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)
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))
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 (force_flush)
1491                         flush_tlb_range(vma, old_addr, old_addr + PMD_SIZE);
1492                 if (new_ptl != old_ptl)
1493                         spin_unlock(new_ptl);
1494                 spin_unlock(old_ptl);
1495                 return true;
1496         }
1497         return false;
1498 }
1499
1500 /*
1501  * Returns
1502  *  - 0 if PMD could not be locked
1503  *  - 1 if PMD was locked but protections unchange and TLB flush unnecessary
1504  *  - HPAGE_PMD_NR is protections changed and TLB flush necessary
1505  */
1506 int change_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
1507                 unsigned long addr, pgprot_t newprot, int prot_numa)
1508 {
1509         struct mm_struct *mm = vma->vm_mm;
1510         spinlock_t *ptl;
1511         pmd_t entry;
1512         bool preserve_write;
1513         int ret;
1514
1515         ptl = __pmd_trans_huge_lock(pmd, vma);
1516         if (!ptl)
1517                 return 0;
1518
1519         preserve_write = prot_numa && pmd_write(*pmd);
1520         ret = 1;
1521
1522         /*
1523          * Avoid trapping faults against the zero page. The read-only
1524          * data is likely to be read-cached on the local CPU and
1525          * local/remote hits to the zero page are not interesting.
1526          */
1527         if (prot_numa && is_huge_zero_pmd(*pmd))
1528                 goto unlock;
1529
1530         if (prot_numa && pmd_protnone(*pmd))
1531                 goto unlock;
1532
1533         /*
1534          * In case prot_numa, we are under down_read(mmap_sem). It's critical
1535          * to not clear pmd intermittently to avoid race with MADV_DONTNEED
1536          * which is also under down_read(mmap_sem):
1537          *
1538          *      CPU0:                           CPU1:
1539          *                              change_huge_pmd(prot_numa=1)
1540          *                               pmdp_huge_get_and_clear_notify()
1541          * madvise_dontneed()
1542          *  zap_pmd_range()
1543          *   pmd_trans_huge(*pmd) == 0 (without ptl)
1544          *   // skip the pmd
1545          *                               set_pmd_at();
1546          *                               // pmd is re-established
1547          *
1548          * The race makes MADV_DONTNEED miss the huge pmd and don't clear it
1549          * which may break userspace.
1550          *
1551          * pmdp_invalidate() is required to make sure we don't miss
1552          * dirty/young flags set by hardware.
1553          */
1554         entry = *pmd;
1555         pmdp_invalidate(vma, addr, pmd);
1556
1557         /*
1558          * Recover dirty/young flags.  It relies on pmdp_invalidate to not
1559          * corrupt them.
1560          */
1561         if (pmd_dirty(*pmd))
1562                 entry = pmd_mkdirty(entry);
1563         if (pmd_young(*pmd))
1564                 entry = pmd_mkyoung(entry);
1565
1566         entry = pmd_modify(entry, newprot);
1567         if (preserve_write)
1568                 entry = pmd_mkwrite(entry);
1569         ret = HPAGE_PMD_NR;
1570         set_pmd_at(mm, addr, pmd, entry);
1571         BUG_ON(vma_is_anonymous(vma) && !preserve_write && pmd_write(entry));
1572 unlock:
1573         spin_unlock(ptl);
1574         return ret;
1575 }
1576
1577 /*
1578  * Returns page table lock pointer if a given pmd maps a thp, NULL otherwise.
1579  *
1580  * Note that if it returns page table lock pointer, this routine returns without
1581  * unlocking page table lock. So callers must unlock it.
1582  */
1583 spinlock_t *__pmd_trans_huge_lock(pmd_t *pmd, struct vm_area_struct *vma)
1584 {
1585         spinlock_t *ptl;
1586         ptl = pmd_lock(vma->vm_mm, pmd);
1587         if (likely(pmd_trans_huge(*pmd) || pmd_devmap(*pmd)))
1588                 return ptl;
1589         spin_unlock(ptl);
1590         return NULL;
1591 }
1592
1593 static void __split_huge_zero_page_pmd(struct vm_area_struct *vma,
1594                 unsigned long haddr, pmd_t *pmd)
1595 {
1596         struct mm_struct *mm = vma->vm_mm;
1597         pgtable_t pgtable;
1598         pmd_t _pmd;
1599         int i;
1600
1601         /* leave pmd empty until pte is filled */
1602         pmdp_huge_clear_flush_notify(vma, haddr, pmd);
1603
1604         pgtable = pgtable_trans_huge_withdraw(mm, pmd);
1605         pmd_populate(mm, &_pmd, pgtable);
1606
1607         for (i = 0; i < HPAGE_PMD_NR; i++, haddr += PAGE_SIZE) {
1608                 pte_t *pte, entry;
1609                 entry = pfn_pte(my_zero_pfn(haddr), vma->vm_page_prot);
1610                 entry = pte_mkspecial(entry);
1611                 pte = pte_offset_map(&_pmd, haddr);
1612                 VM_BUG_ON(!pte_none(*pte));
1613                 set_pte_at(mm, haddr, pte, entry);
1614                 pte_unmap(pte);
1615         }
1616         smp_wmb(); /* make pte visible before pmd */
1617         pmd_populate(mm, pmd, pgtable);
1618 }
1619
1620 static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
1621                 unsigned long haddr, bool freeze)
1622 {
1623         struct mm_struct *mm = vma->vm_mm;
1624         struct page *page;
1625         pgtable_t pgtable;
1626         pmd_t _pmd;
1627         bool young, write, dirty, soft_dirty;
1628         unsigned long addr;
1629         int i;
1630
1631         VM_BUG_ON(haddr & ~HPAGE_PMD_MASK);
1632         VM_BUG_ON_VMA(vma->vm_start > haddr, vma);
1633         VM_BUG_ON_VMA(vma->vm_end < haddr + HPAGE_PMD_SIZE, vma);
1634         VM_BUG_ON(!pmd_trans_huge(*pmd) && !pmd_devmap(*pmd));
1635
1636         count_vm_event(THP_SPLIT_PMD);
1637
1638         if (!vma_is_anonymous(vma)) {
1639                 _pmd = pmdp_huge_clear_flush_notify(vma, haddr, pmd);
1640                 if (vma_is_dax(vma))
1641                         return;
1642                 page = pmd_page(_pmd);
1643                 if (!PageDirty(page) && pmd_dirty(_pmd))
1644                         set_page_dirty(page);
1645                 if (!PageReferenced(page) && pmd_young(_pmd))
1646                         SetPageReferenced(page);
1647                 page_remove_rmap(page, true);
1648                 put_page(page);
1649                 add_mm_counter(mm, MM_FILEPAGES, -HPAGE_PMD_NR);
1650                 return;
1651         } else if (is_huge_zero_pmd(*pmd)) {
1652                 return __split_huge_zero_page_pmd(vma, haddr, pmd);
1653         }
1654
1655         page = pmd_page(*pmd);
1656         VM_BUG_ON_PAGE(!page_count(page), page);
1657         page_ref_add(page, HPAGE_PMD_NR - 1);
1658         write = pmd_write(*pmd);
1659         young = pmd_young(*pmd);
1660         dirty = pmd_dirty(*pmd);
1661         soft_dirty = pmd_soft_dirty(*pmd);
1662
1663         pmdp_huge_split_prepare(vma, haddr, pmd);
1664         pgtable = pgtable_trans_huge_withdraw(mm, pmd);
1665         pmd_populate(mm, &_pmd, pgtable);
1666
1667         for (i = 0, addr = haddr; i < HPAGE_PMD_NR; i++, addr += PAGE_SIZE) {
1668                 pte_t entry, *pte;
1669                 /*
1670                  * Note that NUMA hinting access restrictions are not
1671                  * transferred to avoid any possibility of altering
1672                  * permissions across VMAs.
1673                  */
1674                 if (freeze) {
1675                         swp_entry_t swp_entry;
1676                         swp_entry = make_migration_entry(page + i, write);
1677                         entry = swp_entry_to_pte(swp_entry);
1678                         if (soft_dirty)
1679                                 entry = pte_swp_mksoft_dirty(entry);
1680                 } else {
1681                         entry = mk_pte(page + i, READ_ONCE(vma->vm_page_prot));
1682                         entry = maybe_mkwrite(entry, vma);
1683                         if (!write)
1684                                 entry = pte_wrprotect(entry);
1685                         if (!young)
1686                                 entry = pte_mkold(entry);
1687                         if (soft_dirty)
1688                                 entry = pte_mksoft_dirty(entry);
1689                 }
1690                 if (dirty)
1691                         SetPageDirty(page + i);
1692                 pte = pte_offset_map(&_pmd, addr);
1693                 BUG_ON(!pte_none(*pte));
1694                 set_pte_at(mm, addr, pte, entry);
1695                 atomic_inc(&page[i]._mapcount);
1696                 pte_unmap(pte);
1697         }
1698
1699         /*
1700          * Set PG_double_map before dropping compound_mapcount to avoid
1701          * false-negative page_mapped().
1702          */
1703         if (compound_mapcount(page) > 1 && !TestSetPageDoubleMap(page)) {
1704                 for (i = 0; i < HPAGE_PMD_NR; i++)
1705                         atomic_inc(&page[i]._mapcount);
1706         }
1707
1708         if (atomic_add_negative(-1, compound_mapcount_ptr(page))) {
1709                 /* Last compound_mapcount is gone. */
1710                 __dec_node_page_state(page, NR_ANON_THPS);
1711                 if (TestClearPageDoubleMap(page)) {
1712                         /* No need in mapcount reference anymore */
1713                         for (i = 0; i < HPAGE_PMD_NR; i++)
1714                                 atomic_dec(&page[i]._mapcount);
1715                 }
1716         }
1717
1718         smp_wmb(); /* make pte visible before pmd */
1719         /*
1720          * Up to this point the pmd is present and huge and userland has the
1721          * whole access to the hugepage during the split (which happens in
1722          * place). If we overwrite the pmd with the not-huge version pointing
1723          * to the pte here (which of course we could if all CPUs were bug
1724          * free), userland could trigger a small page size TLB miss on the
1725          * small sized TLB while the hugepage TLB entry is still established in
1726          * the huge TLB. Some CPU doesn't like that.
1727          * See http://support.amd.com/us/Processor_TechDocs/41322.pdf, Erratum
1728          * 383 on page 93. Intel should be safe but is also warns that it's
1729          * only safe if the permission and cache attributes of the two entries
1730          * loaded in the two TLB is identical (which should be the case here).
1731          * But it is generally safer to never allow small and huge TLB entries
1732          * for the same virtual address to be loaded simultaneously. So instead
1733          * of doing "pmd_populate(); flush_pmd_tlb_range();" we first mark the
1734          * current pmd notpresent (atomically because here the pmd_trans_huge
1735          * and pmd_trans_splitting must remain set at all times on the pmd
1736          * until the split is complete for this pmd), then we flush the SMP TLB
1737          * and finally we write the non-huge version of the pmd entry with
1738          * pmd_populate.
1739          */
1740         pmdp_invalidate(vma, haddr, pmd);
1741         pmd_populate(mm, pmd, pgtable);
1742
1743         if (freeze) {
1744                 for (i = 0; i < HPAGE_PMD_NR; i++) {
1745                         page_remove_rmap(page + i, false);
1746                         put_page(page + i);
1747                 }
1748         }
1749 }
1750
1751 void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
1752                 unsigned long address, bool freeze, struct page *page)
1753 {
1754         spinlock_t *ptl;
1755         struct mm_struct *mm = vma->vm_mm;
1756         unsigned long haddr = address & HPAGE_PMD_MASK;
1757
1758         mmu_notifier_invalidate_range_start(mm, haddr, haddr + HPAGE_PMD_SIZE);
1759         ptl = pmd_lock(mm, pmd);
1760
1761         /*
1762          * If caller asks to setup a migration entries, we need a page to check
1763          * pmd against. Otherwise we can end up replacing wrong page.
1764          */
1765         VM_BUG_ON(freeze && !page);
1766         if (page && page != pmd_page(*pmd))
1767                 goto out;
1768
1769         if (pmd_trans_huge(*pmd)) {
1770                 page = pmd_page(*pmd);
1771                 if (PageMlocked(page))
1772                         clear_page_mlock(page);
1773         } else if (!pmd_devmap(*pmd))
1774                 goto out;
1775         __split_huge_pmd_locked(vma, pmd, haddr, freeze);
1776 out:
1777         spin_unlock(ptl);
1778         mmu_notifier_invalidate_range_end(mm, haddr, haddr + HPAGE_PMD_SIZE);
1779 }
1780
1781 void split_huge_pmd_address(struct vm_area_struct *vma, unsigned long address,
1782                 bool freeze, struct page *page)
1783 {
1784         pgd_t *pgd;
1785         pud_t *pud;
1786         pmd_t *pmd;
1787
1788         pgd = pgd_offset(vma->vm_mm, address);
1789         if (!pgd_present(*pgd))
1790                 return;
1791
1792         pud = pud_offset(pgd, address);
1793         if (!pud_present(*pud))
1794                 return;
1795
1796         pmd = pmd_offset(pud, address);
1797
1798         __split_huge_pmd(vma, pmd, address, freeze, page);
1799 }
1800
1801 void vma_adjust_trans_huge(struct vm_area_struct *vma,
1802                              unsigned long start,
1803                              unsigned long end,
1804                              long adjust_next)
1805 {
1806         /*
1807          * If the new start address isn't hpage aligned and it could
1808          * previously contain an hugepage: check if we need to split
1809          * an huge pmd.
1810          */
1811         if (start & ~HPAGE_PMD_MASK &&
1812             (start & HPAGE_PMD_MASK) >= vma->vm_start &&
1813             (start & HPAGE_PMD_MASK) + HPAGE_PMD_SIZE <= vma->vm_end)
1814                 split_huge_pmd_address(vma, start, false, NULL);
1815
1816         /*
1817          * If the new end address isn't hpage aligned and it could
1818          * previously contain an hugepage: check if we need to split
1819          * an huge pmd.
1820          */
1821         if (end & ~HPAGE_PMD_MASK &&
1822             (end & HPAGE_PMD_MASK) >= vma->vm_start &&
1823             (end & HPAGE_PMD_MASK) + HPAGE_PMD_SIZE <= vma->vm_end)
1824                 split_huge_pmd_address(vma, end, false, NULL);
1825
1826         /*
1827          * If we're also updating the vma->vm_next->vm_start, if the new
1828          * vm_next->vm_start isn't page aligned and it could previously
1829          * contain an hugepage: check if we need to split an huge pmd.
1830          */
1831         if (adjust_next > 0) {
1832                 struct vm_area_struct *next = vma->vm_next;
1833                 unsigned long nstart = next->vm_start;
1834                 nstart += adjust_next << PAGE_SHIFT;
1835                 if (nstart & ~HPAGE_PMD_MASK &&
1836                     (nstart & HPAGE_PMD_MASK) >= next->vm_start &&
1837                     (nstart & HPAGE_PMD_MASK) + HPAGE_PMD_SIZE <= next->vm_end)
1838                         split_huge_pmd_address(next, nstart, false, NULL);
1839         }
1840 }
1841
1842 static void freeze_page(struct page *page)
1843 {
1844         enum ttu_flags ttu_flags = TTU_IGNORE_MLOCK | TTU_IGNORE_ACCESS |
1845                 TTU_RMAP_LOCKED;
1846         int i, ret;
1847
1848         VM_BUG_ON_PAGE(!PageHead(page), page);
1849
1850         if (PageAnon(page))
1851                 ttu_flags |= TTU_MIGRATION;
1852
1853         /* We only need TTU_SPLIT_HUGE_PMD once */
1854         ret = try_to_unmap(page, ttu_flags | TTU_SPLIT_HUGE_PMD);
1855         for (i = 1; !ret && i < HPAGE_PMD_NR; i++) {
1856                 /* Cut short if the page is unmapped */
1857                 if (page_count(page) == 1)
1858                         return;
1859
1860                 ret = try_to_unmap(page + i, ttu_flags);
1861         }
1862         VM_BUG_ON_PAGE(ret, page + i - 1);
1863 }
1864
1865 static void unfreeze_page(struct page *page)
1866 {
1867         int i;
1868
1869         for (i = 0; i < HPAGE_PMD_NR; i++)
1870                 remove_migration_ptes(page + i, page + i, true);
1871 }
1872
1873 static void __split_huge_page_tail(struct page *head, int tail,
1874                 struct lruvec *lruvec, struct list_head *list)
1875 {
1876         struct page *page_tail = head + tail;
1877
1878         VM_BUG_ON_PAGE(atomic_read(&page_tail->_mapcount) != -1, page_tail);
1879         VM_BUG_ON_PAGE(page_ref_count(page_tail) != 0, page_tail);
1880
1881         /*
1882          * tail_page->_refcount is zero and not changing from under us. But
1883          * get_page_unless_zero() may be running from under us on the
1884          * tail_page. If we used atomic_set() below instead of atomic_inc() or
1885          * atomic_add(), we would then run atomic_set() concurrently with
1886          * get_page_unless_zero(), and atomic_set() is implemented in C not
1887          * using locked ops. spin_unlock on x86 sometime uses locked ops
1888          * because of PPro errata 66, 92, so unless somebody can guarantee
1889          * atomic_set() here would be safe on all archs (and not only on x86),
1890          * it's safer to use atomic_inc()/atomic_add().
1891          */
1892         if (PageAnon(head)) {
1893                 page_ref_inc(page_tail);
1894         } else {
1895                 /* Additional pin to radix tree */
1896                 page_ref_add(page_tail, 2);
1897         }
1898
1899         page_tail->flags &= ~PAGE_FLAGS_CHECK_AT_PREP;
1900         page_tail->flags |= (head->flags &
1901                         ((1L << PG_referenced) |
1902                          (1L << PG_swapbacked) |
1903                          (1L << PG_mlocked) |
1904                          (1L << PG_uptodate) |
1905                          (1L << PG_active) |
1906                          (1L << PG_locked) |
1907                          (1L << PG_unevictable) |
1908                          (1L << PG_dirty)));
1909
1910         /*
1911          * After clearing PageTail the gup refcount can be released.
1912          * Page flags also must be visible before we make the page non-compound.
1913          */
1914         smp_wmb();
1915
1916         clear_compound_head(page_tail);
1917
1918         if (page_is_young(head))
1919                 set_page_young(page_tail);
1920         if (page_is_idle(head))
1921                 set_page_idle(page_tail);
1922
1923         /* ->mapping in first tail page is compound_mapcount */
1924         VM_BUG_ON_PAGE(tail > 2 && page_tail->mapping != TAIL_MAPPING,
1925                         page_tail);
1926         page_tail->mapping = head->mapping;
1927
1928         page_tail->index = head->index + tail;
1929         page_cpupid_xchg_last(page_tail, page_cpupid_last(head));
1930         lru_add_page_tail(head, page_tail, lruvec, list);
1931 }
1932
1933 static void __split_huge_page(struct page *page, struct list_head *list,
1934                 unsigned long flags)
1935 {
1936         struct page *head = compound_head(page);
1937         struct zone *zone = page_zone(head);
1938         struct lruvec *lruvec;
1939         pgoff_t end = -1;
1940         int i;
1941
1942         lruvec = mem_cgroup_page_lruvec(head, zone->zone_pgdat);
1943
1944         /* complete memcg works before add pages to LRU */
1945         mem_cgroup_split_huge_fixup(head);
1946
1947         if (!PageAnon(page))
1948                 end = DIV_ROUND_UP(i_size_read(head->mapping->host), PAGE_SIZE);
1949
1950         for (i = HPAGE_PMD_NR - 1; i >= 1; i--) {
1951                 __split_huge_page_tail(head, i, lruvec, list);
1952                 /* Some pages can be beyond i_size: drop them from page cache */
1953                 if (head[i].index >= end) {
1954                         __ClearPageDirty(head + i);
1955                         __delete_from_page_cache(head + i, NULL);
1956                         if (IS_ENABLED(CONFIG_SHMEM) && PageSwapBacked(head))
1957                                 shmem_uncharge(head->mapping->host, 1);
1958                         put_page(head + i);
1959                 }
1960         }
1961
1962         ClearPageCompound(head);
1963         /* See comment in __split_huge_page_tail() */
1964         if (PageAnon(head)) {
1965                 page_ref_inc(head);
1966         } else {
1967                 /* Additional pin to radix tree */
1968                 page_ref_add(head, 2);
1969                 spin_unlock(&head->mapping->tree_lock);
1970         }
1971
1972         spin_unlock_irqrestore(zone_lru_lock(page_zone(head)), flags);
1973
1974         unfreeze_page(head);
1975
1976         for (i = 0; i < HPAGE_PMD_NR; i++) {
1977                 struct page *subpage = head + i;
1978                 if (subpage == page)
1979                         continue;
1980                 unlock_page(subpage);
1981
1982                 /*
1983                  * Subpages may be freed if there wasn't any mapping
1984                  * like if add_to_swap() is running on a lru page that
1985                  * had its mapping zapped. And freeing these pages
1986                  * requires taking the lru_lock so we do the put_page
1987                  * of the tail pages after the split is complete.
1988                  */
1989                 put_page(subpage);
1990         }
1991 }
1992
1993 int total_mapcount(struct page *page)
1994 {
1995         int i, compound, ret;
1996
1997         VM_BUG_ON_PAGE(PageTail(page), page);
1998
1999         if (likely(!PageCompound(page)))
2000                 return atomic_read(&page->_mapcount) + 1;
2001
2002         compound = compound_mapcount(page);
2003         if (PageHuge(page))
2004                 return compound;
2005         ret = compound;
2006         for (i = 0; i < HPAGE_PMD_NR; i++)
2007                 ret += atomic_read(&page[i]._mapcount) + 1;
2008         /* File pages has compound_mapcount included in _mapcount */
2009         if (!PageAnon(page))
2010                 return ret - compound * HPAGE_PMD_NR;
2011         if (PageDoubleMap(page))
2012                 ret -= HPAGE_PMD_NR;
2013         return ret;
2014 }
2015
2016 /*
2017  * This calculates accurately how many mappings a transparent hugepage
2018  * has (unlike page_mapcount() which isn't fully accurate). This full
2019  * accuracy is primarily needed to know if copy-on-write faults can
2020  * reuse the page and change the mapping to read-write instead of
2021  * copying them. At the same time this returns the total_mapcount too.
2022  *
2023  * The function returns the highest mapcount any one of the subpages
2024  * has. If the return value is one, even if different processes are
2025  * mapping different subpages of the transparent hugepage, they can
2026  * all reuse it, because each process is reusing a different subpage.
2027  *
2028  * The total_mapcount is instead counting all virtual mappings of the
2029  * subpages. If the total_mapcount is equal to "one", it tells the
2030  * caller all mappings belong to the same "mm" and in turn the
2031  * anon_vma of the transparent hugepage can become the vma->anon_vma
2032  * local one as no other process may be mapping any of the subpages.
2033  *
2034  * It would be more accurate to replace page_mapcount() with
2035  * page_trans_huge_mapcount(), however we only use
2036  * page_trans_huge_mapcount() in the copy-on-write faults where we
2037  * need full accuracy to avoid breaking page pinning, because
2038  * page_trans_huge_mapcount() is slower than page_mapcount().
2039  */
2040 int page_trans_huge_mapcount(struct page *page, int *total_mapcount)
2041 {
2042         int i, ret, _total_mapcount, mapcount;
2043
2044         /* hugetlbfs shouldn't call it */
2045         VM_BUG_ON_PAGE(PageHuge(page), page);
2046
2047         if (likely(!PageTransCompound(page))) {
2048                 mapcount = atomic_read(&page->_mapcount) + 1;
2049                 if (total_mapcount)
2050                         *total_mapcount = mapcount;
2051                 return mapcount;
2052         }
2053
2054         page = compound_head(page);
2055
2056         _total_mapcount = ret = 0;
2057         for (i = 0; i < HPAGE_PMD_NR; i++) {
2058                 mapcount = atomic_read(&page[i]._mapcount) + 1;
2059                 ret = max(ret, mapcount);
2060                 _total_mapcount += mapcount;
2061         }
2062         if (PageDoubleMap(page)) {
2063                 ret -= 1;
2064                 _total_mapcount -= HPAGE_PMD_NR;
2065         }
2066         mapcount = compound_mapcount(page);
2067         ret += mapcount;
2068         _total_mapcount += mapcount;
2069         if (total_mapcount)
2070                 *total_mapcount = _total_mapcount;
2071         return ret;
2072 }
2073
2074 /*
2075  * This function splits huge page into normal pages. @page can point to any
2076  * subpage of huge page to split. Split doesn't change the position of @page.
2077  *
2078  * Only caller must hold pin on the @page, otherwise split fails with -EBUSY.
2079  * The huge page must be locked.
2080  *
2081  * If @list is null, tail pages will be added to LRU list, otherwise, to @list.
2082  *
2083  * Both head page and tail pages will inherit mapping, flags, and so on from
2084  * the hugepage.
2085  *
2086  * GUP pin and PG_locked transferred to @page. Rest subpages can be freed if
2087  * they are not mapped.
2088  *
2089  * Returns 0 if the hugepage is split successfully.
2090  * Returns -EBUSY if the page is pinned or if anon_vma disappeared from under
2091  * us.
2092  */
2093 int split_huge_page_to_list(struct page *page, struct list_head *list)
2094 {
2095         struct page *head = compound_head(page);
2096         struct pglist_data *pgdata = NODE_DATA(page_to_nid(head));
2097         struct anon_vma *anon_vma = NULL;
2098         struct address_space *mapping = NULL;
2099         int count, mapcount, extra_pins, ret;
2100         bool mlocked;
2101         unsigned long flags;
2102
2103         VM_BUG_ON_PAGE(is_huge_zero_page(page), page);
2104         VM_BUG_ON_PAGE(!PageLocked(page), page);
2105         VM_BUG_ON_PAGE(!PageSwapBacked(page), page);
2106         VM_BUG_ON_PAGE(!PageCompound(page), page);
2107
2108         if (PageAnon(head)) {
2109                 /*
2110                  * The caller does not necessarily hold an mmap_sem that would
2111                  * prevent the anon_vma disappearing so we first we take a
2112                  * reference to it and then lock the anon_vma for write. This
2113                  * is similar to page_lock_anon_vma_read except the write lock
2114                  * is taken to serialise against parallel split or collapse
2115                  * operations.
2116                  */
2117                 anon_vma = page_get_anon_vma(head);
2118                 if (!anon_vma) {
2119                         ret = -EBUSY;
2120                         goto out;
2121                 }
2122                 extra_pins = 0;
2123                 mapping = NULL;
2124                 anon_vma_lock_write(anon_vma);
2125         } else {
2126                 mapping = head->mapping;
2127
2128                 /* Truncated ? */
2129                 if (!mapping) {
2130                         ret = -EBUSY;
2131                         goto out;
2132                 }
2133
2134                 /* Addidional pins from radix tree */
2135                 extra_pins = HPAGE_PMD_NR;
2136                 anon_vma = NULL;
2137                 i_mmap_lock_read(mapping);
2138         }
2139
2140         /*
2141          * Racy check if we can split the page, before freeze_page() will
2142          * split PMDs
2143          */
2144         if (total_mapcount(head) != page_count(head) - extra_pins - 1) {
2145                 ret = -EBUSY;
2146                 goto out_unlock;
2147         }
2148
2149         mlocked = PageMlocked(page);
2150         freeze_page(head);
2151         VM_BUG_ON_PAGE(compound_mapcount(head), head);
2152
2153         /* Make sure the page is not on per-CPU pagevec as it takes pin */
2154         if (mlocked)
2155                 lru_add_drain();
2156
2157         /* prevent PageLRU to go away from under us, and freeze lru stats */
2158         spin_lock_irqsave(zone_lru_lock(page_zone(head)), flags);
2159
2160         if (mapping) {
2161                 void **pslot;
2162
2163                 spin_lock(&mapping->tree_lock);
2164                 pslot = radix_tree_lookup_slot(&mapping->page_tree,
2165                                 page_index(head));
2166                 /*
2167                  * Check if the head page is present in radix tree.
2168                  * We assume all tail are present too, if head is there.
2169                  */
2170                 if (radix_tree_deref_slot_protected(pslot,
2171                                         &mapping->tree_lock) != head)
2172                         goto fail;
2173         }
2174
2175         /* Prevent deferred_split_scan() touching ->_refcount */
2176         spin_lock(&pgdata->split_queue_lock);
2177         count = page_count(head);
2178         mapcount = total_mapcount(head);
2179         if (!mapcount && page_ref_freeze(head, 1 + extra_pins)) {
2180                 if (!list_empty(page_deferred_list(head))) {
2181                         pgdata->split_queue_len--;
2182                         list_del(page_deferred_list(head));
2183                 }
2184                 if (mapping)
2185                         __dec_node_page_state(page, NR_SHMEM_THPS);
2186                 spin_unlock(&pgdata->split_queue_lock);
2187                 __split_huge_page(page, list, flags);
2188                 ret = 0;
2189         } else {
2190                 if (IS_ENABLED(CONFIG_DEBUG_VM) && mapcount) {
2191                         pr_alert("total_mapcount: %u, page_count(): %u\n",
2192                                         mapcount, count);
2193                         if (PageTail(page))
2194                                 dump_page(head, NULL);
2195                         dump_page(page, "total_mapcount(head) > 0");
2196                         BUG();
2197                 }
2198                 spin_unlock(&pgdata->split_queue_lock);
2199 fail:           if (mapping)
2200                         spin_unlock(&mapping->tree_lock);
2201                 spin_unlock_irqrestore(zone_lru_lock(page_zone(head)), flags);
2202                 unfreeze_page(head);
2203                 ret = -EBUSY;
2204         }
2205
2206 out_unlock:
2207         if (anon_vma) {
2208                 anon_vma_unlock_write(anon_vma);
2209                 put_anon_vma(anon_vma);
2210         }
2211         if (mapping)
2212                 i_mmap_unlock_read(mapping);
2213 out:
2214         count_vm_event(!ret ? THP_SPLIT_PAGE : THP_SPLIT_PAGE_FAILED);
2215         return ret;
2216 }
2217
2218 void free_transhuge_page(struct page *page)
2219 {
2220         struct pglist_data *pgdata = NODE_DATA(page_to_nid(page));
2221         unsigned long flags;
2222
2223         spin_lock_irqsave(&pgdata->split_queue_lock, flags);
2224         if (!list_empty(page_deferred_list(page))) {
2225                 pgdata->split_queue_len--;
2226                 list_del(page_deferred_list(page));
2227         }
2228         spin_unlock_irqrestore(&pgdata->split_queue_lock, flags);
2229         free_compound_page(page);
2230 }
2231
2232 void deferred_split_huge_page(struct page *page)
2233 {
2234         struct pglist_data *pgdata = NODE_DATA(page_to_nid(page));
2235         unsigned long flags;
2236
2237         VM_BUG_ON_PAGE(!PageTransHuge(page), page);
2238
2239         spin_lock_irqsave(&pgdata->split_queue_lock, flags);
2240         if (list_empty(page_deferred_list(page))) {
2241                 count_vm_event(THP_DEFERRED_SPLIT_PAGE);
2242                 list_add_tail(page_deferred_list(page), &pgdata->split_queue);
2243                 pgdata->split_queue_len++;
2244         }
2245         spin_unlock_irqrestore(&pgdata->split_queue_lock, flags);
2246 }
2247
2248 static unsigned long deferred_split_count(struct shrinker *shrink,
2249                 struct shrink_control *sc)
2250 {
2251         struct pglist_data *pgdata = NODE_DATA(sc->nid);
2252         return ACCESS_ONCE(pgdata->split_queue_len);
2253 }
2254
2255 static unsigned long deferred_split_scan(struct shrinker *shrink,
2256                 struct shrink_control *sc)
2257 {
2258         struct pglist_data *pgdata = NODE_DATA(sc->nid);
2259         unsigned long flags;
2260         LIST_HEAD(list), *pos, *next;
2261         struct page *page;
2262         int split = 0;
2263
2264         spin_lock_irqsave(&pgdata->split_queue_lock, flags);
2265         /* Take pin on all head pages to avoid freeing them under us */
2266         list_for_each_safe(pos, next, &pgdata->split_queue) {
2267                 page = list_entry((void *)pos, struct page, mapping);
2268                 page = compound_head(page);
2269                 if (get_page_unless_zero(page)) {
2270                         list_move(page_deferred_list(page), &list);
2271                 } else {
2272                         /* We lost race with put_compound_page() */
2273                         list_del_init(page_deferred_list(page));
2274                         pgdata->split_queue_len--;
2275                 }
2276                 if (!--sc->nr_to_scan)
2277                         break;
2278         }
2279         spin_unlock_irqrestore(&pgdata->split_queue_lock, flags);
2280
2281         list_for_each_safe(pos, next, &list) {
2282                 page = list_entry((void *)pos, struct page, mapping);
2283                 if (!trylock_page(page))
2284                         goto next;
2285                 /* split_huge_page() removes page from list on success */
2286                 if (!split_huge_page(page))
2287                         split++;
2288                 unlock_page(page);
2289 next:
2290                 put_page(page);
2291         }
2292
2293         spin_lock_irqsave(&pgdata->split_queue_lock, flags);
2294         list_splice_tail(&list, &pgdata->split_queue);
2295         spin_unlock_irqrestore(&pgdata->split_queue_lock, flags);
2296
2297         /*
2298          * Stop shrinker if we didn't split any page, but the queue is empty.
2299          * This can happen if pages were freed under us.
2300          */
2301         if (!split && list_empty(&pgdata->split_queue))
2302                 return SHRINK_STOP;
2303         return split;
2304 }
2305
2306 static struct shrinker deferred_split_shrinker = {
2307         .count_objects = deferred_split_count,
2308         .scan_objects = deferred_split_scan,
2309         .seeks = DEFAULT_SEEKS,
2310         .flags = SHRINKER_NUMA_AWARE,
2311 };
2312
2313 #ifdef CONFIG_DEBUG_FS
2314 static int split_huge_pages_set(void *data, u64 val)
2315 {
2316         struct zone *zone;
2317         struct page *page;
2318         unsigned long pfn, max_zone_pfn;
2319         unsigned long total = 0, split = 0;
2320
2321         if (val != 1)
2322                 return -EINVAL;
2323
2324         for_each_populated_zone(zone) {
2325                 max_zone_pfn = zone_end_pfn(zone);
2326                 for (pfn = zone->zone_start_pfn; pfn < max_zone_pfn; pfn++) {
2327                         if (!pfn_valid(pfn))
2328                                 continue;
2329
2330                         page = pfn_to_page(pfn);
2331                         if (!get_page_unless_zero(page))
2332                                 continue;
2333
2334                         if (zone != page_zone(page))
2335                                 goto next;
2336
2337                         if (!PageHead(page) || PageHuge(page) || !PageLRU(page))
2338                                 goto next;
2339
2340                         total++;
2341                         lock_page(page);
2342                         if (!split_huge_page(page))
2343                                 split++;
2344                         unlock_page(page);
2345 next:
2346                         put_page(page);
2347                 }
2348         }
2349
2350         pr_info("%lu of %lu THP split\n", split, total);
2351
2352         return 0;
2353 }
2354 DEFINE_SIMPLE_ATTRIBUTE(split_huge_pages_fops, NULL, split_huge_pages_set,
2355                 "%llu\n");
2356
2357 static int __init split_huge_pages_debugfs(void)
2358 {
2359         void *ret;
2360
2361         ret = debugfs_create_file("split_huge_pages", 0200, NULL, NULL,
2362                         &split_huge_pages_fops);
2363         if (!ret)
2364                 pr_warn("Failed to create split_huge_pages in debugfs");
2365         return 0;
2366 }
2367 late_initcall(split_huge_pages_debugfs);
2368 #endif