mm/khugepaged.c

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This source file includes following definitions.
scan_sleep_millisecs_show
scan_sleep_millisecs_store
alloc_sleep_millisecs_show
alloc_sleep_millisecs_store
pages_to_scan_show
pages_to_scan_store
pages_collapsed_show
full_scans_show
khugepaged_defrag_show
khugepaged_defrag_store
khugepaged_max_ptes_none_show
khugepaged_max_ptes_none_store
khugepaged_max_ptes_swap_show
khugepaged_max_ptes_swap_store
hugepage_madvise
khugepaged_init
khugepaged_destroy
alloc_mm_slot
free_mm_slot
get_mm_slot
insert_to_mm_slots_hash
khugepaged_test_exit
hugepage_vma_check
__khugepaged_enter
khugepaged_enter_vma_merge
__khugepaged_exit
release_pte_page
release_pte_pages
__collapse_huge_page_isolate
__collapse_huge_page_copy
khugepaged_alloc_sleep
khugepaged_scan_abort
alloc_hugepage_khugepaged_gfpmask
khugepaged_find_target_node
khugepaged_prealloc_page
khugepaged_alloc_page
khugepaged_find_target_node
alloc_khugepaged_hugepage
khugepaged_alloc_hugepage
khugepaged_prealloc_page
khugepaged_alloc_page
hugepage_vma_revalidate
__collapse_huge_page_swapin
collapse_huge_page
khugepaged_scan_pmd
collect_mm_slot
khugepaged_add_pte_mapped_thp
collapse_pte_mapped_thp
khugepaged_collapse_pte_mapped_thps
retract_page_tables
collapse_file
khugepaged_scan_file
khugepaged_scan_file
khugepaged_collapse_pte_mapped_thps
khugepaged_scan_mm_slot
khugepaged_has_work
khugepaged_wait_event
khugepaged_do_scan
khugepaged_should_wakeup
khugepaged_wait_work
khugepaged
set_recommended_min_free_kbytes
start_stop_khugepaged
   1 // SPDX-License-Identifier: GPL-2.0
   2 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
   3 
   4 #include <linux/mm.h>
   5 #include <linux/sched.h>
   6 #include <linux/sched/mm.h>
   7 #include <linux/sched/coredump.h>
   8 #include <linux/mmu_notifier.h>
   9 #include <linux/rmap.h>
  10 #include <linux/swap.h>
  11 #include <linux/mm_inline.h>
  12 #include <linux/kthread.h>
  13 #include <linux/khugepaged.h>
  14 #include <linux/freezer.h>
  15 #include <linux/mman.h>
  16 #include <linux/hashtable.h>
  17 #include <linux/userfaultfd_k.h>
  18 #include <linux/page_idle.h>
  19 #include <linux/swapops.h>
  20 #include <linux/shmem_fs.h>
  21 
  22 #include <asm/tlb.h>
  23 #include <asm/pgalloc.h>
  24 #include "internal.h"
  25 
  26 enum scan_result {
  27         SCAN_FAIL,
  28         SCAN_SUCCEED,
  29         SCAN_PMD_NULL,
  30         SCAN_EXCEED_NONE_PTE,
  31         SCAN_PTE_NON_PRESENT,
  32         SCAN_PAGE_RO,
  33         SCAN_LACK_REFERENCED_PAGE,
  34         SCAN_PAGE_NULL,
  35         SCAN_SCAN_ABORT,
  36         SCAN_PAGE_COUNT,
  37         SCAN_PAGE_LRU,
  38         SCAN_PAGE_LOCK,
  39         SCAN_PAGE_ANON,
  40         SCAN_PAGE_COMPOUND,
  41         SCAN_ANY_PROCESS,
  42         SCAN_VMA_NULL,
  43         SCAN_VMA_CHECK,
  44         SCAN_ADDRESS_RANGE,
  45         SCAN_SWAP_CACHE_PAGE,
  46         SCAN_DEL_PAGE_LRU,
  47         SCAN_ALLOC_HUGE_PAGE_FAIL,
  48         SCAN_CGROUP_CHARGE_FAIL,
  49         SCAN_EXCEED_SWAP_PTE,
  50         SCAN_TRUNCATED,
  51         SCAN_PAGE_HAS_PRIVATE,
  52 };
  53 
  54 #define CREATE_TRACE_POINTS
  55 #include <trace/events/huge_memory.h>
  56 
  57 /* default scan 8*512 pte (or vmas) every 30 second */
  58 static unsigned int khugepaged_pages_to_scan __read_mostly;
  59 static unsigned int khugepaged_pages_collapsed;
  60 static unsigned int khugepaged_full_scans;
  61 static unsigned int khugepaged_scan_sleep_millisecs __read_mostly = 10000;
  62 /* during fragmentation poll the hugepage allocator once every minute */
  63 static unsigned int khugepaged_alloc_sleep_millisecs __read_mostly = 60000;
  64 static unsigned long khugepaged_sleep_expire;
  65 static DEFINE_SPINLOCK(khugepaged_mm_lock);
  66 static DECLARE_WAIT_QUEUE_HEAD(khugepaged_wait);
  67 /*
  68  * default collapse hugepages if there is at least one pte mapped like
  69  * it would have happened if the vma was large enough during page
  70  * fault.
  71  */
  72 static unsigned int khugepaged_max_ptes_none __read_mostly;
  73 static unsigned int khugepaged_max_ptes_swap __read_mostly;
  74 
  75 #define MM_SLOTS_HASH_BITS 10
  76 static __read_mostly DEFINE_HASHTABLE(mm_slots_hash, MM_SLOTS_HASH_BITS);
  77 
  78 static struct kmem_cache *mm_slot_cache __read_mostly;
  79 
  80 #define MAX_PTE_MAPPED_THP 8
  81 
  82 /**
  83  * struct mm_slot - hash lookup from mm to mm_slot
  84  * @hash: hash collision list
  85  * @mm_node: khugepaged scan list headed in khugepaged_scan.mm_head
  86  * @mm: the mm that this information is valid for
  87  */
  88 struct mm_slot {
  89         struct hlist_node hash;
  90         struct list_head mm_node;
  91         struct mm_struct *mm;
  92 
  93         /* pte-mapped THP in this mm */
  94         int nr_pte_mapped_thp;
  95         unsigned long pte_mapped_thp[MAX_PTE_MAPPED_THP];
  96 };
  97 
  98 /**
  99  * struct khugepaged_scan - cursor for scanning
 100  * @mm_head: the head of the mm list to scan
 101  * @mm_slot: the current mm_slot we are scanning
 102  * @address: the next address inside that to be scanned
 103  *
 104  * There is only the one khugepaged_scan instance of this cursor structure.
 105  */
 106 struct khugepaged_scan {
 107         struct list_head mm_head;
 108         struct mm_slot *mm_slot;
 109         unsigned long address;
 110 };
 111 
 112 static struct khugepaged_scan khugepaged_scan = {
 113         .mm_head = LIST_HEAD_INIT(khugepaged_scan.mm_head),
 114 };
 115 
 116 #ifdef CONFIG_SYSFS
 117 static ssize_t scan_sleep_millisecs_show(struct kobject *kobj,
 118                                          struct kobj_attribute *attr,
 119                                          char *buf)
 120 {
 121         return sprintf(buf, "%u\n", khugepaged_scan_sleep_millisecs);
 122 }
 123 
 124 static ssize_t scan_sleep_millisecs_store(struct kobject *kobj,
 125                                           struct kobj_attribute *attr,
 126                                           const char *buf, size_t count)
 127 {
 128         unsigned long msecs;
 129         int err;
 130 
 131         err = kstrtoul(buf, 10, &msecs);
 132         if (err || msecs > UINT_MAX)
 133                 return -EINVAL;
 134 
 135         khugepaged_scan_sleep_millisecs = msecs;
 136         khugepaged_sleep_expire = 0;
 137         wake_up_interruptible(&khugepaged_wait);
 138 
 139         return count;
 140 }
 141 static struct kobj_attribute scan_sleep_millisecs_attr =
 142         __ATTR(scan_sleep_millisecs, 0644, scan_sleep_millisecs_show,
 143                scan_sleep_millisecs_store);
 144 
 145 static ssize_t alloc_sleep_millisecs_show(struct kobject *kobj,
 146                                           struct kobj_attribute *attr,
 147                                           char *buf)
 148 {
 149         return sprintf(buf, "%u\n", khugepaged_alloc_sleep_millisecs);
 150 }
 151 
 152 static ssize_t alloc_sleep_millisecs_store(struct kobject *kobj,
 153                                            struct kobj_attribute *attr,
 154                                            const char *buf, size_t count)
 155 {
 156         unsigned long msecs;
 157         int err;
 158 
 159         err = kstrtoul(buf, 10, &msecs);
 160         if (err || msecs > UINT_MAX)
 161                 return -EINVAL;
 162 
 163         khugepaged_alloc_sleep_millisecs = msecs;
 164         khugepaged_sleep_expire = 0;
 165         wake_up_interruptible(&khugepaged_wait);
 166 
 167         return count;
 168 }
 169 static struct kobj_attribute alloc_sleep_millisecs_attr =
 170         __ATTR(alloc_sleep_millisecs, 0644, alloc_sleep_millisecs_show,
 171                alloc_sleep_millisecs_store);
 172 
 173 static ssize_t pages_to_scan_show(struct kobject *kobj,
 174                                   struct kobj_attribute *attr,
 175                                   char *buf)
 176 {
 177         return sprintf(buf, "%u\n", khugepaged_pages_to_scan);
 178 }
 179 static ssize_t pages_to_scan_store(struct kobject *kobj,
 180                                    struct kobj_attribute *attr,
 181                                    const char *buf, size_t count)
 182 {
 183         int err;
 184         unsigned long pages;
 185 
 186         err = kstrtoul(buf, 10, &pages);
 187         if (err || !pages || pages > UINT_MAX)
 188                 return -EINVAL;
 189 
 190         khugepaged_pages_to_scan = pages;
 191 
 192         return count;
 193 }
 194 static struct kobj_attribute pages_to_scan_attr =
 195         __ATTR(pages_to_scan, 0644, pages_to_scan_show,
 196                pages_to_scan_store);
 197 
 198 static ssize_t pages_collapsed_show(struct kobject *kobj,
 199                                     struct kobj_attribute *attr,
 200                                     char *buf)
 201 {
 202         return sprintf(buf, "%u\n", khugepaged_pages_collapsed);
 203 }
 204 static struct kobj_attribute pages_collapsed_attr =
 205         __ATTR_RO(pages_collapsed);
 206 
 207 static ssize_t full_scans_show(struct kobject *kobj,
 208                                struct kobj_attribute *attr,
 209                                char *buf)
 210 {
 211         return sprintf(buf, "%u\n", khugepaged_full_scans);
 212 }
 213 static struct kobj_attribute full_scans_attr =
 214         __ATTR_RO(full_scans);
 215 
 216 static ssize_t khugepaged_defrag_show(struct kobject *kobj,
 217                                       struct kobj_attribute *attr, char *buf)
 218 {
 219         return single_hugepage_flag_show(kobj, attr, buf,
 220                                 TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG);
 221 }
 222 static ssize_t khugepaged_defrag_store(struct kobject *kobj,
 223                                        struct kobj_attribute *attr,
 224                                        const char *buf, size_t count)
 225 {
 226         return single_hugepage_flag_store(kobj, attr, buf, count,
 227                                  TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG);
 228 }
 229 static struct kobj_attribute khugepaged_defrag_attr =
 230         __ATTR(defrag, 0644, khugepaged_defrag_show,
 231                khugepaged_defrag_store);
 232 
 233 /*
 234  * max_ptes_none controls if khugepaged should collapse hugepages over
 235  * any unmapped ptes in turn potentially increasing the memory
 236  * footprint of the vmas. When max_ptes_none is 0 khugepaged will not
 237  * reduce the available free memory in the system as it
 238  * runs. Increasing max_ptes_none will instead potentially reduce the
 239  * free memory in the system during the khugepaged scan.
 240  */
 241 static ssize_t khugepaged_max_ptes_none_show(struct kobject *kobj,
 242                                              struct kobj_attribute *attr,
 243                                              char *buf)
 244 {
 245         return sprintf(buf, "%u\n", khugepaged_max_ptes_none);
 246 }
 247 static ssize_t khugepaged_max_ptes_none_store(struct kobject *kobj,
 248                                               struct kobj_attribute *attr,
 249                                               const char *buf, size_t count)
 250 {
 251         int err;
 252         unsigned long max_ptes_none;
 253 
 254         err = kstrtoul(buf, 10, &max_ptes_none);
 255         if (err || max_ptes_none > HPAGE_PMD_NR-1)
 256                 return -EINVAL;
 257 
 258         khugepaged_max_ptes_none = max_ptes_none;
 259 
 260         return count;
 261 }
 262 static struct kobj_attribute khugepaged_max_ptes_none_attr =
 263         __ATTR(max_ptes_none, 0644, khugepaged_max_ptes_none_show,
 264                khugepaged_max_ptes_none_store);
 265 
 266 static ssize_t khugepaged_max_ptes_swap_show(struct kobject *kobj,
 267                                              struct kobj_attribute *attr,
 268                                              char *buf)
 269 {
 270         return sprintf(buf, "%u\n", khugepaged_max_ptes_swap);
 271 }
 272 
 273 static ssize_t khugepaged_max_ptes_swap_store(struct kobject *kobj,
 274                                               struct kobj_attribute *attr,
 275                                               const char *buf, size_t count)
 276 {
 277         int err;
 278         unsigned long max_ptes_swap;
 279 
 280         err  = kstrtoul(buf, 10, &max_ptes_swap);
 281         if (err || max_ptes_swap > HPAGE_PMD_NR-1)
 282                 return -EINVAL;
 283 
 284         khugepaged_max_ptes_swap = max_ptes_swap;
 285 
 286         return count;
 287 }
 288 
 289 static struct kobj_attribute khugepaged_max_ptes_swap_attr =
 290         __ATTR(max_ptes_swap, 0644, khugepaged_max_ptes_swap_show,
 291                khugepaged_max_ptes_swap_store);
 292 
 293 static struct attribute *khugepaged_attr[] = {
 294         &khugepaged_defrag_attr.attr,
 295         &khugepaged_max_ptes_none_attr.attr,
 296         &pages_to_scan_attr.attr,
 297         &pages_collapsed_attr.attr,
 298         &full_scans_attr.attr,
 299         &scan_sleep_millisecs_attr.attr,
 300         &alloc_sleep_millisecs_attr.attr,
 301         &khugepaged_max_ptes_swap_attr.attr,
 302         NULL,
 303 };
 304 
 305 struct attribute_group khugepaged_attr_group = {
 306         .attrs = khugepaged_attr,
 307         .name = "khugepaged",
 308 };
 309 #endif /* CONFIG_SYSFS */
 310 
 311 #define VM_NO_KHUGEPAGED (VM_SPECIAL | VM_HUGETLB)
 312 
 313 int hugepage_madvise(struct vm_area_struct *vma,
 314                      unsigned long *vm_flags, int advice)
 315 {
 316         switch (advice) {
 317         case MADV_HUGEPAGE:
 318 #ifdef CONFIG_S390
 319                 /*
 320                  * qemu blindly sets MADV_HUGEPAGE on all allocations, but s390
 321                  * can't handle this properly after s390_enable_sie, so we simply
 322                  * ignore the madvise to prevent qemu from causing a SIGSEGV.
 323                  */
 324                 if (mm_has_pgste(vma->vm_mm))
 325                         return 0;
 326 #endif
 327                 *vm_flags &= ~VM_NOHUGEPAGE;
 328                 *vm_flags |= VM_HUGEPAGE;
 329                 /*
 330                  * If the vma become good for khugepaged to scan,
 331                  * register it here without waiting a page fault that
 332                  * may not happen any time soon.
 333                  */
 334                 if (!(*vm_flags & VM_NO_KHUGEPAGED) &&
 335                                 khugepaged_enter_vma_merge(vma, *vm_flags))
 336                         return -ENOMEM;
 337                 break;
 338         case MADV_NOHUGEPAGE:
 339                 *vm_flags &= ~VM_HUGEPAGE;
 340                 *vm_flags |= VM_NOHUGEPAGE;
 341                 /*
 342                  * Setting VM_NOHUGEPAGE will prevent khugepaged from scanning
 343                  * this vma even if we leave the mm registered in khugepaged if
 344                  * it got registered before VM_NOHUGEPAGE was set.
 345                  */
 346                 break;
 347         }
 348 
 349         return 0;
 350 }
 351 
 352 int __init khugepaged_init(void)
 353 {
 354         mm_slot_cache = kmem_cache_create("khugepaged_mm_slot",
 355                                           sizeof(struct mm_slot),
 356                                           __alignof__(struct mm_slot), 0, NULL);
 357         if (!mm_slot_cache)
 358                 return -ENOMEM;
 359 
 360         khugepaged_pages_to_scan = HPAGE_PMD_NR * 8;
 361         khugepaged_max_ptes_none = HPAGE_PMD_NR - 1;
 362         khugepaged_max_ptes_swap = HPAGE_PMD_NR / 8;
 363 
 364         return 0;
 365 }
 366 
 367 void __init khugepaged_destroy(void)
 368 {
 369         kmem_cache_destroy(mm_slot_cache);
 370 }
 371 
 372 static inline struct mm_slot *alloc_mm_slot(void)
 373 {
 374         if (!mm_slot_cache)     /* initialization failed */
 375                 return NULL;
 376         return kmem_cache_zalloc(mm_slot_cache, GFP_KERNEL);
 377 }
 378 
 379 static inline void free_mm_slot(struct mm_slot *mm_slot)
 380 {
 381         kmem_cache_free(mm_slot_cache, mm_slot);
 382 }
 383 
 384 static struct mm_slot *get_mm_slot(struct mm_struct *mm)
 385 {
 386         struct mm_slot *mm_slot;
 387 
 388         hash_for_each_possible(mm_slots_hash, mm_slot, hash, (unsigned long)mm)
 389                 if (mm == mm_slot->mm)
 390                         return mm_slot;
 391 
 392         return NULL;
 393 }
 394 
 395 static void insert_to_mm_slots_hash(struct mm_struct *mm,
 396                                     struct mm_slot *mm_slot)
 397 {
 398         mm_slot->mm = mm;
 399         hash_add(mm_slots_hash, &mm_slot->hash, (long)mm);
 400 }
 401 
 402 static inline int khugepaged_test_exit(struct mm_struct *mm)
 403 {
 404         return atomic_read(&mm->mm_users) == 0;
 405 }
 406 
 407 static bool hugepage_vma_check(struct vm_area_struct *vma,
 408                                unsigned long vm_flags)
 409 {
 410         if ((!(vm_flags & VM_HUGEPAGE) && !khugepaged_always()) ||
 411             (vm_flags & VM_NOHUGEPAGE) ||
 412             test_bit(MMF_DISABLE_THP, &vma->vm_mm->flags))
 413                 return false;
 414 
 415         if (shmem_file(vma->vm_file) ||
 416             (IS_ENABLED(CONFIG_READ_ONLY_THP_FOR_FS) &&
 417              vma->vm_file &&
 418              (vm_flags & VM_DENYWRITE))) {
 419                 if (!IS_ENABLED(CONFIG_TRANSPARENT_HUGE_PAGECACHE))
 420                         return false;
 421                 return IS_ALIGNED((vma->vm_start >> PAGE_SHIFT) - vma->vm_pgoff,
 422                                 HPAGE_PMD_NR);
 423         }
 424         if (!vma->anon_vma || vma->vm_ops)
 425                 return false;
 426         if (is_vma_temporary_stack(vma))
 427                 return false;
 428         return !(vm_flags & VM_NO_KHUGEPAGED);
 429 }
 430 
 431 int __khugepaged_enter(struct mm_struct *mm)
 432 {
 433         struct mm_slot *mm_slot;
 434         int wakeup;
 435 
 436         mm_slot = alloc_mm_slot();
 437         if (!mm_slot)
 438                 return -ENOMEM;
 439 
 440         /* __khugepaged_exit() must not run from under us */
 441         VM_BUG_ON_MM(khugepaged_test_exit(mm), mm);
 442         if (unlikely(test_and_set_bit(MMF_VM_HUGEPAGE, &mm->flags))) {
 443                 free_mm_slot(mm_slot);
 444                 return 0;
 445         }
 446 
 447         spin_lock(&khugepaged_mm_lock);
 448         insert_to_mm_slots_hash(mm, mm_slot);
 449         /*
 450          * Insert just behind the scanning cursor, to let the area settle
 451          * down a little.
 452          */
 453         wakeup = list_empty(&khugepaged_scan.mm_head);
 454         list_add_tail(&mm_slot->mm_node, &khugepaged_scan.mm_head);
 455         spin_unlock(&khugepaged_mm_lock);
 456 
 457         mmgrab(mm);
 458         if (wakeup)
 459                 wake_up_interruptible(&khugepaged_wait);
 460 
 461         return 0;
 462 }
 463 
 464 int khugepaged_enter_vma_merge(struct vm_area_struct *vma,
 465                                unsigned long vm_flags)
 466 {
 467         unsigned long hstart, hend;
 468 
 469         /*
 470          * khugepaged only supports read-only files for non-shmem files.
 471          * khugepaged does not yet work on special mappings. And
 472          * file-private shmem THP is not supported.
 473          */
 474         if (!hugepage_vma_check(vma, vm_flags))
 475                 return 0;
 476 
 477         hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK;
 478         hend = vma->vm_end & HPAGE_PMD_MASK;
 479         if (hstart < hend)
 480                 return khugepaged_enter(vma, vm_flags);
 481         return 0;
 482 }
 483 
 484 void __khugepaged_exit(struct mm_struct *mm)
 485 {
 486         struct mm_slot *mm_slot;
 487         int free = 0;
 488 
 489         spin_lock(&khugepaged_mm_lock);
 490         mm_slot = get_mm_slot(mm);
 491         if (mm_slot && khugepaged_scan.mm_slot != mm_slot) {
 492                 hash_del(&mm_slot->hash);
 493                 list_del(&mm_slot->mm_node);
 494                 free = 1;
 495         }
 496         spin_unlock(&khugepaged_mm_lock);
 497 
 498         if (free) {
 499                 clear_bit(MMF_VM_HUGEPAGE, &mm->flags);
 500                 free_mm_slot(mm_slot);
 501                 mmdrop(mm);
 502         } else if (mm_slot) {
 503                 /*
 504                  * This is required to serialize against
 505                  * khugepaged_test_exit() (which is guaranteed to run
 506                  * under mmap sem read mode). Stop here (after we
 507                  * return all pagetables will be destroyed) until
 508                  * khugepaged has finished working on the pagetables
 509                  * under the mmap_sem.
 510                  */
 511                 down_write(&mm->mmap_sem);
 512                 up_write(&mm->mmap_sem);
 513         }
 514 }
 515 
 516 static void release_pte_page(struct page *page)
 517 {
 518         dec_node_page_state(page, NR_ISOLATED_ANON + page_is_file_cache(page));
 519         unlock_page(page);
 520         putback_lru_page(page);
 521 }
 522 
 523 static void release_pte_pages(pte_t *pte, pte_t *_pte)
 524 {
 525         while (--_pte >= pte) {
 526                 pte_t pteval = *_pte;
 527                 if (!pte_none(pteval) && !is_zero_pfn(pte_pfn(pteval)))
 528                         release_pte_page(pte_page(pteval));
 529         }
 530 }
 531 
 532 static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
 533                                         unsigned long address,
 534                                         pte_t *pte)
 535 {
 536         struct page *page = NULL;
 537         pte_t *_pte;
 538         int none_or_zero = 0, result = 0, referenced = 0;
 539         bool writable = false;
 540 
 541         for (_pte = pte; _pte < pte+HPAGE_PMD_NR;
 542              _pte++, address += PAGE_SIZE) {
 543                 pte_t pteval = *_pte;
 544                 if (pte_none(pteval) || (pte_present(pteval) &&
 545                                 is_zero_pfn(pte_pfn(pteval)))) {
 546                         if (!userfaultfd_armed(vma) &&
 547                             ++none_or_zero <= khugepaged_max_ptes_none) {
 548                                 continue;
 549                         } else {
 550                                 result = SCAN_EXCEED_NONE_PTE;
 551                                 goto out;
 552                         }
 553                 }
 554                 if (!pte_present(pteval)) {
 555                         result = SCAN_PTE_NON_PRESENT;
 556                         goto out;
 557                 }
 558                 page = vm_normal_page(vma, address, pteval);
 559                 if (unlikely(!page)) {
 560                         result = SCAN_PAGE_NULL;
 561                         goto out;
 562                 }
 563 
 564                 /* TODO: teach khugepaged to collapse THP mapped with pte */
 565                 if (PageCompound(page)) {
 566                         result = SCAN_PAGE_COMPOUND;
 567                         goto out;
 568                 }
 569 
 570                 VM_BUG_ON_PAGE(!PageAnon(page), page);
 571 
 572                 /*
 573                  * We can do it before isolate_lru_page because the
 574                  * page can't be freed from under us. NOTE: PG_lock
 575                  * is needed to serialize against split_huge_page
 576                  * when invoked from the VM.
 577                  */
 578                 if (!trylock_page(page)) {
 579                         result = SCAN_PAGE_LOCK;
 580                         goto out;
 581                 }
 582 
 583                 /*
 584                  * cannot use mapcount: can't collapse if there's a gup pin.
 585                  * The page must only be referenced by the scanned process
 586                  * and page swap cache.
 587                  */
 588                 if (page_count(page) != 1 + PageSwapCache(page)) {
 589                         unlock_page(page);
 590                         result = SCAN_PAGE_COUNT;
 591                         goto out;
 592                 }
 593                 if (pte_write(pteval)) {
 594                         writable = true;
 595                 } else {
 596                         if (PageSwapCache(page) &&
 597                             !reuse_swap_page(page, NULL)) {
 598                                 unlock_page(page);
 599                                 result = SCAN_SWAP_CACHE_PAGE;
 600                                 goto out;
 601                         }
 602                         /*
 603                          * Page is not in the swap cache. It can be collapsed
 604                          * into a THP.
 605                          */
 606                 }
 607 
 608                 /*
 609                  * Isolate the page to avoid collapsing an hugepage
 610                  * currently in use by the VM.
 611                  */
 612                 if (isolate_lru_page(page)) {
 613                         unlock_page(page);
 614                         result = SCAN_DEL_PAGE_LRU;
 615                         goto out;
 616                 }
 617                 inc_node_page_state(page,
 618                                 NR_ISOLATED_ANON + page_is_file_cache(page));
 619                 VM_BUG_ON_PAGE(!PageLocked(page), page);
 620                 VM_BUG_ON_PAGE(PageLRU(page), page);
 621 
 622                 /* There should be enough young pte to collapse the page */
 623                 if (pte_young(pteval) ||
 624                     page_is_young(page) || PageReferenced(page) ||
 625                     mmu_notifier_test_young(vma->vm_mm, address))
 626                         referenced++;
 627         }
 628         if (likely(writable)) {
 629                 if (likely(referenced)) {
 630                         result = SCAN_SUCCEED;
 631                         trace_mm_collapse_huge_page_isolate(page, none_or_zero,
 632                                                             referenced, writable, result);
 633                         return 1;
 634                 }
 635         } else {
 636                 result = SCAN_PAGE_RO;
 637         }
 638 
 639 out:
 640         release_pte_pages(pte, _pte);
 641         trace_mm_collapse_huge_page_isolate(page, none_or_zero,
 642                                             referenced, writable, result);
 643         return 0;
 644 }
 645 
 646 static void __collapse_huge_page_copy(pte_t *pte, struct page *page,
 647                                       struct vm_area_struct *vma,
 648                                       unsigned long address,
 649                                       spinlock_t *ptl)
 650 {
 651         pte_t *_pte;
 652         for (_pte = pte; _pte < pte + HPAGE_PMD_NR;
 653                                 _pte++, page++, address += PAGE_SIZE) {
 654                 pte_t pteval = *_pte;
 655                 struct page *src_page;
 656 
 657                 if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) {
 658                         clear_user_highpage(page, address);
 659                         add_mm_counter(vma->vm_mm, MM_ANONPAGES, 1);
 660                         if (is_zero_pfn(pte_pfn(pteval))) {
 661                                 /*
 662                                  * ptl mostly unnecessary.
 663                                  */
 664                                 spin_lock(ptl);
 665                                 /*
 666                                  * paravirt calls inside pte_clear here are
 667                                  * superfluous.
 668                                  */
 669                                 pte_clear(vma->vm_mm, address, _pte);
 670                                 spin_unlock(ptl);
 671                         }
 672                 } else {
 673                         src_page = pte_page(pteval);
 674                         copy_user_highpage(page, src_page, address, vma);
 675                         VM_BUG_ON_PAGE(page_mapcount(src_page) != 1, src_page);
 676                         release_pte_page(src_page);
 677                         /*
 678                          * ptl mostly unnecessary, but preempt has to
 679                          * be disabled to update the per-cpu stats
 680                          * inside page_remove_rmap().
 681                          */
 682                         spin_lock(ptl);
 683                         /*
 684                          * paravirt calls inside pte_clear here are
 685                          * superfluous.
 686                          */
 687                         pte_clear(vma->vm_mm, address, _pte);
 688                         page_remove_rmap(src_page, false);
 689                         spin_unlock(ptl);
 690                         free_page_and_swap_cache(src_page);
 691                 }
 692         }
 693 }
 694 
 695 static void khugepaged_alloc_sleep(void)
 696 {
 697         DEFINE_WAIT(wait);
 698 
 699         add_wait_queue(&khugepaged_wait, &wait);
 700         freezable_schedule_timeout_interruptible(
 701                 msecs_to_jiffies(khugepaged_alloc_sleep_millisecs));
 702         remove_wait_queue(&khugepaged_wait, &wait);
 703 }
 704 
 705 static int khugepaged_node_load[MAX_NUMNODES];
 706 
 707 static bool khugepaged_scan_abort(int nid)
 708 {
 709         int i;
 710 
 711         /*
 712          * If node_reclaim_mode is disabled, then no extra effort is made to
 713          * allocate memory locally.
 714          */
 715         if (!node_reclaim_mode)
 716                 return false;
 717 
 718         /* If there is a count for this node already, it must be acceptable */
 719         if (khugepaged_node_load[nid])
 720                 return false;
 721 
 722         for (i = 0; i < MAX_NUMNODES; i++) {
 723                 if (!khugepaged_node_load[i])
 724                         continue;
 725                 if (node_distance(nid, i) > node_reclaim_distance)
 726                         return true;
 727         }
 728         return false;
 729 }
 730 
 731 /* Defrag for khugepaged will enter direct reclaim/compaction if necessary */
 732 static inline gfp_t alloc_hugepage_khugepaged_gfpmask(void)
 733 {
 734         return khugepaged_defrag() ? GFP_TRANSHUGE : GFP_TRANSHUGE_LIGHT;
 735 }
 736 
 737 #ifdef CONFIG_NUMA
 738 static int khugepaged_find_target_node(void)
 739 {
 740         static int last_khugepaged_target_node = NUMA_NO_NODE;
 741         int nid, target_node = 0, max_value = 0;
 742 
 743         /* find first node with max normal pages hit */
 744         for (nid = 0; nid < MAX_NUMNODES; nid++)
 745                 if (khugepaged_node_load[nid] > max_value) {
 746                         max_value = khugepaged_node_load[nid];
 747                         target_node = nid;
 748                 }
 749 
 750         /* do some balance if several nodes have the same hit record */
 751         if (target_node <= last_khugepaged_target_node)
 752                 for (nid = last_khugepaged_target_node + 1; nid < MAX_NUMNODES;
 753                                 nid++)
 754                         if (max_value == khugepaged_node_load[nid]) {
 755                                 target_node = nid;
 756                                 break;
 757                         }
 758 
 759         last_khugepaged_target_node = target_node;
 760         return target_node;
 761 }
 762 
 763 static bool khugepaged_prealloc_page(struct page **hpage, bool *wait)
 764 {
 765         if (IS_ERR(*hpage)) {
 766                 if (!*wait)
 767                         return false;
 768 
 769                 *wait = false;
 770                 *hpage = NULL;
 771                 khugepaged_alloc_sleep();
 772         } else if (*hpage) {
 773                 put_page(*hpage);
 774                 *hpage = NULL;
 775         }
 776 
 777         return true;
 778 }
 779 
 780 static struct page *
 781 khugepaged_alloc_page(struct page **hpage, gfp_t gfp, int node)
 782 {
 783         VM_BUG_ON_PAGE(*hpage, *hpage);
 784 
 785         *hpage = __alloc_pages_node(node, gfp, HPAGE_PMD_ORDER);
 786         if (unlikely(!*hpage)) {
 787                 count_vm_event(THP_COLLAPSE_ALLOC_FAILED);
 788                 *hpage = ERR_PTR(-ENOMEM);
 789                 return NULL;
 790         }
 791 
 792         prep_transhuge_page(*hpage);
 793         count_vm_event(THP_COLLAPSE_ALLOC);
 794         return *hpage;
 795 }
 796 #else
 797 static int khugepaged_find_target_node(void)
 798 {
 799         return 0;
 800 }
 801 
 802 static inline struct page *alloc_khugepaged_hugepage(void)
 803 {
 804         struct page *page;
 805 
 806         page = alloc_pages(alloc_hugepage_khugepaged_gfpmask(),
 807                            HPAGE_PMD_ORDER);
 808         if (page)
 809                 prep_transhuge_page(page);
 810         return page;
 811 }
 812 
 813 static struct page *khugepaged_alloc_hugepage(bool *wait)
 814 {
 815         struct page *hpage;
 816 
 817         do {
 818                 hpage = alloc_khugepaged_hugepage();
 819                 if (!hpage) {
 820                         count_vm_event(THP_COLLAPSE_ALLOC_FAILED);
 821                         if (!*wait)
 822                                 return NULL;
 823 
 824                         *wait = false;
 825                         khugepaged_alloc_sleep();
 826                 } else
 827                         count_vm_event(THP_COLLAPSE_ALLOC);
 828         } while (unlikely(!hpage) && likely(khugepaged_enabled()));
 829 
 830         return hpage;
 831 }
 832 
 833 static bool khugepaged_prealloc_page(struct page **hpage, bool *wait)
 834 {
 835         if (!*hpage)
 836                 *hpage = khugepaged_alloc_hugepage(wait);
 837 
 838         if (unlikely(!*hpage))
 839                 return false;
 840 
 841         return true;
 842 }
 843 
 844 static struct page *
 845 khugepaged_alloc_page(struct page **hpage, gfp_t gfp, int node)
 846 {
 847         VM_BUG_ON(!*hpage);
 848 
 849         return  *hpage;
 850 }
 851 #endif
 852 
 853 /*
 854  * If mmap_sem temporarily dropped, revalidate vma
 855  * before taking mmap_sem.
 856  * Return 0 if succeeds, otherwise return none-zero
 857  * value (scan code).
 858  */
 859 
 860 static int hugepage_vma_revalidate(struct mm_struct *mm, unsigned long address,
 861                 struct vm_area_struct **vmap)
 862 {
 863         struct vm_area_struct *vma;
 864         unsigned long hstart, hend;
 865 
 866         if (unlikely(khugepaged_test_exit(mm)))
 867                 return SCAN_ANY_PROCESS;
 868 
 869         *vmap = vma = find_vma(mm, address);
 870         if (!vma)
 871                 return SCAN_VMA_NULL;
 872 
 873         hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK;
 874         hend = vma->vm_end & HPAGE_PMD_MASK;
 875         if (address < hstart || address + HPAGE_PMD_SIZE > hend)
 876                 return SCAN_ADDRESS_RANGE;
 877         if (!hugepage_vma_check(vma, vma->vm_flags))
 878                 return SCAN_VMA_CHECK;
 879         return 0;
 880 }
 881 
 882 /*
 883  * Bring missing pages in from swap, to complete THP collapse.
 884  * Only done if khugepaged_scan_pmd believes it is worthwhile.
 885  *
 886  * Called and returns without pte mapped or spinlocks held,
 887  * but with mmap_sem held to protect against vma changes.
 888  */
 889 
 890 static bool __collapse_huge_page_swapin(struct mm_struct *mm,
 891                                         struct vm_area_struct *vma,
 892                                         unsigned long address, pmd_t *pmd,
 893                                         int referenced)
 894 {
 895         int swapped_in = 0;
 896         vm_fault_t ret = 0;
 897         struct vm_fault vmf = {
 898                 .vma = vma,
 899                 .address = address,
 900                 .flags = FAULT_FLAG_ALLOW_RETRY,
 901                 .pmd = pmd,
 902                 .pgoff = linear_page_index(vma, address),
 903         };
 904 
 905         /* we only decide to swapin, if there is enough young ptes */
 906         if (referenced < HPAGE_PMD_NR/2) {
 907                 trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 0);
 908                 return false;
 909         }
 910         vmf.pte = pte_offset_map(pmd, address);
 911         for (; vmf.address < address + HPAGE_PMD_NR*PAGE_SIZE;
 912                         vmf.pte++, vmf.address += PAGE_SIZE) {
 913                 vmf.orig_pte = *vmf.pte;
 914                 if (!is_swap_pte(vmf.orig_pte))
 915                         continue;
 916                 swapped_in++;
 917                 ret = do_swap_page(&vmf);
 918 
 919                 /* do_swap_page returns VM_FAULT_RETRY with released mmap_sem */
 920                 if (ret & VM_FAULT_RETRY) {
 921                         down_read(&mm->mmap_sem);
 922                         if (hugepage_vma_revalidate(mm, address, &vmf.vma)) {
 923                                 /* vma is no longer available, don't continue to swapin */
 924                                 trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 0);
 925                                 return false;
 926                         }
 927                         /* check if the pmd is still valid */
 928                         if (mm_find_pmd(mm, address) != pmd) {
 929                                 trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 0);
 930                                 return false;
 931                         }
 932                 }
 933                 if (ret & VM_FAULT_ERROR) {
 934                         trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 0);
 935                         return false;
 936                 }
 937                 /* pte is unmapped now, we need to map it */
 938                 vmf.pte = pte_offset_map(pmd, vmf.address);
 939         }
 940         vmf.pte--;
 941         pte_unmap(vmf.pte);
 942         trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 1);
 943         return true;
 944 }
 945 
 946 static void collapse_huge_page(struct mm_struct *mm,
 947                                    unsigned long address,
 948                                    struct page **hpage,
 949                                    int node, int referenced)
 950 {
 951         pmd_t *pmd, _pmd;
 952         pte_t *pte;
 953         pgtable_t pgtable;
 954         struct page *new_page;
 955         spinlock_t *pmd_ptl, *pte_ptl;
 956         int isolated = 0, result = 0;
 957         struct mem_cgroup *memcg;
 958         struct vm_area_struct *vma;
 959         struct mmu_notifier_range range;
 960         gfp_t gfp;
 961 
 962         VM_BUG_ON(address & ~HPAGE_PMD_MASK);
 963 
 964         /* Only allocate from the target node */
 965         gfp = alloc_hugepage_khugepaged_gfpmask() | __GFP_THISNODE;
 966 
 967         /*
 968          * Before allocating the hugepage, release the mmap_sem read lock.
 969          * The allocation can take potentially a long time if it involves
 970          * sync compaction, and we do not need to hold the mmap_sem during
 971          * that. We will recheck the vma after taking it again in write mode.
 972          */
 973         up_read(&mm->mmap_sem);
 974         new_page = khugepaged_alloc_page(hpage, gfp, node);
 975         if (!new_page) {
 976                 result = SCAN_ALLOC_HUGE_PAGE_FAIL;
 977                 goto out_nolock;
 978         }
 979 
 980         if (unlikely(mem_cgroup_try_charge(new_page, mm, gfp, &memcg, true))) {
 981                 result = SCAN_CGROUP_CHARGE_FAIL;
 982                 goto out_nolock;
 983         }
 984 
 985         down_read(&mm->mmap_sem);
 986         result = hugepage_vma_revalidate(mm, address, &vma);
 987         if (result) {
 988                 mem_cgroup_cancel_charge(new_page, memcg, true);
 989                 up_read(&mm->mmap_sem);
 990                 goto out_nolock;
 991         }
 992 
 993         pmd = mm_find_pmd(mm, address);
 994         if (!pmd) {
 995                 result = SCAN_PMD_NULL;
 996                 mem_cgroup_cancel_charge(new_page, memcg, true);
 997                 up_read(&mm->mmap_sem);
 998                 goto out_nolock;
 999         }
1000 
1001         /*
1002          * __collapse_huge_page_swapin always returns with mmap_sem locked.
1003          * If it fails, we release mmap_sem and jump out_nolock.
1004          * Continuing to collapse causes inconsistency.
1005          */
1006         if (!__collapse_huge_page_swapin(mm, vma, address, pmd, referenced)) {
1007                 mem_cgroup_cancel_charge(new_page, memcg, true);
1008                 up_read(&mm->mmap_sem);
1009                 goto out_nolock;
1010         }
1011 
1012         up_read(&mm->mmap_sem);
1013         /*
1014          * Prevent all access to pagetables with the exception of
1015          * gup_fast later handled by the ptep_clear_flush and the VM
1016          * handled by the anon_vma lock + PG_lock.
1017          */
1018         down_write(&mm->mmap_sem);
1019         result = SCAN_ANY_PROCESS;
1020         if (!mmget_still_valid(mm))
1021                 goto out;
1022         result = hugepage_vma_revalidate(mm, address, &vma);
1023         if (result)
1024                 goto out;
1025         /* check if the pmd is still valid */
1026         if (mm_find_pmd(mm, address) != pmd)
1027                 goto out;
1028 
1029         anon_vma_lock_write(vma->anon_vma);
1030 
1031         mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, NULL, mm,
1032                                 address, address + HPAGE_PMD_SIZE);
1033         mmu_notifier_invalidate_range_start(&range);
1034 
1035         pte = pte_offset_map(pmd, address);
1036         pte_ptl = pte_lockptr(mm, pmd);
1037 
1038         pmd_ptl = pmd_lock(mm, pmd); /* probably unnecessary */
1039         /*
1040          * After this gup_fast can't run anymore. This also removes
1041          * any huge TLB entry from the CPU so we won't allow
1042          * huge and small TLB entries for the same virtual address
1043          * to avoid the risk of CPU bugs in that area.
1044          */
1045         _pmd = pmdp_collapse_flush(vma, address, pmd);
1046         spin_unlock(pmd_ptl);
1047         mmu_notifier_invalidate_range_end(&range);
1048 
1049         spin_lock(pte_ptl);
1050         isolated = __collapse_huge_page_isolate(vma, address, pte);
1051         spin_unlock(pte_ptl);
1052 
1053         if (unlikely(!isolated)) {
1054                 pte_unmap(pte);
1055                 spin_lock(pmd_ptl);
1056                 BUG_ON(!pmd_none(*pmd));
1057                 /*
1058                  * We can only use set_pmd_at when establishing
1059                  * hugepmds and never for establishing regular pmds that
1060                  * points to regular pagetables. Use pmd_populate for that
1061                  */
1062                 pmd_populate(mm, pmd, pmd_pgtable(_pmd));
1063                 spin_unlock(pmd_ptl);
1064                 anon_vma_unlock_write(vma->anon_vma);
1065                 result = SCAN_FAIL;
1066                 goto out;
1067         }
1068 
1069         /*
1070          * All pages are isolated and locked so anon_vma rmap
1071          * can't run anymore.
1072          */
1073         anon_vma_unlock_write(vma->anon_vma);
1074 
1075         __collapse_huge_page_copy(pte, new_page, vma, address, pte_ptl);
1076         pte_unmap(pte);
1077         __SetPageUptodate(new_page);
1078         pgtable = pmd_pgtable(_pmd);
1079 
1080         _pmd = mk_huge_pmd(new_page, vma->vm_page_prot);
1081         _pmd = maybe_pmd_mkwrite(pmd_mkdirty(_pmd), vma);
1082 
1083         /*
1084          * spin_lock() below is not the equivalent of smp_wmb(), so
1085          * this is needed to avoid the copy_huge_page writes to become
1086          * visible after the set_pmd_at() write.
1087          */
1088         smp_wmb();
1089 
1090         spin_lock(pmd_ptl);
1091         BUG_ON(!pmd_none(*pmd));
1092         page_add_new_anon_rmap(new_page, vma, address, true);
1093         mem_cgroup_commit_charge(new_page, memcg, false, true);
1094         count_memcg_events(memcg, THP_COLLAPSE_ALLOC, 1);
1095         lru_cache_add_active_or_unevictable(new_page, vma);
1096         pgtable_trans_huge_deposit(mm, pmd, pgtable);
1097         set_pmd_at(mm, address, pmd, _pmd);
1098         update_mmu_cache_pmd(vma, address, pmd);
1099         spin_unlock(pmd_ptl);
1100 
1101         *hpage = NULL;
1102 
1103         khugepaged_pages_collapsed++;
1104         result = SCAN_SUCCEED;
1105 out_up_write:
1106         up_write(&mm->mmap_sem);
1107 out_nolock:
1108         trace_mm_collapse_huge_page(mm, isolated, result);
1109         return;
1110 out:
1111         mem_cgroup_cancel_charge(new_page, memcg, true);
1112         goto out_up_write;
1113 }
1114 
1115 static int khugepaged_scan_pmd(struct mm_struct *mm,
1116                                struct vm_area_struct *vma,
1117                                unsigned long address,
1118                                struct page **hpage)
1119 {
1120         pmd_t *pmd;
1121         pte_t *pte, *_pte;
1122         int ret = 0, none_or_zero = 0, result = 0, referenced = 0;
1123         struct page *page = NULL;
1124         unsigned long _address;
1125         spinlock_t *ptl;
1126         int node = NUMA_NO_NODE, unmapped = 0;
1127         bool writable = false;
1128 
1129         VM_BUG_ON(address & ~HPAGE_PMD_MASK);
1130 
1131         pmd = mm_find_pmd(mm, address);
1132         if (!pmd) {
1133                 result = SCAN_PMD_NULL;
1134                 goto out;
1135         }
1136 
1137         memset(khugepaged_node_load, 0, sizeof(khugepaged_node_load));
1138         pte = pte_offset_map_lock(mm, pmd, address, &ptl);
1139         for (_address = address, _pte = pte; _pte < pte+HPAGE_PMD_NR;
1140              _pte++, _address += PAGE_SIZE) {
1141                 pte_t pteval = *_pte;
1142                 if (is_swap_pte(pteval)) {
1143                         if (++unmapped <= khugepaged_max_ptes_swap) {
1144                                 continue;
1145                         } else {
1146                                 result = SCAN_EXCEED_SWAP_PTE;
1147                                 goto out_unmap;
1148                         }
1149                 }
1150                 if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) {
1151                         if (!userfaultfd_armed(vma) &&
1152                             ++none_or_zero <= khugepaged_max_ptes_none) {
1153                                 continue;
1154                         } else {
1155                                 result = SCAN_EXCEED_NONE_PTE;
1156                                 goto out_unmap;
1157                         }
1158                 }
1159                 if (!pte_present(pteval)) {
1160                         result = SCAN_PTE_NON_PRESENT;
1161                         goto out_unmap;
1162                 }
1163                 if (pte_write(pteval))
1164                         writable = true;
1165 
1166                 page = vm_normal_page(vma, _address, pteval);
1167                 if (unlikely(!page)) {
1168                         result = SCAN_PAGE_NULL;
1169                         goto out_unmap;
1170                 }
1171 
1172                 /* TODO: teach khugepaged to collapse THP mapped with pte */
1173                 if (PageCompound(page)) {
1174                         result = SCAN_PAGE_COMPOUND;
1175                         goto out_unmap;
1176                 }
1177 
1178                 /*
1179                  * Record which node the original page is from and save this
1180                  * information to khugepaged_node_load[].
1181                  * Khupaged will allocate hugepage from the node has the max
1182                  * hit record.
1183                  */
1184                 node = page_to_nid(page);
1185                 if (khugepaged_scan_abort(node)) {
1186                         result = SCAN_SCAN_ABORT;
1187                         goto out_unmap;
1188                 }
1189                 khugepaged_node_load[node]++;
1190                 if (!PageLRU(page)) {
1191                         result = SCAN_PAGE_LRU;
1192                         goto out_unmap;
1193                 }
1194                 if (PageLocked(page)) {
1195                         result = SCAN_PAGE_LOCK;
1196                         goto out_unmap;
1197                 }
1198                 if (!PageAnon(page)) {
1199                         result = SCAN_PAGE_ANON;
1200                         goto out_unmap;
1201                 }
1202 
1203                 /*
1204                  * cannot use mapcount: can't collapse if there's a gup pin.
1205                  * The page must only be referenced by the scanned process
1206                  * and page swap cache.
1207                  */
1208                 if (page_count(page) != 1 + PageSwapCache(page)) {
1209                         result = SCAN_PAGE_COUNT;
1210                         goto out_unmap;
1211                 }
1212                 if (pte_young(pteval) ||
1213                     page_is_young(page) || PageReferenced(page) ||
1214                     mmu_notifier_test_young(vma->vm_mm, address))
1215                         referenced++;
1216         }
1217         if (writable) {
1218                 if (referenced) {
1219                         result = SCAN_SUCCEED;
1220                         ret = 1;
1221                 } else {
1222                         result = SCAN_LACK_REFERENCED_PAGE;
1223                 }
1224         } else {
1225                 result = SCAN_PAGE_RO;
1226         }
1227 out_unmap:
1228         pte_unmap_unlock(pte, ptl);
1229         if (ret) {
1230                 node = khugepaged_find_target_node();
1231                 /* collapse_huge_page will return with the mmap_sem released */
1232                 collapse_huge_page(mm, address, hpage, node, referenced);
1233         }
1234 out:
1235         trace_mm_khugepaged_scan_pmd(mm, page, writable, referenced,
1236                                      none_or_zero, result, unmapped);
1237         return ret;
1238 }
1239 
1240 static void collect_mm_slot(struct mm_slot *mm_slot)
1241 {
1242         struct mm_struct *mm = mm_slot->mm;
1243 
1244         lockdep_assert_held(&khugepaged_mm_lock);
1245 
1246         if (khugepaged_test_exit(mm)) {
1247                 /* free mm_slot */
1248                 hash_del(&mm_slot->hash);
1249                 list_del(&mm_slot->mm_node);
1250 
1251                 /*
1252                  * Not strictly needed because the mm exited already.
1253                  *
1254                  * clear_bit(MMF_VM_HUGEPAGE, &mm->flags);
1255                  */
1256 
1257                 /* khugepaged_mm_lock actually not necessary for the below */
1258                 free_mm_slot(mm_slot);
1259                 mmdrop(mm);
1260         }
1261 }
1262 
1263 #if defined(CONFIG_SHMEM) && defined(CONFIG_TRANSPARENT_HUGE_PAGECACHE)
1264 /*
1265  * Notify khugepaged that given addr of the mm is pte-mapped THP. Then
1266  * khugepaged should try to collapse the page table.
1267  */
1268 static int khugepaged_add_pte_mapped_thp(struct mm_struct *mm,
1269                                          unsigned long addr)
1270 {
1271         struct mm_slot *mm_slot;
1272 
1273         VM_BUG_ON(addr & ~HPAGE_PMD_MASK);
1274 
1275         spin_lock(&khugepaged_mm_lock);
1276         mm_slot = get_mm_slot(mm);
1277         if (likely(mm_slot && mm_slot->nr_pte_mapped_thp < MAX_PTE_MAPPED_THP))
1278                 mm_slot->pte_mapped_thp[mm_slot->nr_pte_mapped_thp++] = addr;
1279         spin_unlock(&khugepaged_mm_lock);
1280         return 0;
1281 }
1282 
1283 /**
1284  * Try to collapse a pte-mapped THP for mm at address haddr.
1285  *
1286  * This function checks whether all the PTEs in the PMD are pointing to the
1287  * right THP. If so, retract the page table so the THP can refault in with
1288  * as pmd-mapped.
1289  */
1290 void collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr)
1291 {
1292         unsigned long haddr = addr & HPAGE_PMD_MASK;
1293         struct vm_area_struct *vma = find_vma(mm, haddr);
1294         struct page *hpage = NULL;
1295         pte_t *start_pte, *pte;
1296         pmd_t *pmd, _pmd;
1297         spinlock_t *ptl;
1298         int count = 0;
1299         int i;
1300 
1301         if (!vma || !vma->vm_file ||
1302             vma->vm_start > haddr || vma->vm_end < haddr + HPAGE_PMD_SIZE)
1303                 return;
1304 
1305         /*
1306          * This vm_flags may not have VM_HUGEPAGE if the page was not
1307          * collapsed by this mm. But we can still collapse if the page is
1308          * the valid THP. Add extra VM_HUGEPAGE so hugepage_vma_check()
1309          * will not fail the vma for missing VM_HUGEPAGE
1310          */
1311         if (!hugepage_vma_check(vma, vma->vm_flags | VM_HUGEPAGE))
1312                 return;
1313 
1314         pmd = mm_find_pmd(mm, haddr);
1315         if (!pmd)
1316                 return;
1317 
1318         start_pte = pte_offset_map_lock(mm, pmd, haddr, &ptl);
1319 
1320         /* step 1: check all mapped PTEs are to the right huge page */
1321         for (i = 0, addr = haddr, pte = start_pte;
1322              i < HPAGE_PMD_NR; i++, addr += PAGE_SIZE, pte++) {
1323                 struct page *page;
1324 
1325                 /* empty pte, skip */
1326                 if (pte_none(*pte))
1327                         continue;
1328 
1329                 /* page swapped out, abort */
1330                 if (!pte_present(*pte))
1331                         goto abort;
1332 
1333                 page = vm_normal_page(vma, addr, *pte);
1334 
1335                 if (!page || !PageCompound(page))
1336                         goto abort;
1337 
1338                 if (!hpage) {
1339                         hpage = compound_head(page);
1340                         /*
1341                          * The mapping of the THP should not change.
1342                          *
1343                          * Note that uprobe, debugger, or MAP_PRIVATE may
1344                          * change the page table, but the new page will
1345                          * not pass PageCompound() check.
1346                          */
1347                         if (WARN_ON(hpage->mapping != vma->vm_file->f_mapping))
1348                                 goto abort;
1349                 }
1350 
1351                 /*
1352                  * Confirm the page maps to the correct subpage.
1353                  *
1354                  * Note that uprobe, debugger, or MAP_PRIVATE may change
1355                  * the page table, but the new page will not pass
1356                  * PageCompound() check.
1357                  */
1358                 if (WARN_ON(hpage + i != page))
1359                         goto abort;
1360                 count++;
1361         }
1362 
1363         /* step 2: adjust rmap */
1364         for (i = 0, addr = haddr, pte = start_pte;
1365              i < HPAGE_PMD_NR; i++, addr += PAGE_SIZE, pte++) {
1366                 struct page *page;
1367 
1368                 if (pte_none(*pte))
1369                         continue;
1370                 page = vm_normal_page(vma, addr, *pte);
1371                 page_remove_rmap(page, false);
1372         }
1373 
1374         pte_unmap_unlock(start_pte, ptl);
1375 
1376         /* step 3: set proper refcount and mm_counters. */
1377         if (hpage) {
1378                 page_ref_sub(hpage, count);
1379                 add_mm_counter(vma->vm_mm, mm_counter_file(hpage), -count);
1380         }
1381 
1382         /* step 4: collapse pmd */
1383         ptl = pmd_lock(vma->vm_mm, pmd);
1384         _pmd = pmdp_collapse_flush(vma, addr, pmd);
1385         spin_unlock(ptl);
1386         mm_dec_nr_ptes(mm);
1387         pte_free(mm, pmd_pgtable(_pmd));
1388         return;
1389 
1390 abort:
1391         pte_unmap_unlock(start_pte, ptl);
1392 }
1393 
1394 static int khugepaged_collapse_pte_mapped_thps(struct mm_slot *mm_slot)
1395 {
1396         struct mm_struct *mm = mm_slot->mm;
1397         int i;
1398 
1399         if (likely(mm_slot->nr_pte_mapped_thp == 0))
1400                 return 0;
1401 
1402         if (!down_write_trylock(&mm->mmap_sem))
1403                 return -EBUSY;
1404 
1405         if (unlikely(khugepaged_test_exit(mm)))
1406                 goto out;
1407 
1408         for (i = 0; i < mm_slot->nr_pte_mapped_thp; i++)
1409                 collapse_pte_mapped_thp(mm, mm_slot->pte_mapped_thp[i]);
1410 
1411 out:
1412         mm_slot->nr_pte_mapped_thp = 0;
1413         up_write(&mm->mmap_sem);
1414         return 0;
1415 }
1416 
1417 static void retract_page_tables(struct address_space *mapping, pgoff_t pgoff)
1418 {
1419         struct vm_area_struct *vma;
1420         unsigned long addr;
1421         pmd_t *pmd, _pmd;
1422 
1423         i_mmap_lock_write(mapping);
1424         vma_interval_tree_foreach(vma, &mapping->i_mmap, pgoff, pgoff) {
1425                 /*
1426                  * Check vma->anon_vma to exclude MAP_PRIVATE mappings that
1427                  * got written to. These VMAs are likely not worth investing
1428                  * down_write(mmap_sem) as PMD-mapping is likely to be split
1429                  * later.
1430                  *
1431                  * Not that vma->anon_vma check is racy: it can be set up after
1432                  * the check but before we took mmap_sem by the fault path.
1433                  * But page lock would prevent establishing any new ptes of the
1434                  * page, so we are safe.
1435                  *
1436                  * An alternative would be drop the check, but check that page
1437                  * table is clear before calling pmdp_collapse_flush() under
1438                  * ptl. It has higher chance to recover THP for the VMA, but
1439                  * has higher cost too.
1440                  */
1441                 if (vma->anon_vma)
1442                         continue;
1443                 addr = vma->vm_start + ((pgoff - vma->vm_pgoff) << PAGE_SHIFT);
1444                 if (addr & ~HPAGE_PMD_MASK)
1445                         continue;
1446                 if (vma->vm_end < addr + HPAGE_PMD_SIZE)
1447                         continue;
1448                 pmd = mm_find_pmd(vma->vm_mm, addr);
1449                 if (!pmd)
1450                         continue;
1451                 /*
1452                  * We need exclusive mmap_sem to retract page table.
1453                  *
1454                  * We use trylock due to lock inversion: we need to acquire
1455                  * mmap_sem while holding page lock. Fault path does it in
1456                  * reverse order. Trylock is a way to avoid deadlock.
1457                  */
1458                 if (down_write_trylock(&vma->vm_mm->mmap_sem)) {
1459                         spinlock_t *ptl = pmd_lock(vma->vm_mm, pmd);
1460                         /* assume page table is clear */
1461                         _pmd = pmdp_collapse_flush(vma, addr, pmd);
1462                         spin_unlock(ptl);
1463                         up_write(&vma->vm_mm->mmap_sem);
1464                         mm_dec_nr_ptes(vma->vm_mm);
1465                         pte_free(vma->vm_mm, pmd_pgtable(_pmd));
1466                 } else {
1467                         /* Try again later */
1468                         khugepaged_add_pte_mapped_thp(vma->vm_mm, addr);
1469                 }
1470         }
1471         i_mmap_unlock_write(mapping);
1472 }
1473 
1474 /**
1475  * collapse_file - collapse filemap/tmpfs/shmem pages into huge one.
1476  *
1477  * Basic scheme is simple, details are more complex:
1478  *  - allocate and lock a new huge page;
1479  *  - scan page cache replacing old pages with the new one
1480  *    + swap/gup in pages if necessary;
1481  *    + fill in gaps;
1482  *    + keep old pages around in case rollback is required;
1483  *  - if replacing succeeds:
1484  *    + copy data over;
1485  *    + free old pages;
1486  *    + unlock huge page;
1487  *  - if replacing failed;
1488  *    + put all pages back and unfreeze them;
1489  *    + restore gaps in the page cache;
1490  *    + unlock and free huge page;
1491  */
1492 static void collapse_file(struct mm_struct *mm,
1493                 struct file *file, pgoff_t start,
1494                 struct page **hpage, int node)
1495 {
1496         struct address_space *mapping = file->f_mapping;
1497         gfp_t gfp;
1498         struct page *new_page;
1499         struct mem_cgroup *memcg;
1500         pgoff_t index, end = start + HPAGE_PMD_NR;
1501         LIST_HEAD(pagelist);
1502         XA_STATE_ORDER(xas, &mapping->i_pages, start, HPAGE_PMD_ORDER);
1503         int nr_none = 0, result = SCAN_SUCCEED;
1504         bool is_shmem = shmem_file(file);
1505 
1506         VM_BUG_ON(!IS_ENABLED(CONFIG_READ_ONLY_THP_FOR_FS) && !is_shmem);
1507         VM_BUG_ON(start & (HPAGE_PMD_NR - 1));
1508 
1509         /* Only allocate from the target node */
1510         gfp = alloc_hugepage_khugepaged_gfpmask() | __GFP_THISNODE;
1511 
1512         new_page = khugepaged_alloc_page(hpage, gfp, node);
1513         if (!new_page) {
1514                 result = SCAN_ALLOC_HUGE_PAGE_FAIL;
1515                 goto out;
1516         }
1517 
1518         if (unlikely(mem_cgroup_try_charge(new_page, mm, gfp, &memcg, true))) {
1519                 result = SCAN_CGROUP_CHARGE_FAIL;
1520                 goto out;
1521         }
1522 
1523         /* This will be less messy when we use multi-index entries */
1524         do {
1525                 xas_lock_irq(&xas);
1526                 xas_create_range(&xas);
1527                 if (!xas_error(&xas))
1528                         break;
1529                 xas_unlock_irq(&xas);
1530                 if (!xas_nomem(&xas, GFP_KERNEL)) {
1531                         mem_cgroup_cancel_charge(new_page, memcg, true);
1532                         result = SCAN_FAIL;
1533                         goto out;
1534                 }
1535         } while (1);
1536 
1537         __SetPageLocked(new_page);
1538         if (is_shmem)
1539                 __SetPageSwapBacked(new_page);
1540         new_page->index = start;
1541         new_page->mapping = mapping;
1542 
1543         /*
1544          * At this point the new_page is locked and not up-to-date.
1545          * It's safe to insert it into the page cache, because nobody would
1546          * be able to map it or use it in another way until we unlock it.
1547          */
1548 
1549         xas_set(&xas, start);
1550         for (index = start; index < end; index++) {
1551                 struct page *page = xas_next(&xas);
1552 
1553                 VM_BUG_ON(index != xas.xa_index);
1554                 if (is_shmem) {
1555                         if (!page) {
1556                                 /*
1557                                  * Stop if extent has been truncated or
1558                                  * hole-punched, and is now completely
1559                                  * empty.
1560                                  */
1561                                 if (index == start) {
1562                                         if (!xas_next_entry(&xas, end - 1)) {
1563                                                 result = SCAN_TRUNCATED;
1564                                                 goto xa_locked;
1565                                         }
1566                                         xas_set(&xas, index);
1567                                 }
1568                                 if (!shmem_charge(mapping->host, 1)) {
1569                                         result = SCAN_FAIL;
1570                                         goto xa_locked;
1571                                 }
1572                                 xas_store(&xas, new_page);
1573                                 nr_none++;
1574                                 continue;
1575                         }
1576 
1577                         if (xa_is_value(page) || !PageUptodate(page)) {
1578                                 xas_unlock_irq(&xas);
1579                                 /* swap in or instantiate fallocated page */
1580                                 if (shmem_getpage(mapping->host, index, &page,
1581                                                   SGP_NOHUGE)) {
1582                                         result = SCAN_FAIL;
1583                                         goto xa_unlocked;
1584                                 }
1585                         } else if (trylock_page(page)) {
1586                                 get_page(page);
1587                                 xas_unlock_irq(&xas);
1588                         } else {
1589                                 result = SCAN_PAGE_LOCK;
1590                                 goto xa_locked;
1591                         }
1592                 } else {        /* !is_shmem */
1593                         if (!page || xa_is_value(page)) {
1594                                 xas_unlock_irq(&xas);
1595                                 page_cache_sync_readahead(mapping, &file->f_ra,
1596                                                           file, index,
1597                                                           PAGE_SIZE);
1598                                 /* drain pagevecs to help isolate_lru_page() */
1599                                 lru_add_drain();
1600                                 page = find_lock_page(mapping, index);
1601                                 if (unlikely(page == NULL)) {
1602                                         result = SCAN_FAIL;
1603                                         goto xa_unlocked;
1604                                 }
1605                         } else if (trylock_page(page)) {
1606                                 get_page(page);
1607                                 xas_unlock_irq(&xas);
1608                         } else {
1609                                 result = SCAN_PAGE_LOCK;
1610                                 goto xa_locked;
1611                         }
1612                 }
1613 
1614                 /*
1615                  * The page must be locked, so we can drop the i_pages lock
1616                  * without racing with truncate.
1617                  */
1618                 VM_BUG_ON_PAGE(!PageLocked(page), page);
1619 
1620                 /* make sure the page is up to date */
1621                 if (unlikely(!PageUptodate(page))) {
1622                         result = SCAN_FAIL;
1623                         goto out_unlock;
1624                 }
1625 
1626                 /*
1627                  * If file was truncated then extended, or hole-punched, before
1628                  * we locked the first page, then a THP might be there already.
1629                  */
1630                 if (PageTransCompound(page)) {
1631                         result = SCAN_PAGE_COMPOUND;
1632                         goto out_unlock;
1633                 }
1634 
1635                 if (page_mapping(page) != mapping) {
1636                         result = SCAN_TRUNCATED;
1637                         goto out_unlock;
1638                 }
1639 
1640                 if (!is_shmem && PageDirty(page)) {
1641                         /*
1642                          * khugepaged only works on read-only fd, so this
1643                          * page is dirty because it hasn't been flushed
1644                          * since first write.
1645                          */
1646                         result = SCAN_FAIL;
1647                         goto out_unlock;
1648                 }
1649 
1650                 if (isolate_lru_page(page)) {
1651                         result = SCAN_DEL_PAGE_LRU;
1652                         goto out_unlock;
1653                 }
1654 
1655                 if (page_has_private(page) &&
1656                     !try_to_release_page(page, GFP_KERNEL)) {
1657                         result = SCAN_PAGE_HAS_PRIVATE;
1658                         putback_lru_page(page);
1659                         goto out_unlock;
1660                 }
1661 
1662                 if (page_mapped(page))
1663                         unmap_mapping_pages(mapping, index, 1, false);
1664 
1665                 xas_lock_irq(&xas);
1666                 xas_set(&xas, index);
1667 
1668                 VM_BUG_ON_PAGE(page != xas_load(&xas), page);
1669                 VM_BUG_ON_PAGE(page_mapped(page), page);
1670 
1671                 /*
1672                  * The page is expected to have page_count() == 3:
1673                  *  - we hold a pin on it;
1674                  *  - one reference from page cache;
1675                  *  - one from isolate_lru_page;
1676                  */
1677                 if (!page_ref_freeze(page, 3)) {
1678                         result = SCAN_PAGE_COUNT;
1679                         xas_unlock_irq(&xas);
1680                         putback_lru_page(page);
1681                         goto out_unlock;
1682                 }
1683 
1684                 /*
1685                  * Add the page to the list to be able to undo the collapse if
1686                  * something go wrong.
1687                  */
1688                 list_add_tail(&page->lru, &pagelist);
1689 
1690                 /* Finally, replace with the new page. */
1691                 xas_store(&xas, new_page);
1692                 continue;
1693 out_unlock:
1694                 unlock_page(page);
1695                 put_page(page);
1696                 goto xa_unlocked;
1697         }
1698 
1699         if (is_shmem)
1700                 __inc_node_page_state(new_page, NR_SHMEM_THPS);
1701         else {
1702                 __inc_node_page_state(new_page, NR_FILE_THPS);
1703                 filemap_nr_thps_inc(mapping);
1704         }
1705 
1706         if (nr_none) {
1707                 struct zone *zone = page_zone(new_page);
1708 
1709                 __mod_node_page_state(zone->zone_pgdat, NR_FILE_PAGES, nr_none);
1710                 if (is_shmem)
1711                         __mod_node_page_state(zone->zone_pgdat,
1712                                               NR_SHMEM, nr_none);
1713         }
1714 
1715 xa_locked:
1716         xas_unlock_irq(&xas);
1717 xa_unlocked:
1718 
1719         if (result == SCAN_SUCCEED) {
1720                 struct page *page, *tmp;
1721 
1722                 /*
1723                  * Replacing old pages with new one has succeeded, now we
1724                  * need to copy the content and free the old pages.
1725                  */
1726                 index = start;
1727                 list_for_each_entry_safe(page, tmp, &pagelist, lru) {
1728                         while (index < page->index) {
1729                                 clear_highpage(new_page + (index % HPAGE_PMD_NR));
1730                                 index++;
1731                         }
1732                         copy_highpage(new_page + (page->index % HPAGE_PMD_NR),
1733                                         page);
1734                         list_del(&page->lru);
1735                         page->mapping = NULL;
1736                         page_ref_unfreeze(page, 1);
1737                         ClearPageActive(page);
1738                         ClearPageUnevictable(page);
1739                         unlock_page(page);
1740                         put_page(page);
1741                         index++;
1742                 }
1743                 while (index < end) {
1744                         clear_highpage(new_page + (index % HPAGE_PMD_NR));
1745                         index++;
1746                 }
1747 
1748                 SetPageUptodate(new_page);
1749                 page_ref_add(new_page, HPAGE_PMD_NR - 1);
1750                 mem_cgroup_commit_charge(new_page, memcg, false, true);
1751 
1752                 if (is_shmem) {
1753                         set_page_dirty(new_page);
1754                         lru_cache_add_anon(new_page);
1755                 } else {
1756                         lru_cache_add_file(new_page);
1757                 }
1758                 count_memcg_events(memcg, THP_COLLAPSE_ALLOC, 1);
1759 
1760                 /*
1761                  * Remove pte page tables, so we can re-fault the page as huge.
1762                  */
1763                 retract_page_tables(mapping, start);
1764                 *hpage = NULL;
1765 
1766                 khugepaged_pages_collapsed++;
1767         } else {
1768                 struct page *page;
1769 
1770                 /* Something went wrong: roll back page cache changes */
1771                 xas_lock_irq(&xas);
1772                 mapping->nrpages -= nr_none;
1773 
1774                 if (is_shmem)
1775                         shmem_uncharge(mapping->host, nr_none);
1776 
1777                 xas_set(&xas, start);
1778                 xas_for_each(&xas, page, end - 1) {
1779                         page = list_first_entry_or_null(&pagelist,
1780                                         struct page, lru);
1781                         if (!page || xas.xa_index < page->index) {
1782                                 if (!nr_none)
1783                                         break;
1784                                 nr_none--;
1785                                 /* Put holes back where they were */
1786                                 xas_store(&xas, NULL);
1787                                 continue;
1788                         }
1789 
1790                         VM_BUG_ON_PAGE(page->index != xas.xa_index, page);
1791 
1792                         /* Unfreeze the page. */
1793                         list_del(&page->lru);
1794                         page_ref_unfreeze(page, 2);
1795                         xas_store(&xas, page);
1796                         xas_pause(&xas);
1797                         xas_unlock_irq(&xas);
1798                         unlock_page(page);
1799                         putback_lru_page(page);
1800                         xas_lock_irq(&xas);
1801                 }
1802                 VM_BUG_ON(nr_none);
1803                 xas_unlock_irq(&xas);
1804 
1805                 mem_cgroup_cancel_charge(new_page, memcg, true);
1806                 new_page->mapping = NULL;
1807         }
1808 
1809         unlock_page(new_page);
1810 out:
1811         VM_BUG_ON(!list_empty(&pagelist));
1812         /* TODO: tracepoints */
1813 }
1814 
1815 static void khugepaged_scan_file(struct mm_struct *mm,
1816                 struct file *file, pgoff_t start, struct page **hpage)
1817 {
1818         struct page *page = NULL;
1819         struct address_space *mapping = file->f_mapping;
1820         XA_STATE(xas, &mapping->i_pages, start);
1821         int present, swap;
1822         int node = NUMA_NO_NODE;
1823         int result = SCAN_SUCCEED;
1824 
1825         present = 0;
1826         swap = 0;
1827         memset(khugepaged_node_load, 0, sizeof(khugepaged_node_load));
1828         rcu_read_lock();
1829         xas_for_each(&xas, page, start + HPAGE_PMD_NR - 1) {
1830                 if (xas_retry(&xas, page))
1831                         continue;
1832 
1833                 if (xa_is_value(page)) {
1834                         if (++swap > khugepaged_max_ptes_swap) {
1835                                 result = SCAN_EXCEED_SWAP_PTE;
1836                                 break;
1837                         }
1838                         continue;
1839                 }
1840 
1841                 if (PageTransCompound(page)) {
1842                         result = SCAN_PAGE_COMPOUND;
1843                         break;
1844                 }
1845 
1846                 node = page_to_nid(page);
1847                 if (khugepaged_scan_abort(node)) {
1848                         result = SCAN_SCAN_ABORT;
1849                         break;
1850                 }
1851                 khugepaged_node_load[node]++;
1852 
1853                 if (!PageLRU(page)) {
1854                         result = SCAN_PAGE_LRU;
1855                         break;
1856                 }
1857 
1858                 if (page_count(page) !=
1859                     1 + page_mapcount(page) + page_has_private(page)) {
1860                         result = SCAN_PAGE_COUNT;
1861                         break;
1862                 }
1863 
1864                 /*
1865                  * We probably should check if the page is referenced here, but
1866                  * nobody would transfer pte_young() to PageReferenced() for us.
1867                  * And rmap walk here is just too costly...
1868                  */
1869 
1870                 present++;
1871 
1872                 if (need_resched()) {
1873                         xas_pause(&xas);
1874                         cond_resched_rcu();
1875                 }
1876         }
1877         rcu_read_unlock();
1878 
1879         if (result == SCAN_SUCCEED) {
1880                 if (present < HPAGE_PMD_NR - khugepaged_max_ptes_none) {
1881                         result = SCAN_EXCEED_NONE_PTE;
1882                 } else {
1883                         node = khugepaged_find_target_node();
1884                         collapse_file(mm, file, start, hpage, node);
1885                 }
1886         }
1887 
1888         /* TODO: tracepoints */
1889 }
1890 #else
1891 static void khugepaged_scan_file(struct mm_struct *mm,
1892                 struct file *file, pgoff_t start, struct page **hpage)
1893 {
1894         BUILD_BUG();
1895 }
1896 
1897 static int khugepaged_collapse_pte_mapped_thps(struct mm_slot *mm_slot)
1898 {
1899         return 0;
1900 }
1901 #endif
1902 
1903 static unsigned int khugepaged_scan_mm_slot(unsigned int pages,
1904                                             struct page **hpage)
1905         __releases(&khugepaged_mm_lock)
1906         __acquires(&khugepaged_mm_lock)
1907 {
1908         struct mm_slot *mm_slot;
1909         struct mm_struct *mm;
1910         struct vm_area_struct *vma;
1911         int progress = 0;
1912 
1913         VM_BUG_ON(!pages);
1914         lockdep_assert_held(&khugepaged_mm_lock);
1915 
1916         if (khugepaged_scan.mm_slot)
1917                 mm_slot = khugepaged_scan.mm_slot;
1918         else {
1919                 mm_slot = list_entry(khugepaged_scan.mm_head.next,
1920                                      struct mm_slot, mm_node);
1921                 khugepaged_scan.address = 0;
1922                 khugepaged_scan.mm_slot = mm_slot;
1923         }
1924         spin_unlock(&khugepaged_mm_lock);
1925         khugepaged_collapse_pte_mapped_thps(mm_slot);
1926 
1927         mm = mm_slot->mm;
1928         /*
1929          * Don't wait for semaphore (to avoid long wait times).  Just move to
1930          * the next mm on the list.
1931          */
1932         vma = NULL;
1933         if (unlikely(!down_read_trylock(&mm->mmap_sem)))
1934                 goto breakouterloop_mmap_sem;
1935         if (likely(!khugepaged_test_exit(mm)))
1936                 vma = find_vma(mm, khugepaged_scan.address);
1937 
1938         progress++;
1939         for (; vma; vma = vma->vm_next) {
1940                 unsigned long hstart, hend;
1941 
1942                 cond_resched();
1943                 if (unlikely(khugepaged_test_exit(mm))) {
1944                         progress++;
1945                         break;
1946                 }
1947                 if (!hugepage_vma_check(vma, vma->vm_flags)) {
1948 skip:
1949                         progress++;
1950                         continue;
1951                 }
1952                 hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK;
1953                 hend = vma->vm_end & HPAGE_PMD_MASK;
1954                 if (hstart >= hend)
1955                         goto skip;
1956                 if (khugepaged_scan.address > hend)
1957                         goto skip;
1958                 if (khugepaged_scan.address < hstart)
1959                         khugepaged_scan.address = hstart;
1960                 VM_BUG_ON(khugepaged_scan.address & ~HPAGE_PMD_MASK);
1961 
1962                 while (khugepaged_scan.address < hend) {
1963                         int ret;
1964                         cond_resched();
1965                         if (unlikely(khugepaged_test_exit(mm)))
1966                                 goto breakouterloop;
1967 
1968                         VM_BUG_ON(khugepaged_scan.address < hstart ||
1969                                   khugepaged_scan.address + HPAGE_PMD_SIZE >
1970                                   hend);
1971                         if (IS_ENABLED(CONFIG_SHMEM) && vma->vm_file) {
1972                                 struct file *file;
1973                                 pgoff_t pgoff = linear_page_index(vma,
1974                                                 khugepaged_scan.address);
1975 
1976                                 if (shmem_file(vma->vm_file)
1977                                     && !shmem_huge_enabled(vma))
1978                                         goto skip;
1979                                 file = get_file(vma->vm_file);
1980                                 up_read(&mm->mmap_sem);
1981                                 ret = 1;
1982                                 khugepaged_scan_file(mm, file, pgoff, hpage);
1983                                 fput(file);
1984                         } else {
1985                                 ret = khugepaged_scan_pmd(mm, vma,
1986                                                 khugepaged_scan.address,
1987                                                 hpage);
1988                         }
1989                         /* move to next address */
1990                         khugepaged_scan.address += HPAGE_PMD_SIZE;
1991                         progress += HPAGE_PMD_NR;
1992                         if (ret)
1993                                 /* we released mmap_sem so break loop */
1994                                 goto breakouterloop_mmap_sem;
1995                         if (progress >= pages)
1996                                 goto breakouterloop;
1997                 }
1998         }
1999 breakouterloop:
2000         up_read(&mm->mmap_sem); /* exit_mmap will destroy ptes after this */
2001 breakouterloop_mmap_sem:
2002 
2003         spin_lock(&khugepaged_mm_lock);
2004         VM_BUG_ON(khugepaged_scan.mm_slot != mm_slot);
2005         /*
2006          * Release the current mm_slot if this mm is about to die, or
2007          * if we scanned all vmas of this mm.
2008          */
2009         if (khugepaged_test_exit(mm) || !vma) {
2010                 /*
2011                  * Make sure that if mm_users is reaching zero while
2012                  * khugepaged runs here, khugepaged_exit will find
2013                  * mm_slot not pointing to the exiting mm.
2014                  */
2015                 if (mm_slot->mm_node.next != &khugepaged_scan.mm_head) {
2016                         khugepaged_scan.mm_slot = list_entry(
2017                                 mm_slot->mm_node.next,
2018                                 struct mm_slot, mm_node);
2019                         khugepaged_scan.address = 0;
2020                 } else {
2021                         khugepaged_scan.mm_slot = NULL;
2022                         khugepaged_full_scans++;
2023                 }
2024 
2025                 collect_mm_slot(mm_slot);
2026         }
2027 
2028         return progress;
2029 }
2030 
2031 static int khugepaged_has_work(void)
2032 {
2033         return !list_empty(&khugepaged_scan.mm_head) &&
2034                 khugepaged_enabled();
2035 }
2036 
2037 static int khugepaged_wait_event(void)
2038 {
2039         return !list_empty(&khugepaged_scan.mm_head) ||
2040                 kthread_should_stop();
2041 }
2042 
2043 static void khugepaged_do_scan(void)
2044 {
2045         struct page *hpage = NULL;
2046         unsigned int progress = 0, pass_through_head = 0;
2047         unsigned int pages = khugepaged_pages_to_scan;
2048         bool wait = true;
2049 
2050         barrier(); /* write khugepaged_pages_to_scan to local stack */
2051 
2052         while (progress < pages) {
2053                 if (!khugepaged_prealloc_page(&hpage, &wait))
2054                         break;
2055 
2056                 cond_resched();
2057 
2058                 if (unlikely(kthread_should_stop() || try_to_freeze()))
2059                         break;
2060 
2061                 spin_lock(&khugepaged_mm_lock);
2062                 if (!khugepaged_scan.mm_slot)
2063                         pass_through_head++;
2064                 if (khugepaged_has_work() &&
2065                     pass_through_head < 2)
2066                         progress += khugepaged_scan_mm_slot(pages - progress,
2067                                                             &hpage);
2068                 else
2069                         progress = pages;
2070                 spin_unlock(&khugepaged_mm_lock);
2071         }
2072 
2073         if (!IS_ERR_OR_NULL(hpage))
2074                 put_page(hpage);
2075 }
2076 
2077 static bool khugepaged_should_wakeup(void)
2078 {
2079         return kthread_should_stop() ||
2080                time_after_eq(jiffies, khugepaged_sleep_expire);
2081 }
2082 
2083 static void khugepaged_wait_work(void)
2084 {
2085         if (khugepaged_has_work()) {
2086                 const unsigned long scan_sleep_jiffies =
2087                         msecs_to_jiffies(khugepaged_scan_sleep_millisecs);
2088 
2089                 if (!scan_sleep_jiffies)
2090                         return;
2091 
2092                 khugepaged_sleep_expire = jiffies + scan_sleep_jiffies;
2093                 wait_event_freezable_timeout(khugepaged_wait,
2094                                              khugepaged_should_wakeup(),
2095                                              scan_sleep_jiffies);
2096                 return;
2097         }
2098 
2099         if (khugepaged_enabled())
2100                 wait_event_freezable(khugepaged_wait, khugepaged_wait_event());
2101 }
2102 
2103 static int khugepaged(void *none)
2104 {
2105         struct mm_slot *mm_slot;
2106 
2107         set_freezable();
2108         set_user_nice(current, MAX_NICE);
2109 
2110         while (!kthread_should_stop()) {
2111                 khugepaged_do_scan();
2112                 khugepaged_wait_work();
2113         }
2114 
2115         spin_lock(&khugepaged_mm_lock);
2116         mm_slot = khugepaged_scan.mm_slot;
2117         khugepaged_scan.mm_slot = NULL;
2118         if (mm_slot)
2119                 collect_mm_slot(mm_slot);
2120         spin_unlock(&khugepaged_mm_lock);
2121         return 0;
2122 }
2123 
2124 static void set_recommended_min_free_kbytes(void)
2125 {
2126         struct zone *zone;
2127         int nr_zones = 0;
2128         unsigned long recommended_min;
2129 
2130         for_each_populated_zone(zone) {
2131                 /*
2132                  * We don't need to worry about fragmentation of
2133                  * ZONE_MOVABLE since it only has movable pages.
2134                  */
2135                 if (zone_idx(zone) > gfp_zone(GFP_USER))
2136                         continue;
2137 
2138                 nr_zones++;
2139         }
2140 
2141         /* Ensure 2 pageblocks are free to assist fragmentation avoidance */
2142         recommended_min = pageblock_nr_pages * nr_zones * 2;
2143 
2144         /*
2145          * Make sure that on average at least two pageblocks are almost free
2146          * of another type, one for a migratetype to fall back to and a
2147          * second to avoid subsequent fallbacks of other types There are 3
2148          * MIGRATE_TYPES we care about.
2149          */
2150         recommended_min += pageblock_nr_pages * nr_zones *
2151                            MIGRATE_PCPTYPES * MIGRATE_PCPTYPES;
2152 
2153         /* don't ever allow to reserve more than 5% of the lowmem */
2154         recommended_min = min(recommended_min,
2155                               (unsigned long) nr_free_buffer_pages() / 20);
2156         recommended_min <<= (PAGE_SHIFT-10);
2157 
2158         if (recommended_min > min_free_kbytes) {
2159                 if (user_min_free_kbytes >= 0)
2160                         pr_info("raising min_free_kbytes from %d to %lu to help transparent hugepage allocations\n",
2161                                 min_free_kbytes, recommended_min);
2162 
2163                 min_free_kbytes = recommended_min;
2164         }
2165         setup_per_zone_wmarks();
2166 }
2167 
2168 int start_stop_khugepaged(void)
2169 {
2170         static struct task_struct *khugepaged_thread __read_mostly;
2171         static DEFINE_MUTEX(khugepaged_mutex);
2172         int err = 0;
2173 
2174         mutex_lock(&khugepaged_mutex);
2175         if (khugepaged_enabled()) {
2176                 if (!khugepaged_thread)
2177                         khugepaged_thread = kthread_run(khugepaged, NULL,
2178                                                         "khugepaged");
2179                 if (IS_ERR(khugepaged_thread)) {
2180                         pr_err("khugepaged: kthread_run(khugepaged) failed\n");
2181                         err = PTR_ERR(khugepaged_thread);
2182                         khugepaged_thread = NULL;
2183                         goto fail;
2184                 }
2185 
2186                 if (!list_empty(&khugepaged_scan.mm_head))
2187                         wake_up_interruptible(&khugepaged_wait);
2188 
2189                 set_recommended_min_free_kbytes();
2190         } else if (khugepaged_thread) {
2191                 kthread_stop(khugepaged_thread);
2192                 khugepaged_thread = NULL;
2193         }
2194 fail:
2195         mutex_unlock(&khugepaged_mutex);
2196         return err;
2197 }
/* [<][>][^][v][top][bottom][index][help] */
root/mm/khugepaged.c

DEFINITIONS
