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 #ifdef CONFIG_DEBUG_VM
 289 static ssize_t debug_cow_show(struct kobject *kobj,
 290                                 struct kobj_attribute *attr, char *buf)
 291 {
 292         return single_hugepage_flag_show(kobj, attr, buf,
 293                                 TRANSPARENT_HUGEPAGE_DEBUG_COW_FLAG);
 294 }
 295 static ssize_t debug_cow_store(struct kobject *kobj,
 296                                struct kobj_attribute *attr,
 297                                const char *buf, size_t count)
 298 {
 299         return single_hugepage_flag_store(kobj, attr, buf, count,
 300                                  TRANSPARENT_HUGEPAGE_DEBUG_COW_FLAG);
 301 }
 302 static struct kobj_attribute debug_cow_attr =
 303         __ATTR(debug_cow, 0644, debug_cow_show, debug_cow_store);
 304 #endif /* CONFIG_DEBUG_VM */
 305
 306 static struct attribute *hugepage_attr[] = {
 307         &enabled_attr.attr,
 308         &defrag_attr.attr,
 309         &use_zero_page_attr.attr,
 310 #if defined(CONFIG_SHMEM) && defined(CONFIG_TRANSPARENT_HUGE_PAGECACHE)
 311         &shmem_enabled_attr.attr,
 312 #endif
 313 #ifdef CONFIG_DEBUG_VM
 314         &debug_cow_attr.attr,
 315 #endif
 316         NULL,
 317 };
 318
 319 static struct attribute_group hugepage_attr_group = {
 320         .attrs = hugepage_attr,
 321 };
 322
 323 static int __init hugepage_init_sysfs(struct kobject **hugepage_kobj)
 324 {
 325         int err;
 326
 327         *hugepage_kobj = kobject_create_and_add("transparent_hugepage", mm_kobj);
 328         if (unlikely(!*hugepage_kobj)) {
 329                 pr_err("failed to create transparent hugepage kobject\n");
 330                 return -ENOMEM;
 331         }
 332
 333         err = sysfs_create_group(*hugepage_kobj, &hugepage_attr_group);
 334         if (err) {
 335                 pr_err("failed to register transparent hugepage group\n");
 336                 goto delete_obj;
 337         }
 338
 339         err = sysfs_create_group(*hugepage_kobj, &khugepaged_attr_group);
 340         if (err) {
 341                 pr_err("failed to register transparent hugepage group\n");
 342                 goto remove_hp_group;
 343         }
 344
 345         return 0;
 346
 347 remove_hp_group:
 348         sysfs_remove_group(*hugepage_kobj, &hugepage_attr_group);
 349 delete_obj:
 350         kobject_put(*hugepage_kobj);
 351         return err;
 352 }
 353
 354 static void __init hugepage_exit_sysfs(struct kobject *hugepage_kobj)
 355 {
 356         sysfs_remove_group(hugepage_kobj, &khugepaged_attr_group);
 357         sysfs_remove_group(hugepage_kobj, &hugepage_attr_group);
 358         kobject_put(hugepage_kobj);
 359 }
 360 #else
 361 static inline int hugepage_init_sysfs(struct kobject **hugepage_kobj)
 362 {
 363         return 0;
 364 }
 365
 366 static inline void hugepage_exit_sysfs(struct kobject *hugepage_kobj)
 367 {
 368 }
 369 #endif /* CONFIG_SYSFS */
 370
 371 static int __init hugepage_init(void)
 372 {
 373         int err;
 374         struct kobject *hugepage_kobj;
 375
 376         if (!has_transparent_hugepage()) {
 377                 transparent_hugepage_flags = 0;
 378                 return -EINVAL;
 379         }
 380
 381         /*
 382          * hugepages can't be allocated by the buddy allocator
 383          */
 384         MAYBE_BUILD_BUG_ON(HPAGE_PMD_ORDER >= MAX_ORDER);
 385         /*
 386          * we use page->mapping and page->index in second tail page
 387          * as list_head: assuming THP order >= 2
 388          */
 389         MAYBE_BUILD_BUG_ON(HPAGE_PMD_ORDER < 2);
 390
 391         err = hugepage_init_sysfs(&hugepage_kobj);
 392         if (err)
 393                 goto err_sysfs;
 394
 395         err = khugepaged_init();
 396         if (err)
 397                 goto err_slab;
 398
 399         err = register_shrinker(&huge_zero_page_shrinker);
 400         if (err)
 401                 goto err_hzp_shrinker;
 402         err = register_shrinker(&deferred_split_shrinker);
 403         if (err)
 404                 goto err_split_shrinker;
 405
 406         /*
 407          * By default disable transparent hugepages on smaller systems,
 408          * where the extra memory used could hurt more than TLB overhead
 409          * is likely to save.  The admin can still enable it through /sys.
 410          */
 411         if (totalram_pages < (512 << (20 - PAGE_SHIFT))) {
 412                 transparent_hugepage_flags = 0;
 413                 return 0;
 414         }
 415
 416         err = start_stop_khugepaged();
 417         if (err)
 418                 goto err_khugepaged;
 419
 420         return 0;
 421 err_khugepaged:
 422         unregister_shrinker(&deferred_split_shrinker);
 423 err_split_shrinker:
 424         unregister_shrinker(&huge_zero_page_shrinker);
 425 err_hzp_shrinker:
 426         khugepaged_destroy();
 427 err_slab:
 428         hugepage_exit_sysfs(hugepage_kobj);
 429 err_sysfs:
 430         return err;
 431 }
 432 subsys_initcall(hugepage_init);
 433
 434 static int __init setup_transparent_hugepage(char *str)
 435 {
 436         int ret = 0;
 437         if (!str)
 438                 goto out;
 439         if (!strcmp(str, "always")) {
 440                 set_bit(TRANSPARENT_HUGEPAGE_FLAG,
 441                         &transparent_hugepage_flags);
 442                 clear_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG,
 443                           &transparent_hugepage_flags);
 444                 ret = 1;
 445         } else if (!strcmp(str, "madvise")) {
 446                 clear_bit(TRANSPARENT_HUGEPAGE_FLAG,
 447                           &transparent_hugepage_flags);
 448                 set_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG,
 449                         &transparent_hugepage_flags);
 450                 ret = 1;
 451         } else if (!strcmp(str, "never")) {
 452                 clear_bit(TRANSPARENT_HUGEPAGE_FLAG,
 453                           &transparent_hugepage_flags);
 454                 clear_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG,
 455                           &transparent_hugepage_flags);
 456                 ret = 1;
 457         }
 458 out:
 459         if (!ret)
 460                 pr_warn("transparent_hugepage= cannot parse, ignored\n");
 461         return ret;
 462 }
 463 __setup("transparent_hugepage=", setup_transparent_hugepage);
 464
 465 pmd_t maybe_pmd_mkwrite(pmd_t pmd, struct vm_area_struct *vma)
 466 {
 467         if (likely(vma->vm_flags & VM_WRITE))
 468                 pmd = pmd_mkwrite(pmd);
 469         return pmd;
 470 }
 471
 472 static inline struct list_head *page_deferred_list(struct page *page)
 473 {
 474         /*
 475          * ->lru in the tail pages is occupied by compound_head.
 476          * Let's use ->mapping + ->index in the second tail page as list_head.
 477          */
 478         return (struct list_head *)&page[2].mapping;
 479 }
 480
 481 void prep_transhuge_page(struct page *page)
 482 {
 483         /*
 484          * we use page->mapping and page->indexlru in second tail page
 485          * as list_head: assuming THP order >= 2
 486          */
 487
 488         INIT_LIST_HEAD(page_deferred_list(page));
 489         set_compound_page_dtor(page, TRANSHUGE_PAGE_DTOR);
 490 }
 491
 492 unsigned long __thp_get_unmapped_area(struct file *filp, unsigned long len,
 493                 loff_t off, unsigned long flags, unsigned long size)
 494 {
 495         unsigned long addr;
 496         loff_t off_end = off + len;
 497         loff_t off_align = round_up(off, size);
 498         unsigned long len_pad;
 499
 500         if (off_end <= off_align || (off_end - off_align) < size)
 501                 return 0;
 502
 503         len_pad = len + size;
 504         if (len_pad < len || (off + len_pad) < off)
 505                 return 0;
 506
 507         addr = current->mm->get_unmapped_area(filp, 0, len_pad,
 508                                               off >> PAGE_SHIFT, flags);
 509         if (IS_ERR_VALUE(addr))
 510                 return 0;
 511
 512         addr += (off - addr) & (size - 1);
 513         return addr;
 514 }
 515
 516 unsigned long thp_get_unmapped_area(struct file *filp, unsigned long addr,
 517                 unsigned long len, unsigned long pgoff, unsigned long flags)
 518 {
 519         loff_t off = (loff_t)pgoff << PAGE_SHIFT;
 520
 521         if (addr)
 522                 goto out;
 523         if (!IS_DAX(filp->f_mapping->host) || !IS_ENABLED(CONFIG_FS_DAX_PMD))
 524                 goto out;
 525
 526         addr = __thp_get_unmapped_area(filp, len, off, flags, PMD_SIZE);
 527         if (addr)
 528                 return addr;
 529
 530  out:
 531         return current->mm->get_unmapped_area(filp, addr, len, pgoff, flags);
 532 }
 533 EXPORT_SYMBOL_GPL(thp_get_unmapped_area);
 534
 535 static int __do_huge_pmd_anonymous_page(struct fault_env *fe, struct page *page,
 536                 gfp_t gfp)
 537 {
 538         struct vm_area_struct *vma = fe->vma;
 539         struct mem_cgroup *memcg;
 540         pgtable_t pgtable;
 541         unsigned long haddr = fe->address & HPAGE_PMD_MASK;
 542
 543         VM_BUG_ON_PAGE(!PageCompound(page), page);
 544
 545         if (mem_cgroup_try_charge(page, vma->vm_mm, gfp | __GFP_NORETRY, &memcg,
 546                                   true)) {
 547                 put_page(page);
 548                 count_vm_event(THP_FAULT_FALLBACK);
 549                 return VM_FAULT_FALLBACK;
 550         }
 551
 552         pgtable = pte_alloc_one(vma->vm_mm, haddr);
 553         if (unlikely(!pgtable)) {
 554                 mem_cgroup_cancel_charge(page, memcg, true);
 555                 put_page(page);
 556                 return VM_FAULT_OOM;
 557         }
 558
 559         clear_huge_page(page, haddr, HPAGE_PMD_NR);
 560         /*
 561          * The memory barrier inside __SetPageUptodate makes sure that
 562          * clear_huge_page writes become visible before the set_pmd_at()
 563          * write.
 564          */
 565         __SetPageUptodate(page);
 566
 567         fe->ptl = pmd_lock(vma->vm_mm, fe->pmd);
 568         if (unlikely(!pmd_none(*fe->pmd))) {
 569                 spin_unlock(fe->ptl);
 570                 mem_cgroup_cancel_charge(page, memcg, true);
 571                 put_page(page);
 572                 pte_free(vma->vm_mm, pgtable);
 573         } else {
 574                 pmd_t entry;
 575
 576                 /* Deliver the page fault to userland */
 577                 if (userfaultfd_missing(vma)) {
 578                         int ret;
 579
 580                         spin_unlock(fe->ptl);
 581                         mem_cgroup_cancel_charge(page, memcg, true);
 582                         put_page(page);
 583                         pte_free(vma->vm_mm, pgtable);
 584                         ret = handle_userfault(fe, VM_UFFD_MISSING);
 585                         VM_BUG_ON(ret & VM_FAULT_FALLBACK);
 586                         return ret;
 587                 }
 588
 589                 entry = mk_huge_pmd(page, vma->vm_page_prot);
 590                 entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
 591                 page_add_new_anon_rmap(page, vma, haddr, true);
 592                 mem_cgroup_commit_charge(page, memcg, false, true);
 593                 lru_cache_add_active_or_unevictable(page, vma);
 594                 pgtable_trans_huge_deposit(vma->vm_mm, fe->pmd, pgtable);
 595                 set_pmd_at(vma->vm_mm, haddr, fe->pmd, entry);
 596                 add_mm_counter(vma->vm_mm, MM_ANONPAGES, HPAGE_PMD_NR);
 597                 atomic_long_inc(&vma->vm_mm->nr_ptes);
 598                 spin_unlock(fe->ptl);
 599                 count_vm_event(THP_FAULT_ALLOC);
 600         }
 601
 602         return 0;
 603 }
 604
 605 /*
 606  * If THP defrag is set to always then directly reclaim/compact as necessary
 607  * If set to defer then do only background reclaim/compact and defer to khugepaged
 608  * If set to madvise and the VMA is flagged then directly reclaim/compact
 609  * When direct reclaim/compact is allowed, don't retry except for flagged VMA's
 610  */
 611 static inline gfp_t alloc_hugepage_direct_gfpmask(struct vm_area_struct *vma)
 612 {
 613         bool vma_madvised = !!(vma->vm_flags & VM_HUGEPAGE);
 614
 615         if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_REQ_MADV_FLAG,
 616                                 &transparent_hugepage_flags) && vma_madvised)
 617                 return GFP_TRANSHUGE;
 618         else if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_FLAG,
 619                                                 &transparent_hugepage_flags))
 620                 return GFP_TRANSHUGE_LIGHT | __GFP_KSWAPD_RECLAIM;
 621         else if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_DIRECT_FLAG,
 622                                                 &transparent_hugepage_flags))
 623                 return GFP_TRANSHUGE | (vma_madvised ? 0 : __GFP_NORETRY);
 624
 625         return GFP_TRANSHUGE_LIGHT;
 626 }
 627
 628 /* Caller must hold page table lock. */
 629 static bool set_huge_zero_page(pgtable_t pgtable, struct mm_struct *mm,
 630                 struct vm_area_struct *vma, unsigned long haddr, pmd_t *pmd,
 631                 struct page *zero_page)
 632 {
 633         pmd_t entry;
 634         if (!pmd_none(*pmd))
 635                 return false;
 636         entry = mk_pmd(zero_page, vma->vm_page_prot);
 637         entry = pmd_mkhuge(entry);
 638         if (pgtable)
 639                 pgtable_trans_huge_deposit(mm, pmd, pgtable);
 640         set_pmd_at(mm, haddr, pmd, entry);
 641         atomic_long_inc(&mm->nr_ptes);
 642         return true;
 643 }
 644
 645 int do_huge_pmd_anonymous_page(struct fault_env *fe)
 646 {
 647         struct vm_area_struct *vma = fe->vma;
 648         gfp_t gfp;
 649         struct page *page;
 650         unsigned long haddr = fe->address & HPAGE_PMD_MASK;
 651
 652         if (haddr < vma->vm_start || haddr + HPAGE_PMD_SIZE > vma->vm_end)
 653                 return VM_FAULT_FALLBACK;
 654         if (unlikely(anon_vma_prepare(vma)))
 655                 return VM_FAULT_OOM;
 656         if (unlikely(khugepaged_enter(vma, vma->vm_flags)))
 657                 return VM_FAULT_OOM;
 658         if (!(fe->flags & FAULT_FLAG_WRITE) &&
 659                         !mm_forbids_zeropage(vma->vm_mm) &&
 660                         transparent_hugepage_use_zero_page()) {
 661                 pgtable_t pgtable;
 662                 struct page *zero_page;
 663                 bool set;
 664                 int ret;
 665                 pgtable = pte_alloc_one(vma->vm_mm, haddr);
 666                 if (unlikely(!pgtable))
 667                         return VM_FAULT_OOM;
 668                 zero_page = mm_get_huge_zero_page(vma->vm_mm);
 669                 if (unlikely(!zero_page)) {
 670                         pte_free(vma->vm_mm, pgtable);
 671                         count_vm_event(THP_FAULT_FALLBACK);
 672                         return VM_FAULT_FALLBACK;
 673                 }
 674                 fe->ptl = pmd_lock(vma->vm_mm, fe->pmd);
 675                 ret = 0;
 676                 set = false;
 677                 if (pmd_none(*fe->pmd)) {
 678                         if (userfaultfd_missing(vma)) {
 679                                 spin_unlock(fe->ptl);
 680                                 ret = handle_userfault(fe, VM_UFFD_MISSING);
 681                                 VM_BUG_ON(ret & VM_FAULT_FALLBACK);
 682                         } else {
 683                                 set_huge_zero_page(pgtable, vma->vm_mm, vma,
 684                                                    haddr, fe->pmd, zero_page);
 685                                 spin_unlock(fe->ptl);
 686                                 set = true;
 687                         }
 688                 } else
 689                         spin_unlock(fe->ptl);
 690                 if (!set)
 691                         pte_free(vma->vm_mm, pgtable);
 692                 return ret;
 693         }
 694         gfp = alloc_hugepage_direct_gfpmask(vma);
 695         page = alloc_hugepage_vma(gfp, vma, haddr, HPAGE_PMD_ORDER);
 696         if (unlikely(!page)) {
 697                 count_vm_event(THP_FAULT_FALLBACK);
 698                 return VM_FAULT_FALLBACK;
 699         }
 700         prep_transhuge_page(page);
 701         return __do_huge_pmd_anonymous_page(fe, page, gfp);
 702 }
 703
 704 static void insert_pfn_pmd(struct vm_area_struct *vma, unsigned long addr,
 705                 pmd_t *pmd, pfn_t pfn, pgprot_t prot, bool write)
 706 {
 707         struct mm_struct *mm = vma->vm_mm;
 708         pmd_t entry;
 709         spinlock_t *ptl;
 710
 711         ptl = pmd_lock(mm, pmd);
 712         entry = pmd_mkhuge(pfn_t_pmd(pfn, prot));
 713         if (pfn_t_devmap(pfn))
 714                 entry = pmd_mkdevmap(entry);
 715         if (write) {
 716                 entry = pmd_mkyoung(pmd_mkdirty(entry));
 717                 entry = maybe_pmd_mkwrite(entry, vma);
 718         }
 719         set_pmd_at(mm, addr, pmd, entry);
 720         update_mmu_cache_pmd(vma, addr, pmd);
 721         spin_unlock(ptl);
 722 }
 723
 724 int vmf_insert_pfn_pmd(struct vm_area_struct *vma, unsigned long addr,
 725                         pmd_t *pmd, pfn_t pfn, bool write)
 726 {
 727         pgprot_t pgprot = vma->vm_page_prot;
 728         /*
 729          * If we had pmd_special, we could avoid all these restrictions,
 730          * but we need to be consistent with PTEs and architectures that
 731          * can't support a 'special' bit.
 732          */
 733         BUG_ON(!(vma->vm_flags & (VM_PFNMAP|VM_MIXEDMAP)));
 734         BUG_ON((vma->vm_flags & (VM_PFNMAP|VM_MIXEDMAP)) ==
 735                                                 (VM_PFNMAP|VM_MIXEDMAP));
 736         BUG_ON((vma->vm_flags & VM_PFNMAP) && is_cow_mapping(vma->vm_flags));
 737         BUG_ON(!pfn_t_devmap(pfn));
 738
 739         if (addr < vma->vm_start || addr >= vma->vm_end)
 740                 return VM_FAULT_SIGBUS;
 741         if (track_pfn_insert(vma, &pgprot, pfn))
 742                 return VM_FAULT_SIGBUS;
 743         insert_pfn_pmd(vma, addr, pmd, pfn, pgprot, write);
 744         return VM_FAULT_NOPAGE;
 745 }
 746 EXPORT_SYMBOL_GPL(vmf_insert_pfn_pmd);
 747
 748 static void touch_pmd(struct vm_area_struct *vma, unsigned long addr,
 749                 pmd_t *pmd, int flags)
 750 {
 751         pmd_t _pmd;
 752
 753         _pmd = pmd_mkyoung(*pmd);
 754         if (flags & FOLL_WRITE)
 755                 _pmd = pmd_mkdirty(_pmd);
 756         if (pmdp_set_access_flags(vma, addr & HPAGE_PMD_MASK,
 757                                 pmd, _pmd, flags & FOLL_WRITE))
 758                 update_mmu_cache_pmd(vma, addr, pmd);
 759 }
 760
 761 struct page *follow_devmap_pmd(struct vm_area_struct *vma, unsigned long addr,
 762                 pmd_t *pmd, int flags)
 763 {
 764         unsigned long pfn = pmd_pfn(*pmd);
 765         struct mm_struct *mm = vma->vm_mm;
 766         struct dev_pagemap *pgmap;
 767         struct page *page;
 768
 769         assert_spin_locked(pmd_lockptr(mm, pmd));
 770
 771         /*
 772          * When we COW a devmap PMD entry, we split it into PTEs, so we should
 773          * not be in this function with `flags & FOLL_COW` set.
 774          */
 775         WARN_ONCE(flags & FOLL_COW, "mm: In follow_devmap_pmd with FOLL_COW set");
 776
 777         if (flags & FOLL_WRITE && !pmd_write(*pmd))
 778                 return NULL;
 779
 780         if (pmd_present(*pmd) && pmd_devmap(*pmd))
 781                 /* pass */;
 782         else
 783                 return NULL;
 784
 785         if (flags & FOLL_TOUCH)
 786                 touch_pmd(vma, addr, pmd, flags);
 787
 788         /*
 789          * device mapped pages can only be returned if the
 790          * caller will manage the page reference count.
 791          */
 792         if (!(flags & FOLL_GET))
 793                 return ERR_PTR(-EEXIST);
 794
 795         pfn += (addr & ~PMD_MASK) >> PAGE_SHIFT;
 796         pgmap = get_dev_pagemap(pfn, NULL);
 797         if (!pgmap)
 798                 return ERR_PTR(-EFAULT);
 799         page = pfn_to_page(pfn);
 800         get_page(page);
 801         put_dev_pagemap(pgmap);
 802
 803         return page;
 804 }
 805
 806 int copy_huge_pmd(struct mm_struct *dst_mm, struct mm_struct *src_mm,
 807                   pmd_t *dst_pmd, pmd_t *src_pmd, unsigned long addr,
 808                   struct vm_area_struct *vma)
 809 {
 810         spinlock_t *dst_ptl, *src_ptl;
 811         struct page *src_page;
 812         pmd_t pmd;
 813         pgtable_t pgtable = NULL;
 814         int ret = -ENOMEM;
 815
 816         /* Skip if can be re-fill on fault */
 817         if (!vma_is_anonymous(vma))
 818                 return 0;
 819
 820         pgtable = pte_alloc_one(dst_mm, addr);
 821         if (unlikely(!pgtable))
 822                 goto out;
 823
 824         dst_ptl = pmd_lock(dst_mm, dst_pmd);
 825         src_ptl = pmd_lockptr(src_mm, src_pmd);
 826         spin_lock_nested(src_ptl, SINGLE_DEPTH_NESTING);
 827
 828         ret = -EAGAIN;
 829         pmd = *src_pmd;
 830         if (unlikely(!pmd_trans_huge(pmd))) {
 831                 pte_free(dst_mm, pgtable);
 832                 goto out_unlock;
 833         }
 834         /*
 835          * When page table lock is held, the huge zero pmd should not be
 836          * under splitting since we don't split the page itself, only pmd to
 837          * a page table.
 838          */
 839         if (is_huge_zero_pmd(pmd)) {
 840                 struct page *zero_page;
 841                 /*
 842                  * get_huge_zero_page() will never allocate a new page here,
 843                  * since we already have a zero page to copy. It just takes a
 844                  * reference.
 845                  */
 846                 zero_page = mm_get_huge_zero_page(dst_mm);
 847                 set_huge_zero_page(pgtable, dst_mm, vma, addr, dst_pmd,
 848                                 zero_page);
 849                 ret = 0;
 850                 goto out_unlock;
 851         }
 852
 853         src_page = pmd_page(pmd);
 854         VM_BUG_ON_PAGE(!PageHead(src_page), src_page);
 855         get_page(src_page);
 856         page_dup_rmap(src_page, true);
 857         add_mm_counter(dst_mm, MM_ANONPAGES, HPAGE_PMD_NR);
 858         atomic_long_inc(&dst_mm->nr_ptes);
 859         pgtable_trans_huge_deposit(dst_mm, dst_pmd, pgtable);
 860
 861         pmdp_set_wrprotect(src_mm, addr, src_pmd);
 862         pmd = pmd_mkold(pmd_wrprotect(pmd));
 863         set_pmd_at(dst_mm, addr, dst_pmd, pmd);
 864
 865         ret = 0;
 866 out_unlock:
 867         spin_unlock(src_ptl);
 868         spin_unlock(dst_ptl);
 869 out:
 870         return ret;
 871 }
 872
 873 void huge_pmd_set_accessed(struct fault_env *fe, pmd_t orig_pmd)
 874 {
 875         pmd_t entry;
 876         unsigned long haddr;
 877         bool write = fe->flags & FAULT_FLAG_WRITE;
 878
 879         fe->ptl = pmd_lock(fe->vma->vm_mm, fe->pmd);
 880         if (unlikely(!pmd_same(*fe->pmd, orig_pmd)))
 881                 goto unlock;
 882
 883         entry = pmd_mkyoung(orig_pmd);
 884         if (write)
 885                 entry = pmd_mkdirty(entry);
 886         haddr = fe->address & HPAGE_PMD_MASK;
 887         if (pmdp_set_access_flags(fe->vma, haddr, fe->pmd, entry, write))
 888                 update_mmu_cache_pmd(fe->vma, fe->address, fe->pmd);
 889
 890 unlock:
 891         spin_unlock(fe->ptl);
 892 }
 893
 894 static int do_huge_pmd_wp_page_fallback(struct fault_env *fe, pmd_t orig_pmd,
 895                 struct page *page)
 896 {
 897         struct vm_area_struct *vma = fe->vma;
 898         unsigned long haddr = fe->address & HPAGE_PMD_MASK;
 899         struct mem_cgroup *memcg;
 900         pgtable_t pgtable;
 901         pmd_t _pmd;
 902         int ret = 0, i;
 903         struct page **pages;
 904         unsigned long mmun_start;       /* For mmu_notifiers */
 905         unsigned long mmun_end;         /* For mmu_notifiers */
 906
 907         pages = kmalloc(sizeof(struct page *) * HPAGE_PMD_NR,
 908                         GFP_KERNEL);
 909         if (unlikely(!pages)) {
 910                 ret |= VM_FAULT_OOM;
 911                 goto out;
 912         }
 913
 914         for (i = 0; i < HPAGE_PMD_NR; i++) {
 915                 pages[i] = alloc_page_vma_node(GFP_HIGHUSER_MOVABLE |
 916                                                __GFP_OTHER_NODE, vma,
 917                                                fe->address, page_to_nid(page));
 918                 if (unlikely(!pages[i] ||
 919                              mem_cgroup_try_charge(pages[i], vma->vm_mm,
 920                                      GFP_KERNEL, &memcg, false))) {
 921                         if (pages[i])
 922                                 put_page(pages[i]);
 923                         while (--i >= 0) {
 924                                 memcg = (void *)page_private(pages[i]);
 925                                 set_page_private(pages[i], 0);
 926                                 mem_cgroup_cancel_charge(pages[i], memcg,
 927                                                 false);
 928                                 put_page(pages[i]);
 929                         }
 930                         kfree(pages);
 931                         ret |= VM_FAULT_OOM;
 932                         goto out;
 933                 }
 934                 set_page_private(pages[i], (unsigned long)memcg);
 935         }
 936
 937         for (i = 0; i < HPAGE_PMD_NR; i++) {
 938                 copy_user_highpage(pages[i], page + i,
 939                                    haddr + PAGE_SIZE * i, vma);
 940                 __SetPageUptodate(pages[i]);
 941                 cond_resched();
 942         }
 943
 944         mmun_start = haddr;
 945         mmun_end   = haddr + HPAGE_PMD_SIZE;
 946         mmu_notifier_invalidate_range_start(vma->vm_mm, mmun_start, mmun_end);
 947
 948         fe->ptl = pmd_lock(vma->vm_mm, fe->pmd);
 949         if (unlikely(!pmd_same(*fe->pmd, orig_pmd)))
 950                 goto out_free_pages;
 951         VM_BUG_ON_PAGE(!PageHead(page), page);
 952
 953         pmdp_huge_clear_flush_notify(vma, haddr, fe->pmd);
 954         /* leave pmd empty until pte is filled */
 955
 956         pgtable = pgtable_trans_huge_withdraw(vma->vm_mm, fe->pmd);
 957         pmd_populate(vma->vm_mm, &_pmd, pgtable);
 958
 959         for (i = 0; i < HPAGE_PMD_NR; i++, haddr += PAGE_SIZE) {
 960                 pte_t entry;
 961                 entry = mk_pte(pages[i], vma->vm_page_prot);
 962                 entry = maybe_mkwrite(pte_mkdirty(entry), vma);
 963                 memcg = (void *)page_private(pages[i]);
 964                 set_page_private(pages[i], 0);
 965                 page_add_new_anon_rmap(pages[i], fe->vma, haddr, false);
 966                 mem_cgroup_commit_charge(pages[i], memcg, false, false);
 967                 lru_cache_add_active_or_unevictable(pages[i], vma);
 968                 fe->pte = pte_offset_map(&_pmd, haddr);
 969                 VM_BUG_ON(!pte_none(*fe->pte));
 970                 set_pte_at(vma->vm_mm, haddr, fe->pte, entry);
 971                 pte_unmap(fe->pte);
 972         }
 973         kfree(pages);
 974
 975         smp_wmb(); /* make pte visible before pmd */
 976         pmd_populate(vma->vm_mm, fe->pmd, pgtable);
 977         page_remove_rmap(page, true);
 978         spin_unlock(fe->ptl);
 979
 980         mmu_notifier_invalidate_range_end(vma->vm_mm, mmun_start, mmun_end);
 981
 982         ret |= VM_FAULT_WRITE;
 983         put_page(page);
 984
 985 out:
 986         return ret;
 987
 988 out_free_pages:
 989         spin_unlock(fe->ptl);
 990         mmu_notifier_invalidate_range_end(vma->vm_mm, mmun_start, mmun_end);
 991         for (i = 0; i < HPAGE_PMD_NR; i++) {
 992                 memcg = (void *)page_private(pages[i]);
 993                 set_page_private(pages[i], 0);
 994                 mem_cgroup_cancel_charge(pages[i], memcg, false);
 995                 put_page(pages[i]);
 996         }
 997         kfree(pages);
 998         goto out;
 999 }
1000
1001 int do_huge_pmd_wp_page(struct fault_env *fe, pmd_t orig_pmd)
1002 {
1003         struct vm_area_struct *vma = fe->vma;
1004         struct page *page = NULL, *new_page;
1005         struct mem_cgroup *memcg;
1006         unsigned long haddr = fe->address & HPAGE_PMD_MASK;
1007         unsigned long mmun_start;       /* For mmu_notifiers */
1008         unsigned long mmun_end;         /* For mmu_notifiers */
1009         gfp_t huge_gfp;                 /* for allocation and charge */
1010         int ret = 0;
1011
1012         fe->ptl = pmd_lockptr(vma->vm_mm, fe->pmd);
1013         VM_BUG_ON_VMA(!vma->anon_vma, vma);
1014         if (is_huge_zero_pmd(orig_pmd))
1015                 goto alloc;
1016         spin_lock(fe->ptl);
1017         if (unlikely(!pmd_same(*fe->pmd, orig_pmd)))
1018                 goto out_unlock;
1019
1020         page = pmd_page(orig_pmd);
1021         VM_BUG_ON_PAGE(!PageCompound(page) || !PageHead(page), page);
1022         /*
1023          * We can only reuse the page if nobody else maps the huge page or it's
1024          * part.
1025          */
1026         if (page_trans_huge_mapcount(page, NULL) == 1) {
1027                 pmd_t entry;
1028                 entry = pmd_mkyoung(orig_pmd);
1029                 entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
1030                 if (pmdp_set_access_flags(vma, haddr, fe->pmd, entry,  1))
1031                         update_mmu_cache_pmd(vma, fe->address, fe->pmd);
1032                 ret |= VM_FAULT_WRITE;
1033                 goto out_unlock;
1034         }
1035         get_page(page);
1036         spin_unlock(fe->ptl);
1037 alloc:
1038         if (transparent_hugepage_enabled(vma) &&
1039             !transparent_hugepage_debug_cow()) {
1040                 huge_gfp = alloc_hugepage_direct_gfpmask(vma);
1041                 new_page = alloc_hugepage_vma(huge_gfp, vma, haddr, HPAGE_PMD_ORDER);
1042         } else
1043                 new_page = NULL;
1044
1045         if (likely(new_page)) {
1046                 prep_transhuge_page(new_page);
1047         } else {
1048                 if (!page) {
1049                         split_huge_pmd(vma, fe->pmd, fe->address);
1050                         ret |= VM_FAULT_FALLBACK;
1051                 } else {
1052                         ret = do_huge_pmd_wp_page_fallback(fe, orig_pmd, page);
1053                         if (ret & VM_FAULT_OOM) {
1054                                 split_huge_pmd(vma, fe->pmd, fe->address);
1055                                 ret |= VM_FAULT_FALLBACK;
1056                         }
1057                         put_page(page);
1058                 }
1059                 count_vm_event(THP_FAULT_FALLBACK);
1060                 goto out;
1061         }
1062
1063         if (unlikely(mem_cgroup_try_charge(new_page, vma->vm_mm,
1064                                 huge_gfp | __GFP_NORETRY, &memcg, true))) {
1065                 put_page(new_page);
1066                 split_huge_pmd(vma, fe->pmd, fe->address);
1067                 if (page)
1068                         put_page(page);
1069                 ret |= VM_FAULT_FALLBACK;
1070                 count_vm_event(THP_FAULT_FALLBACK);
1071                 goto out;
1072         }
1073
1074         count_vm_event(THP_FAULT_ALLOC);
1075
1076         if (!page)
1077                 clear_huge_page(new_page, haddr, HPAGE_PMD_NR);
1078         else
1079                 copy_user_huge_page(new_page, page, haddr, vma, HPAGE_PMD_NR);
1080         __SetPageUptodate(new_page);
1081
1082         mmun_start = haddr;
1083         mmun_end   = haddr + HPAGE_PMD_SIZE;
1084         mmu_notifier_invalidate_range_start(vma->vm_mm, mmun_start, mmun_end);
1085
1086         spin_lock(fe->ptl);
1087         if (page)
1088                 put_page(page);
1089         if (unlikely(!pmd_same(*fe->pmd, orig_pmd))) {
1090                 spin_unlock(fe->ptl);
1091                 mem_cgroup_cancel_charge(new_page, memcg, true);
1092                 put_page(new_page);
1093                 goto out_mn;
1094         } else {
1095                 pmd_t entry;
1096                 entry = mk_huge_pmd(new_page, vma->vm_page_prot);
1097                 entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
1098                 pmdp_huge_clear_flush_notify(vma, haddr, fe->pmd);
1099                 page_add_new_anon_rmap(new_page, vma, haddr, true);
1100                 mem_cgroup_commit_charge(new_page, memcg, false, true);
1101                 lru_cache_add_active_or_unevictable(new_page, vma);
1102                 set_pmd_at(vma->vm_mm, haddr, fe->pmd, entry);
1103                 update_mmu_cache_pmd(vma, fe->address, fe->pmd);
1104                 if (!page) {
1105                         add_mm_counter(vma->vm_mm, MM_ANONPAGES, HPAGE_PMD_NR);
1106                 } else {
1107                         VM_BUG_ON_PAGE(!PageHead(page), page);
1108                         page_remove_rmap(page, true);
1109                         put_page(page);
1110                 }
1111                 ret |= VM_FAULT_WRITE;
1112         }
1113         spin_unlock(fe->ptl);
1114 out_mn:
1115         mmu_notifier_invalidate_range_end(vma->vm_mm, mmun_start, mmun_end);
1116 out:
1117         return ret;
1118 out_unlock:
1119         spin_unlock(fe->ptl);
1120         return ret;
1121 }
1122
1123 /*
1124  * FOLL_FORCE can write to even unwritable pmd's, but only
1125  * after we've gone through a COW cycle and they are dirty.
1126  */
1127 static inline bool can_follow_write_pmd(pmd_t pmd, unsigned int flags)
1128 {
1129         return pmd_write(pmd) ||
1130                ((flags & FOLL_FORCE) && (flags & FOLL_COW) && pmd_dirty(pmd));
1131 }
1132
1133 struct page *follow_trans_huge_pmd(struct vm_area_struct *vma,
1134                                    unsigned long addr,
1135                                    pmd_t *pmd,
1136                                    unsigned int flags)
1137 {
1138         struct mm_struct *mm = vma->vm_mm;
1139         struct page *page = NULL;
1140
1141         assert_spin_locked(pmd_lockptr(mm, pmd));
1142
1143         if (flags & FOLL_WRITE && !can_follow_write_pmd(*pmd, flags))
1144                 goto out;
1145
1146         /* Avoid dumping huge zero page */
1147         if ((flags & FOLL_DUMP) && is_huge_zero_pmd(*pmd))
1148                 return ERR_PTR(-EFAULT);
1149
1150         /* Full NUMA hinting faults to serialise migration in fault paths */
1151         if ((flags & FOLL_NUMA) && pmd_protnone(*pmd))
1152                 goto out;
1153
1154         page = pmd_page(*pmd);
1155         VM_BUG_ON_PAGE(!PageHead(page) && !is_zone_device_page(page), page);
1156         if (flags & FOLL_TOUCH)
1157                 touch_pmd(vma, addr, pmd, flags);
1158         if ((flags & FOLL_MLOCK) && (vma->vm_flags & VM_LOCKED)) {
1159                 /*
1160                  * We don't mlock() pte-mapped THPs. This way we can avoid
1161                  * leaking mlocked pages into non-VM_LOCKED VMAs.
1162                  *
1163                  * For anon THP:
1164                  *
1165                  * In most cases the pmd is the only mapping of the page as we
1166                  * break COW for the mlock() -- see gup_flags |= FOLL_WRITE for
1167                  * writable private mappings in populate_vma_page_range().
1168                  *
1169                  * The only scenario when we have the page shared here is if we
1170                  * mlocking read-only mapping shared over fork(). We skip
1171                  * mlocking such pages.
1172                  *
1173                  * For file THP:
1174                  *
1175                  * We can expect PageDoubleMap() to be stable under page lock:
1176                  * for file pages we set it in page_add_file_rmap(), which
1177                  * requires page to be locked.
1178                  */
1179
1180                 if (PageAnon(page) && compound_mapcount(page) != 1)
1181                         goto skip_mlock;
1182                 if (PageDoubleMap(page) || !page->mapping)
1183                         goto skip_mlock;
1184                 if (!trylock_page(page))
1185                         goto skip_mlock;
1186                 lru_add_drain();
1187                 if (page->mapping && !PageDoubleMap(page))
1188                         mlock_vma_page(page);
1189                 unlock_page(page);
1190         }
1191 skip_mlock:
1192         page += (addr & ~HPAGE_PMD_MASK) >> PAGE_SHIFT;
1193         VM_BUG_ON_PAGE(!PageCompound(page) && !is_zone_device_page(page), page);
1194         if (flags & FOLL_GET)
1195                 get_page(page);
1196
1197 out:
1198         return page;
1199 }
1200
1201 /* NUMA hinting page fault entry point for trans huge pmds */
1202 int do_huge_pmd_numa_page(struct fault_env *fe, pmd_t pmd)
1203 {
1204         struct vm_area_struct *vma = fe->vma;
1205         struct anon_vma *anon_vma = NULL;
1206         struct page *page;
1207         unsigned long haddr = fe->address & HPAGE_PMD_MASK;
1208         int page_nid = -1, this_nid = numa_node_id();
1209         int target_nid, last_cpupid = -1;
1210         bool page_locked;
1211         bool migrated = false;
1212         bool was_writable;
1213         int flags = 0;
1214
1215         fe->ptl = pmd_lock(vma->vm_mm, fe->pmd);
1216         if (unlikely(!pmd_same(pmd, *fe->pmd)))
1217                 goto out_unlock;
1218
1219         /*
1220          * If there are potential migrations, wait for completion and retry
1221          * without disrupting NUMA hinting information. Do not relock and
1222          * check_same as the page may no longer be mapped.
1223          */
1224         if (unlikely(pmd_trans_migrating(*fe->pmd))) {
1225                 page = pmd_page(*fe->pmd);
1226                 if (!get_page_unless_zero(page))
1227                         goto out_unlock;
1228                 spin_unlock(fe->ptl);
1229                 wait_on_page_locked(page);
1230                 put_page(page);
1231                 goto out;
1232         }
1233
1234         page = pmd_page(pmd);
1235         BUG_ON(is_huge_zero_page(page));
1236         page_nid = page_to_nid(page);
1237         last_cpupid = page_cpupid_last(page);
1238         count_vm_numa_event(NUMA_HINT_FAULTS);
1239         if (page_nid == this_nid) {
1240                 count_vm_numa_event(NUMA_HINT_FAULTS_LOCAL);
1241                 flags |= TNF_FAULT_LOCAL;
1242         }
1243
1244         /* See similar comment in do_numa_page for explanation */
1245         if (!pmd_write(pmd))
1246                 flags |= TNF_NO_GROUP;
1247
1248         /*
1249          * Acquire the page lock to serialise THP migrations but avoid dropping
1250          * page_table_lock if at all possible
1251          */
1252         page_locked = trylock_page(page);
1253         target_nid = mpol_misplaced(page, vma, haddr);
1254         if (target_nid == -1) {
1255                 /* If the page was locked, there are no parallel migrations */
1256                 if (page_locked)
1257                         goto clear_pmdnuma;
1258         }
1259
1260         /* Migration could have started since the pmd_trans_migrating check */
1261         if (!page_locked) {
1262                 page_nid = -1;
1263                 if (!get_page_unless_zero(page))
1264                         goto out_unlock;
1265                 spin_unlock(fe->ptl);
1266                 wait_on_page_locked(page);
1267                 put_page(page);
1268                 goto out;
1269         }
1270
1271         /*
1272          * Page is misplaced. Page lock serialises migrations. Acquire anon_vma
1273          * to serialises splits
1274          */
1275         get_page(page);
1276         spin_unlock(fe->ptl);
1277         anon_vma = page_lock_anon_vma_read(page);
1278
1279         /* Confirm the PMD did not change while page_table_lock was released */
1280         spin_lock(fe->ptl);
1281         if (unlikely(!pmd_same(pmd, *fe->pmd))) {
1282                 unlock_page(page);
1283                 put_page(page);
1284                 page_nid = -1;
1285                 goto out_unlock;
1286         }
1287
1288         /* Bail if we fail to protect against THP splits for any reason */
1289         if (unlikely(!anon_vma)) {
1290                 put_page(page);
1291                 page_nid = -1;
1292                 goto clear_pmdnuma;
1293         }
1294
1295         /*
1296          * Migrate the THP to the requested node, returns with page unlocked
1297          * and access rights restored.
1298          */
1299         spin_unlock(fe->ptl);
1300         migrated = migrate_misplaced_transhuge_page(vma->vm_mm, vma,
1301                                 fe->pmd, pmd, fe->address, page, target_nid);
1302         if (migrated) {
1303                 flags |= TNF_MIGRATED;
1304                 page_nid = target_nid;
1305         } else
1306                 flags |= TNF_MIGRATE_FAIL;
1307
1308         goto out;
1309 clear_pmdnuma:
1310         BUG_ON(!PageLocked(page));
1311         was_writable = pmd_write(pmd);
1312         pmd = pmd_modify(pmd, vma->vm_page_prot);
1313         pmd = pmd_mkyoung(pmd);
1314         if (was_writable)
1315                 pmd = pmd_mkwrite(pmd);
1316         set_pmd_at(vma->vm_mm, haddr, fe->pmd, pmd);
1317         update_mmu_cache_pmd(vma, fe->address, fe->pmd);
1318         unlock_page(page);
1319 out_unlock:
1320         spin_unlock(fe->ptl);
1321
1322 out:
1323         if (anon_vma)
1324                 page_unlock_anon_vma_read(anon_vma);
1325
1326         if (page_nid != -1)
1327                 task_numa_fault(last_cpupid, page_nid, HPAGE_PMD_NR, fe->flags);
1328
1329         return 0;
1330 }
1331
1332 /*
1333  * Return true if we do MADV_FREE successfully on entire pmd page.
1334  * Otherwise, return false.
1335  */
1336 bool madvise_free_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
1337                 pmd_t *pmd, unsigned long addr, unsigned long next)
1338 {
1339         spinlock_t *ptl;
1340         pmd_t orig_pmd;
1341         struct page *page;
1342         struct mm_struct *mm = tlb->mm;
1343         bool ret = false;
1344
1345         ptl = pmd_trans_huge_lock(pmd, vma);
1346         if (!ptl)
1347                 goto out_unlocked;
1348
1349         orig_pmd = *pmd;
1350         if (is_huge_zero_pmd(orig_pmd))
1351                 goto out;
1352
1353         page = pmd_page(orig_pmd);
1354         /*
1355          * If other processes are mapping this page, we couldn't discard
1356          * the page unless they all do MADV_FREE so let's skip the page.
1357          */
1358         if (page_mapcount(page) != 1)
1359                 goto out;
1360
1361         if (!trylock_page(page))
1362                 goto out;
1363
1364         /*
1365          * If user want to discard part-pages of THP, split it so MADV_FREE
1366          * will deactivate only them.
1367          */
1368         if (next - addr != HPAGE_PMD_SIZE) {
1369                 get_page(page);
1370                 spin_unlock(ptl);
1371                 split_huge_page(page);
1372                 unlock_page(page);
1373                 put_page(page);
1374                 goto out_unlocked;
1375         }
1376
1377         if (PageDirty(page))
1378                 ClearPageDirty(page);
1379         unlock_page(page);
1380
1381         if (PageActive(page))
1382                 deactivate_page(page);
1383
1384         if (pmd_young(orig_pmd) || pmd_dirty(orig_pmd)) {
1385                 pmdp_invalidate(vma, addr, pmd);
1386                 orig_pmd = pmd_mkold(orig_pmd);
1387                 orig_pmd = pmd_mkclean(orig_pmd);
1388
1389                 set_pmd_at(mm, addr, pmd, orig_pmd);
1390                 tlb_remove_pmd_tlb_entry(tlb, pmd, addr);
1391         }
1392         ret = true;
1393 out:
1394         spin_unlock(ptl);
1395 out_unlocked:
1396         return ret;
1397 }
1398
1399 int zap_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
1400                  pmd_t *pmd, unsigned long addr)
1401 {
1402         pmd_t orig_pmd;
1403         spinlock_t *ptl;
1404
1405         ptl = __pmd_trans_huge_lock(pmd, vma);
1406         if (!ptl)
1407                 return 0;
1408         /*
1409          * For architectures like ppc64 we look at deposited pgtable
1410          * when calling pmdp_huge_get_and_clear. So do the
1411          * pgtable_trans_huge_withdraw after finishing pmdp related
1412          * operations.
1413          */
1414         orig_pmd = pmdp_huge_get_and_clear_full(tlb->mm, addr, pmd,
1415                         tlb->fullmm);
1416         tlb_remove_pmd_tlb_entry(tlb, pmd, addr);
1417         if (vma_is_dax(vma)) {
1418                 spin_unlock(ptl);
1419                 if (is_huge_zero_pmd(orig_pmd))
1420                         tlb_remove_page(tlb, pmd_page(orig_pmd));
1421         } else if (is_huge_zero_pmd(orig_pmd)) {
1422                 pte_free(tlb->mm, pgtable_trans_huge_withdraw(tlb->mm, pmd));
1423                 atomic_long_dec(&tlb->mm->nr_ptes);
1424                 spin_unlock(ptl);
1425                 tlb_remove_page(tlb, pmd_page(orig_pmd));
1426         } else {
1427                 struct page *page = pmd_page(orig_pmd);
1428                 page_remove_rmap(page, true);
1429                 VM_BUG_ON_PAGE(page_mapcount(page) < 0, page);
1430                 VM_BUG_ON_PAGE(!PageHead(page), page);
1431                 if (PageAnon(page)) {
1432                         pgtable_t pgtable;
1433                         pgtable = pgtable_trans_huge_withdraw(tlb->mm, pmd);
1434                         pte_free(tlb->mm, pgtable);
1435                         atomic_long_dec(&tlb->mm->nr_ptes);
1436                         add_mm_counter(tlb->mm, MM_ANONPAGES, -HPAGE_PMD_NR);
1437                 } else {
1438                         add_mm_counter(tlb->mm, MM_FILEPAGES, -HPAGE_PMD_NR);
1439                 }
1440                 spin_unlock(ptl);
1441                 tlb_remove_page_size(tlb, page, HPAGE_PMD_SIZE);
1442         }
1443         return 1;
1444 }
1445
1446 bool move_huge_pmd(struct vm_area_struct *vma, unsigned long old_addr,
1447                   unsigned long new_addr, unsigned long old_end,
1448                   pmd_t *old_pmd, pmd_t *new_pmd, bool *need_flush)
1449 {
1450         spinlock_t *old_ptl, *new_ptl;
1451         pmd_t pmd;
1452         struct mm_struct *mm = vma->vm_mm;
1453         bool force_flush = false;
1454
1455         if ((old_addr & ~HPAGE_PMD_MASK) ||
1456             (new_addr & ~HPAGE_PMD_MASK) ||
1457             old_end - old_addr < HPAGE_PMD_SIZE)
1458                 return false;
1459
1460         /*
1461          * The destination pmd shouldn't be established, free_pgtables()
1462          * should have release it.
1463          */
1464         if (WARN_ON(!pmd_none(*new_pmd))) {
1465                 VM_BUG_ON(pmd_trans_huge(*new_pmd));
1466                 return false;
1467         }
1468
1469         /*
1470          * We don't have to worry about the ordering of src and dst
1471          * ptlocks because exclusive mmap_sem prevents deadlock.
1472          */
1473         old_ptl = __pmd_trans_huge_lock(old_pmd, vma);
1474         if (old_ptl) {
1475                 new_ptl = pmd_lockptr(mm, new_pmd);
1476                 if (new_ptl != old_ptl)
1477                         spin_lock_nested(new_ptl, SINGLE_DEPTH_NESTING);
1478                 pmd = pmdp_huge_get_and_clear(mm, old_addr, old_pmd);
1479                 if (pmd_present(pmd) && pmd_dirty(pmd))
1480                         force_flush = true;
1481                 VM_BUG_ON(!pmd_none(*new_pmd));
1482
1483                 if (pmd_move_must_withdraw(new_ptl, old_ptl) &&
1484                                 vma_is_anonymous(vma)) {
1485                         pgtable_t pgtable;
1486                         pgtable = pgtable_trans_huge_withdraw(mm, old_pmd);
1487                         pgtable_trans_huge_deposit(mm, new_pmd, pgtable);
1488                 }
1489                 set_pmd_at(mm, new_addr, new_pmd, pmd_mksoft_dirty(pmd));
1490                 if (new_ptl != old_ptl)
1491                         spin_unlock(new_ptl);
1492                 if (force_flush)
1493                         flush_tlb_range(vma, old_addr, old_addr + PMD_SIZE);
1494                 else
1495                         *need_flush = true;
1496                 spin_unlock(old_ptl);
1497                 return true;
1498         }
1499         return false;
1500 }
1501
1502 /*
1503  * Returns
1504  *  - 0 if PMD could not be locked
1505  *  - 1 if PMD was locked but protections unchange and TLB flush unnecessary
1506  *  - HPAGE_PMD_NR is protections changed and TLB flush necessary
1507  */
1508 int change_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
1509                 unsigned long addr, pgprot_t newprot, int prot_numa)
1510 {
1511         struct mm_struct *mm = vma->vm_mm;
1512         spinlock_t *ptl;
1513         pmd_t entry;
1514         bool preserve_write;
1515         int ret;
1516
1517         ptl = __pmd_trans_huge_lock(pmd, vma);
1518         if (!ptl)
1519                 return 0;
1520
1521         preserve_write = prot_numa && pmd_write(*pmd);
1522         ret = 1;
1523
1524         /*
1525          * Avoid trapping faults against the zero page. The read-only
1526          * data is likely to be read-cached on the local CPU and
1527          * local/remote hits to the zero page are not interesting.
1528          */
1529         if (prot_numa && is_huge_zero_pmd(*pmd))
1530                 goto unlock;
1531
1532         if (prot_numa && pmd_protnone(*pmd))
1533                 goto unlock;
1534
1535         /*
1536          * In case prot_numa, we are under down_read(mmap_sem). It's critical
1537          * to not clear pmd intermittently to avoid race with MADV_DONTNEED
1538          * which is also under down_read(mmap_sem):
1539          *
1540          *      CPU0:                           CPU1:
1541          *                              change_huge_pmd(prot_numa=1)
1542          *                               pmdp_huge_get_and_clear_notify()
1543          * madvise_dontneed()
1544          *  zap_pmd_range()
1545          *   pmd_trans_huge(*pmd) == 0 (without ptl)
1546          *   // skip the pmd
1547          *                               set_pmd_at();
1548          *                               // pmd is re-established
1549          *
1550          * The race makes MADV_DONTNEED miss the huge pmd and don't clear it
1551          * which may break userspace.
1552          *
1553          * pmdp_invalidate() is required to make sure we don't miss
1554          * dirty/young flags set by hardware.
1555          */
1556         entry = *pmd;
1557         pmdp_invalidate(vma, addr, pmd);
1558
1559         /*
1560          * Recover dirty/young flags.  It relies on pmdp_invalidate to not
1561          * corrupt them.
1562          */
1563         if (pmd_dirty(*pmd))
1564                 entry = pmd_mkdirty(entry);
1565         if (pmd_young(*pmd))
1566                 entry = pmd_mkyoung(entry);
1567
1568         entry = pmd_modify(entry, newprot);
1569         if (preserve_write)
1570                 entry = pmd_mkwrite(entry);
1571         ret = HPAGE_PMD_NR;
1572         set_pmd_at(mm, addr, pmd, entry);
1573         BUG_ON(vma_is_anonymous(vma) && !preserve_write && pmd_write(entry));
1574 unlock:
1575         spin_unlock(ptl);
1576         return ret;
1577 }
1578
1579 /*
1580  * Returns page table lock pointer if a given pmd maps a thp, NULL otherwise.
1581  *
1582  * Note that if it returns page table lock pointer, this routine returns without
1583  * unlocking page table lock. So callers must unlock it.
1584  */
1585 spinlock_t *__pmd_trans_huge_lock(pmd_t *pmd, struct vm_area_struct *vma)
1586 {
1587         spinlock_t *ptl;
1588         ptl = pmd_lock(vma->vm_mm, pmd);
1589         if (likely(pmd_trans_huge(*pmd) || pmd_devmap(*pmd)))
1590                 return ptl;
1591         spin_unlock(ptl);
1592         return NULL;
1593 }
1594
1595 static void __split_huge_zero_page_pmd(struct vm_area_struct *vma,
1596                 unsigned long haddr, pmd_t *pmd)
1597 {
1598         struct mm_struct *mm = vma->vm_mm;
1599         pgtable_t pgtable;
1600         pmd_t _pmd;
1601         int i;
1602
1603         /* leave pmd empty until pte is filled */
1604         pmdp_huge_clear_flush_notify(vma, haddr, pmd);
1605
1606         pgtable = pgtable_trans_huge_withdraw(mm, pmd);
1607         pmd_populate(mm, &_pmd, pgtable);
1608
1609         for (i = 0; i < HPAGE_PMD_NR; i++, haddr += PAGE_SIZE) {
1610                 pte_t *pte, entry;
1611                 entry = pfn_pte(my_zero_pfn(haddr), vma->vm_page_prot);
1612                 entry = pte_mkspecial(entry);
1613                 pte = pte_offset_map(&_pmd, haddr);
1614                 VM_BUG_ON(!pte_none(*pte));
1615                 set_pte_at(mm, haddr, pte, entry);
1616                 pte_unmap(pte);
1617         }
1618         smp_wmb(); /* make pte visible before pmd */
1619         pmd_populate(mm, pmd, pgtable);
1620 }
1621
1622 static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
1623                 unsigned long haddr, bool freeze)
1624 {
1625         struct mm_struct *mm = vma->vm_mm;
1626         struct page *page;
1627         pgtable_t pgtable;
1628         pmd_t _pmd;
1629         bool young, write, dirty, soft_dirty;
1630         unsigned long addr;
1631         int i;
1632
1633         VM_BUG_ON(haddr & ~HPAGE_PMD_MASK);
1634         VM_BUG_ON_VMA(vma->vm_start > haddr, vma);
1635         VM_BUG_ON_VMA(vma->vm_end < haddr + HPAGE_PMD_SIZE, vma);
1636         VM_BUG_ON(!pmd_trans_huge(*pmd) && !pmd_devmap(*pmd));
1637
1638         count_vm_event(THP_SPLIT_PMD);
1639
1640         if (!vma_is_anonymous(vma)) {
1641                 _pmd = pmdp_huge_clear_flush_notify(vma, haddr, pmd);
1642                 if (vma_is_dax(vma))
1643                         return;
1644                 page = pmd_page(_pmd);
1645                 if (!PageDirty(page) && pmd_dirty(_pmd))
1646                         set_page_dirty(page);
1647                 if (!PageReferenced(page) && pmd_young(_pmd))
1648                         SetPageReferenced(page);
1649                 page_remove_rmap(page, true);
1650                 put_page(page);
1651                 add_mm_counter(mm, MM_FILEPAGES, -HPAGE_PMD_NR);
1652                 return;
1653         } else if (is_huge_zero_pmd(*pmd)) {
1654                 return __split_huge_zero_page_pmd(vma, haddr, pmd);
1655         }
1656
1657         page = pmd_page(*pmd);
1658         VM_BUG_ON_PAGE(!page_count(page), page);
1659         page_ref_add(page, HPAGE_PMD_NR - 1);
1660         write = pmd_write(*pmd);
1661         young = pmd_young(*pmd);
1662         dirty = pmd_dirty(*pmd);
1663         soft_dirty = pmd_soft_dirty(*pmd);
1664
1665         pmdp_huge_split_prepare(vma, haddr, pmd);
1666         pgtable = pgtable_trans_huge_withdraw(mm, pmd);
1667         pmd_populate(mm, &_pmd, pgtable);
1668
1669         for (i = 0, addr = haddr; i < HPAGE_PMD_NR; i++, addr += PAGE_SIZE) {
1670                 pte_t entry, *pte;
1671                 /*
1672                  * Note that NUMA hinting access restrictions are not
1673                  * transferred to avoid any possibility of altering
1674                  * permissions across VMAs.
1675                  */
1676                 if (freeze) {
1677                         swp_entry_t swp_entry;
1678                         swp_entry = make_migration_entry(page + i, write);
1679                         entry = swp_entry_to_pte(swp_entry);
1680                         if (soft_dirty)
1681                                 entry = pte_swp_mksoft_dirty(entry);
1682                 } else {
1683                         entry = mk_pte(page + i, READ_ONCE(vma->vm_page_prot));
1684                         entry = maybe_mkwrite(entry, vma);
1685                         if (!write)
1686                                 entry = pte_wrprotect(entry);
1687                         if (!young)
1688                                 entry = pte_mkold(entry);
1689                         if (soft_dirty)
1690                                 entry = pte_mksoft_dirty(entry);
1691                 }
1692                 if (dirty)
1693                         SetPageDirty(page + i);
1694                 pte = pte_offset_map(&_pmd, addr);
1695                 BUG_ON(!pte_none(*pte));
1696                 set_pte_at(mm, addr, pte, entry);
1697                 atomic_inc(&page[i]._mapcount);
1698                 pte_unmap(pte);
1699         }
1700
1701         /*
1702          * Set PG_double_map before dropping compound_mapcount to avoid
1703          * false-negative page_mapped().
1704          */
1705         if (compound_mapcount(page) > 1 && !TestSetPageDoubleMap(page)) {
1706                 for (i = 0; i < HPAGE_PMD_NR; i++)
1707                         atomic_inc(&page[i]._mapcount);
1708         }
1709
1710         if (atomic_add_negative(-1, compound_mapcount_ptr(page))) {
1711                 /* Last compound_mapcount is gone. */
1712                 __dec_node_page_state(page, NR_ANON_THPS);
1713                 if (TestClearPageDoubleMap(page)) {
1714                         /* No need in mapcount reference anymore */
1715                         for (i = 0; i < HPAGE_PMD_NR; i++)
1716                                 atomic_dec(&page[i]._mapcount);
1717                 }
1718         }
1719
1720         smp_wmb(); /* make pte visible before pmd */
1721         /*
1722          * Up to this point the pmd is present and huge and userland has the
1723          * whole access to the hugepage during the split (which happens in
1724          * place). If we overwrite the pmd with the not-huge version pointing
1725          * to the pte here (which of course we could if all CPUs were bug
1726          * free), userland could trigger a small page size TLB miss on the
1727          * small sized TLB while the hugepage TLB entry is still established in
1728          * the huge TLB. Some CPU doesn't like that.
1729          * See http://support.amd.com/us/Processor_TechDocs/41322.pdf, Erratum
1730          * 383 on page 93. Intel should be safe but is also warns that it's
1731          * only safe if the permission and cache attributes of the two entries
1732          * loaded in the two TLB is identical (which should be the case here).
1733          * But it is generally safer to never allow small and huge TLB entries
1734          * for the same virtual address to be loaded simultaneously. So instead
1735          * of doing "pmd_populate(); flush_pmd_tlb_range();" we first mark the
1736          * current pmd notpresent (atomically because here the pmd_trans_huge
1737          * and pmd_trans_splitting must remain set at all times on the pmd
1738          * until the split is complete for this pmd), then we flush the SMP TLB
1739          * and finally we write the non-huge version of the pmd entry with
1740          * pmd_populate.
1741          */
1742         pmdp_invalidate(vma, haddr, pmd);
1743         pmd_populate(mm, pmd, pgtable);
1744
1745         if (freeze) {
1746                 for (i = 0; i < HPAGE_PMD_NR; i++) {
1747                         page_remove_rmap(page + i, false);
1748                         put_page(page + i);
1749                 }
1750         }
1751 }
1752
1753 void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
1754                 unsigned long address, bool freeze, struct page *page)
1755 {
1756         spinlock_t *ptl;
1757         struct mm_struct *mm = vma->vm_mm;
1758         unsigned long haddr = address & HPAGE_PMD_MASK;
1759
1760         mmu_notifier_invalidate_range_start(mm, haddr, haddr + HPAGE_PMD_SIZE);
1761         ptl = pmd_lock(mm, pmd);
1762
1763         /*
1764          * If caller asks to setup a migration entries, we need a page to check
1765          * pmd against. Otherwise we can end up replacing wrong page.
1766          */
1767         VM_BUG_ON(freeze && !page);
1768         if (page && page != pmd_page(*pmd))
1769                 goto out;
1770
1771         if (pmd_trans_huge(*pmd)) {
1772                 page = pmd_page(*pmd);
1773                 if (PageMlocked(page))
1774                         clear_page_mlock(page);
1775         } else if (!pmd_devmap(*pmd))
1776                 goto out;
1777         __split_huge_pmd_locked(vma, pmd, haddr, freeze);
1778 out:
1779         spin_unlock(ptl);
1780         mmu_notifier_invalidate_range_end(mm, haddr, haddr + HPAGE_PMD_SIZE);
1781 }
1782
1783 void split_huge_pmd_address(struct vm_area_struct *vma, unsigned long address,
1784                 bool freeze, struct page *page)
1785 {
1786         pgd_t *pgd;
1787         pud_t *pud;
1788         pmd_t *pmd;
1789
1790         pgd = pgd_offset(vma->vm_mm, address);
1791         if (!pgd_present(*pgd))
1792                 return;
1793
1794         pud = pud_offset(pgd, address);
1795         if (!pud_present(*pud))
1796                 return;
1797
1798         pmd = pmd_offset(pud, address);
1799
1800         __split_huge_pmd(vma, pmd, address, freeze, page);
1801 }
1802
1803 void vma_adjust_trans_huge(struct vm_area_struct *vma,
1804                              unsigned long start,
1805                              unsigned long end,
1806                              long adjust_next)
1807 {
1808         /*
1809          * If the new start address isn't hpage aligned and it could
1810          * previously contain an hugepage: check if we need to split
1811          * an huge pmd.
1812          */
1813         if (start & ~HPAGE_PMD_MASK &&
1814             (start & HPAGE_PMD_MASK) >= vma->vm_start &&
1815             (start & HPAGE_PMD_MASK) + HPAGE_PMD_SIZE <= vma->vm_end)
1816                 split_huge_pmd_address(vma, start, false, NULL);
1817
1818         /*
1819          * If the new end address isn't hpage aligned and it could
1820          * previously contain an hugepage: check if we need to split
1821          * an huge pmd.
1822          */
1823         if (end & ~HPAGE_PMD_MASK &&
1824             (end & HPAGE_PMD_MASK) >= vma->vm_start &&
1825             (end & HPAGE_PMD_MASK) + HPAGE_PMD_SIZE <= vma->vm_end)
1826                 split_huge_pmd_address(vma, end, false, NULL);
1827
1828         /*
1829          * If we're also updating the vma->vm_next->vm_start, if the new
1830          * vm_next->vm_start isn't page aligned and it could previously
1831          * contain an hugepage: check if we need to split an huge pmd.
1832          */
1833         if (adjust_next > 0) {
1834                 struct vm_area_struct *next = vma->vm_next;
1835                 unsigned long nstart = next->vm_start;
1836                 nstart += adjust_next << PAGE_SHIFT;
1837                 if (nstart & ~HPAGE_PMD_MASK &&
1838                     (nstart & HPAGE_PMD_MASK) >= next->vm_start &&
1839                     (nstart & HPAGE_PMD_MASK) + HPAGE_PMD_SIZE <= next->vm_end)
1840                         split_huge_pmd_address(next, nstart, false, NULL);
1841         }
1842 }
1843
1844 static void freeze_page(struct page *page)
1845 {
1846         enum ttu_flags ttu_flags = TTU_IGNORE_MLOCK | TTU_IGNORE_ACCESS |
1847                 TTU_RMAP_LOCKED;
1848         int i, ret;
1849
1850         VM_BUG_ON_PAGE(!PageHead(page), page);
1851
1852         if (PageAnon(page))
1853                 ttu_flags |= TTU_MIGRATION;
1854
1855         /* We only need TTU_SPLIT_HUGE_PMD once */
1856         ret = try_to_unmap(page, ttu_flags | TTU_SPLIT_HUGE_PMD);
1857         for (i = 1; !ret && i < HPAGE_PMD_NR; i++) {
1858                 /* Cut short if the page is unmapped */
1859                 if (page_count(page) == 1)
1860                         return;
1861
1862                 ret = try_to_unmap(page + i, ttu_flags);
1863         }
1864         VM_BUG_ON_PAGE(ret, page + i - 1);
1865 }
1866
1867 static void unfreeze_page(struct page *page)
1868 {
1869         int i;
1870
1871         for (i = 0; i < HPAGE_PMD_NR; i++)
1872                 remove_migration_ptes(page + i, page + i, true);
1873 }
1874
1875 static void __split_huge_page_tail(struct page *head, int tail,
1876                 struct lruvec *lruvec, struct list_head *list)
1877 {
1878         struct page *page_tail = head + tail;
1879
1880         VM_BUG_ON_PAGE(atomic_read(&page_tail->_mapcount) != -1, page_tail);
1881         VM_BUG_ON_PAGE(page_ref_count(page_tail) != 0, page_tail);
1882
1883         /*
1884          * tail_page->_refcount is zero and not changing from under us. But
1885          * get_page_unless_zero() may be running from under us on the
1886          * tail_page. If we used atomic_set() below instead of atomic_inc() or
1887          * atomic_add(), we would then run atomic_set() concurrently with
1888          * get_page_unless_zero(), and atomic_set() is implemented in C not
1889          * using locked ops. spin_unlock on x86 sometime uses locked ops
1890          * because of PPro errata 66, 92, so unless somebody can guarantee
1891          * atomic_set() here would be safe on all archs (and not only on x86),
1892          * it's safer to use atomic_inc()/atomic_add().
1893          */
1894         if (PageAnon(head)) {
1895                 page_ref_inc(page_tail);
1896         } else {
1897                 /* Additional pin to radix tree */
1898                 page_ref_add(page_tail, 2);
1899         }
1900
1901         page_tail->flags &= ~PAGE_FLAGS_CHECK_AT_PREP;
1902         page_tail->flags |= (head->flags &
1903                         ((1L << PG_referenced) |
1904                          (1L << PG_swapbacked) |
1905                          (1L << PG_mlocked) |
1906                          (1L << PG_uptodate) |
1907                          (1L << PG_active) |
1908                          (1L << PG_locked) |
1909                          (1L << PG_unevictable) |
1910                          (1L << PG_dirty)));
1911
1912         /*
1913          * After clearing PageTail the gup refcount can be released.
1914          * Page flags also must be visible before we make the page non-compound.
1915          */
1916         smp_wmb();
1917
1918         clear_compound_head(page_tail);
1919
1920         if (page_is_young(head))
1921                 set_page_young(page_tail);
1922         if (page_is_idle(head))
1923                 set_page_idle(page_tail);
1924
1925         /* ->mapping in first tail page is compound_mapcount */
1926         VM_BUG_ON_PAGE(tail > 2 && page_tail->mapping != TAIL_MAPPING,
1927                         page_tail);
1928         page_tail->mapping = head->mapping;
1929
1930         page_tail->index = head->index + tail;
1931         page_cpupid_xchg_last(page_tail, page_cpupid_last(head));
1932         lru_add_page_tail(head, page_tail, lruvec, list);
1933 }
1934
1935 static void __split_huge_page(struct page *page, struct list_head *list,
1936                 unsigned long flags)
1937 {
1938         struct page *head = compound_head(page);
1939         struct zone *zone = page_zone(head);
1940         struct lruvec *lruvec;
1941         pgoff_t end = -1;
1942         int i;
1943
1944         lruvec = mem_cgroup_page_lruvec(head, zone->zone_pgdat);
1945
1946         /* complete memcg works before add pages to LRU */
1947         mem_cgroup_split_huge_fixup(head);
1948
1949         if (!PageAnon(page))
1950                 end = DIV_ROUND_UP(i_size_read(head->mapping->host), PAGE_SIZE);
1951
1952         for (i = HPAGE_PMD_NR - 1; i >= 1; i--) {
1953                 __split_huge_page_tail(head, i, lruvec, list);
1954                 /* Some pages can be beyond i_size: drop them from page cache */
1955                 if (head[i].index >= end) {
1956                         __ClearPageDirty(head + i);
1957                         __delete_from_page_cache(head + i, NULL);
1958                         if (IS_ENABLED(CONFIG_SHMEM) && PageSwapBacked(head))
1959                                 shmem_uncharge(head->mapping->host, 1);
1960                         put_page(head + i);
1961                 }
1962         }
1963
1964         ClearPageCompound(head);
1965         /* See comment in __split_huge_page_tail() */
1966         if (PageAnon(head)) {
1967                 page_ref_inc(head);
1968         } else {
1969                 /* Additional pin to radix tree */
1970                 page_ref_add(head, 2);
1971                 spin_unlock(&head->mapping->tree_lock);
1972         }
1973
1974         spin_unlock_irqrestore(zone_lru_lock(page_zone(head)), flags);
1975
1976         unfreeze_page(head);
1977
1978         for (i = 0; i < HPAGE_PMD_NR; i++) {
1979                 struct page *subpage = head + i;
1980                 if (subpage == page)
1981                         continue;
1982                 unlock_page(subpage);
1983
1984                 /*
1985                  * Subpages may be freed if there wasn't any mapping
1986                  * like if add_to_swap() is running on a lru page that
1987                  * had its mapping zapped. And freeing these pages
1988                  * requires taking the lru_lock so we do the put_page
1989                  * of the tail pages after the split is complete.
1990                  */
1991                 put_page(subpage);
1992         }
1993 }
1994
1995 int total_mapcount(struct page *page)
1996 {
1997         int i, compound, ret;
1998
1999         VM_BUG_ON_PAGE(PageTail(page), page);
2000
2001         if (likely(!PageCompound(page)))
2002                 return atomic_read(&page->_mapcount) + 1;
2003
2004         compound = compound_mapcount(page);
2005         if (PageHuge(page))
2006                 return compound;
2007         ret = compound;
2008         for (i = 0; i < HPAGE_PMD_NR; i++)
2009                 ret += atomic_read(&page[i]._mapcount) + 1;
2010         /* File pages has compound_mapcount included in _mapcount */
2011         if (!PageAnon(page))
2012                 return ret - compound * HPAGE_PMD_NR;
2013         if (PageDoubleMap(page))
2014                 ret -= HPAGE_PMD_NR;
2015         return ret;
2016 }
2017
2018 /*
2019  * This calculates accurately how many mappings a transparent hugepage
2020  * has (unlike page_mapcount() which isn't fully accurate). This full
2021  * accuracy is primarily needed to know if copy-on-write faults can
2022  * reuse the page and change the mapping to read-write instead of
2023  * copying them. At the same time this returns the total_mapcount too.
2024  *
2025  * The function returns the highest mapcount any one of the subpages
2026  * has. If the return value is one, even if different processes are
2027  * mapping different subpages of the transparent hugepage, they can
2028  * all reuse it, because each process is reusing a different subpage.
2029  *
2030  * The total_mapcount is instead counting all virtual mappings of the
2031  * subpages. If the total_mapcount is equal to "one", it tells the
2032  * caller all mappings belong to the same "mm" and in turn the
2033  * anon_vma of the transparent hugepage can become the vma->anon_vma
2034  * local one as no other process may be mapping any of the subpages.
2035  *
2036  * It would be more accurate to replace page_mapcount() with
2037  * page_trans_huge_mapcount(), however we only use
2038  * page_trans_huge_mapcount() in the copy-on-write faults where we
2039  * need full accuracy to avoid breaking page pinning, because
2040  * page_trans_huge_mapcount() is slower than page_mapcount().
2041  */
2042 int page_trans_huge_mapcount(struct page *page, int *total_mapcount)
2043 {
2044         int i, ret, _total_mapcount, mapcount;
2045
2046         /* hugetlbfs shouldn't call it */
2047         VM_BUG_ON_PAGE(PageHuge(page), page);
2048
2049         if (likely(!PageTransCompound(page))) {
2050                 mapcount = atomic_read(&page->_mapcount) + 1;
2051                 if (total_mapcount)
2052                         *total_mapcount = mapcount;
2053                 return mapcount;
2054         }
2055
2056         page = compound_head(page);
2057
2058         _total_mapcount = ret = 0;
2059         for (i = 0; i < HPAGE_PMD_NR; i++) {
2060                 mapcount = atomic_read(&page[i]._mapcount) + 1;
2061                 ret = max(ret, mapcount);
2062                 _total_mapcount += mapcount;
2063         }
2064         if (PageDoubleMap(page)) {
2065                 ret -= 1;
2066                 _total_mapcount -= HPAGE_PMD_NR;
2067         }
2068         mapcount = compound_mapcount(page);
2069         ret += mapcount;
2070         _total_mapcount += mapcount;
2071         if (total_mapcount)
2072                 *total_mapcount = _total_mapcount;
2073         return ret;
2074 }
2075
2076 /*
2077  * This function splits huge page into normal pages. @page can point to any
2078  * subpage of huge page to split. Split doesn't change the position of @page.
2079  *
2080  * Only caller must hold pin on the @page, otherwise split fails with -EBUSY.
2081  * The huge page must be locked.
2082  *
2083  * If @list is null, tail pages will be added to LRU list, otherwise, to @list.
2084  *
2085  * Both head page and tail pages will inherit mapping, flags, and so on from
2086  * the hugepage.
2087  *
2088  * GUP pin and PG_locked transferred to @page. Rest subpages can be freed if
2089  * they are not mapped.
2090  *
2091  * Returns 0 if the hugepage is split successfully.
2092  * Returns -EBUSY if the page is pinned or if anon_vma disappeared from under
2093  * us.
2094  */
2095 int split_huge_page_to_list(struct page *page, struct list_head *list)
2096 {
2097         struct page *head = compound_head(page);
2098         struct pglist_data *pgdata = NODE_DATA(page_to_nid(head));
2099         struct anon_vma *anon_vma = NULL;
2100         struct address_space *mapping = NULL;
2101         int count, mapcount, extra_pins, ret;
2102         bool mlocked;
2103         unsigned long flags;
2104
2105         VM_BUG_ON_PAGE(is_huge_zero_page(page), page);
2106         VM_BUG_ON_PAGE(!PageLocked(page), page);
2107         VM_BUG_ON_PAGE(!PageSwapBacked(page), page);
2108         VM_BUG_ON_PAGE(!PageCompound(page), page);
2109
2110         if (PageAnon(head)) {
2111                 /*
2112                  * The caller does not necessarily hold an mmap_sem that would
2113                  * prevent the anon_vma disappearing so we first we take a
2114                  * reference to it and then lock the anon_vma for write. This
2115                  * is similar to page_lock_anon_vma_read except the write lock
2116                  * is taken to serialise against parallel split or collapse
2117                  * operations.
2118                  */
2119                 anon_vma = page_get_anon_vma(head);
2120                 if (!anon_vma) {
2121                         ret = -EBUSY;
2122                         goto out;
2123                 }
2124                 extra_pins = 0;
2125                 mapping = NULL;
2126                 anon_vma_lock_write(anon_vma);
2127         } else {
2128                 mapping = head->mapping;
2129
2130                 /* Truncated ? */
2131                 if (!mapping) {
2132                         ret = -EBUSY;
2133                         goto out;
2134                 }
2135
2136                 /* Addidional pins from radix tree */
2137                 extra_pins = HPAGE_PMD_NR;
2138                 anon_vma = NULL;
2139                 i_mmap_lock_read(mapping);
2140         }
2141
2142         /*
2143          * Racy check if we can split the page, before freeze_page() will
2144          * split PMDs
2145          */
2146         if (total_mapcount(head) != page_count(head) - extra_pins - 1) {
2147                 ret = -EBUSY;
2148                 goto out_unlock;
2149         }
2150
2151         mlocked = PageMlocked(page);
2152         freeze_page(head);
2153         VM_BUG_ON_PAGE(compound_mapcount(head), head);
2154
2155         /* Make sure the page is not on per-CPU pagevec as it takes pin */
2156         if (mlocked)
2157                 lru_add_drain();
2158
2159         /* prevent PageLRU to go away from under us, and freeze lru stats */
2160         spin_lock_irqsave(zone_lru_lock(page_zone(head)), flags);
2161
2162         if (mapping) {
2163                 void **pslot;
2164
2165                 spin_lock(&mapping->tree_lock);
2166                 pslot = radix_tree_lookup_slot(&mapping->page_tree,
2167                                 page_index(head));
2168                 /*
2169                  * Check if the head page is present in radix tree.
2170                  * We assume all tail are present too, if head is there.
2171                  */
2172                 if (radix_tree_deref_slot_protected(pslot,
2173                                         &mapping->tree_lock) != head)
2174                         goto fail;
2175         }
2176
2177         /* Prevent deferred_split_scan() touching ->_refcount */
2178         spin_lock(&pgdata->split_queue_lock);
2179         count = page_count(head);
2180         mapcount = total_mapcount(head);
2181         if (!mapcount && page_ref_freeze(head, 1 + extra_pins)) {
2182                 if (!list_empty(page_deferred_list(head))) {
2183                         pgdata->split_queue_len--;
2184                         list_del(page_deferred_list(head));
2185                 }
2186                 if (mapping)
2187                         __dec_node_page_state(page, NR_SHMEM_THPS);
2188                 spin_unlock(&pgdata->split_queue_lock);
2189                 __split_huge_page(page, list, flags);
2190                 ret = 0;
2191         } else {
2192                 if (IS_ENABLED(CONFIG_DEBUG_VM) && mapcount) {
2193                         pr_alert("total_mapcount: %u, page_count(): %u\n",
2194                                         mapcount, count);
2195                         if (PageTail(page))
2196                                 dump_page(head, NULL);
2197                         dump_page(page, "total_mapcount(head) > 0");
2198                         BUG();
2199                 }
2200                 spin_unlock(&pgdata->split_queue_lock);
2201 fail:           if (mapping)
2202                         spin_unlock(&mapping->tree_lock);
2203                 spin_unlock_irqrestore(zone_lru_lock(page_zone(head)), flags);
2204                 unfreeze_page(head);
2205                 ret = -EBUSY;
2206         }
2207
2208 out_unlock:
2209         if (anon_vma) {
2210                 anon_vma_unlock_write(anon_vma);
2211                 put_anon_vma(anon_vma);
2212         }
2213         if (mapping)
2214                 i_mmap_unlock_read(mapping);
2215 out:
2216         count_vm_event(!ret ? THP_SPLIT_PAGE : THP_SPLIT_PAGE_FAILED);
2217         return ret;
2218 }
2219
2220 void free_transhuge_page(struct page *page)
2221 {
2222         struct pglist_data *pgdata = NODE_DATA(page_to_nid(page));
2223         unsigned long flags;
2224
2225         spin_lock_irqsave(&pgdata->split_queue_lock, flags);
2226         if (!list_empty(page_deferred_list(page))) {
2227                 pgdata->split_queue_len--;
2228                 list_del(page_deferred_list(page));
2229         }
2230         spin_unlock_irqrestore(&pgdata->split_queue_lock, flags);
2231         free_compound_page(page);
2232 }
2233
2234 void deferred_split_huge_page(struct page *page)
2235 {
2236         struct pglist_data *pgdata = NODE_DATA(page_to_nid(page));
2237         unsigned long flags;
2238
2239         VM_BUG_ON_PAGE(!PageTransHuge(page), page);
2240
2241         spin_lock_irqsave(&pgdata->split_queue_lock, flags);
2242         if (list_empty(page_deferred_list(page))) {
2243                 count_vm_event(THP_DEFERRED_SPLIT_PAGE);
2244                 list_add_tail(page_deferred_list(page), &pgdata->split_queue);
2245                 pgdata->split_queue_len++;
2246         }
2247         spin_unlock_irqrestore(&pgdata->split_queue_lock, flags);
2248 }
2249
2250 static unsigned long deferred_split_count(struct shrinker *shrink,
2251                 struct shrink_control *sc)
2252 {
2253         struct pglist_data *pgdata = NODE_DATA(sc->nid);
2254         return ACCESS_ONCE(pgdata->split_queue_len);
2255 }
2256
2257 static unsigned long deferred_split_scan(struct shrinker *shrink,
2258                 struct shrink_control *sc)
2259 {
2260         struct pglist_data *pgdata = NODE_DATA(sc->nid);
2261         unsigned long flags;
2262         LIST_HEAD(list), *pos, *next;
2263         struct page *page;
2264         int split = 0;
2265
2266         spin_lock_irqsave(&pgdata->split_queue_lock, flags);
2267         /* Take pin on all head pages to avoid freeing them under us */
2268         list_for_each_safe(pos, next, &pgdata->split_queue) {
2269                 page = list_entry((void *)pos, struct page, mapping);
2270                 page = compound_head(page);
2271                 if (get_page_unless_zero(page)) {
2272                         list_move(page_deferred_list(page), &list);
2273                 } else {
2274                         /* We lost race with put_compound_page() */
2275                         list_del_init(page_deferred_list(page));
2276                         pgdata->split_queue_len--;
2277                 }
2278                 if (!--sc->nr_to_scan)
2279                         break;
2280         }
2281         spin_unlock_irqrestore(&pgdata->split_queue_lock, flags);
2282
2283         list_for_each_safe(pos, next, &list) {
2284                 page = list_entry((void *)pos, struct page, mapping);
2285                 if (!trylock_page(page))
2286                         goto next;
2287                 /* split_huge_page() removes page from list on success */
2288                 if (!split_huge_page(page))
2289                         split++;
2290                 unlock_page(page);
2291 next:
2292                 put_page(page);
2293         }
2294
2295         spin_lock_irqsave(&pgdata->split_queue_lock, flags);
2296         list_splice_tail(&list, &pgdata->split_queue);
2297         spin_unlock_irqrestore(&pgdata->split_queue_lock, flags);
2298
2299         /*
2300          * Stop shrinker if we didn't split any page, but the queue is empty.
2301          * This can happen if pages were freed under us.
2302          */
2303         if (!split && list_empty(&pgdata->split_queue))
2304                 return SHRINK_STOP;
2305         return split;
2306 }
2307
2308 static struct shrinker deferred_split_shrinker = {
2309         .count_objects = deferred_split_count,
2310         .scan_objects = deferred_split_scan,
2311         .seeks = DEFAULT_SEEKS,
2312         .flags = SHRINKER_NUMA_AWARE,
2313 };
2314
2315 #ifdef CONFIG_DEBUG_FS
2316 static int split_huge_pages_set(void *data, u64 val)
2317 {
2318         struct zone *zone;
2319         struct page *page;
2320         unsigned long pfn, max_zone_pfn;
2321         unsigned long total = 0, split = 0;
2322
2323         if (val != 1)
2324                 return -EINVAL;
2325
2326         for_each_populated_zone(zone) {
2327                 max_zone_pfn = zone_end_pfn(zone);
2328                 for (pfn = zone->zone_start_pfn; pfn < max_zone_pfn; pfn++) {
2329                         if (!pfn_valid(pfn))
2330                                 continue;
2331
2332                         page = pfn_to_page(pfn);
2333                         if (!get_page_unless_zero(page))
2334                                 continue;
2335
2336                         if (zone != page_zone(page))
2337                                 goto next;
2338
2339                         if (!PageHead(page) || PageHuge(page) || !PageLRU(page))
2340                                 goto next;
2341
2342                         total++;
2343                         lock_page(page);
2344                         if (!split_huge_page(page))
2345                                 split++;
2346                         unlock_page(page);
2347 next:
2348                         put_page(page);
2349                 }
2350         }
2351
2352         pr_info("%lu of %lu THP split\n", split, total);
2353
2354         return 0;
2355 }
2356 DEFINE_SIMPLE_ATTRIBUTE(split_huge_pages_fops, NULL, split_huge_pages_set,
2357                 "%llu\n");
2358
2359 static int __init split_huge_pages_debugfs(void)
2360 {
2361         void *ret;
2362
2363         ret = debugfs_create_file("split_huge_pages", 0200, NULL, NULL,
2364                         &split_huge_pages_fops);
2365         if (!ret)
2366                 pr_warn("Failed to create split_huge_pages in debugfs");
2367         return 0;
2368 }
2369 late_initcall(split_huge_pages_debugfs);
2370 #endif