 1;
 394         khugepaged_max_ptes_swap = HPAGE_PMD_NR / 8;
 395         khugepaged_max_ptes_shared = HPAGE_PMD_NR / 2;
 396
 397         return 0;
 398 }
 399
 400 void __init khugepaged_destroy(void)
 401 {
 402         kmem_cache_destroy(mm_slot_cache);
 403 }
 404
 405 static inline struct mm_slot *alloc_mm_slot(void)
 406 {
 407         if (!mm_slot_cache)     /* initialization failed */
 408                 return NULL;
 409         return kmem_cache_zalloc(mm_slot_cache, GFP_KERNEL);
 410 }
 411
 412 static inline void free_mm_slot(struct mm_slot *mm_slot)
 413 {
 414         kmem_cache_free(mm_slot_cache, mm_slot);
 415 }
 416
 417 static struct mm_slot *get_mm_slot(struct mm_struct *mm)
 418 {
 419         struct mm_slot *mm_slot;
 420
 421         hash_for_each_possible(mm_slots_hash, mm_slot, hash, (unsigned long)mm)
 422                 if (mm == mm_slot->mm)
 423                         return mm_slot;
 424
 425         return NULL;
 426 }
 427
 428 static void insert_to_mm_slots_hash(struct mm_struct *mm,
 429                                     struct mm_slot *mm_slot)
 430 {
 431         mm_slot->mm = mm;
 432         hash_add(mm_slots_hash, &mm_slot->hash, (long)mm);
 433 }
 434
 435 static inline int khugepaged_test_exit(struct mm_struct *mm)
 436 {
 437         return atomic_read(&mm->mm_users) == 0;
 438 }
 439
 440 static bool hugepage_vma_check(struct vm_area_struct *vma,
 441                                unsigned long vm_flags)
 442 {
 443         if (!transhuge_vma_enabled(vma, vm_flags))
 444                 return false;
 445
 446         if (vma->vm_file && !IS_ALIGNED((vma->vm_start >> PAGE_SHIFT) -
 447                                 vma->vm_pgoff, HPAGE_PMD_NR))
 448                 return false;
 449
 450         /* Enabled via shmem mount options or sysfs settings. */
 451         if (shmem_file(vma->vm_file))
 452                 return shmem_huge_enabled(vma);
 453
 454         /* THP settings require madvise. */
 455         if (!(vm_flags & VM_HUGEPAGE) && !khugepaged_always())
 456                 return false;
 457
 458         /* Only regular file is valid */
 459         if (IS_ENABLED(CONFIG_READ_ONLY_THP_FOR_FS) && vma->vm_file &&
 460             (vm_flags & VM_DENYWRITE)) {
 461                 struct inode *inode = vma->vm_file->f_inode;
 462
 463                 return S_ISREG(inode->i_mode);
 464         }
 465
 466         if (!vma->anon_vma || vma->vm_ops)
 467                 return false;
 468         if (vma_is_temporary_stack(vma))
 469                 return false;
 470         return !(vm_flags & VM_NO_KHUGEPAGED);
 471 }
 472
 473 int __khugepaged_enter(struct mm_struct *mm)
 474 {
 475         struct mm_slot *mm_slot;
 476         int wakeup;
 477
 478         mm_slot = alloc_mm_slot();
 479         if (!mm_slot)
 480                 return -ENOMEM;
 481
 482         /* __khugepaged_exit() must not run from under us */
 483         VM_BUG_ON_MM(atomic_read(&mm->mm_users) == 0, mm);
 484         if (unlikely(test_and_set_bit(MMF_VM_HUGEPAGE, &mm->flags))) {
 485                 free_mm_slot(mm_slot);
 486                 return 0;
 487         }
 488
 489         spin_lock(&khugepaged_mm_lock);
 490         insert_to_mm_slots_hash(mm, mm_slot);
 491         /*
 492          * Insert just behind the scanning cursor, to let the area settle
 493          * down a little.
 494          */
 495         wakeup = list_empty(&khugepaged_scan.mm_head);
 496         list_add_tail(&mm_slot->mm_node, &khugepaged_scan.mm_head);
 497         spin_unlock(&khugepaged_mm_lock);
 498
 499         mmgrab(mm);
 500         if (wakeup)
 501                 wake_up_interruptible(&khugepaged_wait);
 502
 503         return 0;
 504 }
 505
 506 int khugepaged_enter_vma_merge(struct vm_area_struct *vma,
 507                                unsigned long vm_flags)
 508 {
 509         unsigned long hstart, hend;
 510
 511         /*
 512          * khugepaged only supports read-only files for non-shmem files.
 513          * khugepaged does not yet work on special mappings. And
 514          * file-private shmem THP is not supported.
 515          */
 516         if (!hugepage_vma_check(vma, vm_flags))
 517                 return 0;
 518
 519         hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK;
 520         hend = vma->vm_end & HPAGE_PMD_MASK;
 521         if (hstart < hend)
 522                 return khugepaged_enter(vma, vm_flags);
 523         return 0;
 524 }
 525
 526 void __khugepaged_exit(struct mm_struct *mm)
 527 {
 528         struct mm_slot *mm_slot;
 529         int free = 0;
 530
 531         spin_lock(&khugepaged_mm_lock);
 532         mm_slot = get_mm_slot(mm);
 533         if (mm_slot && khugepaged_scan.mm_slot != mm_slot) {
 534                 hash_del(&mm_slot->hash);
 535                 list_del(&mm_slot->mm_node);
 536                 free = 1;
 537         }
 538         spin_unlock(&khugepaged_mm_lock);
 539
 540         if (free) {
 541                 clear_bit(MMF_VM_HUGEPAGE, &mm->flags);
 542                 free_mm_slot(mm_slot);
 543                 mmdrop(mm);
 544         } else if (mm_slot) {
 545                 /*
 546                  * This is required to serialize against
 547                  * khugepaged_test_exit() (which is guaranteed to run
 548                  * under mmap sem read mode). Stop here (after we
 549                  * return all pagetables will be destroyed) until
 550                  * khugepaged has finished working on the pagetables
 551                  * under the mmap_lock.
 552                  */
 553                 mmap_write_lock(mm);
 554                 mmap_write_unlock(mm);
 555         }
 556 }
 557
 558 static void release_pte_page(struct page *page)
 559 {
 560         mod_node_page_state(page_pgdat(page),
 561                         NR_ISOLATED_ANON + page_is_file_lru(page),
 562                         -compound_nr(page));
 563         unlock_page(page);
 564         putback_lru_page(page);
 565 }
 566
 567 static void release_pte_pages(pte_t *pte, pte_t *_pte,
 568                 struct list_head *compound_pagelist)
 569 {
 570         struct page *page, *tmp;
 571
 572         while (--_pte >= pte) {
 573                 pte_t pteval = *_pte;
 574
 575                 page = pte_page(pteval);
 576                 if (!pte_none(pteval) && !is_zero_pfn(pte_pfn(pteval)) &&
 577                                 !PageCompound(page))
 578                         release_pte_page(page);
 579         }
 580
 581         list_for_each_entry_safe(page, tmp, compound_pagelist, lru) {
 582                 list_del(&page->lru);
 583                 release_pte_page(page);
 584         }
 585 }
 586
 587 static bool is_refcount_suitable(struct page *page)
 588 {
 589         int expected_refcount;
 590
 591         expected_refcount = total_mapcount(page);
 592         if (PageSwapCache(page))
 593                 expected_refcount += compound_nr(page);
 594
 595         return page_count(page) == expected_refcount;
 596 }
 597
 598 static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
 599                                         unsigned long address,
 600                                         pte_t *pte,
 601                                         struct list_head *compound_pagelist)
 602 {
 603         struct page *page = NULL;
 604         pte_t *_pte;
 605         int none_or_zero = 0, shared = 0, result = 0, referenced = 0;
 606         bool writable = false;
 607
 608         for (_pte = pte; _pte < pte+HPAGE_PMD_NR;
 609              _pte++, address += PAGE_SIZE) {
 610                 pte_t pteval = *_pte;
 611                 if (pte_none(pteval) || (pte_present(pteval) &&
 612                                 is_zero_pfn(pte_pfn(pteval)))) {
 613                         if (!userfaultfd_armed(vma) &&
 614                             ++none_or_zero <= khugepaged_max_ptes_none) {
 615                                 continue;
 616                         } else {
 617                                 result = SCAN_EXCEED_NONE_PTE;
 618                                 goto out;
 619                         }
 620                 }
 621                 if (!pte_present(pteval)) {
 622                         result = SCAN_PTE_NON_PRESENT;
 623                         goto out;
 624                 }
 625                 page = vm_normal_page(vma, address, pteval);
 626                 if (unlikely(!page)) {
 627                         result = SCAN_PAGE_NULL;
 628                         goto out;
 629                 }
 630
 631                 VM_BUG_ON_PAGE(!PageAnon(page), page);
 632
 633                 if (page_mapcount(page) > 1 &&
 634                                 ++shared > khugepaged_max_ptes_shared) {
 635                         result = SCAN_EXCEED_SHARED_PTE;
 636                         goto out;
 637                 }
 638
 639                 if (PageCompound(page)) {
 640                         struct page *p;
 641                         page = compound_head(page);
 642
 643                         /*
 644                          * Check if we have dealt with the compound page
 645                          * already
 646                          */
 647                         list_for_each_entry(p, compound_pagelist, lru) {
 648                                 if (page == p)
 649                                         goto next;
 650                         }
 651                 }
 652
 653                 /*
 654                  * We can do it before isolate_lru_page because the
 655                  * page can't be freed from under us. NOTE: PG_lock
 656                  * is needed to serialize against split_huge_page
 657                  * when invoked from the VM.
 658                  */
 659                 if (!trylock_page(page)) {
 660                         result = SCAN_PAGE_LOCK;
 661                         goto out;
 662                 }
 663
 664                 /*
 665                  * Check if the page has any GUP (or other external) pins.
 666                  *
 667                  * The page table that maps the page has been already unlinked
 668                  * from the page table tree and this process cannot get
 669                  * an additinal pin on the page.
 670                  *
 671                  * New pins can come later if the page is shared across fork,
 672                  * but not from this process. The other process cannot write to
 673                  * the page, only trigger CoW.
 674                  */
 675                 if (!is_refcount_suitable(page)) {
 676                         unlock_page(page);
 677                         result = SCAN_PAGE_COUNT;
 678                         goto out;
 679                 }
 680                 if (!pte_write(pteval) && PageSwapCache(page) &&
 681                                 !reuse_swap_page(page, NULL)) {
 682                         /*
 683                          * Page is in the swap cache and cannot be re-used.
 684                          * It cannot be collapsed into a THP.
 685                          */
 686                         unlock_page(page);
 687                         result = SCAN_SWAP_CACHE_PAGE;
 688                         goto out;
 689                 }
 690
 691                 /*
 692                  * Isolate the page to avoid collapsing an hugepage
 693                  * currently in use by the VM.
 694                  */
 695                 if (isolate_lru_page(page)) {
 696                         unlock_page(page);
 697                         result = SCAN_DEL_PAGE_LRU;
 698                         goto out;
 699                 }
 700                 mod_node_page_state(page_pgdat(page),
 701                                 NR_ISOLATED_ANON + page_is_file_lru(page),
 702                                 compound_nr(page));
 703                 VM_BUG_ON_PAGE(!PageLocked(page), page);
 704                 VM_BUG_ON_PAGE(PageLRU(page), page);
 705
 706                 if (PageCompound(page))
 707                         list_add_tail(&page->lru, compound_pagelist);
 708 next:
 709                 /* There should be enough young pte to collapse the page */
 710                 if (pte_young(pteval) ||
 711                     page_is_young(page) || PageReferenced(page) ||
 712                     mmu_notifier_test_young(vma->vm_mm, address))
 713                         referenced++;
 714
 715                 if (pte_write(pteval))
 716                         writable = true;
 717         }
 718
 719         if (unlikely(!writable)) {
 720                 result = SCAN_PAGE_RO;
 721         } else if (unlikely(!referenced)) {
 722                 result = SCAN_LACK_REFERENCED_PAGE;
 723         } else {
 724                 result = SCAN_SUCCEED;
 725                 trace_mm_collapse_huge_page_isolate(page, none_or_zero,
 726                                                     referenced, writable, result);
 727                 return 1;
 728         }
 729 out:
 730         release_pte_pages(pte, _pte, compound_pagelist);
 731         trace_mm_collapse_huge_page_isolate(page, none_or_zero,
 732                                             referenced, writable, result);
 733         return 0;
 734 }
 735
 736 static void __collapse_huge_page_copy(pte_t *pte, struct page *page,
 737                                       struct vm_area_struct *vma,
 738                                       unsigned long address,
 739                                       spinlock_t *ptl,
 740                                       struct list_head *compound_pagelist)
 741 {
 742         struct page *src_page, *tmp;
 743         pte_t *_pte;
 744         for (_pte = pte; _pte < pte + HPAGE_PMD_NR;
 745                                 _pte++, page++, address += PAGE_SIZE) {
 746                 pte_t pteval = *_pte;
 747
 748                 if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) {
 749                         clear_user_highpage(page, address);
 750                         add_mm_counter(vma->vm_mm, MM_ANONPAGES, 1);
 751                         if (is_zero_pfn(pte_pfn(pteval))) {
 752                                 /*
 753                                  * ptl mostly unnecessary.
 754                                  */
 755                                 spin_lock(ptl);
 756                                 /*
 757                                  * paravirt calls inside pte_clear here are
 758                                  * superfluous.
 759                                  */
 760                                 pte_clear(vma->vm_mm, address, _pte);
 761                                 spin_unlock(ptl);
 762                         }
 763                 } else {
 764                         src_page = pte_page(pteval);
 765                         copy_user_highpage(page, src_page, address, vma);
 766                         if (!PageCompound(src_page))
 767                                 release_pte_page(src_page);
 768                         /*
 769                          * ptl mostly unnecessary, but preempt has to
 770                          * be disabled to update the per-cpu stats
 771                          * inside page_remove_rmap().
 772                          */
 773                         spin_lock(ptl);
 774                         /*
 775                          * paravirt calls inside pte_clear here are
 776                          * superfluous.
 777                          */
 778                         pte_clear(vma->vm_mm, address, _pte);
 779                         page_remove_rmap(src_page, false);
 780                         spin_unlock(ptl);
 781                         free_page_and_swap_cache(src_page);
 782                 }
 783         }
 784
 785         list_for_each_entry_safe(src_page, tmp, compound_pagelist, lru) {
 786                 list_del(&src_page->lru);
 787                 release_pte_page(src_page);
 788         }
 789 }
 790
 791 static void khugepaged_alloc_sleep(void)
 792 {
 793         DEFINE_WAIT(wait);
 794
 795         add_wait_queue(&khugepaged_wait, &wait);
 796         freezable_schedule_timeout_interruptible(
 797                 msecs_to_jiffies(khugepaged_alloc_sleep_millisecs));
 798         remove_wait_queue(&khugepaged_wait, &wait);
 799 }
 800
 801 static int khugepaged_node_load[MAX_NUMNODES];
 802
 803 static bool khugepaged_scan_abort(int nid)
 804 {
 805         int i;
 806
 807         /*
 808          * If node_reclaim_mode is disabled, then no extra effort is made to
 809          * allocate memory locally.
 810          */
 811         if (!node_reclaim_mode)
 812                 return false;
 813
 814         /* If there is a count for this node already, it must be acceptable */
 815         if (khugepaged_node_load[nid])
 816                 return false;
 817
 818         for (i = 0; i < MAX_NUMNODES; i++) {
 819                 if (!khugepaged_node_load[i])
 820                         continue;
 821                 if (node_distance(nid, i) > node_reclaim_distance)
 822                         return true;
 823         }
 824         return false;
 825 }
 826
 827 /* Defrag for khugepaged will enter direct reclaim/compaction if necessary */
 828 static inline gfp_t alloc_hugepage_khugepaged_gfpmask(void)
 829 {
 830         return khugepaged_defrag() ? GFP_TRANSHUGE : GFP_TRANSHUGE_LIGHT;
 831 }
 832
 833 #ifdef CONFIG_NUMA
 834 static int khugepaged_find_target_node(void)
 835 {
 836         static int last_khugepaged_target_node = NUMA_NO_NODE;
 837         int nid, target_node = 0, max_value = 0;
 838
 839         /* find first node with max normal pages hit */
 840         for (nid = 0; nid < MAX_NUMNODES; nid++)
 841                 if (khugepaged_node_load[nid] > max_value) {
 842                         max_value = khugepaged_node_load[nid];
 843                         target_node = nid;
 844                 }
 845
 846         /* do some balance if several nodes have the same hit record */
 847         if (target_node <= last_khugepaged_target_node)
 848                 for (nid = last_khugepaged_target_node + 1; nid < MAX_NUMNODES;
 849                                 nid++)
 850                         if (max_value == khugepaged_node_load[nid]) {
 851                                 target_node = nid;
 852                                 break;
 853                         }
 854
 855         last_khugepaged_target_node = target_node;
 856         return target_node;
 857 }
 858
 859 static bool khugepaged_prealloc_page(struct page **hpage, bool *wait)
 860 {
 861         if (IS_ERR(*hpage)) {
 862                 if (!*wait)
 863                         return false;
 864
 865                 *wait = false;
 866                 *hpage = NULL;
 867                 khugepaged_alloc_sleep();
 868         } else if (*hpage) {
 869                 put_page(*hpage);
 870                 *hpage = NULL;
 871         }
 872
 873         return true;
 874 }
 875
 876 static struct page *
 877 khugepaged_alloc_page(struct page **hpage, gfp_t gfp, int node)
 878 {
 879         VM_BUG_ON_PAGE(*hpage, *hpage);
 880
 881         *hpage = __alloc_pages_node(node, gfp, HPAGE_PMD_ORDER);
 882         if (unlikely(!*hpage)) {
 883                 count_vm_event(THP_COLLAPSE_ALLOC_FAILED);
 884                 *hpage = ERR_PTR(-ENOMEM);
 885                 return NULL;
 886         }
 887
 888         prep_transhuge_page(*hpage);
 889         count_vm_event(THP_COLLAPSE_ALLOC);
 890         return *hpage;
 891 }
 892 #else
 893 static int khugepaged_find_target_node(void)
 894 {
 895         return 0;
 896 }
 897
 898 static inline struct page *alloc_khugepaged_hugepage(void)
 899 {
 900         struct page *page;
 901
 902         page = alloc_pages(alloc_hugepage_khugepaged_gfpmask(),
 903                            HPAGE_PMD_ORDER);
 904         if (page)
 905                 prep_transhuge_page(page);
 906         return page;
 907 }
 908
 909 static struct page *khugepaged_alloc_hugepage(bool *wait)
 910 {
 911         struct page *hpage;
 912
 913         do {
 914                 hpage = alloc_khugepaged_hugepage();
 915                 if (!hpage) {
 916                         count_vm_event(THP_COLLAPSE_ALLOC_FAILED);
 917                         if (!*wait)
 918                                 return NULL;
 919
 920                         *wait = false;
 921                         khugepaged_alloc_sleep();
 922                 } else
 923                         count_vm_event(THP_COLLAPSE_ALLOC);
 924         } while (unlikely(!hpage) && likely(khugepaged_enabled()));
 925
 926         return hpage;
 927 }
 928
 929 static bool khugepaged_prealloc_page(struct page **hpage, bool *wait)
 930 {
 931         /*
 932          * If the hpage allocated earlier was briefly exposed in page cache
 933          * before collapse_file() failed, it is possible that racing lookups
 934          * have not yet completed, and would then be unpleasantly surprised by
 935          * finding the hpage reused for the same mapping at a different offset.
 936          * Just release the previous allocation if there is any danger of that.
 937          */
 938         if (*hpage && page_count(*hpage) > 1) {
 939                 put_page(*hpage);
 940                 *hpage = NULL;
 941         }
 942
 943         if (!*hpage)
 944                 *hpage = khugepaged_alloc_hugepage(wait);
 945
 946         if (unlikely(!*hpage))
 947                 return false;
 948
 949         return true;
 950 }
 951
 952 static struct page *
 953 khugepaged_alloc_page(struct page **hpage, gfp_t gfp, int node)
 954 {
 955         VM_BUG_ON(!*hpage);
 956
 957         return  *hpage;
 958 }
 959 #endif
 960
 961 /*
 962  * If mmap_lock temporarily dropped, revalidate vma
 963  * before taking mmap_lock.
 964  * Return 0 if succeeds, otherwise return none-zero
 965  * value (scan code).
 966  */
 967
 968 static int hugepage_vma_revalidate(struct mm_struct *mm, unsigned long address,
 969                 struct vm_area_struct **vmap)
 970 {
 971         struct vm_area_struct *vma;
 972         unsigned long hstart, hend;
 973
 974         if (unlikely(khugepaged_test_exit(mm)))
 975                 return SCAN_ANY_PROCESS;
 976
 977         *vmap = vma = find_vma(mm, address);
 978         if (!vma)
 979                 return SCAN_VMA_NULL;
 980
 981         hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK;
 982         hend = vma->vm_end & HPAGE_PMD_MASK;
 983         if (address < hstart || address + HPAGE_PMD_SIZE > hend)
 984                 return SCAN_ADDRESS_RANGE;
 985         if (!hugepage_vma_check(vma, vma->vm_flags))
 986                 return SCAN_VMA_CHECK;
 987         /* Anon VMA expected */
 988         if (!vma->anon_vma || vma->vm_ops)
 989                 return SCAN_VMA_CHECK;
 990         return 0;
 991 }
 992
 993 /*
 994  * Bring missing pages in from swap, to complete THP collapse.
 995  * Only done if khugepaged_scan_pmd believes it is worthwhile.
 996  *
 997  * Called and returns without pte mapped or spinlocks held,
 998  * but with mmap_lock held to protect against vma changes.
 999  */
1000
1001 static bool __collapse_huge_page_swapin(struct mm_struct *mm,
1002                                         struct vm_area_struct *vma,
1003                                         unsigned long address, pmd_t *pmd,
1004                                         int referenced)
1005 {
1006         int swapped_in = 0;
1007         vm_fault_t ret = 0;
1008         struct vm_fault vmf = {
1009                 .vma = vma,
1010                 .address = address,
1011                 .flags = FAULT_FLAG_ALLOW_RETRY,
1012                 .pmd = pmd,
1013                 .pgoff = linear_page_index(vma, address),
1014         };
1015
1016         vmf.pte = pte_offset_map(pmd, address);
1017         for (; vmf.address < address + HPAGE_PMD_NR*PAGE_SIZE;
1018                         vmf.pte++, vmf.address += PAGE_SIZE) {
1019                 vmf.orig_pte = *vmf.pte;
1020                 if (!is_swap_pte(vmf.orig_pte))
1021                         continue;
1022                 swapped_in++;
1023                 ret = do_swap_page(&vmf);
1024
1025                 /* do_swap_page returns VM_FAULT_RETRY with released mmap_lock */
1026                 if (ret & VM_FAULT_RETRY) {
1027                         mmap_read_lock(mm);
1028                         if (hugepage_vma_revalidate(mm, address, &vmf.vma)) {
1029                                 /* vma is no longer available, don't continue to swapin */
1030                                 trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 0);
1031                                 return false;
1032                         }
1033                         /* check if the pmd is still valid */
1034                         if (mm_find_pmd(mm, address) != pmd) {
1035                                 trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 0);
1036                                 return false;
1037                         }
1038                 }
1039                 if (ret & VM_FAULT_ERROR) {
1040                         trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 0);
1041                         return false;
1042                 }
1043                 /* pte is unmapped now, we need to map it */
1044                 vmf.pte = pte_offset_map(pmd, vmf.address);
1045         }
1046         vmf.pte--;
1047         pte_unmap(vmf.pte);
1048
1049         /* Drain LRU add pagevec to remove extra pin on the swapped in pages */
1050         if (swapped_in)
1051                 lru_add_drain();
1052
1053         trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 1);
1054         return true;
1055 }
1056
1057 static void collapse_huge_page(struct mm_struct *mm,
1058                                    unsigned long address,
1059                                    struct page **hpage,
1060                                    int node, int referenced, int unmapped)
1061 {
1062         LIST_HEAD(compound_pagelist);
1063         pmd_t *pmd, _pmd;
1064         pte_t *pte;
1065         pgtable_t pgtable;
1066         struct page *new_page;
1067         spinlock_t *pmd_ptl, *pte_ptl;
1068         int isolated = 0, result = 0;
1069         struct vm_area_struct *vma;
1070         struct mmu_notifier_range range;
1071         gfp_t gfp;
1072
1073         VM_BUG_ON(address & ~HPAGE_PMD_MASK);
1074
1075         /* Only allocate from the target node */
1076         gfp = alloc_hugepage_khugepaged_gfpmask() | __GFP_THISNODE;
1077
1078         /*
1079          * Before allocating the hugepage, release the mmap_lock read lock.
1080          * The allocation can take potentially a long time if it involves
1081          * sync compaction, and we do not need to hold the mmap_lock during
1082          * that. We will recheck the vma after taking it again in write mode.
1083          */
1084         mmap_read_unlock(mm);
1085         new_page = khugepaged_alloc_page(hpage, gfp, node);
1086         if (!new_page) {
1087                 result = SCAN_ALLOC_HUGE_PAGE_FAIL;
1088                 goto out_nolock;
1089         }
1090
1091         if (unlikely(mem_cgroup_charge(new_page, mm, gfp))) {
1092                 result = SCAN_CGROUP_CHARGE_FAIL;
1093                 goto out_nolock;
1094         }
1095         count_memcg_page_event(new_page, THP_COLLAPSE_ALLOC);
1096
1097         mmap_read_lock(mm);
1098         result = hugepage_vma_revalidate(mm, address, &vma);
1099         if (result) {
1100                 mmap_read_unlock(mm);
1101                 goto out_nolock;
1102         }
1103
1104         pmd = mm_find_pmd(mm, address);
1105         if (!pmd) {
1106                 result = SCAN_PMD_NULL;
1107                 mmap_read_unlock(mm);
1108                 goto out_nolock;
1109         }
1110
1111         /*
1112          * __collapse_huge_page_swapin always returns with mmap_lock locked.
1113          * If it fails, we release mmap_lock and jump out_nolock.
1114          * Continuing to collapse causes inconsistency.
1115          */
1116         if (unmapped && !__collapse_huge_page_swapin(mm, vma, address,
1117                                                      pmd, referenced)) {
1118                 mmap_read_unlock(mm);
1119                 goto out_nolock;
1120         }
1121
1122         mmap_read_unlock(mm);
1123         /*
1124          * Prevent all access to pagetables with the exception of
1125          * gup_fast later handled by the ptep_clear_flush and the VM
1126          * handled by the anon_vma lock + PG_lock.
1127          */
1128         mmap_write_lock(mm);
1129         result = hugepage_vma_revalidate(mm, address, &vma);
1130         if (result)
1131                 goto out;
1132         /* check if the pmd is still valid */
1133         if (mm_find_pmd(mm, address) != pmd)
1134                 goto out;
1135
1136         anon_vma_lock_write(vma->anon_vma);
1137
1138         mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, NULL, mm,
1139                                 address, address + HPAGE_PMD_SIZE);
1140         mmu_notifier_invalidate_range_start(&range);
1141
1142         pte = pte_offset_map(pmd, address);
1143         pte_ptl = pte_lockptr(mm, pmd);
1144
1145         pmd_ptl = pmd_lock(mm, pmd); /* probably unnecessary */
1146         /*
1147          * After this gup_fast can't run anymore. This also removes
1148          * any huge TLB entry from the CPU so we won't allow
1149          * huge and small TLB entries for the same virtual address
1150          * to avoid the risk of CPU bugs in that area.
1151          */
1152         _pmd = pmdp_collapse_flush(vma, address, pmd);
1153         spin_unlock(pmd_ptl);
1154         mmu_notifier_invalidate_range_end(&range);
1155
1156         spin_lock(pte_ptl);
1157         isolated = __collapse_huge_page_isolate(vma, address, pte,
1158                         &compound_pagelist);
1159         spin_unlock(pte_ptl);
1160
1161         if (unlikely(!isolated)) {
1162                 pte_unmap(pte);
1163                 spin_lock(pmd_ptl);
1164                 BUG_ON(!pmd_none(*pmd));
1165                 /*
1166                  * We can only use set_pmd_at when establishing
1167                  * hugepmds and never for establishing regular pmds that
1168                  * points to regular pagetables. Use pmd_populate for that
1169                  */
1170                 pmd_populate(mm, pmd, pmd_pgtable(_pmd));
1171                 spin_unlock(pmd_ptl);
1172                 anon_vma_unlock_write(vma->anon_vma);
1173                 result = SCAN_FAIL;
1174                 goto out;
1175         }
1176
1177         /*
1178          * All pages are isolated and locked so anon_vma rmap
1179          * can't run anymore.
1180          */
1181         anon_vma_unlock_write(vma->anon_vma);
1182
1183         __collapse_huge_page_copy(pte, new_page, vma, address, pte_ptl,
1184                         &compound_pagelist);
1185         pte_unmap(pte);
1186         __SetPageUptodate(new_page);
1187         pgtable = pmd_pgtable(_pmd);
1188
1189         _pmd = mk_huge_pmd(new_page, vma->vm_page_prot);
1190         _pmd = maybe_pmd_mkwrite(pmd_mkdirty(_pmd), vma);
1191
1192         /*
1193          * spin_lock() below is not the equivalent of smp_wmb(), so
1194          * this is needed to avoid the copy_huge_page writes to become
1195          * visible after the set_pmd_at() write.
1196          */
1197         smp_wmb();
1198
1199         spin_lock(pmd_ptl);
1200         BUG_ON(!pmd_none(*pmd));
1201         page_add_new_anon_rmap(new_page, vma, address, true);
1202         lru_cache_add_inactive_or_unevictable(new_page, vma);
1203         pgtable_trans_huge_deposit(mm, pmd, pgtable);
1204         set_pmd_at(mm, address, pmd, _pmd);
1205         update_mmu_cache_pmd(vma, address, pmd);
1206         spin_unlock(pmd_ptl);
1207
1208         *hpage = NULL;
1209
1210         khugepaged_pages_collapsed++;
1211         result = SCAN_SUCCEED;
1212 out_up_write:
1213         mmap_write_unlock(mm);
1214 out_nolock:
1215         if (!IS_ERR_OR_NULL(*hpage))
1216                 mem_cgroup_uncharge(*hpage);
1217         trace_mm_collapse_huge_page(mm, isolated, result);
1218         return;
1219 out:
1220         goto out_up_write;
1221 }
1222
1223 static int khugepaged_scan_pmd(struct mm_struct *mm,
1224                                struct vm_area_struct *vma,
1225                                unsigned long address,
1226                                struct page **hpage)
1227 {
1228         pmd_t *pmd;
1229         pte_t *pte, *_pte;
1230         int ret = 0, result = 0, referenced = 0;
1231         int none_or_zero = 0, shared = 0;
1232         struct page *page = NULL;
1233         unsigned long _address;
1234         spinlock_t *ptl;
1235         int node = NUMA_NO_NODE, unmapped = 0;
1236         bool writable = false;
1237
1238         VM_BUG_ON(address & ~HPAGE_PMD_MASK);
1239
1240         pmd = mm_find_pmd(mm, address);
1241         if (!pmd) {
1242                 result = SCAN_PMD_NULL;
1243                 goto out;
1244         }
1245
1246         memset(khugepaged_node_load, 0, sizeof(khugepaged_node_load));
1247         pte = pte_offset_map_lock(mm, pmd, address, &ptl);
1248         for (_address = address, _pte = pte; _pte < pte+HPAGE_PMD_NR;
1249              _pte++, _address += PAGE_SIZE) {
1250                 pte_t pteval = *_pte;
1251                 if (is_swap_pte(pteval)) {
1252                         if (++unmapped <= khugepaged_max_ptes_swap) {
1253                                 /*
1254                                  * Always be strict with uffd-wp
1255                                  * enabled swap entries.  Please see
1256                                  * comment below for pte_uffd_wp().
1257                                  */
1258                                 if (pte_swp_uffd_wp(pteval)) {
1259                                         result = SCAN_PTE_UFFD_WP;
1260                                         goto out_unmap;
1261                                 }
1262                                 continue;
1263                         } else {
1264                                 result = SCAN_EXCEED_SWAP_PTE;
1265                                 goto out_unmap;
1266                         }
1267                 }
1268                 if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) {
1269                         if (!userfaultfd_armed(vma) &&
1270                             ++none_or_zero <= khugepaged_max_ptes_none) {
1271                                 continue;
1272                         } else {
1273                                 result = SCAN_EXCEED_NONE_PTE;
1274                                 goto out_unmap;
1275                         }
1276                 }
1277                 if (!pte_present(pteval)) {
1278                         result = SCAN_PTE_NON_PRESENT;
1279                         goto out_unmap;
1280                 }
1281                 if (pte_uffd_wp(pteval)) {
1282                         /*
1283                          * Don't collapse the page if any of the small
1284                          * PTEs are armed with uffd write protection.
1285                          * Here we can also mark the new huge pmd as
1286                          * write protected if any of the small ones is
1287                          * marked but that could bring uknown
1288                          * userfault messages that falls outside of
1289                          * the registered range.  So, just be simple.
1290                          */
1291                         result = SCAN_PTE_UFFD_WP;
1292                         goto out_unmap;
1293                 }
1294                 if (pte_write(pteval))
1295                         writable = true;
1296
1297                 page = vm_normal_page(vma, _address, pteval);
1298                 if (unlikely(!page)) {
1299                         result = SCAN_PAGE_NULL;
1300                         goto out_unmap;
1301                 }
1302
1303                 if (page_mapcount(page) > 1 &&
1304                                 ++shared > khugepaged_max_ptes_shared) {
1305                         result = SCAN_EXCEED_SHARED_PTE;
1306                         goto out_unmap;
1307                 }
1308
1309                 page = compound_head(page);
1310
1311                 /*
1312                  * Record which node the original page is from and save this
1313                  * information to khugepaged_node_load[].
1314                  * Khupaged will allocate hugepage from the node has the max
1315                  * hit record.
1316                  */
1317                 node = page_to_nid(page);
1318                 if (khugepaged_scan_abort(node)) {
1319                         result = SCAN_SCAN_ABORT;
1320                         goto out_unmap;
1321                 }
1322                 khugepaged_node_load[node]++;
1323                 if (!PageLRU(page)) {
1324                         result = SCAN_PAGE_LRU;
1325                         goto out_unmap;
1326                 }
1327                 if (PageLocked(page)) {
1328                         result = SCAN_PAGE_LOCK;
1329                         goto out_unmap;
1330                 }
1331                 if (!PageAnon(page)) {
1332                         result = SCAN_PAGE_ANON;
1333                         goto out_unmap;
1334                 }
1335
1336                 /*
1337                  * Check if the page has any GUP (or other external) pins.
1338                  *
1339                  * Here the check is racy it may see totmal_mapcount > refcount
1340                  * in some cases.
1341                  * For example, one process with one forked child process.
1342                  * The parent has the PMD split due to MADV_DONTNEED, then
1343                  * the child is trying unmap the whole PMD, but khugepaged
1344                  * may be scanning the parent between the child has
1345                  * PageDoubleMap flag cleared and dec the mapcount.  So
1346                  * khugepaged may see total_mapcount > refcount.
1347                  *
1348                  * But such case is ephemeral we could always retry collapse
1349                  * later.  However it may report false positive if the page
1350                  * has excessive GUP pins (i.e. 512).  Anyway the same check
1351                  * will be done again later the risk seems low.
1352                  */
1353                 if (!is_refcount_suitable(page)) {
1354                         result = SCAN_PAGE_COUNT;
1355                         goto out_unmap;
1356                 }
1357                 if (pte_young(pteval) ||
1358                     page_is_young(page) || PageReferenced(page) ||
1359                     mmu_notifier_test_young(vma->vm_mm, address))
1360                         referenced++;
1361         }
1362         if (!writable) {
1363                 result = SCAN_PAGE_RO;
1364         } else if (!referenced || (unmapped && referenced < HPAGE_PMD_NR/2)) {
1365                 result = SCAN_LACK_REFERENCED_PAGE;
1366         } else {
1367                 result = SCAN_SUCCEED;
1368                 ret = 1;
1369         }
1370 out_unmap:
1371         pte_unmap_unlock(pte, ptl);
1372         if (ret) {
1373                 node = khugepaged_find_target_node();
1374                 /* collapse_huge_page will return with the mmap_lock released */
1375                 collapse_huge_page(mm, address, hpage, node,
1376                                 referenced, unmapped);
1377         }
1378 out:
1379         trace_mm_khugepaged_scan_pmd(mm, page, writable, referenced,
1380                                      none_or_zero, result, unmapped);
1381         return ret;
1382 }
1383
1384 static void collect_mm_slot(struct mm_slot *mm_slot)
1385 {
1386         struct mm_struct *mm = mm_slot->mm;
1387
1388         lockdep_assert_held(&khugepaged_mm_lock);
1389
1390         if (khugepaged_test_exit(mm)) {
1391                 /* free mm_slot */
1392                 hash_del(&mm_slot->hash);
1393                 list_del(&mm_slot->mm_node);
1394
1395                 /*
1396                  * Not strictly needed because the mm exited already.
1397                  *
1398                  * clear_bit(MMF_VM_HUGEPAGE, &mm->flags);
1399                  */
1400
1401                 /* khugepaged_mm_lock actually not necessary for the below */
1402                 free_mm_slot(mm_slot);
1403                 mmdrop(mm);
1404         }
1405 }
1406
1407 #ifdef CONFIG_SHMEM
1408 /*
1409  * Notify khugepaged that given addr of the mm is pte-mapped THP. Then
1410  * khugepaged should try to collapse the page table.
1411  */
1412 static int khugepaged_add_pte_mapped_thp(struct mm_struct *mm,
1413                                          unsigned long addr)
1414 {
1415         struct mm_slot *mm_slot;
1416
1417         VM_BUG_ON(addr & ~HPAGE_PMD_MASK);
1418
1419         spin_lock(&khugepaged_mm_lock);
1420         mm_slot = get_mm_slot(mm);
1421         if (likely(mm_slot && mm_slot->nr_pte_mapped_thp < MAX_PTE_MAPPED_THP))
1422                 mm_slot->pte_mapped_thp[mm_slot->nr_pte_mapped_thp++] = addr;
1423         spin_unlock(&khugepaged_mm_lock);
1424         return 0;
1425 }
1426
1427 /**
1428  * Try to collapse a pte-mapped THP for mm at address haddr.
1429  *
1430  * This function checks whether all the PTEs in the PMD are pointing to the
1431  * right THP. If so, retract the page table so the THP can refault in with
1432  * as pmd-mapped.
1433  */
1434 void collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr)
1435 {
1436         unsigned long haddr = addr & HPAGE_PMD_MASK;
1437         struct vm_area_struct *vma = find_vma(mm, haddr);
1438         struct page *hpage;
1439         pte_t *start_pte, *pte;
1440         pmd_t *pmd, _pmd;
1441         spinlock_t *ptl;
1442         int count = 0;
1443         int i;
1444
1445         if (!vma || !vma->vm_file ||
1446             vma->vm_start > haddr || vma->vm_end < haddr + HPAGE_PMD_SIZE)
1447                 return;
1448
1449         /*
1450          * This vm_flags may not have VM_HUGEPAGE if the page was not
1451          * collapsed by this mm. But we can still collapse if the page is
1452          * the valid THP. Add extra VM_HUGEPAGE so hugepage_vma_check()
1453          * will not fail the vma for missing VM_HUGEPAGE
1454          */
1455         if (!hugepage_vma_check(vma, vma->vm_flags | VM_HUGEPAGE))
1456                 return;
1457
1458         hpage = find_lock_page(vma->vm_file->f_mapping,
1459                                linear_page_index(vma, haddr));
1460         if (!hpage)
1461                 return;
1462
1463         if (!PageHead(hpage))
1464                 goto drop_hpage;
1465
1466         pmd = mm_find_pmd(mm, haddr);
1467         if (!pmd)
1468                 goto drop_hpage;
1469
1470         start_pte = pte_offset_map_lock(mm, pmd, haddr, &ptl);
1471
1472         /* step 1: check all mapped PTEs are to the right huge page */
1473         for (i = 0, addr = haddr, pte = start_pte;
1474              i < HPAGE_PMD_NR; i++, addr += PAGE_SIZE, pte++) {
1475                 struct page *page;
1476
1477                 /* empty pte, skip */
1478                 if (pte_none(*pte))
1479                         continue;
1480
1481                 /* page swapped out, abort */
1482                 if (!pte_present(*pte))
1483                         goto abort;
1484
1485                 page = vm_normal_page(vma, addr, *pte);
1486
1487                 /*
1488                  * Note that uprobe, debugger, or MAP_PRIVATE may change the
1489                  * page table, but the new page will not be a subpage of hpage.
1490                  */
1491                 if (hpage + i != page)
1492                         goto abort;
1493                 count++;
1494         }
1495
1496         /* step 2: adjust rmap */
1497         for (i = 0, addr = haddr, pte = start_pte;
1498              i < HPAGE_PMD_NR; i++, addr += PAGE_SIZE, pte++) {
1499                 struct page *page;
1500
1501                 if (pte_none(*pte))
1502                         continue;
1503                 page = vm_normal_page(vma, addr, *pte);
1504                 page_remove_rmap(page, false);
1505         }
1506
1507         pte_unmap_unlock(start_pte, ptl);
1508
1509         /* step 3: set proper refcount and mm_counters. */
1510         if (count) {
1511                 page_ref_sub(hpage, count);
1512                 add_mm_counter(vma->vm_mm, mm_counter_file(hpage), -count);
1513         }
1514
1515         /* step 4: collapse pmd */
1516         ptl = pmd_lock(vma->vm_mm, pmd);
1517         _pmd = pmdp_collapse_flush(vma, haddr, pmd);
1518         spin_unlock(ptl);
1519         mm_dec_nr_ptes(mm);
1520         pte_free(mm, pmd_pgtable(_pmd));
1521
1522 drop_hpage:
1523         unlock_page(hpage);
1524         put_page(hpage);
1525         return;
1526
1527 abort:
1528         pte_unmap_unlock(start_pte, ptl);
1529         goto drop_hpage;
1530 }
1531
1532 static int khugepaged_collapse_pte_mapped_thps(struct mm_slot *mm_slot)
1533 {
1534         struct mm_struct *mm = mm_slot->mm;
1535         int i;
1536
1537         if (likely(mm_slot->nr_pte_mapped_thp == 0))
1538                 return 0;
1539
1540         if (!mmap_write_trylock(mm))
1541                 return -EBUSY;
1542
1543         if (unlikely(khugepaged_test_exit(mm)))
1544                 goto out;
1545
1546         for (i = 0; i < mm_slot->nr_pte_mapped_thp; i++)
1547                 collapse_pte_mapped_thp(mm, mm_slot->pte_mapped_thp[i]);
1548
1549 out:
1550         mm_slot->nr_pte_mapped_thp = 0;
1551         mmap_write_unlock(mm);
1552         return 0;
1553 }
1554
1555 static void retract_page_tables(struct address_space *mapping, pgoff_t pgoff)
1556 {
1557         struct vm_area_struct *vma;
1558         struct mm_struct *mm;
1559         unsigned long addr;
1560         pmd_t *pmd, _pmd;
1561
1562         i_mmap_lock_write(mapping);
1563         vma_interval_tree_foreach(vma, &mapping->i_mmap, pgoff, pgoff) {
1564                 /*
1565                  * Check vma->anon_vma to exclude MAP_PRIVATE mappings that
1566                  * got written to. These VMAs are likely not worth investing
1567                  * mmap_write_lock(mm) as PMD-mapping is likely to be split
1568                  * later.
1569                  *
1570                  * Not that vma->anon_vma check is racy: it can be set up after
1571                  * the check but before we took mmap_lock by the fault path.
1572                  * But page lock would prevent establishing any new ptes of the
1573                  * page, so we are safe.
1574                  *
1575                  * An alternative would be drop the check, but check that page
1576                  * table is clear before calling pmdp_collapse_flush() under
1577                  * ptl. It has higher chance to recover THP for the VMA, but
1578                  * has higher cost too.
1579                  */
1580                 if (vma->anon_vma)
1581                         continue;
1582                 addr = vma->vm_start + ((pgoff - vma->vm_pgoff) << PAGE_SHIFT);
1583                 if (addr & ~HPAGE_PMD_MASK)
1584                         continue;
1585                 if (vma->vm_end < addr + HPAGE_PMD_SIZE)
1586                         continue;
1587                 mm = vma->vm_mm;
1588                 pmd = mm_find_pmd(mm, addr);
1589                 if (!pmd)
1590                         continue;
1591                 /*
1592                  * We need exclusive mmap_lock to retract page table.
1593                  *
1594                  * We use trylock due to lock inversion: we need to acquire
1595                  * mmap_lock while holding page lock. Fault path does it in
1596                  * reverse order. Trylock is a way to avoid deadlock.
1597                  */
1598                 if (mmap_write_trylock(mm)) {
1599                         if (!khugepaged_test_exit(mm)) {
1600                                 spinlock_t *ptl = pmd_lock(mm, pmd);
1601                                 /* assume page table is clear */
1602                                 _pmd = pmdp_collapse_flush(vma, addr, pmd);
1603                                 spin_unlock(ptl);
1604                                 mm_dec_nr_ptes(mm);
1605                                 pte_free(mm, pmd_pgtable(_pmd));
1606                         }
1607                         mmap_write_unlock(mm);
1608                 } else {
1609                         /* Try again later */
1610                         khugepaged_add_pte_mapped_thp(mm, addr);
1611                 }
1612         }
1613         i_mmap_unlock_write(mapping);
1614 }
1615
1616 /**
1617  * collapse_file - collapse filemap/tmpfs/shmem pages into huge one.
1618  *
1619  * Basic scheme is simple, details are more complex:
1620  *  - allocate and lock a new huge page;
1621  *  - scan page cache replacing old pages with the new one
1622  *    + swap/gup in pages if necessary;
1623  *    + fill in gaps;
1624  *    + keep old pages around in case rollback is required;
1625  *  - if replacing succeeds:
1626  *    + copy data over;
1627  *    + free old pages;
1628  *    + unlock huge page;
1629  *  - if replacing failed;
1630  *    + put all pages back and unfreeze them;
1631  *    + restore gaps in the page cache;
1632  *    + unlock and free huge page;
1633  */
1634 static void collapse_file(struct mm_struct *mm,
1635                 struct file *file, pgoff_t start,
1636                 struct page **hpage, int node)
1637 {
1638         struct address_space *mapping = file->f_mapping;
1639         gfp_t gfp;
1640         struct page *new_page;
1641         pgoff_t index, end = start + HPAGE_PMD_NR;
1642         LIST_HEAD(pagelist);
1643         XA_STATE_ORDER(xas, &mapping->i_pages, start, HPAGE_PMD_ORDER);
1644         int nr_none = 0, result = SCAN_SUCCEED;
1645         bool is_shmem = shmem_file(file);
1646
1647         VM_BUG_ON(!IS_ENABLED(CONFIG_READ_ONLY_THP_FOR_FS) && !is_shmem);
1648         VM_BUG_ON(start & (HPAGE_PMD_NR - 1));
1649
1650         /* Only allocate from the target node */
1651         gfp = alloc_hugepage_khugepaged_gfpmask() | __GFP_THISNODE;
1652
1653         new_page = khugepaged_alloc_page(hpage, gfp, node);
1654         if (!new_page) {
1655                 result = SCAN_ALLOC_HUGE_PAGE_FAIL;
1656                 goto out;
1657         }
1658
1659         if (unlikely(mem_cgroup_charge(new_page, mm, gfp))) {
1660                 result = SCAN_CGROUP_CHARGE_FAIL;
1661                 goto out;
1662         }
1663         count_memcg_page_event(new_page, THP_COLLAPSE_ALLOC);
1664
1665         /* This will be less messy when we use multi-index entries */
1666         do {
1667                 xas_lock_irq(&xas);
1668                 xas_create_range(&xas);
1669                 if (!xas_error(&xas))
1670                         break;
1671                 xas_unlock_irq(&xas);
1672                 if (!xas_nomem(&xas, GFP_KERNEL)) {
1673                         result = SCAN_FAIL;
1674                         goto out;
1675                 }
1676         } while (1);
1677
1678         __SetPageLocked(new_page);
1679         if (is_shmem)
1680                 __SetPageSwapBacked(new_page);
1681         new_page->index = start;
1682         new_page->mapping = mapping;
1683
1684         /*
1685          * At this point the new_page is locked and not up-to-date.
1686          * It's safe to insert it into the page cache, because nobody would
1687          * be able to map it or use it in another way until we unlock it.
1688          */
1689
1690         xas_set(&xas, start);
1691         for (index = start; index < end; index++) {
1692                 struct page *page = xas_next(&xas);
1693
1694                 VM_BUG_ON(index != xas.xa_index);
1695                 if (is_shmem) {
1696                         if (!page) {
1697                                 /*
1698                                  * Stop if extent has been truncated or
1699                                  * hole-punched, and is now completely
1700                                  * empty.
1701                                  */
1702                                 if (index == start) {
1703                                         if (!xas_next_entry(&xas, end - 1)) {
1704                                                 result = SCAN_TRUNCATED;
1705                                                 goto xa_locked;
1706                                         }
1707                                         xas_set(&xas, index);
1708                                 }
1709                                 if (!shmem_charge(mapping->host, 1)) {
1710                                         result = SCAN_FAIL;
1711                                         goto xa_locked;
1712                                 }
1713                                 xas_store(&xas, new_page);
1714                                 nr_none++;
1715                                 continue;
1716                         }
1717
1718                         if (xa_is_value(page) || !PageUptodate(page)) {
1719                                 xas_unlock_irq(&xas);
1720                                 /* swap in or instantiate fallocated page */
1721                                 if (shmem_getpage(mapping->host, index, &page,
1722                                                   SGP_NOHUGE)) {
1723                                         result = SCAN_FAIL;
1724                                         goto xa_unlocked;
1725                                 }
1726                         } else if (trylock_page(page)) {
1727                                 get_page(page);
1728                                 xas_unlock_irq(&xas);
1729                         } else {
1730                                 result = SCAN_PAGE_LOCK;
1731                                 goto xa_locked;
1732                         }
1733                 } else {        /* !is_shmem */
1734                         if (!page || xa_is_value(page)) {
1735                                 xas_unlock_irq(&xas);
1736                                 page_cache_sync_readahead(mapping, &file->f_ra,
1737                                                           file, index,
1738                                                           end - index);
1739                                 /* drain pagevecs to help isolate_lru_page() */
1740                                 lru_add_drain();
1741                                 page = find_lock_page(mapping, index);
1742                                 if (unlikely(page == NULL)) {
1743                                         result = SCAN_FAIL;
1744                                         goto xa_unlocked;
1745                                 }
1746                         } else if (PageDirty(page)) {
1747                                 /*
1748                                  * khugepaged only works on read-only fd,
1749                                  * so this page is dirty because it hasn't
1750                                  * been flushed since first write. There
1751                                  * won't be new dirty pages.
1752                                  *
1753                                  * Trigger async flush here and hope the
1754                                  * writeback is done when khugepaged
1755                                  * revisits this page.
1756                                  *
1757                                  * This is a one-off situation. We are not
1758                                  * forcing writeback in loop.
1759                                  */
1760                                 xas_unlock_irq(&xas);
1761                                 filemap_flush(mapping);
1762                                 result = SCAN_FAIL;
1763                                 goto xa_unlocked;
1764                         } else if (PageWriteback(page)) {
1765                                 xas_unlock_irq(&xas);
1766                                 result = SCAN_FAIL;
1767                                 goto xa_unlocked;
1768                         } else if (trylock_page(page)) {
1769                                 get_page(page);
1770                                 xas_unlock_irq(&xas);
1771                         } else {
1772                                 result = SCAN_PAGE_LOCK;
1773                                 goto xa_locked;
1774                         }
1775                 }
1776
1777                 /*
1778                  * The page must be locked, so we can drop the i_pages lock
1779                  * without racing with truncate.
1780                  */
1781                 VM_BUG_ON_PAGE(!PageLocked(page), page);
1782
1783                 /* make sure the page is up to date */
1784                 if (unlikely(!PageUptodate(page))) {
1785                         result = SCAN_FAIL;
1786                         goto out_unlock;
1787                 }
1788
1789                 /*
1790                  * If file was truncated then extended, or hole-punched, before
1791                  * we locked the first page, then a THP might be there already.
1792                  */
1793                 if (PageTransCompound(page)) {
1794                         result = SCAN_PAGE_COMPOUND;
1795                         goto out_unlock;
1796                 }
1797
1798                 if (page_mapping(page) != mapping) {
1799                         result = SCAN_TRUNCATED;
1800                         goto out_unlock;
1801                 }
1802
1803                 if (!is_shmem && (PageDirty(page) ||
1804                                   PageWriteback(page))) {
1805                         /*
1806                          * khugepaged only works on read-only fd, so this
1807                          * page is dirty because it hasn't been flushed
1808                          * since first write.
1809                          */
1810                         result = SCAN_FAIL;
1811                         goto out_unlock;
1812                 }
1813
1814                 if (isolate_lru_page(page)) {
1815                         result = SCAN_DEL_PAGE_LRU;
1816                         goto out_unlock;
1817                 }
1818
1819                 if (page_has_private(page) &&
1820                     !try_to_release_page(page, GFP_KERNEL)) {
1821                         result = SCAN_PAGE_HAS_PRIVATE;
1822                         putback_lru_page(page);
1823                         goto out_unlock;
1824                 }
1825
1826                 if (page_mapped(page))
1827                         unmap_mapping_pages(mapping, index, 1, false);
1828
1829                 xas_lock_irq(&xas);
1830                 xas_set(&xas, index);
1831
1832                 VM_BUG_ON_PAGE(page != xas_load(&xas), page);
1833                 VM_BUG_ON_PAGE(page_mapped(page), page);
1834
1835                 /*
1836                  * The page is expected to have page_count() == 3:
1837                  *  - we hold a pin on it;
1838                  *  - one reference from page cache;
1839                  *  - one from isolate_lru_page;
1840                  */
1841                 if (!page_ref_freeze(page, 3)) {
1842                         result = SCAN_PAGE_COUNT;
1843                         xas_unlock_irq(&xas);
1844                         putback_lru_page(page);
1845                         goto out_unlock;
1846                 }
1847
1848                 /*
1849                  * Add the page to the list to be able to undo the collapse if
1850                  * something go wrong.
1851                  */
1852                 list_add_tail(&page->lru, &pagelist);
1853
1854                 /* Finally, replace with the new page. */
1855                 xas_store(&xas, new_page);
1856                 continue;
1857 out_unlock:
1858                 unlock_page(page);
1859                 put_page(page);
1860                 goto xa_unlocked;
1861         }
1862
1863         if (is_shmem)
1864                 __inc_node_page_state(new_page, NR_SHMEM_THPS);
1865         else {
1866                 __inc_node_page_state(new_page, NR_FILE_THPS);
1867                 filemap_nr_thps_inc(mapping);
1868         }
1869
1870         if (nr_none) {
1871                 __mod_lruvec_page_state(new_page, NR_FILE_PAGES, nr_none);
1872                 if (is_shmem)
1873                         __mod_lruvec_page_state(new_page, NR_SHMEM, nr_none);
1874         }
1875
1876 xa_locked:
1877         xas_unlock_irq(&xas);
1878 xa_unlocked:
1879
1880         if (result == SCAN_SUCCEED) {
1881                 struct page *page, *tmp;
1882
1883                 /*
1884                  * Replacing old pages with new one has succeeded, now we
1885                  * need to copy the content and free the old pages.
1886                  */
1887                 index = start;
1888                 list_for_each_entry_safe(page, tmp, &pagelist, lru) {
1889                         while (index < page->index) {
1890                                 clear_highpage(new_page + (index % HPAGE_PMD_NR));
1891                                 index++;
1892                         }
1893                         copy_highpage(new_page + (page->index % HPAGE_PMD_NR),
1894                                         page);
1895                         list_del(&page->lru);
1896                         page->mapping = NULL;
1897                         page_ref_unfreeze(page, 1);
1898                         ClearPageActive(page);
1899                         ClearPageUnevictable(page);
1900                         unlock_page(page);
1901                         put_page(page);
1902                         index++;
1903                 }
1904                 while (index < end) {
1905                         clear_highpage(new_page + (index % HPAGE_PMD_NR));
1906                         index++;
1907                 }
1908
1909                 SetPageUptodate(new_page);
1910                 page_ref_add(new_page, HPAGE_PMD_NR - 1);
1911                 if (is_shmem)
1912                         set_page_dirty(new_page);
1913                 lru_cache_add(new_page);
1914
1915                 /*
1916                  * Remove pte page tables, so we can re-fault the page as huge.
1917                  */
1918                 retract_page_tables(mapping, start);
1919                 *hpage = NULL;
1920
1921                 khugepaged_pages_collapsed++;
1922         } else {
1923                 struct page *page;
1924
1925                 /* Something went wrong: roll back page cache changes */
1926                 xas_lock_irq(&xas);
1927                 mapping->nrpages -= nr_none;
1928
1929                 if (is_shmem)
1930                         shmem_uncharge(mapping->host, nr_none);
1931
1932                 xas_set(&xas, start);
1933                 xas_for_each(&xas, page, end - 1) {
1934                         page = list_first_entry_or_null(&pagelist,
1935                                         struct page, lru);
1936                         if (!page || xas.xa_index < page->index) {
1937                                 if (!nr_none)
1938                                         break;
1939                                 nr_none--;
1940                                 /* Put holes back where they were */
1941                                 xas_store(&xas, NULL);
1942                                 continue;
1943                         }
1944
1945                         VM_BUG_ON_PAGE(page->index != xas.xa_index, page);
1946
1947                         /* Unfreeze the page. */
1948                         list_del(&page->lru);
1949                         page_ref_unfreeze(page, 2);
1950                         xas_store(&xas, page);
1951                         xas_pause(&xas);
1952                         xas_unlock_irq(&xas);
1953                         unlock_page(page);
1954                         putback_lru_page(page);
1955                         xas_lock_irq(&xas);
1956                 }
1957                 VM_BUG_ON(nr_none);
1958                 xas_unlock_irq(&xas);
1959
1960                 new_page->mapping = NULL;
1961         }
1962
1963         unlock_page(new_page);
1964 out:
1965         VM_BUG_ON(!list_empty(&pagelist));
1966         if (!IS_ERR_OR_NULL(*hpage))
1967                 mem_cgroup_uncharge(*hpage);
1968         /* TODO: tracepoints */
1969 }
1970
1971 static void khugepaged_scan_file(struct mm_struct *mm,
1972                 struct file *file, pgoff_t start, struct page **hpage)
1973 {
1974         struct page *page = NULL;
1975         struct address_space *mapping = file->f_mapping;
1976         XA_STATE(xas, &mapping->i_pages, start);
1977         int present, swap;
1978         int node = NUMA_NO_NODE;
1979         int result = SCAN_SUCCEED;
1980
1981         present = 0;
1982         swap = 0;
1983         memset(khugepaged_node_load, 0, sizeof(khugepaged_node_load));
1984         rcu_read_lock();
1985         xas_for_each(&xas, page, start + HPAGE_PMD_NR - 1) {
1986                 if (xas_retry(&xas, page))
1987                         continue;
1988
1989                 if (xa_is_value(page)) {
1990                         if (++swap > khugepaged_max_ptes_swap) {
1991                                 result = SCAN_EXCEED_SWAP_PTE;
1992                                 break;
1993                         }
1994                         continue;
1995                 }
1996
1997                 if (PageTransCompound(page)) {
1998                         result = SCAN_PAGE_COMPOUND;
1999                         break;
2000                 }
2001
2002                 node = page_to_nid(page);
2003                 if (khugepaged_scan_abort(node)) {
2004                         result = SCAN_SCAN_ABORT;
2005                         break;
2006                 }
2007                 khugepaged_node_load[node]++;
2008
2009                 if (!PageLRU(page)) {
2010                         result = SCAN_PAGE_LRU;
2011                         break;
2012                 }
2013
2014                 if (page_count(page) !=
2015                     1 + page_mapcount(page) + page_has_private(page)) {
2016                         result = SCAN_PAGE_COUNT;
2017                         break;
2018                 }
2019
2020                 /*
2021                  * We probably should check if the page is referenced here, but
2022                  * nobody would transfer pte_young() to PageReferenced() for us.
2023                  * And rmap walk here is just too costly...
2024                  */
2025
2026                 present++;
2027
2028                 if (need_resched()) {
2029                         xas_pause(&xas);
2030                         cond_resched_rcu();
2031                 }
2032         }
2033         rcu_read_unlock();
2034
2035         if (result == SCAN_SUCCEED) {
2036                 if (present < HPAGE_PMD_NR - khugepaged_max_ptes_none) {
2037                         result = SCAN_EXCEED_NONE_PTE;
2038                 } else {
2039                         node = khugepaged_find_target_node();
2040                         collapse_file(mm, file, start, hpage, node);
2041                 }
2042         }
2043
2044         /* TODO: tracepoints */
2045 }
2046 #else
2047 static void khugepaged_scan_file(struct mm_struct *mm,
2048                 struct file *file, pgoff_t start, struct page **hpage)
2049 {
2050         BUILD_BUG();
2051 }
2052
2053 static int khugepaged_collapse_pte_mapped_thps(struct mm_slot *mm_slot)
2054 {
2055         return 0;
2056 }
2057 #endif
2058
2059 static unsigned int khugepaged_scan_mm_slot(unsigned int pages,
2060                                             struct page **hpage)
2061         __releases(&khugepaged_mm_lock)
2062         __acquires(&khugepaged_mm_lock)
2063 {
2064         struct mm_slot *mm_slot;
2065         struct mm_struct *mm;
2066         struct vm_area_struct *vma;
2067         int progress = 0;
2068
2069         VM_BUG_ON(!pages);
2070         lockdep_assert_held(&khugepaged_mm_lock);
2071
2072         if (khugepaged_scan.mm_slot)
2073                 mm_slot = khugepaged_scan.mm_slot;
2074         else {
2075                 mm_slot = list_entry(khugepaged_scan.mm_head.next,
2076                                      struct mm_slot, mm_node);
2077                 khugepaged_scan.address = 0;
2078                 khugepaged_scan.mm_slot = mm_slot;
2079         }
2080         spin_unlock(&khugepaged_mm_lock);
2081         khugepaged_collapse_pte_mapped_thps(mm_slot);
2082
2083         mm = mm_slot->mm;
2084         /*
2085          * Don't wait for semaphore (to avoid long wait times).  Just move to
2086          * the next mm on the list.
2087          */
2088         vma = NULL;
2089         if (unlikely(!mmap_read_trylock(mm)))
2090                 goto breakouterloop_mmap_lock;
2091         if (likely(!khugepaged_test_exit(mm)))
2092                 vma = find_vma(mm, khugepaged_scan.address);
2093
2094         progress++;
2095         for (; vma; vma = vma->vm_next) {
2096                 unsigned long hstart, hend;
2097
2098                 cond_resched();
2099                 if (unlikely(khugepaged_test_exit(mm))) {
2100                         progress++;
2101                         break;
2102                 }
2103                 if (!hugepage_vma_check(vma, vma->vm_flags)) {
2104 skip:
2105                         progress++;
2106                         continue;
2107                 }
2108                 hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK;
2109                 hend = vma->vm_end & HPAGE_PMD_MASK;
2110                 if (hstart >= hend)
2111                         goto skip;
2112                 if (khugepaged_scan.address > hend)
2113                         goto skip;
2114                 if (khugepaged_scan.address < hstart)
2115                         khugepaged_scan.address = hstart;
2116                 VM_BUG_ON(khugepaged_scan.address & ~HPAGE_PMD_MASK);
2117                 if (shmem_file(vma->vm_file) && !shmem_huge_enabled(vma))
2118                         goto skip;
2119
2120                 while (khugepaged_scan.address < hend) {
2121                         int ret;
2122                         cond_resched();
2123                         if (unlikely(khugepaged_test_exit(mm)))
2124                                 goto breakouterloop;
2125
2126                         VM_BUG_ON(khugepaged_scan.address < hstart ||
2127                                   khugepaged_scan.address + HPAGE_PMD_SIZE >
2128                                   hend);
2129                         if (IS_ENABLED(CONFIG_SHMEM) && vma->vm_file) {
2130                                 struct file *file = get_file(vma->vm_file);
2131                                 pgoff_t pgoff = linear_page_index(vma,
2132                                                 khugepaged_scan.address);
2133
2134                                 mmap_read_unlock(mm);
2135                                 ret = 1;
2136                                 khugepaged_scan_file(mm, file, pgoff, hpage);
2137                                 fput(file);
2138                         } else {
2139                                 ret = khugepaged_scan_pmd(mm, vma,
2140                                                 khugepaged_scan.address,
2141                                                 hpage);
2142                         }
2143                         /* move to next address */
2144                         khugepaged_scan.address += HPAGE_PMD_SIZE;
2145                         progress += HPAGE_PMD_NR;
2146                         if (ret)
2147                                 /* we released mmap_lock so break loop */
2148                                 goto breakouterloop_mmap_lock;
2149                         if (progress >= pages)
2150                                 goto breakouterloop;
2151                 }
2152         }
2153 breakouterloop:
2154         mmap_read_unlock(mm); /* exit_mmap will destroy ptes after this */
2155 breakouterloop_mmap_lock:
2156
2157         spin_lock(&khugepaged_mm_lock);
2158         VM_BUG_ON(khugepaged_scan.mm_slot != mm_slot);
2159         /*
2160          * Release the current mm_slot if this mm is about to die, or
2161          * if we scanned all vmas of this mm.
2162          */
2163         if (khugepaged_test_exit(mm) || !vma) {
2164                 /*
2165                  * Make sure that if mm_users is reaching zero while
2166                  * khugepaged runs here, khugepaged_exit will find
2167                  * mm_slot not pointing to the exiting mm.
2168                  */
2169                 if (mm_slot->mm_node.next != &khugepaged_scan.mm_head) {
2170                         khugepaged_scan.mm_slot = list_entry(
2171                                 mm_slot->mm_node.next,
2172                                 struct mm_slot, mm_node);
2173                         khugepaged_scan.address = 0;
2174                 } else {
2175                         khugepaged_scan.mm_slot = NULL;
2176                         khugepaged_full_scans++;
2177                 }
2178
2179                 collect_mm_slot(mm_slot);
2180         }
2181
2182         return progress;
2183 }
2184
2185 static int khugepaged_has_work(void)
2186 {
2187         return !list_empty(&khugepaged_scan.mm_head) &&
2188                 khugepaged_enabled();
2189 }
2190
2191 static int khugepaged_wait_event(void)
2192 {
2193         return !list_empty(&khugepaged_scan.mm_head) ||
2194                 kthread_should_stop();
2195 }
2196
2197 static void khugepaged_do_scan(void)
2198 {
2199         struct page *hpage = NULL;
2200         unsigned int progress = 0, pass_through_head = 0;
2201         unsigned int pages = khugepaged_pages_to_scan;
2202         bool wait = true;
2203
2204         barrier(); /* write khugepaged_pages_to_scan to local stack */
2205
2206         lru_add_drain_all();
2207
2208         while (progress < pages) {
2209                 if (!khugepaged_prealloc_page(&hpage, &wait))
2210                         break;
2211
2212                 cond_resched();
2213
2214                 if (unlikely(kthread_should_stop() || try_to_freeze()))
2215                         break;
2216
2217                 spin_lock(&khugepaged_mm_lock);
2218                 if (!khugepaged_scan.mm_slot)
2219                         pass_through_head++;
2220                 if (khugepaged_has_work() &&
2221                     pass_through_head < 2)
2222                         progress += khugepaged_scan_mm_slot(pages - progress,
2223                                                             &hpage);
2224                 else
2225                         progress = pages;
2226                 spin_unlock(&khugepaged_mm_lock);
2227         }
2228
2229         if (!IS_ERR_OR_NULL(hpage))
2230                 put_page(hpage);
2231 }
2232
2233 static bool khugepaged_should_wakeup(void)
2234 {
2235         return kthread_should_stop() ||
2236                time_after_eq(jiffies, khugepaged_sleep_expire);
2237 }
2238
2239 static void khugepaged_wait_work(void)
2240 {
2241         if (khugepaged_has_work()) {
2242                 const unsigned long scan_sleep_jiffies =
2243                         msecs_to_jiffies(khugepaged_scan_sleep_millisecs);
2244
2245                 if (!scan_sleep_jiffies)
2246                         return;
2247
2248                 khugepaged_sleep_expire = jiffies + scan_sleep_jiffies;
2249                 wait_event_freezable_timeout(khugepaged_wait,
2250                                              khugepaged_should_wakeup(),
2251                                              scan_sleep_jiffies);
2252                 return;
2253         }
2254
2255         if (khugepaged_enabled())
2256                 wait_event_freezable(khugepaged_wait, khugepaged_wait_event());
2257 }
2258
2259 static int khugepaged(void *none)
2260 {
2261         struct mm_slot *mm_slot;
2262
2263         set_freezable();
2264         set_user_nice(current, MAX_NICE);
2265
2266         while (!kthread_should_stop()) {
2267                 khugepaged_do_scan();
2268                 khugepaged_wait_work();
2269         }
2270
2271         spin_lock(&khugepaged_mm_lock);
2272         mm_slot = khugepaged_scan.mm_slot;
2273         khugepaged_scan.mm_slot = NULL;
2274         if (mm_slot)
2275                 collect_mm_slot(mm_slot);
2276         spin_unlock(&khugepaged_mm_lock);
2277         return 0;
2278 }
2279
2280 static void set_recommended_min_free_kbytes(void)
2281 {
2282         struct zone *zone;
2283         int nr_zones = 0;
2284         unsigned long recommended_min;
2285
2286         for_each_populated_zone(zone) {
2287                 /*
2288                  * We don't need to worry about fragmentation of
2289                  * ZONE_MOVABLE since it only has movable pages.
2290                  */
2291                 if (zone_idx(zone) > gfp_zone(GFP_USER))
2292                         continue;
2293
2294                 nr_zones++;
2295         }
2296
2297         /* Ensure 2 pageblocks are free to assist fragmentation avoidance */
2298         recommended_min = pageblock_nr_pages * nr_zones * 2;
2299
2300         /*
2301          * Make sure that on average at least two pageblocks are almost free
2302          * of another type, one for a migratetype to fall back to and a
2303          * second to avoid subsequent fallbacks of other types There are 3
2304          * MIGRATE_TYPES we care about.
2305          */
2306         recommended_min += pageblock_nr_pages * nr_zones *
2307                            MIGRATE_PCPTYPES * MIGRATE_PCPTYPES;
2308
2309         /* don't ever allow to reserve more than 5% of the lowmem */
2310         recommended_min = min(recommended_min,
2311                               (unsigned long) nr_free_buffer_pages() / 20);
2312         recommended_min <<= (PAGE_SHIFT-10);
2313
2314         if (recommended_min > min_free_kbytes) {
2315                 if (user_min_free_kbytes >= 0)
2316                         pr_info("raising min_free_kbytes from %d to %lu to help transparent hugepage allocations\n",
2317                                 min_free_kbytes, recommended_min);
2318
2319                 min_free_kbytes = recommended_min;
2320         }
2321         setup_per_zone_wmarks();
2322 }
2323
2324 int start_stop_khugepaged(void)
2325 {
2326         int err = 0;
2327
2328         mutex_lock(&khugepaged_mutex);
2329         if (khugepaged_enabled()) {
2330                 if (!khugepaged_thread)
2331                         khugepaged_thread = kthread_run(khugepaged, NULL,
2332                                                         "khugepaged");
2333                 if (IS_ERR(khugepaged_thread)) {
2334                         pr_err("khugepaged: kthread_run(khugepaged) failed\n");
2335                         err = PTR_ERR(khugepaged_thread);
2336                         khugepaged_thread = NULL;
2337                         goto fail;
2338                 }
2339
2340                 if (!list_empty(&khugepaged_scan.mm_head))
2341                         wake_up_interruptible(&khugepaged_wait);
2342
2343                 set_recommended_min_free_kbytes();
2344         } else if (khugepaged_thread) {
2345                 kthread_stop(khugepaged_thread);
2346                 khugepaged_thread = NULL;
2347         }
2348 fail:
2349         mutex_unlock(&khugepaged_mutex);
2350         return err;
2351 }
2352
2353 void khugepaged_min_free_kbytes_update(void)
2354 {
2355         mutex_lock(&khugepaged_mutex);
2356         if (khugepaged_enabled() && khugepaged_thread)
2357                 set_recommended_min_free_kbytes();
2358         mutex_unlock(&khugepaged_mutex);
2359 }