mm/huge_memory.c

   1 /*
   2  *  Copyright (C) 2009  Red Hat, Inc.
   3  *
   4  *  This work is licensed under the terms of the GNU GPL, version 2. See
   5  *  the COPYING file in the top-level directory.
   6  */
   7
   8 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
   9
  10 #include <linux/mm.h>
  11 #include <linux/sched.h>
  12 #include <linux/highmem.h>
  13 #include <linux/hugetlb.h>
  14 #include <linux/mmu_notifier.h>
  15 #include <linux/rmap.h>
  16 #include <linux/swap.h>
  17 #include <linux/shrinker.h>
  18 #include <linux/mm_inline.h>
  19 #include <linux/swapops.h>
  20 #include <linux/dax.h>
  21 #include <linux/khugepaged.h>
  22 #include <linux/freezer.h>
  23 #include <linux/pfn_t.h>
  24 #include <linux/mman.h>
  25 #include <linux/memremap.h>
  26 #include <linux/pagemap.h>
  27 #include <linux/debugfs.h>
  28 #include <linux/migrate.h>
  29 #include <linux/hashtable.h>
  30 #include <linux/userfaultfd_k.h>
  31 #include <linux/page_idle.h>
  32 #include <linux/shmem_fs.h>
  33
  34 #include <asm/tlb.h>
  35 #include <asm/pgalloc.h>
  36 #include "internal.h"
  37
  38 /*
  39  * By default transparent hugepage support is disabled in order that avoid
  40  * to risk increase the memory footprint of applications without a guaranteed
  41  * benefit. When transparent hugepage support is enabled, is for all mappings,
  42  * and khugepaged scans all mappings.
  43  * Defrag is invoked by khugepaged hugepage allocations and by page faults
  44  * for all hugepage allocations.
  45  */
  46 unsigned long transparent_hugepage_flags __read_mostly =
  47 #ifdef CONFIG_TRANSPARENT_HUGEPAGE_ALWAYS
  48         (1<<TRANSPARENT_HUGEPAGE_FLAG)|
  49 #endif
  50 #ifdef CONFIG_TRANSPARENT_HUGEPAGE_MADVISE
  51         (1<<TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG)|
  52 #endif
  53         (1<<TRANSPARENT_HUGEPAGE_DEFRAG_REQ_MADV_FLAG)|
  54         (1<<TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG)|
  55         (1<<TRANSPARENT_HUGEPAGE_USE_ZERO_PAGE_FLAG);
  56
  57 static struct shrinker deferred_split_shrinker;
  58
  59 static atomic_t huge_zero_refcount;
  60 struct page *huge_zero_page __read_mostly;
  61
  62 static struct page *get_huge_zero_page(void)
  63 {
  64         struct page *zero_page;
  65 retry:
  66         if (likely(atomic_inc_not_zero(&huge_zero_refcount)))
  67                 return READ_ONCE(huge_zero_page);
  68
  69         zero_page = alloc_pages((GFP_TRANSHUGE | __GFP_ZERO) & ~__GFP_MOVABLE,
  70                         HPAGE_PMD_ORDER);
  71         if (!zero_page) {
  72                 count_vm_event(THP_ZERO_PAGE_ALLOC_FAILED);
  73                 return NULL;
  74         }
  75         count_vm_event(THP_ZERO_PAGE_ALLOC);
  76         preempt_disable();
  77         if (cmpxchg(&huge_zero_page, NULL, zero_page)) {
  78                 preempt_enable();
  79                 __free_pages(zero_page, compound_order(zero_page));
  80                 goto retry;
  81         }
  82
  83         /* We take additional reference here. It will be put back by shrinker */
  84         atomic_set(&huge_zero_refcount, 2);
  85         preempt_enable();
  86         return READ_ONCE(huge_zero_page);
  87 }
  88
  89 static void put_huge_zero_page(void)
  90 {
  91         /*
  92          * Counter should never go to zero here. Only shrinker can put
  93          * last reference.
  94          */
  95         BUG_ON(atomic_dec_and_test(&huge_zero_refcount));
  96 }
  97
  98 struct page *mm_get_huge_zero_page(struct mm_struct *mm)
  99 {
 100         if (test_bit(MMF_HUGE_ZERO_PAGE, &mm->flags))
 101                 return READ_ONCE(huge_zero_page);
 102
 103         if (!get_huge_zero_page())
 104                 return NULL;
 105
 106         if (test_and_set_bit(MMF_HUGE_ZERO_PAGE, &mm->flags))
 107                 put_huge_zero_page();
 108
 109         return READ_ONCE(huge_zero_page);
 110 }
 111
 112 void mm_put_huge_zero_page(struct mm_struct *mm)
 113 {
 114         if (test_bit(MMF_HUGE_ZERO_PAGE, &mm->flags))
 115                 put_huge_zero_page();
 116 }
 117
 118 static unsigned long shrink_huge_zero_page_count(struct shrinker *shrink,
 119                                         struct shrink_control *sc)
 120 {
 121         /* we can free zero page only if last reference remains */
 122         return atomic_read(&huge_zero_refcount) == 1 ? HPAGE_PMD_NR : 0;
 123 }
 124
 125 static unsigned long shrink_huge_zero_page_scan(struct shrinker *shrink,
 126                                        struct shrink_control *sc)
 127 {
 128         if (atomic_cmpxchg(&huge_zero_refcount, 1, 0) == 1) {
 129                 struct page *zero_page = xchg(&huge_zero_page, NULL);
 130                 BUG_ON(zero_page == NULL);
 131                 __free_pages(zero_page, compound_order(zero_page));
 132                 return HPAGE_PMD_NR;
 133         }
 134
 135         return 0;
 136 }
 137
 138 static struct shrinker huge_zero_page_shrinker = {
 139         .count_objects = shrink_huge_zero_page_count,
 140         .scan_objects = shrink_huge_zero_page_scan,
 141         .seeks = DEFAULT_SEEKS,
 142 };
 143
 144 #ifdef CONFIG_SYSFS
 145
 146 static ssize_t triple_flag_store(struct kobject *kobj,
 147                                  struct kobj_attribute *attr,
 148                                  const char *buf, size_t count,
 149                                  enum transparent_hugepage_flag enabled,
 150                                  enum transparent_hugepage_flag deferred,
 151                                  enum transparent_hugepage_flag req_madv)
 152 {
 153         if (!memcmp("defer", buf,
 154                     min(sizeof("defer")-1, count))) {
 155                 if (enabled == deferred)
 156                         return -EINVAL;
 157                 clear_bit(enabled, &transparent_hugepage_flags);
 158                 clear_bit(req_madv, &transparent_hugepage_flags);
 159                 set_bit(deferred, &transparent_hugepage_flags);
 160         } else if (!memcmp("always", buf,
 161                     min(sizeof("always")-1, count))) {
 162                 clear_bit(deferred, &transparent_hugepage_flags);
 163                 clear_bit(req_madv, &transparent_hugepage_flags);
 164                 set_bit(enabled, &transparent_hugepage_flags);
 165         } else if (!memcmp("madvise", buf,
 166                            min(sizeof("madvise")-1, count))) {
 167                 clear_bit(enabled, &transparent_hugepage_flags);
 168                 clear_bit(deferred, &transparent_hugepage_flags);
 169                 set_bit(req_madv, &transparent_hugepage_flags);
 170         } else if (!memcmp("never", buf,
 171                            min(sizeof("never")-1, count))) {
 172                 clear_bit(enabled, &transparent_hugepage_flags);
 173                 clear_bit(req_madv, &transparent_hugepage_flags);
 174                 clear_bit(deferred, &transparent_hugepage_flags);
 175         } else
 176                 return -EINVAL;
 177
 178         return count;
 179 }
 180
 181 static ssize_t enabled_show(struct kobject *kobj,
 182                             struct kobj_attribute *attr, char *buf)
 183 {
 184         if (test_bit(TRANSPARENT_HUGEPAGE_FLAG, &transparent_hugepage_flags))
 185                 return sprintf(buf, "[always] madvise never\n");
 186         else if (test_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG, &transparent_hugepage_flags))
 187                 return sprintf(buf, "always [madvise] never\n");
 188         else
 189                 return sprintf(buf, "always madvise [never]\n");
 190 }
 191
 192 static ssize_t enabled_store(struct kobject *kobj,
 193                              struct kobj_attribute *attr,
 194                              const char *buf, size_t count)
 195 {
 196         ssize_t ret;
 197
 198         ret = triple_flag_store(kobj, attr, buf, count,
 199                                 TRANSPARENT_HUGEPAGE_FLAG,
 200                                 TRANSPARENT_HUGEPAGE_FLAG,
 201                                 TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG);
 202
 203         if (ret > 0) {
 204                 int err = start_stop_khugepaged();
 205                 if (err)
 206                         ret = err;
 207         }
 208
 209         return ret;
 210 }
 211 static struct kobj_attribute enabled_attr =
 212         __ATTR(enabled, 0644, enabled_show, enabled_store);
 213
 214 ssize_t single_hugepage_flag_show(struct kobject *kobj,
 215                                 struct kobj_attribute *attr, char *buf,
 216                                 enum transparent_hugepage_flag flag)
 217 {
 218         return sprintf(buf, "%d\n",
 219                        !!test_bit(flag, &transparent_hugepage_flags));
 220 }
 221
 222 ssize_t single_hugepage_flag_store(struct kobject *kobj,
 223                                  struct kobj_attribute *attr,
 224                                  const char *buf, size_t count,
 225                                  enum transparent_hugepage_flag flag)
 226 {
 227         unsigned long value;
 228         int ret;
 229
 230         ret = kstrtoul(buf, 10, &value);
 231         if (ret < 0)
 232                 return ret;
 233         if (value > 1)
 234                 return -EINVAL;
 235
 236         if (value)
 237                 set_bit(flag, &transparent_hugepage_flags);
 238         else
 239                 clear_bit(flag, &transparent_hugepage_flags);
 240
 241         return count;
 242 }
 243
 244 /*
 245  * Currently defrag only disables __GFP_NOWAIT for allocation. A blind
 246  * __GFP_REPEAT is too aggressive, it's never worth swapping tons of
 247  * memory just to allocate one more hugepage.
 248  */
 249 static ssize_t defrag_show(struct kobject *kobj,
 250                            struct kobj_attribute *attr, char *buf)
 251 {
 252         if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_DIRECT_FLAG, &transparent_hugepage_flags))
 253                 return sprintf(buf, "[always] defer madvise never\n");
 254         if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_FLAG, &transparent_hugepage_flags))
 255                 return sprintf(buf, "always [defer] madvise never\n");
 256         else if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_REQ_MADV_FLAG, &transparent_hugepage_flags))
 257                 return sprintf(buf, "always defer [madvise] never\n");
 258         else
 259                 return sprintf(buf, "always defer madvise [never]\n");
 260
 261 }
 262 static ssize_t defrag_store(struct kobject *kobj,
 263                             struct kobj_attribute *attr,
 264                             const char *buf, size_t count)
 265 {
 266         return triple_flag_store(kobj, attr, buf, count,
 267                                  TRANSPARENT_HUGEPAGE_DEFRAG_DIRECT_FLAG,
 268                                  TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_FLAG,
 269                                  TRANSPARENT_HUGEPAGE_DEFRAG_REQ_MADV_FLAG);
 270 }
 271 static struct kobj_attribute defrag_attr =
 272         __ATTR(defrag, 0644, defrag_show, defrag_store);
 273
 274 static ssize_t use_zero_page_show(struct kobject *kobj,
 275                 struct kobj_attribute *attr, char *buf)
 276 {
 277         return single_hugepage_flag_show(kobj, attr, buf,
 278                                 TRANSPARENT_HUGEPAGE_USE_ZERO_PAGE_FLAG);
 279 }
 280 static ssize_t use_zero_page_store(struct kobject *kobj,
 281                 struct kobj_attribute *attr, const char *buf, size_t count)
 282 {
 283         return single_hugepage_flag_store(kobj, attr, buf, count,
 284                                  TRANSPARENT_HUGEPAGE_USE_ZERO_PAGE_FLAG);
 285 }
 286 static struct kobj_attribute use_zero_page_attr =
 287         __ATTR(use_zero_page, 0644, use_zero_page_show, use_zero_page_store);
 288
 289 static ssize_t hpage_pmd_size_show(struct kobject *kobj,
 290                 struct kobj_attribute *attr, char *buf)
 291 {
 292         return sprintf(buf, "%lu\n", HPAGE_PMD_SIZE);
 293 }
 294 static struct kobj_attribute hpage_pmd_size_attr =
 295         __ATTR_RO(hpage_pmd_size);
 296
 297 #ifdef CONFIG_DEBUG_VM
 298 static ssize_t debug_cow_show(struct kobject *kobj,
 299                                 struct kobj_attribute *attr, char *buf)
 300 {
 301         return single_hugepage_flag_show(kobj, attr, buf,
 302                                 TRANSPARENT_HUGEPAGE_DEBUG_COW_FLAG);
 303 }
 304 static ssize_t debug_cow_store(struct kobject *kobj,
 305                                struct kobj_attribute *attr,
 306                                const char *buf, size_t count)
 307 {
 308         return single_hugepage_flag_store(kobj, attr, buf, count,
 309                                  TRANSPARENT_HUGEPAGE_DEBUG_COW_FLAG);
 310 }
 311 static struct kobj_attribute debug_cow_attr =
 312         __ATTR(debug_cow, 0644, debug_cow_show, debug_cow_store);
 313 #endif /* CONFIG_DEBUG_VM */
 314
 315 static struct attribute *hugepage_attr[] = {
 316         &enabled_attr.attr,
 317         &defrag_attr.attr,
 318         &use_zero_page_attr.attr,
 319         &hpage_pmd_size_attr.attr,
 320 #if defined(CONFIG_SHMEM) && defined(CONFIG_TRANSPARENT_HUGE_PAGECACHE)
 321         &shmem_enabled_attr.attr,
 322 #endif
 323 #ifdef CONFIG_DEBUG_VM
 324         &debug_cow_attr.attr,
 325 #endif
 326         NULL,
 327 };
 328
 329 static struct attribute_group hugepage_attr_group = {
 330         .attrs = hugepage_attr,
 331 };
 332
 333 static int __init hugepage_init_sysfs(struct kobject **hugepage_kobj)
 334 {
 335         int err;
 336
 337         *hugepage_kobj = kobject_create_and_add("transparent_hugepage", mm_kobj);
 338         if (unlikely(!*hugepage_kobj)) {
 339                 pr_err("failed to create transparent hugepage kobject\n");
 340                 return -ENOMEM;
 341         }
 342
 343         err = sysfs_create_group(*hugepage_kobj, &hugepage_attr_group);
 344         if (err) {
 345                 pr_err("failed to register transparent hugepage group\n");
 346                 goto delete_obj;
 347         }
 348
 349         err = sysfs_create_group(*hugepage_kobj, &khugepaged_attr_group);
 350         if (err) {
 351                 pr_err("failed to register transparent hugepage group\n");
 352                 goto remove_hp_group;
 353         }
 354
 355         return 0;
 356
 357 remove_hp_group:
 358         sysfs_remove_group(*hugepage_kobj, &hugepage_attr_group);
 359 delete_obj:
 360         kobject_put(*hugepage_kobj);
 361         return err;
 362 }
 363
 364 static void __init hugepage_exit_sysfs(struct kobject *hugepage_kobj)
 365 {
 366         sysfs_remove_group(hugepage_kobj, &khugepaged_attr_group);
 367         sysfs_remove_group(hugepage_kobj, &hugepage_attr_group);
 368         kobject_put(hugepage_kobj);
 369 }
 370 #else
 371 static inline int hugepage_init_sysfs(struct kobject **hugepage_kobj)
 372 {
 373         return 0;
 374 }
 375
 376 static inline void hugepage_exit_sysfs(struct kobject *hugepage_kobj)
 377 {
 378 }
 379 #endif /* CONFIG_SYSFS */
 380
 381 static int __init hugepage_init(void)
 382 {
 383         int err;
 384         struct kobject *hugepage_kobj;
 385
 386         if (!has_transparent_hugepage()) {
 387                 transparent_hugepage_flags = 0;
 388                 return -EINVAL;
 389         }
 390
 391         /*
 392          * hugepages can't be allocated by the buddy allocator
 393          */
 394         MAYBE_BUILD_BUG_ON(HPAGE_PMD_ORDER >= MAX_ORDER);
 395         /*
 396          * we use page->mapping and page->index in second tail page
 397          * as list_head: assuming THP order >= 2
 398          */
 399         MAYBE_BUILD_BUG_ON(HPAGE_PMD_ORDER < 2);
 400
 401         err = hugepage_init_sysfs(&hugepage_kobj);
 402         if (err)
 403                 goto err_sysfs;
 404
 405         err = khugepaged_init();
 406         if (err)
 407                 goto err_slab;
 408
 409         err = register_shrinker(&huge_zero_page_shrinker);
 410         if (err)
 411                 goto err_hzp_shrinker;
 412         err = register_shrinker(&deferred_split_shrinker);
 413         if (err)
 414                 goto err_split_shrinker;
 415
 416         /*
 417          * By default disable transparent hugepages on smaller systems,
 418          * where the extra memory used could hurt more than TLB overhead
 419          * is likely to save.  The admin can still enable it through /sys.
 420          */
 421         if (totalram_pages < (512 << (20 - PAGE_SHIFT))) {
 422                 transparent_hugepage_flags = 0;
 423                 return 0;
 424         }
 425
 426         err = start_stop_khugepaged();
 427         if (err)
 428                 goto err_khugepaged;
 429
 430         return 0;
 431 err_khugepaged:
 432         unregister_shrinker(&deferred_split_shrinker);
 433 err_split_shrinker:
 434         unregister_shrinker(&huge_zero_page_shrinker);
 435 err_hzp_shrinker:
 436         khugepaged_destroy();
 437 err_slab:
 438         hugepage_exit_sysfs(hugepage_kobj);
 439 err_sysfs:
 440         return err;
 441 }
 442 subsys_initcall(hugepage_init);
 443
 444 static int __init setup_transparent_hugepage(char *str)
 445 {
 446         int ret = 0;
 447         if (!str)
 448                 goto out;
 449         if (!strcmp(str, "always")) {
 450                 set_bit(TRANSPARENT_HUGEPAGE_FLAG,
 451                         &transparent_hugepage_flags);
 452                 clear_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG,
 453                           &transparent_hugepage_flags);
 454                 ret = 1;
 455         } else if (!strcmp(str, "madvise")) {
 456                 clear_bit(TRANSPARENT_HUGEPAGE_FLAG,
 457                           &transparent_hugepage_flags);
 458                 set_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG,
 459                         &transparent_hugepage_flags);
 460                 ret = 1;
 461         } else if (!strcmp(str, "never")) {
 462                 clear_bit(TRANSPARENT_HUGEPAGE_FLAG,
 463                           &transparent_hugepage_flags);
 464                 clear_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG,
 465                           &transparent_hugepage_flags);
 466                 ret = 1;
 467         }
 468 out:
 469         if (!ret)
 470                 pr_warn("transparent_hugepage= cannot parse, ignored\n");
 471         return ret;
 472 }
 473 __setup("transparent_hugepage=", setup_transparent_hugepage);
 474
 475 pmd_t maybe_pmd_mkwrite(pmd_t pmd, struct vm_area_struct *vma)
 476 {
 477         if (likely(vma->vm_flags & VM_WRITE))
 478                 pmd = pmd_mkwrite(pmd);
 479         return pmd;
 480 }
 481
 482 static inline struct list_head *page_deferred_list(struct page *page)
 483 {
 484         /*
 485          * ->lru in the tail pages is occupied by compound_head.
 486          * Let's use ->mapping + ->index in the second tail page as list_head.
 487          */
 488         return (struct list_head *)&page[2].mapping;
 489 }
 490
 491 void prep_transhuge_page(struct page *page)
 492 {
 493         /*
 494          * we use page->mapping and page->indexlru in second tail page
 495          * as list_head: assuming THP order >= 2
 496          */
 497
 498         INIT_LIST_HEAD(page_deferred_list(page));
 499         set_compound_page_dtor(page, TRANSHUGE_PAGE_DTOR);
 500 }
 501
 502 unsigned long __thp_get_unmapped_area(struct file *filp, unsigned long len,
 503                 loff_t off, unsigned long flags, unsigned long size)
 504 {
 505         unsigned long addr;
 506         loff_t off_end = off + len;
 507         loff_t off_align = round_up(off, size);
 508         unsigned long len_pad;
 509
 510         if (off_end <= off_align || (off_end - off_align) < size)
 511                 return 0;
 512
 513         len_pad = len + size;
 514         if (len_pad < len || (off + len_pad) < off)
 515                 return 0;
 516
 517         addr = current->mm->get_unmapped_area(filp, 0, len_pad,
 518                                               off >> PAGE_SHIFT, flags);
 519         if (IS_ERR_VALUE(addr))
 520                 return 0;
 521
 522         addr += (off - addr) & (size - 1);
 523         return addr;
 524 }
 525
 526 unsigned long thp_get_unmapped_area(struct file *filp, unsigned long addr,
 527                 unsigned long len, unsigned long pgoff, unsigned long flags)
 528 {
 529         loff_t off = (loff_t)pgoff << PAGE_SHIFT;
 530
 531         if (addr)
 532                 goto out;
 533         if (!IS_DAX(filp->f_mapping->host) || !IS_ENABLED(CONFIG_FS_DAX_PMD))
 534                 goto out;
 535
 536         addr = __thp_get_unmapped_area(filp, len, off, flags, PMD_SIZE);
 537         if (addr)
 538                 return addr;
 539
 540  out:
 541         return current->mm->get_unmapped_area(filp, addr, len, pgoff, flags);
 542 }
 543 EXPORT_SYMBOL_GPL(thp_get_unmapped_area);
 544
 545 static int __do_huge_pmd_anonymous_page(struct vm_fault *vmf, struct page *page,
 546                 gfp_t gfp)
 547 {
 548         struct vm_area_struct *vma = vmf->vma;
 549         struct mem_cgroup *memcg;
 550         pgtable_t pgtable;
 551         unsigned long haddr = vmf->address & HPAGE_PMD_MASK;
 552
 553         VM_BUG_ON_PAGE(!PageCompound(page), page);
 554
 555         if (mem_cgroup_try_charge(page, vma->vm_mm, gfp, &memcg, true)) {
 556                 put_page(page);
 557                 count_vm_event(THP_FAULT_FALLBACK);
 558                 return VM_FAULT_FALLBACK;
 559         }
 560
 561         pgtable = pte_alloc_one(vma->vm_mm, haddr);
 562         if (unlikely(!pgtable)) {
 563                 mem_cgroup_cancel_charge(page, memcg, true);
 564                 put_page(page);
 565                 return VM_FAULT_OOM;
 566         }
 567
 568         clear_huge_page(page, haddr, HPAGE_PMD_NR);
 569         /*
 570          * The memory barrier inside __SetPageUptodate makes sure that
 571          * clear_huge_page writes become visible before the set_pmd_at()
 572          * write.
 573          */
 574         __SetPageUptodate(page);
 575
 576         vmf->ptl = pmd_lock(vma->vm_mm, vmf->pmd);
 577         if (unlikely(!pmd_none(*vmf->pmd))) {
 578                 spin_unlock(vmf->ptl);
 579                 mem_cgroup_cancel_charge(page, memcg, true);
 580                 put_page(page);
 581                 pte_free(vma->vm_mm, pgtable);
 582         } else {
 583                 pmd_t entry;
 584
 585                 /* Deliver the page fault to userland */
 586                 if (userfaultfd_missing(vma)) {
 587                         int ret;
 588
 589                         spin_unlock(vmf->ptl);
 590                         mem_cgroup_cancel_charge(page, memcg, true);
 591                         put_page(page);
 592                         pte_free(vma->vm_mm, pgtable);
 593                         ret = handle_userfault(vmf, VM_UFFD_MISSING);
 594                         VM_BUG_ON(ret & VM_FAULT_FALLBACK);
 595                         return ret;
 596                 }
 597
 598                 entry = mk_huge_pmd(page, vma->vm_page_prot);
 599                 entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
 600                 page_add_new_anon_rmap(page, vma, haddr, true);
 601                 mem_cgroup_commit_charge(page, memcg, false, true);
 602                 lru_cache_add_active_or_unevictable(page, vma);
 603                 pgtable_trans_huge_deposit(vma->vm_mm, vmf->pmd, pgtable);
 604                 set_pmd_at(vma->vm_mm, haddr, vmf->pmd, entry);
 605                 add_mm_counter(vma->vm_mm, MM_ANONPAGES, HPAGE_PMD_NR);
 606                 atomic_long_inc(&vma->vm_mm->nr_ptes);
 607                 spin_unlock(vmf->ptl);
 608                 count_vm_event(THP_FAULT_ALLOC);
 609         }
 610
 611         return 0;
 612 }
 613
 614 /*
 615  * If THP defrag is set to always then directly reclaim/compact as necessary
 616  * If set to defer then do only background reclaim/compact and defer to khugepaged
 617  * If set to madvise and the VMA is flagged then directly reclaim/compact
 618  * When direct reclaim/compact is allowed, don't retry except for flagged VMA's
 619  */
 620 static inline gfp_t alloc_hugepage_direct_gfpmask(struct vm_area_struct *vma)
 621 {
 622         bool vma_madvised = !!(vma->vm_flags & VM_HUGEPAGE);
 623
 624         if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_REQ_MADV_FLAG,
 625                                 &transparent_hugepage_flags) && vma_madvised)
 626                 return GFP_TRANSHUGE;
 627         else if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_FLAG,
 628                                                 &transparent_hugepage_flags))
 629                 return GFP_TRANSHUGE_LIGHT | __GFP_KSWAPD_RECLAIM;
 630         else if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_DIRECT_FLAG,
 631                                                 &transparent_hugepage_flags))
 632                 return GFP_TRANSHUGE | (vma_madvised ? 0 : __GFP_NORETRY);
 633
 634         return GFP_TRANSHUGE_LIGHT;
 635 }
 636
 637 /* Caller must hold page table lock. */
 638 static bool set_huge_zero_page(pgtable_t pgtable, struct mm_struct *mm,
 639                 struct vm_area_struct *vma, unsigned long haddr, pmd_t *pmd,
 640                 struct page *zero_page)
 641 {
 642         pmd_t entry;
 643         if (!pmd_none(*pmd))
 644                 return false;
 645         entry = mk_pmd(zero_page, vma->vm_page_prot);
 646         entry = pmd_mkhuge(entry);
 647         if (pgtable)
 648                 pgtable_trans_huge_deposit(mm, pmd, pgtable);
 649         set_pmd_at(mm, haddr, pmd, entry);
 650         atomic_long_inc(&mm->nr_ptes);
 651         return true;
 652 }
 653
 654 int do_huge_pmd_anonymous_page(struct vm_fault *vmf)
 655 {
 656         struct vm_area_struct *vma = vmf->vma;
 657         gfp_t gfp;
 658         struct page *page;
 659         unsigned long haddr = vmf->address & HPAGE_PMD_MASK;
 660
 661         if (haddr < vma->vm_start || haddr + HPAGE_PMD_SIZE > vma->vm_end)
 662                 return VM_FAULT_FALLBACK;
 663         if (unlikely(anon_vma_prepare(vma)))
 664                 return VM_FAULT_OOM;
 665         if (unlikely(khugepaged_enter(vma, vma->vm_flags)))
 666                 return VM_FAULT_OOM;
 667         if (!(vmf->flags & FAULT_FLAG_WRITE) &&
 668                         !mm_forbids_zeropage(vma->vm_mm) &&
 669                         transparent_hugepage_use_zero_page()) {
 670                 pgtable_t pgtable;
 671                 struct page *zero_page;
 672                 bool set;
 673                 int ret;
 674                 pgtable = pte_alloc_one(vma->vm_mm, haddr);
 675                 if (unlikely(!pgtable))
 676                         return VM_FAULT_OOM;
 677                 zero_page = mm_get_huge_zero_page(vma->vm_mm);
 678                 if (unlikely(!zero_page)) {
 679                         pte_free(vma->vm_mm, pgtable);
 680                         count_vm_event(THP_FAULT_FALLBACK);
 681                         return VM_FAULT_FALLBACK;
 682                 }
 683                 vmf->ptl = pmd_lock(vma->vm_mm, vmf->pmd);
 684                 ret = 0;
 685                 set = false;
 686                 if (pmd_none(*vmf->pmd)) {
 687                         if (userfaultfd_missing(vma)) {
 688                                 spin_unlock(vmf->ptl);
 689                                 ret = handle_userfault(vmf, VM_UFFD_MISSING);
 690                                 VM_BUG_ON(ret & VM_FAULT_FALLBACK);
 691                         } else {
 692                                 set_huge_zero_page(pgtable, vma->vm_mm, vma,
 693                                                    haddr, vmf->pmd, zero_page);
 694                                 spin_unlock(vmf->ptl);
 695                                 set = true;
 696                         }
 697                 } else
 698                         spin_unlock(vmf->ptl);
 699                 if (!set)
 700                         pte_free(vma->vm_mm, pgtable);
 701                 return ret;
 702         }
 703         gfp = alloc_hugepage_direct_gfpmask(vma);
 704         page = alloc_hugepage_vma(gfp, vma, haddr, HPAGE_PMD_ORDER);
 705         if (unlikely(!page)) {
 706                 count_vm_event(THP_FAULT_FALLBACK);
 707                 return VM_FAULT_FALLBACK;
 708         }
 709         prep_transhuge_page(page);
 710         return __do_huge_pmd_anonymous_page(vmf, page, gfp);
 711 }
 712
 713 static void insert_pfn_pmd(struct vm_area_struct *vma, unsigned long addr,
 714                 pmd_t *pmd, pfn_t pfn, pgprot_t prot, bool write)
 715 {
 716         struct mm_struct *mm = vma->vm_mm;
 717         pmd_t entry;
 718         spinlock_t *ptl;
 719
 720         ptl = pmd_lock(mm, pmd);
 721         entry = pmd_mkhuge(pfn_t_pmd(pfn, prot));
 722         if (pfn_t_devmap(pfn))
 723                 entry = pmd_mkdevmap(entry);
 724         if (write) {
 725                 entry = pmd_mkyoung(pmd_mkdirty(entry));
 726                 entry = maybe_pmd_mkwrite(entry, vma);
 727         }
 728         set_pmd_at(mm, addr, pmd, entry);
 729         update_mmu_cache_pmd(vma, addr, pmd);
 730         spin_unlock(ptl);
 731 }
 732
 733 int vmf_insert_pfn_pmd(struct vm_area_struct *vma, unsigned long addr,
 734                         pmd_t *pmd, pfn_t pfn, bool write)
 735 {
 736         pgprot_t pgprot = vma->vm_page_prot;
 737         /*
 738          * If we had pmd_special, we could avoid all these restrictions,
 739          * but we need to be consistent with PTEs and architectures that
 740          * can't support a 'special' bit.
 741          */
 742         BUG_ON(!(vma->vm_flags & (VM_PFNMAP|VM_MIXEDMAP)));
 743         BUG_ON((vma->vm_flags & (VM_PFNMAP|VM_MIXEDMAP)) ==
 744                                                 (VM_PFNMAP|VM_MIXEDMAP));
 745         BUG_ON((vma->vm_flags & VM_PFNMAP) && is_cow_mapping(vma->vm_flags));
 746         BUG_ON(!pfn_t_devmap(pfn));
 747
 748         if (addr < vma->vm_start || addr >= vma->vm_end)
 749                 return VM_FAULT_SIGBUS;
 750
 751         track_pfn_insert(vma, &pgprot, pfn);
 752
 753         insert_pfn_pmd(vma, addr, pmd, pfn, pgprot, write);
 754         return VM_FAULT_NOPAGE;
 755 }
 756 EXPORT_SYMBOL_GPL(vmf_insert_pfn_pmd);
 757
 758 static void touch_pmd(struct vm_area_struct *vma, unsigned long addr,
 759                 pmd_t *pmd)
 760 {
 761         pmd_t _pmd;
 762
 763         /*
 764          * We should set the dirty bit only for FOLL_WRITE but for now
 765          * the dirty bit in the pmd is meaningless.  And if the dirty
 766          * bit will become meaningful and we'll only set it with
 767          * FOLL_WRITE, an atomic set_bit will be required on the pmd to
 768          * set the young bit, instead of the current set_pmd_at.
 769          */
 770         _pmd = pmd_mkyoung(pmd_mkdirty(*pmd));
 771         if (pmdp_set_access_flags(vma, addr & HPAGE_PMD_MASK,
 772                                 pmd, _pmd,  1))
 773                 update_mmu_cache_pmd(vma, addr, pmd);
 774 }
 775
 776 struct page *follow_devmap_pmd(struct vm_area_struct *vma, unsigned long addr,
 777                 pmd_t *pmd, int flags)
 778 {
 779         unsigned long pfn = pmd_pfn(*pmd);
 780         struct mm_struct *mm = vma->vm_mm;
 781         struct dev_pagemap *pgmap;
 782         struct page *page;
 783
 784         assert_spin_locked(pmd_lockptr(mm, pmd));
 785
 786         if (flags & FOLL_WRITE && !pmd_write(*pmd))
 787                 return NULL;
 788
 789         if (pmd_present(*pmd) && pmd_devmap(*pmd))
 790                 /* pass */;
 791         else
 792                 return NULL;
 793
 794         if (flags & FOLL_TOUCH)
 795                 touch_pmd(vma, addr, pmd);
 796
 797         /*
 798          * device mapped pages can only be returned if the
 799          * caller will manage the page reference count.
 800          */
 801         if (!(flags & FOLL_GET))
 802                 return ERR_PTR(-EEXIST);
 803
 804         pfn += (addr & ~PMD_MASK) >> PAGE_SHIFT;
 805         pgmap = get_dev_pagemap(pfn, NULL);
 806         if (!pgmap)
 807                 return ERR_PTR(-EFAULT);
 808         page = pfn_to_page(pfn);
 809         get_page(page);
 810         put_dev_pagemap(pgmap);
 811
 812         return page;
 813 }
 814
 815 int copy_huge_pmd(struct mm_struct *dst_mm, struct mm_struct *src_mm,
 816                   pmd_t *dst_pmd, pmd_t *src_pmd, unsigned long addr,
 817                   struct vm_area_struct *vma)
 818 {
 819         spinlock_t *dst_ptl, *src_ptl;
 820         struct page *src_page;
 821         pmd_t pmd;
 822         pgtable_t pgtable = NULL;
 823         int ret = -ENOMEM;
 824
 825         /* Skip if can be re-fill on fault */
 826         if (!vma_is_anonymous(vma))
 827                 return 0;
 828
 829         pgtable = pte_alloc_one(dst_mm, addr);
 830         if (unlikely(!pgtable))
 831                 goto out;
 832
 833         dst_ptl = pmd_lock(dst_mm, dst_pmd);
 834         src_ptl = pmd_lockptr(src_mm, src_pmd);
 835         spin_lock_nested(src_ptl, SINGLE_DEPTH_NESTING);
 836
 837         ret = -EAGAIN;
 838         pmd = *src_pmd;
 839         if (unlikely(!pmd_trans_huge(pmd))) {
 840                 pte_free(dst_mm, pgtable);
 841                 goto out_unlock;
 842         }
 843         /*
 844          * When page table lock is held, the huge zero pmd should not be
 845          * under splitting since we don't split the page itself, only pmd to
 846          * a page table.
 847          */
 848         if (is_huge_zero_pmd(pmd)) {
 849                 struct page *zero_page;
 850                 /*
 851                  * get_huge_zero_page() will never allocate a new page here,
 852                  * since we already have a zero page to copy. It just takes a
 853                  * reference.
 854                  */
 855                 zero_page = mm_get_huge_zero_page(dst_mm);
 856                 set_huge_zero_page(pgtable, dst_mm, vma, addr, dst_pmd,
 857                                 zero_page);
 858                 ret = 0;
 859                 goto out_unlock;
 860         }
 861
 862         src_page = pmd_page(pmd);
 863         VM_BUG_ON_PAGE(!PageHead(src_page), src_page);
 864         get_page(src_page);
 865         page_dup_rmap(src_page, true);
 866         add_mm_counter(dst_mm, MM_ANONPAGES, HPAGE_PMD_NR);
 867         atomic_long_inc(&dst_mm->nr_ptes);
 868         pgtable_trans_huge_deposit(dst_mm, dst_pmd, pgtable);
 869
 870         pmdp_set_wrprotect(src_mm, addr, src_pmd);
 871         pmd = pmd_mkold(pmd_wrprotect(pmd));
 872         set_pmd_at(dst_mm, addr, dst_pmd, pmd);
 873
 874         ret = 0;
 875 out_unlock:
 876         spin_unlock(src_ptl);
 877         spin_unlock(dst_ptl);
 878 out:
 879         return ret;
 880 }
 881
 882 void huge_pmd_set_accessed(struct vm_fault *vmf, pmd_t orig_pmd)
 883 {
 884         pmd_t entry;
 885         unsigned long haddr;
 886         bool write = vmf->flags & FAULT_FLAG_WRITE;
 887
 888         vmf->ptl = pmd_lock(vmf->vma->vm_mm, vmf->pmd);
 889         if (unlikely(!pmd_same(*vmf->pmd, orig_pmd)))
 890                 goto unlock;
 891
 892         entry = pmd_mkyoung(orig_pmd);
 893         if (write)
 894                 entry = pmd_mkdirty(entry);
 895         haddr = vmf->address & HPAGE_PMD_MASK;
 896         if (pmdp_set_access_flags(vmf->vma, haddr, vmf->pmd, entry, write))
 897                 update_mmu_cache_pmd(vmf->vma, vmf->address, vmf->pmd);
 898
 899 unlock:
 900         spin_unlock(vmf->ptl);
 901 }
 902
 903 static int do_huge_pmd_wp_page_fallback(struct vm_fault *vmf, pmd_t orig_pmd,
 904                 struct page *page)
 905 {
 906         struct vm_area_struct *vma = vmf->vma;
 907         unsigned long haddr = vmf->address & HPAGE_PMD_MASK;
 908         struct mem_cgroup *memcg;
 909         pgtable_t pgtable;
 910         pmd_t _pmd;
 911         int ret = 0, i;
 912         struct page **pages;
 913         unsigned long mmun_start;       /* For mmu_notifiers */
 914         unsigned long mmun_end;         /* For mmu_notifiers */
 915
 916         pages = kmalloc(sizeof(struct page *) * HPAGE_PMD_NR,
 917                         GFP_KERNEL);
 918         if (unlikely(!pages)) {
 919                 ret |= VM_FAULT_OOM;
 920                 goto out;
 921         }
 922
 923         for (i = 0; i < HPAGE_PMD_NR; i++) {
 924                 pages[i] = alloc_page_vma_node(GFP_HIGHUSER_MOVABLE, vma,
 925                                                vmf->address, page_to_nid(page));
 926                 if (unlikely(!pages[i] ||
 927                              mem_cgroup_try_charge(pages[i], vma->vm_mm,
 928                                      GFP_KERNEL, &memcg, false))) {
 929                         if (pages[i])
 930                                 put_page(pages[i]);
 931                         while (--i >= 0) {
 932                                 memcg = (void *)page_private(pages[i]);
 933                                 set_page_private(pages[i], 0);
 934                                 mem_cgroup_cancel_charge(pages[i], memcg,
 935                                                 false);
 936                                 put_page(pages[i]);
 937                         }
 938                         kfree(pages);
 939                         ret |= VM_FAULT_OOM;
 940                         goto out;
 941                 }
 942                 set_page_private(pages[i], (unsigned long)memcg);
 943         }
 944
 945         for (i = 0; i < HPAGE_PMD_NR; i++) {
 946                 copy_user_highpage(pages[i], page + i,
 947                                    haddr + PAGE_SIZE * i, vma);
 948                 __SetPageUptodate(pages[i]);
 949                 cond_resched();
 950         }
 951
 952         mmun_start = haddr;
 953         mmun_end   = haddr + HPAGE_PMD_SIZE;
 954         mmu_notifier_invalidate_range_start(vma->vm_mm, mmun_start, mmun_end);
 955
 956         vmf->ptl = pmd_lock(vma->vm_mm, vmf->pmd);
 957         if (unlikely(!pmd_same(*vmf->pmd, orig_pmd)))
 958                 goto out_free_pages;
 959         VM_BUG_ON_PAGE(!PageHead(page), page);
 960
 961         pmdp_huge_clear_flush_notify(vma, haddr, vmf->pmd);
 962         /* leave pmd empty until pte is filled */
 963
 964         pgtable = pgtable_trans_huge_withdraw(vma->vm_mm, vmf->pmd);
 965         pmd_populate(vma->vm_mm, &_pmd, pgtable);
 966
 967         for (i = 0; i < HPAGE_PMD_NR; i++, haddr += PAGE_SIZE) {
 968                 pte_t entry;
 969                 entry = mk_pte(pages[i], vma->vm_page_prot);
 970                 entry = maybe_mkwrite(pte_mkdirty(entry), vma);
 971                 memcg = (void *)page_private(pages[i]);
 972                 set_page_private(pages[i], 0);
 973                 page_add_new_anon_rmap(pages[i], vmf->vma, haddr, false);
 974                 mem_cgroup_commit_charge(pages[i], memcg, false, false);
 975                 lru_cache_add_active_or_unevictable(pages[i], vma);
 976                 vmf->pte = pte_offset_map(&_pmd, haddr);
 977                 VM_BUG_ON(!pte_none(*vmf->pte));
 978                 set_pte_at(vma->vm_mm, haddr, vmf->pte, entry);
 979                 pte_unmap(vmf->pte);
 980         }
 981         kfree(pages);
 982
 983         smp_wmb(); /* make pte visible before pmd */
 984         pmd_populate(vma->vm_mm, vmf->pmd, pgtable);
 985         page_remove_rmap(page, true);
 986         spin_unlock(vmf->ptl);
 987
 988         mmu_notifier_invalidate_range_end(vma->vm_mm, mmun_start, mmun_end);
 989
 990         ret |= VM_FAULT_WRITE;
 991         put_page(page);
 992
 993 out:
 994         return ret;
 995
 996 out_free_pages:
 997         spin_unlock(vmf->ptl);
 998         mmu_notifier_invalidate_range_end(vma->vm_mm, mmun_start, mmun_end);
 999         for (i = 0; i < HPAGE_PMD_NR; i++) {
1000                 memcg = (void *)page_private(pages[i]);
1001                 set_page_private(pages[i], 0);
1002                 mem_cgroup_cancel_charge(pages[i], memcg, false);
1003                 put_page(pages[i]);
1004         }
1005         kfree(pages);
1006         goto out;
1007 }
1008
1009 int do_huge_pmd_wp_page(struct vm_fault *vmf, pmd_t orig_pmd)
1010 {
1011         struct vm_area_struct *vma = vmf->vma;
1012         struct page *page = NULL, *new_page;
1013         struct mem_cgroup *memcg;
1014         unsigned long haddr = vmf->address & HPAGE_PMD_MASK;
1015         unsigned long mmun_start;       /* For mmu_notifiers */
1016         unsigned long mmun_end;         /* For mmu_notifiers */
1017         gfp_t huge_gfp;                 /* for allocation and charge */
1018         int ret = 0;
1019
1020         vmf->ptl = pmd_lockptr(vma->vm_mm, vmf->pmd);
1021         VM_BUG_ON_VMA(!vma->anon_vma, vma);
1022         if (is_huge_zero_pmd(orig_pmd))
1023                 goto alloc;
1024         spin_lock(vmf->ptl);
1025         if (unlikely(!pmd_same(*vmf->pmd, orig_pmd)))
1026                 goto out_unlock;
1027
1028         page = pmd_page(orig_pmd);
1029         VM_BUG_ON_PAGE(!PageCompound(page) || !PageHead(page), page);
1030         /*
1031          * We can only reuse the page if nobody else maps the huge page or it's
1032          * part.
1033          */
1034         if (page_trans_huge_mapcount(page, NULL) == 1) {
1035                 pmd_t entry;
1036                 entry = pmd_mkyoung(orig_pmd);
1037                 entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
1038                 if (pmdp_set_access_flags(vma, haddr, vmf->pmd, entry,  1))
1039                         update_mmu_cache_pmd(vma, vmf->address, vmf->pmd);
1040                 ret |= VM_FAULT_WRITE;
1041                 goto out_unlock;
1042         }
1043         get_page(page);
1044         spin_unlock(vmf->ptl);
1045 alloc:
1046         if (transparent_hugepage_enabled(vma) &&
1047             !transparent_hugepage_debug_cow()) {
1048                 huge_gfp = alloc_hugepage_direct_gfpmask(vma);
1049                 new_page = alloc_hugepage_vma(huge_gfp, vma, haddr, HPAGE_PMD_ORDER);
1050         } else
1051                 new_page = NULL;
1052
1053         if (likely(new_page)) {
1054                 prep_transhuge_page(new_page);
1055         } else {
1056                 if (!page) {
1057                         split_huge_pmd(vma, vmf->pmd, vmf->address);
1058                         ret |= VM_FAULT_FALLBACK;
1059                 } else {
1060                         ret = do_huge_pmd_wp_page_fallback(vmf, orig_pmd, page);
1061                         if (ret & VM_FAULT_OOM) {
1062                                 split_huge_pmd(vma, vmf->pmd, vmf->address);
1063                                 ret |= VM_FAULT_FALLBACK;
1064                         }
1065                         put_page(page);
1066                 }
1067                 count_vm_event(THP_FAULT_FALLBACK);
1068                 goto out;
1069         }
1070
1071         if (unlikely(mem_cgroup_try_charge(new_page, vma->vm_mm,
1072                                         huge_gfp, &memcg, true))) {
1073                 put_page(new_page);
1074                 split_huge_pmd(vma, vmf->pmd, vmf->address);
1075                 if (page)
1076                         put_page(page);
1077                 ret |= VM_FAULT_FALLBACK;
1078                 count_vm_event(THP_FAULT_FALLBACK);
1079                 goto out;
1080         }
1081
1082         count_vm_event(THP_FAULT_ALLOC);
1083
1084         if (!page)
1085                 clear_huge_page(new_page, haddr, HPAGE_PMD_NR);
1086         else
1087                 copy_user_huge_page(new_page, page, haddr, vma, HPAGE_PMD_NR);
1088         __SetPageUptodate(new_page);
1089
1090         mmun_start = haddr;
1091         mmun_end   = haddr + HPAGE_PMD_SIZE;
1092         mmu_notifier_invalidate_range_start(vma->vm_mm, mmun_start, mmun_end);
1093
1094         spin_lock(vmf->ptl);
1095         if (page)
1096                 put_page(page);
1097         if (unlikely(!pmd_same(*vmf->pmd, orig_pmd))) {
1098                 spin_unlock(vmf->ptl);
1099                 mem_cgroup_cancel_charge(new_page, memcg, true);
1100                 put_page(new_page);
1101                 goto out_mn;
1102         } else {
1103                 pmd_t entry;
1104                 entry = mk_huge_pmd(new_page, vma->vm_page_prot);
1105                 entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
1106                 pmdp_huge_clear_flush_notify(vma, haddr, vmf->pmd);
1107                 page_add_new_anon_rmap(new_page, vma, haddr, true);
1108                 mem_cgroup_commit_charge(new_page, memcg, false, true);
1109                 lru_cache_add_active_or_unevictable(new_page, vma);
1110                 set_pmd_at(vma->vm_mm, haddr, vmf->pmd, entry);
1111                 update_mmu_cache_pmd(vma, vmf->address, vmf->pmd);
1112                 if (!page) {
1113                         add_mm_counter(vma->vm_mm, MM_ANONPAGES, HPAGE_PMD_NR);
1114                 } else {
1115                         VM_BUG_ON_PAGE(!PageHead(page), page);
1116                         page_remove_rmap(page, true);
1117                         put_page(page);
1118                 }
1119                 ret |= VM_FAULT_WRITE;
1120         }
1121         spin_unlock(vmf->ptl);
1122 out_mn:
1123         mmu_notifier_invalidate_range_end(vma->vm_mm, mmun_start, mmun_end);
1124 out:
1125         return ret;
1126 out_unlock:
1127         spin_unlock(vmf->ptl);
1128         return ret;
1129 }
1130
1131 struct page *follow_trans_huge_pmd(struct vm_area_struct *vma,
1132                                    unsigned long addr,
1133                                    pmd_t *pmd,
1134                                    unsigned int flags)
1135 {
1136         struct mm_struct *mm = vma->vm_mm;
1137         struct page *page = NULL;
1138
1139         assert_spin_locked(pmd_lockptr(mm, pmd));
1140
1141         if (flags & FOLL_WRITE && !pmd_write(*pmd))
1142                 goto out;
1143
1144         /* Avoid dumping huge zero page */
1145         if ((flags & FOLL_DUMP) && is_huge_zero_pmd(*pmd))
1146                 return ERR_PTR(-EFAULT);
1147
1148         /* Full NUMA hinting faults to serialise migration in fault paths */
1149         if ((flags & FOLL_NUMA) && pmd_protnone(*pmd))
1150                 goto out;
1151
1152         page = pmd_page(*pmd);
1153         VM_BUG_ON_PAGE(!PageHead(page) && !is_zone_device_page(page), page);
1154         if (flags & FOLL_TOUCH)
1155                 touch_pmd(vma, addr, pmd);
1156         if ((flags & FOLL_MLOCK) && (vma->vm_flags & VM_LOCKED)) {
1157                 /*
1158                  * We don't mlock() pte-mapped THPs. This way we can avoid
1159                  * leaking mlocked pages into non-VM_LOCKED VMAs.
1160                  *
1161                  * For anon THP:
1162                  *
1163                  * In most cases the pmd is the only mapping of the page as we
1164                  * break COW for the mlock() -- see gup_flags |= FOLL_WRITE for
1165                  * writable private mappings in populate_vma_page_range().
1166                  *
1167                  * The only scenario when we have the page shared here is if we
1168                  * mlocking read-only mapping shared over fork(). We skip
1169                  * mlocking such pages.
1170                  *
1171                  * For file THP:
1172                  *
1173                  * We can expect PageDoubleMap() to be stable under page lock:
1174                  * for file pages we set it in page_add_file_rmap(), which
1175                  * requires page to be locked.
1176                  */
1177
1178                 if (PageAnon(page) && compound_mapcount(page) != 1)
1179                         goto skip_mlock;
1180                 if (PageDoubleMap(page) || !page->mapping)
1181                         goto skip_mlock;
1182                 if (!trylock_page(page))
1183                         goto skip_mlock;
1184                 lru_add_drain();
1185                 if (page->mapping && !PageDoubleMap(page))
1186                         mlock_vma_page(page);
1187                 unlock_page(page);
1188         }
1189 skip_mlock:
1190         page += (addr & ~HPAGE_PMD_MASK) >> PAGE_SHIFT;
1191         VM_BUG_ON_PAGE(!PageCompound(page) && !is_zone_device_page(page), page);
1192         if (flags & FOLL_GET)
1193                 get_page(page);
1194
1195 out:
1196         return page;
1197 }
1198
1199 /* NUMA hinting page fault entry point for trans huge pmds */
1200 int do_huge_pmd_numa_page(struct vm_fault *vmf, pmd_t pmd)
1201 {
1202         struct vm_area_struct *vma = vmf->vma;
1203         struct anon_vma *anon_vma = NULL;
1204         struct page *page;
1205         unsigned long haddr = vmf->address & HPAGE_PMD_MASK;
1206         int page_nid = -1, this_nid = numa_node_id();
1207         int target_nid, last_cpupid = -1;
1208         bool page_locked;
1209         bool migrated = false;
1210         bool was_writable;
1211         int flags = 0;
1212
1213         vmf->ptl = pmd_lock(vma->vm_mm, vmf->pmd);
1214         if (unlikely(!pmd_same(pmd, *vmf->pmd)))
1215                 goto out_unlock;
1216
1217         /*
1218          * If there are potential migrations, wait for completion and retry
1219          * without disrupting NUMA hinting information. Do not relock and
1220          * check_same as the page may no longer be mapped.
1221          */
1222         if (unlikely(pmd_trans_migrating(*vmf->pmd))) {
1223                 page = pmd_page(*vmf->pmd);
1224                 spin_unlock(vmf->ptl);
1225                 wait_on_page_locked(page);
1226                 goto out;
1227         }
1228
1229         page = pmd_page(pmd);
1230         BUG_ON(is_huge_zero_page(page));
1231         page_nid = page_to_nid(page);
1232         last_cpupid = page_cpupid_last(page);
1233         count_vm_numa_event(NUMA_HINT_FAULTS);
1234         if (page_nid == this_nid) {
1235                 count_vm_numa_event(NUMA_HINT_FAULTS_LOCAL);
1236                 flags |= TNF_FAULT_LOCAL;
1237         }
1238
1239         /* See similar comment in do_numa_page for explanation */
1240         if (!pmd_write(pmd))
1241                 flags |= TNF_NO_GROUP;
1242
1243         /*
1244          * Acquire the page lock to serialise THP migrations but avoid dropping
1245          * page_table_lock if at all possible
1246          */
1247         page_locked = trylock_page(page);
1248         target_nid = mpol_misplaced(page, vma, haddr);
1249         if (target_nid == -1) {
1250                 /* If the page was locked, there are no parallel migrations */
1251                 if (page_locked)
1252                         goto clear_pmdnuma;
1253         }
1254
1255         /* Migration could have started since the pmd_trans_migrating check */
1256         if (!page_locked) {
1257                 spin_unlock(vmf->ptl);
1258                 wait_on_page_locked(page);
1259                 page_nid = -1;
1260                 goto out;
1261         }
1262
1263         /*
1264          * Page is misplaced. Page lock serialises migrations. Acquire anon_vma
1265          * to serialises splits
1266          */
1267         get_page(page);
1268         spin_unlock(vmf->ptl);
1269         anon_vma = page_lock_anon_vma_read(page);
1270
1271         /* Confirm the PMD did not change while page_table_lock was released */
1272         spin_lock(vmf->ptl);
1273         if (unlikely(!pmd_same(pmd, *vmf->pmd))) {
1274                 unlock_page(page);
1275                 put_page(page);
1276                 page_nid = -1;
1277                 goto out_unlock;
1278         }
1279
1280         /* Bail if we fail to protect against THP splits for any reason */
1281         if (unlikely(!anon_vma)) {
1282                 put_page(page);
1283                 page_nid = -1;
1284                 goto clear_pmdnuma;
1285         }
1286
1287         /*
1288          * Migrate the THP to the requested node, returns with page unlocked
1289          * and access rights restored.
1290          */
1291         spin_unlock(vmf->ptl);
1292         migrated = migrate_misplaced_transhuge_page(vma->vm_mm, vma,
1293                                 vmf->pmd, pmd, vmf->address, page, target_nid);
1294         if (migrated) {
1295                 flags |= TNF_MIGRATED;
1296                 page_nid = target_nid;
1297         } else
1298                 flags |= TNF_MIGRATE_FAIL;
1299
1300         goto out;
1301 clear_pmdnuma:
1302         BUG_ON(!PageLocked(page));
1303         was_writable = pmd_write(pmd);
1304         pmd = pmd_modify(pmd, vma->vm_page_prot);
1305         pmd = pmd_mkyoung(pmd);
1306         if (was_writable)
1307                 pmd = pmd_mkwrite(pmd);
1308         set_pmd_at(vma->vm_mm, haddr, vmf->pmd, pmd);
1309         update_mmu_cache_pmd(vma, vmf->address, vmf->pmd);
1310         unlock_page(page);
1311 out_unlock:
1312         spin_unlock(vmf->ptl);
1313
1314 out:
1315         if (anon_vma)
1316                 page_unlock_anon_vma_read(anon_vma);
1317
1318         if (page_nid != -1)
1319                 task_numa_fault(last_cpupid, page_nid, HPAGE_PMD_NR,
1320                                 vmf->flags);
1321
1322         return 0;
1323 }
1324
1325 /*
1326  * Return true if we do MADV_FREE successfully on entire pmd page.
1327  * Otherwise, return false.
1328  */
1329 bool madvise_free_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
1330                 pmd_t *pmd, unsigned long addr, unsigned long next)
1331 {
1332         spinlock_t *ptl;
1333         pmd_t orig_pmd;
1334         struct page *page;
1335         struct mm_struct *mm = tlb->mm;
1336         bool ret = false;
1337
1338         tlb_remove_check_page_size_change(tlb, HPAGE_PMD_SIZE);
1339
1340         ptl = pmd_trans_huge_lock(pmd, vma);
1341         if (!ptl)
1342                 goto out_unlocked;
1343
1344         orig_pmd = *pmd;
1345         if (is_huge_zero_pmd(orig_pmd))
1346                 goto out;
1347
1348         page = pmd_page(orig_pmd);
1349         /*
1350          * If other processes are mapping this page, we couldn't discard
1351          * the page unless they all do MADV_FREE so let's skip the page.
1352          */
1353         if (page_mapcount(page) != 1)
1354                 goto out;
1355
1356         if (!trylock_page(page))
1357                 goto out;
1358
1359         /*
1360          * If user want to discard part-pages of THP, split it so MADV_FREE
1361          * will deactivate only them.
1362          */
1363         if (next - addr != HPAGE_PMD_SIZE) {
1364                 get_page(page);
1365                 spin_unlock(ptl);
1366                 split_huge_page(page);
1367                 put_page(page);
1368                 unlock_page(page);
1369                 goto out_unlocked;
1370         }
1371
1372         if (PageDirty(page))
1373                 ClearPageDirty(page);
1374         unlock_page(page);
1375
1376         if (PageActive(page))
1377                 deactivate_page(page);
1378
1379         if (pmd_young(orig_pmd) || pmd_dirty(orig_pmd)) {
1380                 orig_pmd = pmdp_huge_get_and_clear_full(tlb->mm, addr, pmd,
1381                         tlb->fullmm);
1382                 orig_pmd = pmd_mkold(orig_pmd);
1383                 orig_pmd = pmd_mkclean(orig_pmd);
1384
1385                 set_pmd_at(mm, addr, pmd, orig_pmd);
1386                 tlb_remove_pmd_tlb_entry(tlb, pmd, addr);
1387         }
1388         ret = true;
1389 out:
1390         spin_unlock(ptl);
1391 out_unlocked:
1392         return ret;
1393 }
1394
1395 static inline void zap_deposited_table(struct mm_struct *mm, pmd_t *pmd)
1396 {
1397         pgtable_t pgtable;
1398
1399         pgtable = pgtable_trans_huge_withdraw(mm, pmd);
1400         pte_free(mm, pgtable);
1401         atomic_long_dec(&mm->nr_ptes);
1402 }
1403
1404 int zap_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
1405                  pmd_t *pmd, unsigned long addr)
1406 {
1407         pmd_t orig_pmd;
1408         spinlock_t *ptl;
1409
1410         tlb_remove_check_page_size_change(tlb, HPAGE_PMD_SIZE);
1411
1412         ptl = __pmd_trans_huge_lock(pmd, vma);
1413         if (!ptl)
1414                 return 0;
1415         /*
1416          * For architectures like ppc64 we look at deposited pgtable
1417          * when calling pmdp_huge_get_and_clear. So do the
1418          * pgtable_trans_huge_withdraw after finishing pmdp related
1419          * operations.
1420          */
1421         orig_pmd = pmdp_huge_get_and_clear_full(tlb->mm, addr, pmd,
1422                         tlb->fullmm);
1423         tlb_remove_pmd_tlb_entry(tlb, pmd, addr);
1424         if (vma_is_dax(vma)) {
1425                 spin_unlock(ptl);
1426                 if (is_huge_zero_pmd(orig_pmd))
1427                         tlb_remove_page_size(tlb, pmd_page(orig_pmd), HPAGE_PMD_SIZE);
1428         } else if (is_huge_zero_pmd(orig_pmd)) {
1429                 pte_free(tlb->mm, pgtable_trans_huge_withdraw(tlb->mm, pmd));
1430                 atomic_long_dec(&tlb->mm->nr_ptes);
1431                 spin_unlock(ptl);
1432                 tlb_remove_page_size(tlb, pmd_page(orig_pmd), HPAGE_PMD_SIZE);
1433         } else {
1434                 struct page *page = pmd_page(orig_pmd);
1435                 page_remove_rmap(page, true);
1436                 VM_BUG_ON_PAGE(page_mapcount(page) < 0, page);
1437                 VM_BUG_ON_PAGE(!PageHead(page), page);
1438                 if (PageAnon(page)) {
1439                         pgtable_t pgtable;
1440                         pgtable = pgtable_trans_huge_withdraw(tlb->mm, pmd);
1441                         pte_free(tlb->mm, pgtable);
1442                         atomic_long_dec(&tlb->mm->nr_ptes);
1443                         add_mm_counter(tlb->mm, MM_ANONPAGES, -HPAGE_PMD_NR);
1444                 } else {
1445                         if (arch_needs_pgtable_deposit())
1446                                 zap_deposited_table(tlb->mm, pmd);
1447                         add_mm_counter(tlb->mm, MM_FILEPAGES, -HPAGE_PMD_NR);
1448                 }
1449                 spin_unlock(ptl);
1450                 tlb_remove_page_size(tlb, page, HPAGE_PMD_SIZE);
1451         }
1452         return 1;
1453 }
1454
1455 #ifndef pmd_move_must_withdraw
1456 static inline int pmd_move_must_withdraw(spinlock_t *new_pmd_ptl,
1457                                          spinlock_t *old_pmd_ptl,
1458                                          struct vm_area_struct *vma)
1459 {
1460         /*
1461          * With split pmd lock we also need to move preallocated
1462          * PTE page table if new_pmd is on different PMD page table.
1463          *
1464          * We also don't deposit and withdraw tables for file pages.
1465          */
1466         return (new_pmd_ptl != old_pmd_ptl) && vma_is_anonymous(vma);
1467 }
1468 #endif
1469
1470 bool move_huge_pmd(struct vm_area_struct *vma, unsigned long old_addr,
1471                   unsigned long new_addr, unsigned long old_end,
1472                   pmd_t *old_pmd, pmd_t *new_pmd, bool *need_flush)
1473 {
1474         spinlock_t *old_ptl, *new_ptl;
1475         pmd_t pmd;
1476         struct mm_struct *mm = vma->vm_mm;
1477         bool force_flush = false;
1478
1479         if ((old_addr & ~HPAGE_PMD_MASK) ||
1480             (new_addr & ~HPAGE_PMD_MASK) ||
1481             old_end - old_addr < HPAGE_PMD_SIZE)
1482                 return false;
1483
1484         /*
1485          * The destination pmd shouldn't be established, free_pgtables()
1486          * should have release it.
1487          */
1488         if (WARN_ON(!pmd_none(*new_pmd))) {
1489                 VM_BUG_ON(pmd_trans_huge(*new_pmd));
1490                 return false;
1491         }
1492
1493         /*
1494          * We don't have to worry about the ordering of src and dst
1495          * ptlocks because exclusive mmap_sem prevents deadlock.
1496          */
1497         old_ptl = __pmd_trans_huge_lock(old_pmd, vma);
1498         if (old_ptl) {
1499                 new_ptl = pmd_lockptr(mm, new_pmd);
1500                 if (new_ptl != old_ptl)
1501                         spin_lock_nested(new_ptl, SINGLE_DEPTH_NESTING);
1502                 pmd = pmdp_huge_get_and_clear(mm, old_addr, old_pmd);
1503                 if (pmd_present(pmd) && pmd_dirty(pmd))
1504                         force_flush = true;
1505                 VM_BUG_ON(!pmd_none(*new_pmd));
1506
1507                 if (pmd_move_must_withdraw(new_ptl, old_ptl, vma)) {
1508                         pgtable_t pgtable;
1509                         pgtable = pgtable_trans_huge_withdraw(mm, old_pmd);
1510                         pgtable_trans_huge_deposit(mm, new_pmd, pgtable);
1511                 }
1512                 set_pmd_at(mm, new_addr, new_pmd, pmd_mksoft_dirty(pmd));
1513                 if (new_ptl != old_ptl)
1514                         spin_unlock(new_ptl);
1515                 if (force_flush)
1516                         flush_tlb_range(vma, old_addr, old_addr + PMD_SIZE);
1517                 else
1518                         *need_flush = true;
1519                 spin_unlock(old_ptl);
1520                 return true;
1521         }
1522         return false;
1523 }
1524
1525 /*
1526  * Returns
1527  *  - 0 if PMD could not be locked
1528  *  - 1 if PMD was locked but protections unchange and TLB flush unnecessary
1529  *  - HPAGE_PMD_NR is protections changed and TLB flush necessary
1530  */
1531 int change_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
1532                 unsigned long addr, pgprot_t newprot, int prot_numa)
1533 {
1534         struct mm_struct *mm = vma->vm_mm;
1535         spinlock_t *ptl;
1536         int ret = 0;
1537
1538         ptl = __pmd_trans_huge_lock(pmd, vma);
1539         if (ptl) {
1540                 pmd_t entry;
1541                 bool preserve_write = prot_numa && pmd_write(*pmd);
1542                 ret = 1;
1543
1544                 /*
1545                  * Avoid trapping faults against the zero page. The read-only
1546                  * data is likely to be read-cached on the local CPU and
1547                  * local/remote hits to the zero page are not interesting.
1548                  */
1549                 if (prot_numa && is_huge_zero_pmd(*pmd)) {
1550                         spin_unlock(ptl);
1551                         return ret;
1552                 }
1553
1554                 if (!prot_numa || !pmd_protnone(*pmd)) {
1555                         entry = pmdp_huge_get_and_clear_notify(mm, addr, pmd);
1556                         entry = pmd_modify(entry, newprot);
1557                         if (preserve_write)
1558                                 entry = pmd_mkwrite(entry);
1559                         ret = HPAGE_PMD_NR;
1560                         set_pmd_at(mm, addr, pmd, entry);
1561                         BUG_ON(vma_is_anonymous(vma) && !preserve_write &&
1562                                         pmd_write(entry));
1563                 }
1564                 spin_unlock(ptl);
1565         }
1566
1567         return ret;
1568 }
1569
1570 /*
1571  * Returns page table lock pointer if a given pmd maps a thp, NULL otherwise.
1572  *
1573  * Note that if it returns page table lock pointer, this routine returns without
1574  * unlocking page table lock. So callers must unlock it.
1575  */
1576 spinlock_t *__pmd_trans_huge_lock(pmd_t *pmd, struct vm_area_struct *vma)
1577 {
1578         spinlock_t *ptl;
1579         ptl = pmd_lock(vma->vm_mm, pmd);
1580         if (likely(pmd_trans_huge(*pmd) || pmd_devmap(*pmd)))
1581                 return ptl;
1582         spin_unlock(ptl);
1583         return NULL;
1584 }
1585
1586 static void __split_huge_zero_page_pmd(struct vm_area_struct *vma,
1587                 unsigned long haddr, pmd_t *pmd)
1588 {
1589         struct mm_struct *mm = vma->vm_mm;
1590         pgtable_t pgtable;
1591         pmd_t _pmd;
1592         int i;
1593
1594         /* leave pmd empty until pte is filled */
1595         pmdp_huge_clear_flush_notify(vma, haddr, pmd);
1596
1597         pgtable = pgtable_trans_huge_withdraw(mm, pmd);
1598         pmd_populate(mm, &_pmd, pgtable);
1599
1600         for (i = 0; i < HPAGE_PMD_NR; i++, haddr += PAGE_SIZE) {
1601                 pte_t *pte, entry;
1602                 entry = pfn_pte(my_zero_pfn(haddr), vma->vm_page_prot);
1603                 entry = pte_mkspecial(entry);
1604                 pte = pte_offset_map(&_pmd, haddr);
1605                 VM_BUG_ON(!pte_none(*pte));
1606                 set_pte_at(mm, haddr, pte, entry);
1607                 pte_unmap(pte);
1608         }
1609         smp_wmb(); /* make pte visible before pmd */
1610         pmd_populate(mm, pmd, pgtable);
1611 }
1612
1613 static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
1614                 unsigned long haddr, bool freeze)
1615 {
1616         struct mm_struct *mm = vma->vm_mm;
1617         struct page *page;
1618         pgtable_t pgtable;
1619         pmd_t _pmd;
1620         bool young, write, dirty, soft_dirty;
1621         unsigned long addr;
1622         int i;
1623
1624         VM_BUG_ON(haddr & ~HPAGE_PMD_MASK);
1625         VM_BUG_ON_VMA(vma->vm_start > haddr, vma);
1626         VM_BUG_ON_VMA(vma->vm_end < haddr + HPAGE_PMD_SIZE, vma);
1627         VM_BUG_ON(!pmd_trans_huge(*pmd) && !pmd_devmap(*pmd));
1628
1629         count_vm_event(THP_SPLIT_PMD);
1630
1631         if (!vma_is_anonymous(vma)) {
1632                 _pmd = pmdp_huge_clear_flush_notify(vma, haddr, pmd);
1633                 /*
1634                  * We are going to unmap this huge page. So
1635                  * just go ahead and zap it
1636                  */
1637                 if (arch_needs_pgtable_deposit())
1638                         zap_deposited_table(mm, pmd);
1639                 if (vma_is_dax(vma))
1640                         return;
1641                 page = pmd_page(_pmd);
1642                 if (!PageReferenced(page) && pmd_young(_pmd))
1643                         SetPageReferenced(page);
1644                 page_remove_rmap(page, true);
1645                 put_page(page);
1646                 add_mm_counter(mm, MM_FILEPAGES, -HPAGE_PMD_NR);
1647                 return;
1648         } else if (is_huge_zero_pmd(*pmd)) {
1649                 return __split_huge_zero_page_pmd(vma, haddr, pmd);
1650         }
1651
1652         page = pmd_page(*pmd);
1653         VM_BUG_ON_PAGE(!page_count(page), page);
1654         page_ref_add(page, HPAGE_PMD_NR - 1);
1655         write = pmd_write(*pmd);
1656         young = pmd_young(*pmd);
1657         dirty = pmd_dirty(*pmd);
1658         soft_dirty = pmd_soft_dirty(*pmd);
1659
1660         pmdp_huge_split_prepare(vma, haddr, pmd);
1661         pgtable = pgtable_trans_huge_withdraw(mm, pmd);
1662         pmd_populate(mm, &_pmd, pgtable);
1663
1664         for (i = 0, addr = haddr; i < HPAGE_PMD_NR; i++, addr += PAGE_SIZE) {
1665                 pte_t entry, *pte;
1666                 /*
1667                  * Note that NUMA hinting access restrictions are not
1668                  * transferred to avoid any possibility of altering
1669                  * permissions across VMAs.
1670                  */
1671                 if (freeze) {
1672                         swp_entry_t swp_entry;
1673                         swp_entry = make_migration_entry(page + i, write);
1674                         entry = swp_entry_to_pte(swp_entry);
1675                         if (soft_dirty)
1676                                 entry = pte_swp_mksoft_dirty(entry);
1677                 } else {
1678                         entry = mk_pte(page + i, READ_ONCE(vma->vm_page_prot));
1679                         entry = maybe_mkwrite(entry, vma);
1680                         if (!write)
1681                                 entry = pte_wrprotect(entry);
1682                         if (!young)
1683                                 entry = pte_mkold(entry);
1684                         if (soft_dirty)
1685                                 entry = pte_mksoft_dirty(entry);
1686                 }
1687                 if (dirty)
1688                         SetPageDirty(page + i);
1689                 pte = pte_offset_map(&_pmd, addr);
1690                 BUG_ON(!pte_none(*pte));
1691                 set_pte_at(mm, addr, pte, entry);
1692                 atomic_inc(&page[i]._mapcount);
1693                 pte_unmap(pte);
1694         }
1695
1696         /*
1697          * Set PG_double_map before dropping compound_mapcount to avoid
1698          * false-negative page_mapped().
1699          */
1700         if (compound_mapcount(page) > 1 && !TestSetPageDoubleMap(page)) {
1701                 for (i = 0; i < HPAGE_PMD_NR; i++)
1702                         atomic_inc(&page[i]._mapcount);
1703         }
1704
1705         if (atomic_add_negative(-1, compound_mapcount_ptr(page))) {
1706                 /* Last compound_mapcount is gone. */
1707                 __dec_node_page_state(page, NR_ANON_THPS);
1708                 if (TestClearPageDoubleMap(page)) {
1709                         /* No need in mapcount reference anymore */
1710                         for (i = 0; i < HPAGE_PMD_NR; i++)
1711                                 atomic_dec(&page[i]._mapcount);
1712                 }
1713         }
1714
1715         smp_wmb(); /* make pte visible before pmd */
1716         /*
1717          * Up to this point the pmd is present and huge and userland has the
1718          * whole access to the hugepage during the split (which happens in
1719          * place). If we overwrite the pmd with the not-huge version pointing
1720          * to the pte here (which of course we could if all CPUs were bug
1721          * free), userland could trigger a small page size TLB miss on the
1722          * small sized TLB while the hugepage TLB entry is still established in
1723          * the huge TLB. Some CPU doesn't like that.
1724          * See http://support.amd.com/us/Processor_TechDocs/41322.pdf, Erratum
1725          * 383 on page 93. Intel should be safe but is also warns that it's
1726          * only safe if the permission and cache attributes of the two entries
1727          * loaded in the two TLB is identical (which should be the case here).
1728          * But it is generally safer to never allow small and huge TLB entries
1729          * for the same virtual address to be loaded simultaneously. So instead
1730          * of doing "pmd_populate(); flush_pmd_tlb_range();" we first mark the
1731          * current pmd notpresent (atomically because here the pmd_trans_huge
1732          * and pmd_trans_splitting must remain set at all times on the pmd
1733          * until the split is complete for this pmd), then we flush the SMP TLB
1734          * and finally we write the non-huge version of the pmd entry with
1735          * pmd_populate.
1736          */
1737         pmdp_invalidate(vma, haddr, pmd);
1738         pmd_populate(mm, pmd, pgtable);
1739
1740         if (freeze) {
1741                 for (i = 0; i < HPAGE_PMD_NR; i++) {
1742                         page_remove_rmap(page + i, false);
1743                         put_page(page + i);
1744                 }
1745         }
1746 }
1747
1748 void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
1749                 unsigned long address, bool freeze, struct page *page)
1750 {
1751         spinlock_t *ptl;
1752         struct mm_struct *mm = vma->vm_mm;
1753         unsigned long haddr = address & HPAGE_PMD_MASK;
1754
1755         mmu_notifier_invalidate_range_start(mm, haddr, haddr + HPAGE_PMD_SIZE);
1756         ptl = pmd_lock(mm, pmd);
1757
1758         /*
1759          * If caller asks to setup a migration entries, we need a page to check
1760          * pmd against. Otherwise we can end up replacing wrong page.
1761          */
1762         VM_BUG_ON(freeze && !page);
1763         if (page && page != pmd_page(*pmd))
1764                 goto out;
1765
1766         if (pmd_trans_huge(*pmd)) {
1767                 page = pmd_page(*pmd);
1768                 if (PageMlocked(page))
1769                         clear_page_mlock(page);
1770         } else if (!pmd_devmap(*pmd))
1771                 goto out;
1772         __split_huge_pmd_locked(vma, pmd, haddr, freeze);
1773 out:
1774         spin_unlock(ptl);
1775         mmu_notifier_invalidate_range_end(mm, haddr, haddr + HPAGE_PMD_SIZE);
1776 }
1777
1778 void split_huge_pmd_address(struct vm_area_struct *vma, unsigned long address,
1779                 bool freeze, struct page *page)
1780 {
1781         pgd_t *pgd;
1782         pud_t *pud;
1783         pmd_t *pmd;
1784
1785         pgd = pgd_offset(vma->vm_mm, address);
1786         if (!pgd_present(*pgd))
1787                 return;
1788
1789         pud = pud_offset(pgd, address);
1790         if (!pud_present(*pud))
1791                 return;
1792
1793         pmd = pmd_offset(pud, address);
1794
1795         __split_huge_pmd(vma, pmd, address, freeze, page);
1796 }
1797
1798 void vma_adjust_trans_huge(struct vm_area_struct *vma,
1799                              unsigned long start,
1800                              unsigned long end,
1801                              long adjust_next)
1802 {
1803         /*
1804          * If the new start address isn't hpage aligned and it could
1805          * previously contain an hugepage: check if we need to split
1806          * an huge pmd.
1807          */
1808         if (start & ~HPAGE_PMD_MASK &&
1809             (start & HPAGE_PMD_MASK) >= vma->vm_start &&
1810             (start & HPAGE_PMD_MASK) + HPAGE_PMD_SIZE <= vma->vm_end)
1811                 split_huge_pmd_address(vma, start, false, NULL);
1812
1813         /*
1814          * If the new end address isn't hpage aligned and it could
1815          * previously contain an hugepage: check if we need to split
1816          * an huge pmd.
1817          */
1818         if (end & ~HPAGE_PMD_MASK &&
1819             (end & HPAGE_PMD_MASK) >= vma->vm_start &&
1820             (end & HPAGE_PMD_MASK) + HPAGE_PMD_SIZE <= vma->vm_end)
1821                 split_huge_pmd_address(vma, end, false, NULL);
1822
1823         /*
1824          * If we're also updating the vma->vm_next->vm_start, if the new
1825          * vm_next->vm_start isn't page aligned and it could previously
1826          * contain an hugepage: check if we need to split an huge pmd.
1827          */
1828         if (adjust_next > 0) {
1829                 struct vm_area_struct *next = vma->vm_next;
1830                 unsigned long nstart = next->vm_start;
1831                 nstart += adjust_next << PAGE_SHIFT;
1832                 if (nstart & ~HPAGE_PMD_MASK &&
1833                     (nstart & HPAGE_PMD_MASK) >= next->vm_start &&
1834                     (nstart & HPAGE_PMD_MASK) + HPAGE_PMD_SIZE <= next->vm_end)
1835                         split_huge_pmd_address(next, nstart, false, NULL);
1836         }
1837 }
1838
1839 static void freeze_page(struct page *page)
1840 {
1841         enum ttu_flags ttu_flags = TTU_IGNORE_MLOCK | TTU_IGNORE_ACCESS |
1842                 TTU_RMAP_LOCKED;
1843         int i, ret;
1844
1845         VM_BUG_ON_PAGE(!PageHead(page), page);
1846
1847         if (PageAnon(page))
1848                 ttu_flags |= TTU_MIGRATION;
1849
1850         /* We only need TTU_SPLIT_HUGE_PMD once */
1851         ret = try_to_unmap(page, ttu_flags | TTU_SPLIT_HUGE_PMD);
1852         for (i = 1; !ret && i < HPAGE_PMD_NR; i++) {
1853                 /* Cut short if the page is unmapped */
1854                 if (page_count(page) == 1)
1855                         return;
1856
1857                 ret = try_to_unmap(page + i, ttu_flags);
1858         }
1859         VM_BUG_ON_PAGE(ret, page + i - 1);
1860 }
1861
1862 static void unfreeze_page(struct page *page)
1863 {
1864         int i;
1865
1866         for (i = 0; i < HPAGE_PMD_NR; i++)
1867                 remove_migration_ptes(page + i, page + i, true);
1868 }
1869
1870 static void __split_huge_page_tail(struct page *head, int tail,
1871                 struct lruvec *lruvec, struct list_head *list)
1872 {
1873         struct page *page_tail = head + tail;
1874
1875         VM_BUG_ON_PAGE(atomic_read(&page_tail->_mapcount) != -1, page_tail);
1876         VM_BUG_ON_PAGE(page_ref_count(page_tail) != 0, page_tail);
1877
1878         /*
1879          * tail_page->_refcount is zero and not changing from under us. But
1880          * get_page_unless_zero() may be running from under us on the
1881          * tail_page. If we used atomic_set() below instead of atomic_inc() or
1882          * atomic_add(), we would then run atomic_set() concurrently with
1883          * get_page_unless_zero(), and atomic_set() is implemented in C not
1884          * using locked ops. spin_unlock on x86 sometime uses locked ops
1885          * because of PPro errata 66, 92, so unless somebody can guarantee
1886          * atomic_set() here would be safe on all archs (and not only on x86),
1887          * it's safer to use atomic_inc()/atomic_add().
1888          */
1889         if (PageAnon(head)) {
1890                 page_ref_inc(page_tail);
1891         } else {
1892                 /* Additional pin to radix tree */
1893                 page_ref_add(page_tail, 2);
1894         }
1895
1896         page_tail->flags &= ~PAGE_FLAGS_CHECK_AT_PREP;
1897         page_tail->flags |= (head->flags &
1898                         ((1L << PG_referenced) |
1899                          (1L << PG_swapbacked) |
1900                          (1L << PG_mlocked) |
1901                          (1L << PG_uptodate) |
1902                          (1L << PG_active) |
1903                          (1L << PG_locked) |
1904                          (1L << PG_unevictable) |
1905                          (1L << PG_dirty)));
1906
1907         /*
1908          * After clearing PageTail the gup refcount can be released.
1909          * Page flags also must be visible before we make the page non-compound.
1910          */
1911         smp_wmb();
1912
1913         clear_compound_head(page_tail);
1914
1915         if (page_is_young(head))
1916                 set_page_young(page_tail);
1917         if (page_is_idle(head))
1918                 set_page_idle(page_tail);
1919
1920         /* ->mapping in first tail page is compound_mapcount */
1921         VM_BUG_ON_PAGE(tail > 2 && page_tail->mapping != TAIL_MAPPING,
1922                         page_tail);
1923         page_tail->mapping = head->mapping;
1924
1925         page_tail->index = head->index + tail;
1926         page_cpupid_xchg_last(page_tail, page_cpupid_last(head));
1927         lru_add_page_tail(head, page_tail, lruvec, list);
1928 }
1929
1930 static void __split_huge_page(struct page *page, struct list_head *list,
1931                 unsigned long flags)
1932 {
1933         struct page *head = compound_head(page);
1934         struct zone *zone = page_zone(head);
1935         struct lruvec *lruvec;
1936         pgoff_t end = -1;
1937         int i;
1938
1939         lruvec = mem_cgroup_page_lruvec(head, zone->zone_pgdat);
1940
1941         /* complete memcg works before add pages to LRU */
1942         mem_cgroup_split_huge_fixup(head);
1943
1944         if (!PageAnon(page))
1945                 end = DIV_ROUND_UP(i_size_read(head->mapping->host), PAGE_SIZE);
1946
1947         for (i = HPAGE_PMD_NR - 1; i >= 1; i--) {
1948                 __split_huge_page_tail(head, i, lruvec, list);
1949                 /* Some pages can be beyond i_size: drop them from page cache */
1950                 if (head[i].index >= end) {
1951                         __ClearPageDirty(head + i);
1952                         __delete_from_page_cache(head + i, NULL);
1953                         if (IS_ENABLED(CONFIG_SHMEM) && PageSwapBacked(head))
1954                                 shmem_uncharge(head->mapping->host, 1);
1955                         put_page(head + i);
1956                 }
1957         }
1958
1959         ClearPageCompound(head);
1960         /* See comment in __split_huge_page_tail() */
1961         if (PageAnon(head)) {
1962                 page_ref_inc(head);
1963         } else {
1964                 /* Additional pin to radix tree */
1965                 page_ref_add(head, 2);
1966                 spin_unlock(&head->mapping->tree_lock);
1967         }
1968
1969         spin_unlock_irqrestore(zone_lru_lock(page_zone(head)), flags);
1970
1971         unfreeze_page(head);
1972
1973         for (i = 0; i < HPAGE_PMD_NR; i++) {
1974                 struct page *subpage = head + i;
1975                 if (subpage == page)
1976                         continue;
1977                 unlock_page(subpage);
1978
1979                 /*
1980                  * Subpages may be freed if there wasn't any mapping
1981                  * like if add_to_swap() is running on a lru page that
1982                  * had its mapping zapped. And freeing these pages
1983                  * requires taking the lru_lock so we do the put_page
1984                  * of the tail pages after the split is complete.
1985                  */
1986                 put_page(subpage);
1987         }
1988 }
1989
1990 int total_mapcount(struct page *page)
1991 {
1992         int i, compound, ret;
1993
1994         VM_BUG_ON_PAGE(PageTail(page), page);
1995
1996         if (likely(!PageCompound(page)))
1997                 return atomic_read(&page->_mapcount) + 1;
1998
1999         compound = compound_mapcount(page);
2000         if (PageHuge(page))
2001                 return compound;
2002         ret = compound;
2003         for (i = 0; i < HPAGE_PMD_NR; i++)
2004                 ret += atomic_read(&page[i]._mapcount) + 1;
2005         /* File pages has compound_mapcount included in _mapcount */
2006         if (!PageAnon(page))
2007                 return ret - compound * HPAGE_PMD_NR;
2008         if (PageDoubleMap(page))
2009                 ret -= HPAGE_PMD_NR;
2010         return ret;
2011 }
2012
2013 /*
2014  * This calculates accurately how many mappings a transparent hugepage
2015  * has (unlike page_mapcount() which isn't fully accurate). This full
2016  * accuracy is primarily needed to know if copy-on-write faults can
2017  * reuse the page and change the mapping to read-write instead of
2018  * copying them. At the same time this returns the total_mapcount too.
2019  *
2020  * The function returns the highest mapcount any one of the subpages
2021  * has. If the return value is one, even if different processes are
2022  * mapping different subpages of the transparent hugepage, they can
2023  * all reuse it, because each process is reusing a different subpage.
2024  *
2025  * The total_mapcount is instead counting all virtual mappings of the
2026  * subpages. If the total_mapcount is equal to "one", it tells the
2027  * caller all mappings belong to the same "mm" and in turn the
2028  * anon_vma of the transparent hugepage can become the vma->anon_vma
2029  * local one as no other process may be mapping any of the subpages.
2030  *
2031  * It would be more accurate to replace page_mapcount() with
2032  * page_trans_huge_mapcount(), however we only use
2033  * page_trans_huge_mapcount() in the copy-on-write faults where we
2034  * need full accuracy to avoid breaking page pinning, because
2035  * page_trans_huge_mapcount() is slower than page_mapcount().
2036  */
2037 int page_trans_huge_mapcount(struct page *page, int *total_mapcount)
2038 {
2039         int i, ret, _total_mapcount, mapcount;
2040
2041         /* hugetlbfs shouldn't call it */
2042         VM_BUG_ON_PAGE(PageHuge(page), page);
2043
2044         if (likely(!PageTransCompound(page))) {
2045                 mapcount = atomic_read(&page->_mapcount) + 1;
2046                 if (total_mapcount)
2047                         *total_mapcount = mapcount;
2048                 return mapcount;
2049         }
2050
2051         page = compound_head(page);
2052
2053         _total_mapcount = ret = 0;
2054         for (i = 0; i < HPAGE_PMD_NR; i++) {
2055                 mapcount = atomic_read(&page[i]._mapcount) + 1;
2056                 ret = max(ret, mapcount);
2057                 _total_mapcount += mapcount;
2058         }
2059         if (PageDoubleMap(page)) {
2060                 ret -= 1;
2061                 _total_mapcount -= HPAGE_PMD_NR;
2062         }
2063         mapcount = compound_mapcount(page);
2064         ret += mapcount;
2065         _total_mapcount += mapcount;
2066         if (total_mapcount)
2067                 *total_mapcount = _total_mapcount;
2068         return ret;
2069 }
2070
2071 /*
2072  * This function splits huge page into normal pages. @page can point to any
2073  * subpage of huge page to split. Split doesn't change the position of @page.
2074  *
2075  * Only caller must hold pin on the @page, otherwise split fails with -EBUSY.
2076  * The huge page must be locked.
2077  *
2078  * If @list is null, tail pages will be added to LRU list, otherwise, to @list.
2079  *
2080  * Both head page and tail pages will inherit mapping, flags, and so on from
2081  * the hugepage.
2082  *
2083  * GUP pin and PG_locked transferred to @page. Rest subpages can be freed if
2084  * they are not mapped.
2085  *
2086  * Returns 0 if the hugepage is split successfully.
2087  * Returns -EBUSY if the page is pinned or if anon_vma disappeared from under
2088  * us.
2089  */
2090 int split_huge_page_to_list(struct page *page, struct list_head *list)
2091 {
2092         struct page *head = compound_head(page);
2093         struct pglist_data *pgdata = NODE_DATA(page_to_nid(head));
2094         struct anon_vma *anon_vma = NULL;
2095         struct address_space *mapping = NULL;
2096         int count, mapcount, extra_pins, ret;
2097         bool mlocked;
2098         unsigned long flags;
2099
2100         VM_BUG_ON_PAGE(is_huge_zero_page(page), page);
2101         VM_BUG_ON_PAGE(!PageLocked(page), page);
2102         VM_BUG_ON_PAGE(!PageSwapBacked(page), page);
2103         VM_BUG_ON_PAGE(!PageCompound(page), page);
2104
2105         if (PageAnon(head)) {
2106                 /*
2107                  * The caller does not necessarily hold an mmap_sem that would
2108                  * prevent the anon_vma disappearing so we first we take a
2109                  * reference to it and then lock the anon_vma for write. This
2110                  * is similar to page_lock_anon_vma_read except the write lock
2111                  * is taken to serialise against parallel split or collapse
2112                  * operations.
2113                  */
2114                 anon_vma = page_get_anon_vma(head);
2115                 if (!anon_vma) {
2116                         ret = -EBUSY;
2117                         goto out;
2118                 }
2119                 extra_pins = 0;
2120                 mapping = NULL;
2121                 anon_vma_lock_write(anon_vma);
2122         } else {
2123                 mapping = head->mapping;
2124
2125                 /* Truncated ? */
2126                 if (!mapping) {
2127                         ret = -EBUSY;
2128                         goto out;
2129                 }
2130
2131                 /* Addidional pins from radix tree */
2132                 extra_pins = HPAGE_PMD_NR;
2133                 anon_vma = NULL;
2134                 i_mmap_lock_read(mapping);
2135         }
2136
2137         /*
2138          * Racy check if we can split the page, before freeze_page() will
2139          * split PMDs
2140          */
2141         if (total_mapcount(head) != page_count(head) - extra_pins - 1) {
2142                 ret = -EBUSY;
2143                 goto out_unlock;
2144         }
2145
2146         mlocked = PageMlocked(page);
2147         freeze_page(head);
2148         VM_BUG_ON_PAGE(compound_mapcount(head), head);
2149
2150         /* Make sure the page is not on per-CPU pagevec as it takes pin */
2151         if (mlocked)
2152                 lru_add_drain();
2153
2154         /* prevent PageLRU to go away from under us, and freeze lru stats */
2155         spin_lock_irqsave(zone_lru_lock(page_zone(head)), flags);
2156
2157         if (mapping) {
2158                 void **pslot;
2159
2160                 spin_lock(&mapping->tree_lock);
2161                 pslot = radix_tree_lookup_slot(&mapping->page_tree,
2162                                 page_index(head));
2163                 /*
2164                  * Check if the head page is present in radix tree.
2165                  * We assume all tail are present too, if head is there.
2166                  */
2167                 if (radix_tree_deref_slot_protected(pslot,
2168                                         &mapping->tree_lock) != head)
2169                         goto fail;
2170         }
2171
2172         /* Prevent deferred_split_scan() touching ->_refcount */
2173         spin_lock(&pgdata->split_queue_lock);
2174         count = page_count(head);
2175         mapcount = total_mapcount(head);
2176         if (!mapcount && page_ref_freeze(head, 1 + extra_pins)) {
2177                 if (!list_empty(page_deferred_list(head))) {
2178                         pgdata->split_queue_len--;
2179                         list_del(page_deferred_list(head));
2180                 }
2181                 if (mapping)
2182                         __dec_node_page_state(page, NR_SHMEM_THPS);
2183                 spin_unlock(&pgdata->split_queue_lock);
2184                 __split_huge_page(page, list, flags);
2185                 ret = 0;
2186         } else {
2187                 if (IS_ENABLED(CONFIG_DEBUG_VM) && mapcount) {
2188                         pr_alert("total_mapcount: %u, page_count(): %u\n",
2189                                         mapcount, count);
2190                         if (PageTail(page))
2191                                 dump_page(head, NULL);
2192                         dump_page(page, "total_mapcount(head) > 0");
2193                         BUG();
2194                 }
2195                 spin_unlock(&pgdata->split_queue_lock);
2196 fail:           if (mapping)
2197                         spin_unlock(&mapping->tree_lock);
2198                 spin_unlock_irqrestore(zone_lru_lock(page_zone(head)), flags);
2199                 unfreeze_page(head);
2200                 ret = -EBUSY;
2201         }
2202
2203 out_unlock:
2204         if (anon_vma) {
2205                 anon_vma_unlock_write(anon_vma);
2206                 put_anon_vma(anon_vma);
2207         }
2208         if (mapping)
2209                 i_mmap_unlock_read(mapping);
2210 out:
2211         count_vm_event(!ret ? THP_SPLIT_PAGE : THP_SPLIT_PAGE_FAILED);
2212         return ret;
2213 }
2214
2215 void free_transhuge_page(struct page *page)
2216 {
2217         struct pglist_data *pgdata = NODE_DATA(page_to_nid(page));
2218         unsigned long flags;
2219
2220         spin_lock_irqsave(&pgdata->split_queue_lock, flags);
2221         if (!list_empty(page_deferred_list(page))) {
2222                 pgdata->split_queue_len--;
2223                 list_del(page_deferred_list(page));
2224         }
2225         spin_unlock_irqrestore(&pgdata->split_queue_lock, flags);
2226         free_compound_page(page);
2227 }
2228
2229 void deferred_split_huge_page(struct page *page)
2230 {
2231         struct pglist_data *pgdata = NODE_DATA(page_to_nid(page));
2232         unsigned long flags;
2233
2234         VM_BUG_ON_PAGE(!PageTransHuge(page), page);
2235
2236         spin_lock_irqsave(&pgdata->split_queue_lock, flags);
2237         if (list_empty(page_deferred_list(page))) {
2238                 count_vm_event(THP_DEFERRED_SPLIT_PAGE);
2239                 list_add_tail(page_deferred_list(page), &pgdata->split_queue);
2240                 pgdata->split_queue_len++;
2241         }
2242         spin_unlock_irqrestore(&pgdata->split_queue_lock, flags);
2243 }
2244
2245 static unsigned long deferred_split_count(struct shrinker *shrink,
2246                 struct shrink_control *sc)
2247 {
2248         struct pglist_data *pgdata = NODE_DATA(sc->nid);
2249         return ACCESS_ONCE(pgdata->split_queue_len);
2250 }
2251
2252 static unsigned long deferred_split_scan(struct shrinker *shrink,
2253                 struct shrink_control *sc)
2254 {
2255         struct pglist_data *pgdata = NODE_DATA(sc->nid);
2256         unsigned long flags;
2257         LIST_HEAD(list), *pos, *next;
2258         struct page *page;
2259         int split = 0;
2260
2261         spin_lock_irqsave(&pgdata->split_queue_lock, flags);
2262         /* Take pin on all head pages to avoid freeing them under us */
2263         list_for_each_safe(pos, next, &pgdata->split_queue) {
2264                 page = list_entry((void *)pos, struct page, mapping);
2265                 page = compound_head(page);
2266                 if (get_page_unless_zero(page)) {
2267                         list_move(page_deferred_list(page), &list);
2268                 } else {
2269                         /* We lost race with put_compound_page() */
2270                         list_del_init(page_deferred_list(page));
2271                         pgdata->split_queue_len--;
2272                 }
2273                 if (!--sc->nr_to_scan)
2274                         break;
2275         }
2276         spin_unlock_irqrestore(&pgdata->split_queue_lock, flags);
2277
2278         list_for_each_safe(pos, next, &list) {
2279                 page = list_entry((void *)pos, struct page, mapping);
2280                 lock_page(page);
2281                 /* split_huge_page() removes page from list on success */
2282                 if (!split_huge_page(page))
2283                         split++;
2284                 unlock_page(page);
2285                 put_page(page);
2286         }
2287
2288         spin_lock_irqsave(&pgdata->split_queue_lock, flags);
2289         list_splice_tail(&list, &pgdata->split_queue);
2290         spin_unlock_irqrestore(&pgdata->split_queue_lock, flags);
2291
2292         /*
2293          * Stop shrinker if we didn't split any page, but the queue is empty.
2294          * This can happen if pages were freed under us.
2295          */
2296         if (!split && list_empty(&pgdata->split_queue))
2297                 return SHRINK_STOP;
2298         return split;
2299 }
2300
2301 static struct shrinker deferred_split_shrinker = {
2302         .count_objects = deferred_split_count,
2303         .scan_objects = deferred_split_scan,
2304         .seeks = DEFAULT_SEEKS,
2305         .flags = SHRINKER_NUMA_AWARE,
2306 };
2307
2308 #ifdef CONFIG_DEBUG_FS
2309 static int split_huge_pages_set(void *data, u64 val)
2310 {
2311         struct zone *zone;
2312         struct page *page;
2313         unsigned long pfn, max_zone_pfn;
2314         unsigned long total = 0, split = 0;
2315
2316         if (val != 1)
2317                 return -EINVAL;
2318
2319         for_each_populated_zone(zone) {
2320                 max_zone_pfn = zone_end_pfn(zone);
2321                 for (pfn = zone->zone_start_pfn; pfn < max_zone_pfn; pfn++) {
2322                         if (!pfn_valid(pfn))
2323                                 continue;
2324
2325                         page = pfn_to_page(pfn);
2326                         if (!get_page_unless_zero(page))
2327                                 continue;
2328
2329                         if (zone != page_zone(page))
2330                                 goto next;
2331
2332                         if (!PageHead(page) || PageHuge(page) || !PageLRU(page))
2333                                 goto next;
2334
2335                         total++;
2336                         lock_page(page);
2337                         if (!split_huge_page(page))
2338                                 split++;
2339                         unlock_page(page);
2340 next:
2341                         put_page(page);
2342                 }
2343         }
2344
2345         pr_info("%lu of %lu THP split\n", split, total);
2346
2347         return 0;
2348 }
2349 DEFINE_SIMPLE_ATTRIBUTE(split_huge_pages_fops, NULL, split_huge_pages_set,
2350                 "%llu\n");
2351
2352 static int __init split_huge_pages_debugfs(void)
2353 {
2354         void *ret;
2355
2356         ret = debugfs_create_file("split_huge_pages", 0200, NULL, NULL,
2357                         &split_huge_pages_fops);
2358         if (!ret)
2359                 pr_warn("Failed to create split_huge_pages in debugfs");
2360         return 0;
2361 }
2362 late_initcall(split_huge_pages_debugfs);
2363 #endif