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