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 #include <linux/page_owner.h>
  34
  35 #include <asm/tlb.h>
  36 #include <asm/pgalloc.h>
  37 #include "internal.h"
  38
  39 /*
  40  * By default transparent hugepage support is disabled in order that avoid
  41  * to risk increase the memory footprint of applications without a guaranteed
  42  * benefit. When transparent hugepage support is enabled, is for all mappings,
  43  * and khugepaged scans all mappings.
  44  * Defrag is invoked by khugepaged hugepage allocations and by page faults
  45  * for all hugepage allocations.
  46  */
  47 unsigned long transparent_hugepage_flags __read_mostly =
  48 #ifdef CONFIG_TRANSPARENT_HUGEPAGE_ALWAYS
  49         (1<<TRANSPARENT_HUGEPAGE_FLAG)|
  50 #endif
  51 #ifdef CONFIG_TRANSPARENT_HUGEPAGE_MADVISE
  52         (1<<TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG)|
  53 #endif
  54         (1<<TRANSPARENT_HUGEPAGE_DEFRAG_REQ_MADV_FLAG)|
  55         (1<<TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG)|
  56         (1<<TRANSPARENT_HUGEPAGE_USE_ZERO_PAGE_FLAG);
  57
  58 static struct shrinker deferred_split_shrinker;
  59
  60 static atomic_t huge_zero_refcount;
  61 struct page *huge_zero_page __read_mostly;
  62
  63 static struct page *get_huge_zero_page(void)
  64 {
  65         struct page *zero_page;
  66 retry:
  67         if (likely(atomic_inc_not_zero(&huge_zero_refcount)))
  68                 return READ_ONCE(huge_zero_page);
  69
  70         zero_page = alloc_pages((GFP_TRANSHUGE | __GFP_ZERO) & ~__GFP_MOVABLE,
  71                         HPAGE_PMD_ORDER);
  72         if (!zero_page) {
  73                 count_vm_event(THP_ZERO_PAGE_ALLOC_FAILED);
  74                 return NULL;
  75         }
  76         count_vm_event(THP_ZERO_PAGE_ALLOC);
  77         preempt_disable();
  78         if (cmpxchg(&huge_zero_page, NULL, zero_page)) {
  79                 preempt_enable();
  80                 __free_pages(zero_page, compound_order(zero_page));
  81                 goto retry;
  82         }
  83
  84         /* We take additional reference here. It will be put back by shrinker */
  85         atomic_set(&huge_zero_refcount, 2);
  86         preempt_enable();
  87         return READ_ONCE(huge_zero_page);
  88 }
  89
  90 static void put_huge_zero_page(void)
  91 {
  92         /*
  93          * Counter should never go to zero here. Only shrinker can put
  94          * last reference.
  95          */
  96         BUG_ON(atomic_dec_and_test(&huge_zero_refcount));
  97 }
  98
  99 struct page *mm_get_huge_zero_page(struct mm_struct *mm)
 100 {
 101         if (test_bit(MMF_HUGE_ZERO_PAGE, &mm->flags))
 102                 return READ_ONCE(huge_zero_page);
 103
 104         if (!get_huge_zero_page())
 105                 return NULL;
 106
 107         if (test_and_set_bit(MMF_HUGE_ZERO_PAGE, &mm->flags))
 108                 put_huge_zero_page();
 109
 110         return READ_ONCE(huge_zero_page);
 111 }
 112
 113 void mm_put_huge_zero_page(struct mm_struct *mm)
 114 {
 115         if (test_bit(MMF_HUGE_ZERO_PAGE, &mm->flags))
 116                 put_huge_zero_page();
 117 }
 118
 119 static unsigned long shrink_huge_zero_page_count(struct shrinker *shrink,
 120                                         struct shrink_control *sc)
 121 {
 122         /* we can free zero page only if last reference remains */
 123         return atomic_read(&huge_zero_refcount) == 1 ? HPAGE_PMD_NR : 0;
 124 }
 125
 126 static unsigned long shrink_huge_zero_page_scan(struct shrinker *shrink,
 127                                        struct shrink_control *sc)
 128 {
 129         if (atomic_cmpxchg(&huge_zero_refcount, 1, 0) == 1) {
 130                 struct page *zero_page = xchg(&huge_zero_page, NULL);
 131                 BUG_ON(zero_page == NULL);
 132                 __free_pages(zero_page, compound_order(zero_page));
 133                 return HPAGE_PMD_NR;
 134         }
 135
 136         return 0;
 137 }
 138
 139 static struct shrinker huge_zero_page_shrinker = {
 140         .count_objects = shrink_huge_zero_page_count,
 141         .scan_objects = shrink_huge_zero_page_scan,
 142         .seeks = DEFAULT_SEEKS,
 143 };
 144
 145 #ifdef CONFIG_SYSFS
 146
 147 static ssize_t triple_flag_store(struct kobject *kobj,
 148                                  struct kobj_attribute *attr,
 149                                  const char *buf, size_t count,
 150                                  enum transparent_hugepage_flag enabled,
 151                                  enum transparent_hugepage_flag deferred,
 152                                  enum transparent_hugepage_flag req_madv)
 153 {
 154         if (!memcmp("defer", buf,
 155                     min(sizeof("defer")-1, count))) {
 156                 if (enabled == deferred)
 157                         return -EINVAL;
 158                 clear_bit(enabled, &transparent_hugepage_flags);
 159                 clear_bit(req_madv, &transparent_hugepage_flags);
 160                 set_bit(deferred, &transparent_hugepage_flags);
 161         } else if (!memcmp("always", buf,
 162                     min(sizeof("always")-1, count))) {
 163                 clear_bit(deferred, &transparent_hugepage_flags);
 164                 clear_bit(req_madv, &transparent_hugepage_flags);
 165                 set_bit(enabled, &transparent_hugepage_flags);
 166         } else if (!memcmp("madvise", buf,
 167                            min(sizeof("madvise")-1, count))) {
 168                 clear_bit(enabled, &transparent_hugepage_flags);
 169                 clear_bit(deferred, &transparent_hugepage_flags);
 170                 set_bit(req_madv, &transparent_hugepage_flags);
 171         } else if (!memcmp("never", buf,
 172                            min(sizeof("never")-1, count))) {
 173                 clear_bit(enabled, &transparent_hugepage_flags);
 174                 clear_bit(req_madv, &transparent_hugepage_flags);
 175                 clear_bit(deferred, &transparent_hugepage_flags);
 176         } else
 177                 return -EINVAL;
 178
 179         return count;
 180 }
 181
 182 static ssize_t enabled_show(struct kobject *kobj,
 183                             struct kobj_attribute *attr, char *buf)
 184 {
 185         if (test_bit(TRANSPARENT_HUGEPAGE_FLAG, &transparent_hugepage_flags))
 186                 return sprintf(buf, "[always] madvise never\n");
 187         else if (test_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG, &transparent_hugepage_flags))
 188                 return sprintf(buf, "always [madvise] never\n");
 189         else
 190                 return sprintf(buf, "always madvise [never]\n");
 191 }
 192
 193 static ssize_t enabled_store(struct kobject *kobj,
 194                              struct kobj_attribute *attr,
 195                              const char *buf, size_t count)
 196 {
 197         ssize_t ret;
 198
 199         ret = triple_flag_store(kobj, attr, buf, count,
 200                                 TRANSPARENT_HUGEPAGE_FLAG,
 201                                 TRANSPARENT_HUGEPAGE_FLAG,
 202                                 TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG);
 203
 204         if (ret > 0) {
 205                 int err = start_stop_khugepaged();
 206                 if (err)
 207                         ret = err;
 208         }
 209
 210         return ret;
 211 }
 212 static struct kobj_attribute enabled_attr =
 213         __ATTR(enabled, 0644, enabled_show, enabled_store);
 214
 215 ssize_t single_hugepage_flag_show(struct kobject *kobj,
 216                                 struct kobj_attribute *attr, char *buf,
 217                                 enum transparent_hugepage_flag flag)
 218 {
 219         return sprintf(buf, "%d\n",
 220                        !!test_bit(flag, &transparent_hugepage_flags));
 221 }
 222
 223 ssize_t single_hugepage_flag_store(struct kobject *kobj,
 224                                  struct kobj_attribute *attr,
 225                                  const char *buf, size_t count,
 226                                  enum transparent_hugepage_flag flag)
 227 {
 228         unsigned long value;
 229         int ret;
 230
 231         ret = kstrtoul(buf, 10, &value);
 232         if (ret < 0)
 233                 return ret;
 234         if (value > 1)
 235                 return -EINVAL;
 236
 237         if (value)
 238                 set_bit(flag, &transparent_hugepage_flags);
 239         else
 240                 clear_bit(flag, &transparent_hugepage_flags);
 241
 242         return count;
 243 }
 244
 245 /*
 246  * Currently defrag only disables __GFP_NOWAIT for allocation. A blind
 247  * __GFP_REPEAT is too aggressive, it's never worth swapping tons of
 248  * memory just to allocate one more hugepage.
 249  */
 250 static ssize_t defrag_show(struct kobject *kobj,
 251                            struct kobj_attribute *attr, char *buf)
 252 {
 253         if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_DIRECT_FLAG, &transparent_hugepage_flags))
 254                 return sprintf(buf, "[always] defer madvise never\n");
 255         if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_FLAG, &transparent_hugepage_flags))
 256                 return sprintf(buf, "always [defer] madvise never\n");
 257         else if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_REQ_MADV_FLAG, &transparent_hugepage_flags))
 258                 return sprintf(buf, "always defer [madvise] never\n");
 259         else
 260                 return sprintf(buf, "always defer madvise [never]\n");
 261
 262 }
 263 static ssize_t defrag_store(struct kobject *kobj,
 264                             struct kobj_attribute *attr,
 265                             const char *buf, size_t count)
 266 {
 267         return triple_flag_store(kobj, attr, buf, count,
 268                                  TRANSPARENT_HUGEPAGE_DEFRAG_DIRECT_FLAG,
 269                                  TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_FLAG,
 270                                  TRANSPARENT_HUGEPAGE_DEFRAG_REQ_MADV_FLAG);
 271 }
 272 static struct kobj_attribute defrag_attr =
 273         __ATTR(defrag, 0644, defrag_show, defrag_store);
 274
 275 static ssize_t use_zero_page_show(struct kobject *kobj,
 276                 struct kobj_attribute *attr, char *buf)
 277 {
 278         return single_hugepage_flag_show(kobj, attr, buf,
 279                                 TRANSPARENT_HUGEPAGE_USE_ZERO_PAGE_FLAG);
 280 }
 281 static ssize_t use_zero_page_store(struct kobject *kobj,
 282                 struct kobj_attribute *attr, const char *buf, size_t count)
 283 {
 284         return single_hugepage_flag_store(kobj, attr, buf, count,
 285                                  TRANSPARENT_HUGEPAGE_USE_ZERO_PAGE_FLAG);
 286 }
 287 static struct kobj_attribute use_zero_page_attr =
 288         __ATTR(use_zero_page, 0644, use_zero_page_show, use_zero_page_store);
 289 #ifdef CONFIG_DEBUG_VM
 290 static ssize_t debug_cow_show(struct kobject *kobj,
 291                                 struct kobj_attribute *attr, char *buf)
 292 {
 293         return single_hugepage_flag_show(kobj, attr, buf,
 294                                 TRANSPARENT_HUGEPAGE_DEBUG_COW_FLAG);
 295 }
 296 static ssize_t debug_cow_store(struct kobject *kobj,
 297                                struct kobj_attribute *attr,
 298                                const char *buf, size_t count)
 299 {
 300         return single_hugepage_flag_store(kobj, attr, buf, count,
 301                                  TRANSPARENT_HUGEPAGE_DEBUG_COW_FLAG);
 302 }
 303 static struct kobj_attribute debug_cow_attr =
 304         __ATTR(debug_cow, 0644, debug_cow_show, debug_cow_store);
 305 #endif /* CONFIG_DEBUG_VM */
 306
 307 static struct attribute *hugepage_attr[] = {
 308         &enabled_attr.attr,
 309         &defrag_attr.attr,
 310         &use_zero_page_attr.attr,
 311 #if defined(CONFIG_SHMEM) && defined(CONFIG_TRANSPARENT_HUGE_PAGECACHE)
 312         &shmem_enabled_attr.attr,
 313 #endif
 314 #ifdef CONFIG_DEBUG_VM
 315         &debug_cow_attr.attr,
 316 #endif
 317         NULL,
 318 };
 319
 320 static struct attribute_group hugepage_attr_group = {
 321         .attrs = hugepage_attr,
 322 };
 323
 324 static int __init hugepage_init_sysfs(struct kobject **hugepage_kobj)
 325 {
 326         int err;
 327
 328         *hugepage_kobj = kobject_create_and_add("transparent_hugepage", mm_kobj);
 329         if (unlikely(!*hugepage_kobj)) {
 330                 pr_err("failed to create transparent hugepage kobject\n");
 331                 return -ENOMEM;
 332         }
 333
 334         err = sysfs_create_group(*hugepage_kobj, &hugepage_attr_group);
 335         if (err) {
 336                 pr_err("failed to register transparent hugepage group\n");
 337                 goto delete_obj;
 338         }
 339
 340         err = sysfs_create_group(*hugepage_kobj, &khugepaged_attr_group);
 341         if (err) {
 342                 pr_err("failed to register transparent hugepage group\n");
 343                 goto remove_hp_group;
 344         }
 345
 346         return 0;
 347
 348 remove_hp_group:
 349         sysfs_remove_group(*hugepage_kobj, &hugepage_attr_group);
 350 delete_obj:
 351         kobject_put(*hugepage_kobj);
 352         return err;
 353 }
 354
 355 static void __init hugepage_exit_sysfs(struct kobject *hugepage_kobj)
 356 {
 357         sysfs_remove_group(hugepage_kobj, &khugepaged_attr_group);
 358         sysfs_remove_group(hugepage_kobj, &hugepage_attr_group);
 359         kobject_put(hugepage_kobj);
 360 }
 361 #else
 362 static inline int hugepage_init_sysfs(struct kobject **hugepage_kobj)
 363 {
 364         return 0;
 365 }
 366
 367 static inline void hugepage_exit_sysfs(struct kobject *hugepage_kobj)
 368 {
 369 }
 370 #endif /* CONFIG_SYSFS */
 371
 372 static int __init hugepage_init(void)
 373 {
 374         int err;
 375         struct kobject *hugepage_kobj;
 376
 377         if (!has_transparent_hugepage()) {
 378                 transparent_hugepage_flags = 0;
 379                 return -EINVAL;
 380         }
 381
 382         /*
 383          * hugepages can't be allocated by the buddy allocator
 384          */
 385         MAYBE_BUILD_BUG_ON(HPAGE_PMD_ORDER >= MAX_ORDER);
 386         /*
 387          * we use page->mapping and page->index in second tail page
 388          * as list_head: assuming THP order >= 2
 389          */
 390         MAYBE_BUILD_BUG_ON(HPAGE_PMD_ORDER < 2);
 391
 392         err = hugepage_init_sysfs(&hugepage_kobj);
 393         if (err)
 394                 goto err_sysfs;
 395
 396         err = khugepaged_init();
 397         if (err)
 398                 goto err_slab;
 399
 400         err = register_shrinker(&huge_zero_page_shrinker);
 401         if (err)
 402                 goto err_hzp_shrinker;
 403         err = register_shrinker(&deferred_split_shrinker);
 404         if (err)
 405                 goto err_split_shrinker;
 406
 407         /*
 408          * By default disable transparent hugepages on smaller systems,
 409          * where the extra memory used could hurt more than TLB overhead
 410          * is likely to save.  The admin can still enable it through /sys.
 411          */
 412         if (totalram_pages < (512 << (20 - PAGE_SHIFT))) {
 413                 transparent_hugepage_flags = 0;
 414                 return 0;
 415         }
 416
 417         err = start_stop_khugepaged();
 418         if (err)
 419                 goto err_khugepaged;
 420
 421         return 0;
 422 err_khugepaged:
 423         unregister_shrinker(&deferred_split_shrinker);
 424 err_split_shrinker:
 425         unregister_shrinker(&huge_zero_page_shrinker);
 426 err_hzp_shrinker:
 427         khugepaged_destroy();
 428 err_slab:
 429         hugepage_exit_sysfs(hugepage_kobj);
 430 err_sysfs:
 431         return err;
 432 }
 433 subsys_initcall(hugepage_init);
 434
 435 static int __init setup_transparent_hugepage(char *str)
 436 {
 437         int ret = 0;
 438         if (!str)
 439                 goto out;
 440         if (!strcmp(str, "always")) {
 441                 set_bit(TRANSPARENT_HUGEPAGE_FLAG,
 442                         &transparent_hugepage_flags);
 443                 clear_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG,
 444                           &transparent_hugepage_flags);
 445                 ret = 1;
 446         } else if (!strcmp(str, "madvise")) {
 447                 clear_bit(TRANSPARENT_HUGEPAGE_FLAG,
 448                           &transparent_hugepage_flags);
 449                 set_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG,
 450                         &transparent_hugepage_flags);
 451                 ret = 1;
 452         } else if (!strcmp(str, "never")) {
 453                 clear_bit(TRANSPARENT_HUGEPAGE_FLAG,
 454                           &transparent_hugepage_flags);
 455                 clear_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG,
 456                           &transparent_hugepage_flags);
 457                 ret = 1;
 458         }
 459 out:
 460         if (!ret)
 461                 pr_warn("transparent_hugepage= cannot parse, ignored\n");
 462         return ret;
 463 }
 464 __setup("transparent_hugepage=", setup_transparent_hugepage);
 465
 466 pmd_t maybe_pmd_mkwrite(pmd_t pmd, struct vm_area_struct *vma)
 467 {
 468         if (likely(vma->vm_flags & VM_WRITE))
 469                 pmd = pmd_mkwrite(pmd);
 470         return pmd;
 471 }
 472
 473 static inline struct list_head *page_deferred_list(struct page *page)
 474 {
 475         /*
 476          * ->lru in the tail pages is occupied by compound_head.
 477          * Let's use ->mapping + ->index in the second tail page as list_head.
 478          */
 479         return (struct list_head *)&page[2].mapping;
 480 }
 481
 482 void prep_transhuge_page(struct page *page)
 483 {
 484         /*
 485          * we use page->mapping and page->indexlru in second tail page
 486          * as list_head: assuming THP order >= 2
 487          */
 488
 489         INIT_LIST_HEAD(page_deferred_list(page));
 490         set_compound_page_dtor(page, TRANSHUGE_PAGE_DTOR);
 491 }
 492
 493 unsigned long __thp_get_unmapped_area(struct file *filp, unsigned long len,
 494                 loff_t off, unsigned long flags, unsigned long size)
 495 {
 496         unsigned long addr;
 497         loff_t off_end = off + len;
 498         loff_t off_align = round_up(off, size);
 499         unsigned long len_pad;
 500
 501         if (off_end <= off_align || (off_end - off_align) < size)
 502                 return 0;
 503
 504         len_pad = len + size;
 505         if (len_pad < len || (off + len_pad) < off)
 506                 return 0;
 507
 508         addr = current->mm->get_unmapped_area(filp, 0, len_pad,
 509                                               off >> PAGE_SHIFT, flags);
 510         if (IS_ERR_VALUE(addr))
 511                 return 0;
 512
 513         addr += (off - addr) & (size - 1);
 514         return addr;
 515 }
 516
 517 unsigned long thp_get_unmapped_area(struct file *filp, unsigned long addr,
 518                 unsigned long len, unsigned long pgoff, unsigned long flags)
 519 {
 520         loff_t off = (loff_t)pgoff << PAGE_SHIFT;
 521
 522         if (addr)
 523                 goto out;
 524         if (!IS_DAX(filp->f_mapping->host) || !IS_ENABLED(CONFIG_FS_DAX_PMD))
 525                 goto out;
 526
 527         addr = __thp_get_unmapped_area(filp, len, off, flags, PMD_SIZE);
 528         if (addr)
 529                 return addr;
 530
 531  out:
 532         return current->mm->get_unmapped_area(filp, addr, len, pgoff, flags);
 533 }
 534 EXPORT_SYMBOL_GPL(thp_get_unmapped_area);
 535
 536 static int __do_huge_pmd_anonymous_page(struct fault_env *fe, struct page *page,
 537                 gfp_t gfp)
 538 {
 539         struct vm_area_struct *vma = fe->vma;
 540         struct mem_cgroup *memcg;
 541         pgtable_t pgtable;
 542         unsigned long haddr = fe->address & HPAGE_PMD_MASK;
 543
 544         VM_BUG_ON_PAGE(!PageCompound(page), page);
 545
 546         if (mem_cgroup_try_charge(page, vma->vm_mm, gfp | __GFP_NORETRY, &memcg,
 547                                   true)) {
 548                 put_page(page);
 549                 count_vm_event(THP_FAULT_FALLBACK);
 550                 return VM_FAULT_FALLBACK;
 551         }
 552
 553         pgtable = pte_alloc_one(vma->vm_mm, haddr);
 554         if (unlikely(!pgtable)) {
 555                 mem_cgroup_cancel_charge(page, memcg, true);
 556                 put_page(page);
 557                 return VM_FAULT_OOM;
 558         }
 559
 560         clear_huge_page(page, haddr, HPAGE_PMD_NR);
 561         /*
 562          * The memory barrier inside __SetPageUptodate makes sure that
 563          * clear_huge_page writes become visible before the set_pmd_at()
 564          * write.
 565          */
 566         __SetPageUptodate(page);
 567
 568         fe->ptl = pmd_lock(vma->vm_mm, fe->pmd);
 569         if (unlikely(!pmd_none(*fe->pmd))) {
 570                 spin_unlock(fe->ptl);
 571                 mem_cgroup_cancel_charge(page, memcg, true);
 572                 put_page(page);
 573                 pte_free(vma->vm_mm, pgtable);
 574         } else {
 575                 pmd_t entry;
 576
 577                 /* Deliver the page fault to userland */
 578                 if (userfaultfd_missing(vma)) {
 579                         int ret;
 580
 581                         spin_unlock(fe->ptl);
 582                         mem_cgroup_cancel_charge(page, memcg, true);
 583                         put_page(page);
 584                         pte_free(vma->vm_mm, pgtable);
 585                         ret = handle_userfault(fe, VM_UFFD_MISSING);
 586                         VM_BUG_ON(ret & VM_FAULT_FALLBACK);
 587                         return ret;
 588                 }
 589
 590                 entry = mk_huge_pmd(page, vma->vm_page_prot);
 591                 entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
 592                 page_add_new_anon_rmap(page, vma, haddr, true);
 593                 mem_cgroup_commit_charge(page, memcg, false, true);
 594                 lru_cache_add_active_or_unevictable(page, vma);
 595                 pgtable_trans_huge_deposit(vma->vm_mm, fe->pmd, pgtable);
 596                 set_pmd_at(vma->vm_mm, haddr, fe->pmd, entry);
 597                 add_mm_counter(vma->vm_mm, MM_ANONPAGES, HPAGE_PMD_NR);
 598                 atomic_long_inc(&vma->vm_mm->nr_ptes);
 599                 spin_unlock(fe->ptl);
 600                 count_vm_event(THP_FAULT_ALLOC);
 601         }
 602
 603         return 0;
 604 }
 605
 606 /*
 607  * If THP defrag is set to always then directly reclaim/compact as necessary
 608  * If set to defer then do only background reclaim/compact and defer to khugepaged
 609  * If set to madvise and the VMA is flagged then directly reclaim/compact
 610  * When direct reclaim/compact is allowed, don't retry except for flagged VMA's
 611  */
 612 static inline gfp_t alloc_hugepage_direct_gfpmask(struct vm_area_struct *vma)
 613 {
 614         bool vma_madvised = !!(vma->vm_flags & VM_HUGEPAGE);
 615
 616         if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_REQ_MADV_FLAG,
 617                                 &transparent_hugepage_flags) && vma_madvised)
 618                 return GFP_TRANSHUGE;
 619         else if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_FLAG,
 620                                                 &transparent_hugepage_flags))
 621                 return GFP_TRANSHUGE_LIGHT | __GFP_KSWAPD_RECLAIM;
 622         else if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_DIRECT_FLAG,
 623                                                 &transparent_hugepage_flags))
 624                 return GFP_TRANSHUGE | (vma_madvised ? 0 : __GFP_NORETRY);
 625
 626         return GFP_TRANSHUGE_LIGHT;
 627 }
 628
 629 /* Caller must hold page table lock. */
 630 static bool set_huge_zero_page(pgtable_t pgtable, struct mm_struct *mm,
 631                 struct vm_area_struct *vma, unsigned long haddr, pmd_t *pmd,
 632                 struct page *zero_page)
 633 {
 634         pmd_t entry;
 635         if (!pmd_none(*pmd))
 636                 return false;
 637         entry = mk_pmd(zero_page, vma->vm_page_prot);
 638         entry = pmd_mkhuge(entry);
 639         if (pgtable)
 640                 pgtable_trans_huge_deposit(mm, pmd, pgtable);
 641         set_pmd_at(mm, haddr, pmd, entry);
 642         atomic_long_inc(&mm->nr_ptes);
 643         return true;
 644 }
 645
 646 int do_huge_pmd_anonymous_page(struct fault_env *fe)
 647 {
 648         struct vm_area_struct *vma = fe->vma;
 649         gfp_t gfp;
 650         struct page *page;
 651         unsigned long haddr = fe->address & HPAGE_PMD_MASK;
 652
 653         if (haddr < vma->vm_start || haddr + HPAGE_PMD_SIZE > vma->vm_end)
 654                 return VM_FAULT_FALLBACK;
 655         if (unlikely(anon_vma_prepare(vma)))
 656                 return VM_FAULT_OOM;
 657         if (unlikely(khugepaged_enter(vma, vma->vm_flags)))
 658                 return VM_FAULT_OOM;
 659         if (!(fe->flags & FAULT_FLAG_WRITE) &&
 660                         !mm_forbids_zeropage(vma->vm_mm) &&
 661                         transparent_hugepage_use_zero_page()) {
 662                 pgtable_t pgtable;
 663                 struct page *zero_page;
 664                 bool set;
 665                 int ret;
 666                 pgtable = pte_alloc_one(vma->vm_mm, haddr);
 667                 if (unlikely(!pgtable))
 668                         return VM_FAULT_OOM;
 669                 zero_page = mm_get_huge_zero_page(vma->vm_mm);
 670                 if (unlikely(!zero_page)) {
 671                         pte_free(vma->vm_mm, pgtable);
 672                         count_vm_event(THP_FAULT_FALLBACK);
 673                         return VM_FAULT_FALLBACK;
 674                 }
 675                 fe->ptl = pmd_lock(vma->vm_mm, fe->pmd);
 676                 ret = 0;
 677                 set = false;
 678                 if (pmd_none(*fe->pmd)) {
 679                         if (userfaultfd_missing(vma)) {
 680                                 spin_unlock(fe->ptl);
 681                                 ret = handle_userfault(fe, VM_UFFD_MISSING);
 682                                 VM_BUG_ON(ret & VM_FAULT_FALLBACK);
 683                         } else {
 684                                 set_huge_zero_page(pgtable, vma->vm_mm, vma,
 685                                                    haddr, fe->pmd, zero_page);
 686                                 spin_unlock(fe->ptl);
 687                                 set = true;
 688                         }
 689                 } else
 690                         spin_unlock(fe->ptl);
 691                 if (!set)
 692                         pte_free(vma->vm_mm, pgtable);
 693                 return ret;
 694         }
 695         gfp = alloc_hugepage_direct_gfpmask(vma);
 696         page = alloc_hugepage_vma(gfp, vma, haddr, HPAGE_PMD_ORDER);
 697         if (unlikely(!page)) {
 698                 count_vm_event(THP_FAULT_FALLBACK);
 699                 return VM_FAULT_FALLBACK;
 700         }
 701         prep_transhuge_page(page);
 702         return __do_huge_pmd_anonymous_page(fe, page, gfp);
 703 }
 704
 705 static void insert_pfn_pmd(struct vm_area_struct *vma, unsigned long addr,
 706                 pmd_t *pmd, pfn_t pfn, pgprot_t prot, bool write)
 707 {
 708         struct mm_struct *mm = vma->vm_mm;
 709         pmd_t entry;
 710         spinlock_t *ptl;
 711
 712         ptl = pmd_lock(mm, pmd);
 713         entry = pmd_mkhuge(pfn_t_pmd(pfn, prot));
 714         if (pfn_t_devmap(pfn))
 715                 entry = pmd_mkdevmap(entry);
 716         if (write) {
 717                 entry = pmd_mkyoung(pmd_mkdirty(entry));
 718                 entry = maybe_pmd_mkwrite(entry, vma);
 719         }
 720         set_pmd_at(mm, addr, pmd, entry);
 721         update_mmu_cache_pmd(vma, addr, pmd);
 722         spin_unlock(ptl);
 723 }
 724
 725 int vmf_insert_pfn_pmd(struct vm_area_struct *vma, unsigned long addr,
 726                         pmd_t *pmd, pfn_t pfn, bool write)
 727 {
 728         pgprot_t pgprot = vma->vm_page_prot;
 729         /*
 730          * If we had pmd_special, we could avoid all these restrictions,
 731          * but we need to be consistent with PTEs and architectures that
 732          * can't support a 'special' bit.
 733          */
 734         BUG_ON(!(vma->vm_flags & (VM_PFNMAP|VM_MIXEDMAP)));
 735         BUG_ON((vma->vm_flags & (VM_PFNMAP|VM_MIXEDMAP)) ==
 736                                                 (VM_PFNMAP|VM_MIXEDMAP));
 737         BUG_ON((vma->vm_flags & VM_PFNMAP) && is_cow_mapping(vma->vm_flags));
 738         BUG_ON(!pfn_t_devmap(pfn));
 739
 740         if (addr < vma->vm_start || addr >= vma->vm_end)
 741                 return VM_FAULT_SIGBUS;
 742         if (track_pfn_insert(vma, &pgprot, pfn))
 743                 return VM_FAULT_SIGBUS;
 744         insert_pfn_pmd(vma, addr, pmd, pfn, pgprot, write);
 745         return VM_FAULT_NOPAGE;
 746 }
 747 EXPORT_SYMBOL_GPL(vmf_insert_pfn_pmd);
 748
 749 static void touch_pmd(struct vm_area_struct *vma, unsigned long addr,
 750                 pmd_t *pmd, int flags)
 751 {
 752         pmd_t _pmd;
 753
 754         _pmd = pmd_mkyoung(*pmd);
 755         if (flags & FOLL_WRITE)
 756                 _pmd = pmd_mkdirty(_pmd);
 757         if (pmdp_set_access_flags(vma, addr & HPAGE_PMD_MASK,
 758                                 pmd, _pmd, flags & FOLL_WRITE))
 759                 update_mmu_cache_pmd(vma, addr, pmd);
 760 }
 761
 762 struct page *follow_devmap_pmd(struct vm_area_struct *vma, unsigned long addr,
 763                 pmd_t *pmd, int flags)
 764 {
 765         unsigned long pfn = pmd_pfn(*pmd);
 766         struct mm_struct *mm = vma->vm_mm;
 767         struct dev_pagemap *pgmap;
 768         struct page *page;
 769
 770         assert_spin_locked(pmd_lockptr(mm, pmd));
 771
 772         /*
 773          * When we COW a devmap PMD entry, we split it into PTEs, so we should
 774          * not be in this function with `flags & FOLL_COW` set.
 775          */
 776         WARN_ONCE(flags & FOLL_COW, "mm: In follow_devmap_pmd with FOLL_COW set");
 777
 778         if (flags & FOLL_WRITE && !pmd_write(*pmd))
 779                 return NULL;
 780
 781         if (pmd_present(*pmd) && pmd_devmap(*pmd))
 782                 /* pass */;
 783         else
 784                 return NULL;
 785
 786         if (flags & FOLL_TOUCH)
 787                 touch_pmd(vma, addr, pmd, flags);
 788
 789         /*
 790          * device mapped pages can only be returned if the
 791          * caller will manage the page reference count.
 792          */
 793         if (!(flags & FOLL_GET))
 794                 return ERR_PTR(-EEXIST);
 795
 796         pfn += (addr & ~PMD_MASK) >> PAGE_SHIFT;
 797         pgmap = get_dev_pagemap(pfn, NULL);
 798         if (!pgmap)
 799                 return ERR_PTR(-EFAULT);
 800         page = pfn_to_page(pfn);
 801         get_page(page);
 802         put_dev_pagemap(pgmap);
 803
 804         return page;
 805 }
 806
 807 int copy_huge_pmd(struct mm_struct *dst_mm, struct mm_struct *src_mm,
 808                   pmd_t *dst_pmd, pmd_t *src_pmd, unsigned long addr,
 809                   struct vm_area_struct *vma)
 810 {
 811         spinlock_t *dst_ptl, *src_ptl;
 812         struct page *src_page;
 813         pmd_t pmd;
 814         pgtable_t pgtable = NULL;
 815         int ret = -ENOMEM;
 816
 817         /* Skip if can be re-fill on fault */
 818         if (!vma_is_anonymous(vma))
 819                 return 0;
 820
 821         pgtable = pte_alloc_one(dst_mm, addr);
 822         if (unlikely(!pgtable))
 823                 goto out;
 824
 825         dst_ptl = pmd_lock(dst_mm, dst_pmd);
 826         src_ptl = pmd_lockptr(src_mm, src_pmd);
 827         spin_lock_nested(src_ptl, SINGLE_DEPTH_NESTING);
 828
 829         ret = -EAGAIN;
 830         pmd = *src_pmd;
 831         if (unlikely(!pmd_trans_huge(pmd))) {
 832                 pte_free(dst_mm, pgtable);
 833                 goto out_unlock;
 834         }
 835         /*
 836          * When page table lock is held, the huge zero pmd should not be
 837          * under splitting since we don't split the page itself, only pmd to
 838          * a page table.
 839          */
 840         if (is_huge_zero_pmd(pmd)) {
 841                 struct page *zero_page;
 842                 /*
 843                  * get_huge_zero_page() will never allocate a new page here,
 844                  * since we already have a zero page to copy. It just takes a
 845                  * reference.
 846                  */
 847                 zero_page = mm_get_huge_zero_page(dst_mm);
 848                 set_huge_zero_page(pgtable, dst_mm, vma, addr, dst_pmd,
 849                                 zero_page);
 850                 ret = 0;
 851                 goto out_unlock;
 852         }
 853
 854         src_page = pmd_page(pmd);
 855         VM_BUG_ON_PAGE(!PageHead(src_page), src_page);
 856         get_page(src_page);
 857         page_dup_rmap(src_page, true);
 858         add_mm_counter(dst_mm, MM_ANONPAGES, HPAGE_PMD_NR);
 859         atomic_long_inc(&dst_mm->nr_ptes);
 860         pgtable_trans_huge_deposit(dst_mm, dst_pmd, pgtable);
 861
 862         pmdp_set_wrprotect(src_mm, addr, src_pmd);
 863         pmd = pmd_mkold(pmd_wrprotect(pmd));
 864         set_pmd_at(dst_mm, addr, dst_pmd, pmd);
 865
 866         ret = 0;
 867 out_unlock:
 868         spin_unlock(src_ptl);
 869         spin_unlock(dst_ptl);
 870 out:
 871         return ret;
 872 }
 873
 874 void huge_pmd_set_accessed(struct fault_env *fe, pmd_t orig_pmd)
 875 {
 876         pmd_t entry;
 877         unsigned long haddr;
 878         bool write = fe->flags & FAULT_FLAG_WRITE;
 879
 880         fe->ptl = pmd_lock(fe->vma->vm_mm, fe->pmd);
 881         if (unlikely(!pmd_same(*fe->pmd, orig_pmd)))
 882                 goto unlock;
 883
 884         entry = pmd_mkyoung(orig_pmd);
 885         if (write)
 886                 entry = pmd_mkdirty(entry);
 887         haddr = fe->address & HPAGE_PMD_MASK;
 888         if (pmdp_set_access_flags(fe->vma, haddr, fe->pmd, entry, write))
 889                 update_mmu_cache_pmd(fe->vma, fe->address, fe->pmd);
 890
 891 unlock:
 892         spin_unlock(fe->ptl);
 893 }
 894
 895 static int do_huge_pmd_wp_page_fallback(struct fault_env *fe, pmd_t orig_pmd,
 896                 struct page *page)
 897 {
 898         struct vm_area_struct *vma = fe->vma;
 899         unsigned long haddr = fe->address & HPAGE_PMD_MASK;
 900         struct mem_cgroup *memcg;
 901         pgtable_t pgtable;
 902         pmd_t _pmd;
 903         int ret = 0, i;
 904         struct page **pages;
 905         unsigned long mmun_start;       /* For mmu_notifiers */
 906         unsigned long mmun_end;         /* For mmu_notifiers */
 907
 908         pages = kmalloc(sizeof(struct page *) * HPAGE_PMD_NR,
 909                         GFP_KERNEL);
 910         if (unlikely(!pages)) {
 911                 ret |= VM_FAULT_OOM;
 912                 goto out;
 913         }
 914
 915         for (i = 0; i < HPAGE_PMD_NR; i++) {
 916                 pages[i] = alloc_page_vma_node(GFP_HIGHUSER_MOVABLE |
 917                                                __GFP_OTHER_NODE, vma,
 918                                                fe->address, page_to_nid(page));
 919                 if (unlikely(!pages[i] ||
 920                              mem_cgroup_try_charge(pages[i], vma->vm_mm,
 921                                      GFP_KERNEL, &memcg, false))) {
 922                         if (pages[i])
 923                                 put_page(pages[i]);
 924                         while (--i >= 0) {
 925                                 memcg = (void *)page_private(pages[i]);
 926                                 set_page_private(pages[i], 0);
 927                                 mem_cgroup_cancel_charge(pages[i], memcg,
 928                                                 false);
 929                                 put_page(pages[i]);
 930                         }
 931                         kfree(pages);
 932                         ret |= VM_FAULT_OOM;
 933                         goto out;
 934                 }
 935                 set_page_private(pages[i], (unsigned long)memcg);
 936         }
 937
 938         for (i = 0; i < HPAGE_PMD_NR; i++) {
 939                 copy_user_highpage(pages[i], page + i,
 940                                    haddr + PAGE_SIZE * i, vma);
 941                 __SetPageUptodate(pages[i]);
 942                 cond_resched();
 943         }
 944
 945         mmun_start = haddr;
 946         mmun_end   = haddr + HPAGE_PMD_SIZE;
 947         mmu_notifier_invalidate_range_start(vma->vm_mm, mmun_start, mmun_end);
 948
 949         fe->ptl = pmd_lock(vma->vm_mm, fe->pmd);
 950         if (unlikely(!pmd_same(*fe->pmd, orig_pmd)))
 951                 goto out_free_pages;
 952         VM_BUG_ON_PAGE(!PageHead(page), page);
 953
 954         pmdp_huge_clear_flush_notify(vma, haddr, fe->pmd);
 955         /* leave pmd empty until pte is filled */
 956
 957         pgtable = pgtable_trans_huge_withdraw(vma->vm_mm, fe->pmd);
 958         pmd_populate(vma->vm_mm, &_pmd, pgtable);
 959
 960         for (i = 0; i < HPAGE_PMD_NR; i++, haddr += PAGE_SIZE) {
 961                 pte_t entry;
 962                 entry = mk_pte(pages[i], vma->vm_page_prot);
 963                 entry = maybe_mkwrite(pte_mkdirty(entry), vma);
 964                 memcg = (void *)page_private(pages[i]);
 965                 set_page_private(pages[i], 0);
 966                 page_add_new_anon_rmap(pages[i], fe->vma, haddr, false);
 967                 mem_cgroup_commit_charge(pages[i], memcg, false, false);
 968                 lru_cache_add_active_or_unevictable(pages[i], vma);
 969                 fe->pte = pte_offset_map(&_pmd, haddr);
 970                 VM_BUG_ON(!pte_none(*fe->pte));
 971                 set_pte_at(vma->vm_mm, haddr, fe->pte, entry);
 972                 pte_unmap(fe->pte);
 973         }
 974         kfree(pages);
 975
 976         smp_wmb(); /* make pte visible before pmd */
 977         pmd_populate(vma->vm_mm, fe->pmd, pgtable);
 978         page_remove_rmap(page, true);
 979         spin_unlock(fe->ptl);
 980
 981         mmu_notifier_invalidate_range_end(vma->vm_mm, mmun_start, mmun_end);
 982
 983         ret |= VM_FAULT_WRITE;
 984         put_page(page);
 985
 986 out:
 987         return ret;
 988
 989 out_free_pages:
 990         spin_unlock(fe->ptl);
 991         mmu_notifier_invalidate_range_end(vma->vm_mm, mmun_start, mmun_end);
 992         for (i = 0; i < HPAGE_PMD_NR; i++) {
 993                 memcg = (void *)page_private(pages[i]);
 994                 set_page_private(pages[i], 0);
 995                 mem_cgroup_cancel_charge(pages[i], memcg, false);
 996                 put_page(pages[i]);
 997         }
 998         kfree(pages);
 999         goto out;
1000 }
1001
1002 int do_huge_pmd_wp_page(struct fault_env *fe, pmd_t orig_pmd)
1003 {
1004         struct vm_area_struct *vma = fe->vma;
1005         struct page *page = NULL, *new_page;
1006         struct mem_cgroup *memcg;
1007         unsigned long haddr = fe->address & HPAGE_PMD_MASK;
1008         unsigned long mmun_start;       /* For mmu_notifiers */
1009         unsigned long mmun_end;         /* For mmu_notifiers */
1010         gfp_t huge_gfp;                 /* for allocation and charge */
1011         int ret = 0;
1012
1013         fe->ptl = pmd_lockptr(vma->vm_mm, fe->pmd);
1014         VM_BUG_ON_VMA(!vma->anon_vma, vma);
1015         if (is_huge_zero_pmd(orig_pmd))
1016                 goto alloc;
1017         spin_lock(fe->ptl);
1018         if (unlikely(!pmd_same(*fe->pmd, orig_pmd)))
1019                 goto out_unlock;
1020
1021         page = pmd_page(orig_pmd);
1022         VM_BUG_ON_PAGE(!PageCompound(page) || !PageHead(page), page);
1023         /*
1024          * We can only reuse the page if nobody else maps the huge page or it's
1025          * part.
1026          */
1027         if (page_trans_huge_mapcount(page, NULL) == 1) {
1028                 pmd_t entry;
1029                 entry = pmd_mkyoung(orig_pmd);
1030                 entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
1031                 if (pmdp_set_access_flags(vma, haddr, fe->pmd, entry,  1))
1032                         update_mmu_cache_pmd(vma, fe->address, fe->pmd);
1033                 ret |= VM_FAULT_WRITE;
1034                 goto out_unlock;
1035         }
1036         get_page(page);
1037         spin_unlock(fe->ptl);
1038 alloc:
1039         if (transparent_hugepage_enabled(vma) &&
1040             !transparent_hugepage_debug_cow()) {
1041                 huge_gfp = alloc_hugepage_direct_gfpmask(vma);
1042                 new_page = alloc_hugepage_vma(huge_gfp, vma, haddr, HPAGE_PMD_ORDER);
1043         } else
1044                 new_page = NULL;
1045
1046         if (likely(new_page)) {
1047                 prep_transhuge_page(new_page);
1048         } else {
1049                 if (!page) {
1050                         split_huge_pmd(vma, fe->pmd, fe->address);
1051                         ret |= VM_FAULT_FALLBACK;
1052                 } else {
1053                         ret = do_huge_pmd_wp_page_fallback(fe, orig_pmd, page);
1054                         if (ret & VM_FAULT_OOM) {
1055                                 split_huge_pmd(vma, fe->pmd, fe->address);
1056                                 ret |= VM_FAULT_FALLBACK;
1057                         }
1058                         put_page(page);
1059                 }
1060                 count_vm_event(THP_FAULT_FALLBACK);
1061                 goto out;
1062         }
1063
1064         if (unlikely(mem_cgroup_try_charge(new_page, vma->vm_mm,
1065                                 huge_gfp | __GFP_NORETRY, &memcg, true))) {
1066                 put_page(new_page);
1067                 split_huge_pmd(vma, fe->pmd, fe->address);
1068                 if (page)
1069                         put_page(page);
1070                 ret |= VM_FAULT_FALLBACK;
1071                 count_vm_event(THP_FAULT_FALLBACK);
1072                 goto out;
1073         }
1074
1075         count_vm_event(THP_FAULT_ALLOC);
1076
1077         if (!page)
1078                 clear_huge_page(new_page, haddr, HPAGE_PMD_NR);
1079         else
1080                 copy_user_huge_page(new_page, page, haddr, vma, HPAGE_PMD_NR);
1081         __SetPageUptodate(new_page);
1082
1083         mmun_start = haddr;
1084         mmun_end   = haddr + HPAGE_PMD_SIZE;
1085         mmu_notifier_invalidate_range_start(vma->vm_mm, mmun_start, mmun_end);
1086
1087         spin_lock(fe->ptl);
1088         if (page)
1089                 put_page(page);
1090         if (unlikely(!pmd_same(*fe->pmd, orig_pmd))) {
1091                 spin_unlock(fe->ptl);
1092                 mem_cgroup_cancel_charge(new_page, memcg, true);
1093                 put_page(new_page);
1094                 goto out_mn;
1095         } else {
1096                 pmd_t entry;
1097                 entry = mk_huge_pmd(new_page, vma->vm_page_prot);
1098                 entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
1099                 pmdp_huge_clear_flush_notify(vma, haddr, fe->pmd);
1100                 page_add_new_anon_rmap(new_page, vma, haddr, true);
1101                 mem_cgroup_commit_charge(new_page, memcg, false, true);
1102                 lru_cache_add_active_or_unevictable(new_page, vma);
1103                 set_pmd_at(vma->vm_mm, haddr, fe->pmd, entry);
1104                 update_mmu_cache_pmd(vma, fe->address, fe->pmd);
1105                 if (!page) {
1106                         add_mm_counter(vma->vm_mm, MM_ANONPAGES, HPAGE_PMD_NR);
1107                 } else {
1108                         VM_BUG_ON_PAGE(!PageHead(page), page);
1109                         page_remove_rmap(page, true);
1110                         put_page(page);
1111                 }
1112                 ret |= VM_FAULT_WRITE;
1113         }
1114         spin_unlock(fe->ptl);
1115 out_mn:
1116         mmu_notifier_invalidate_range_end(vma->vm_mm, mmun_start, mmun_end);
1117 out:
1118         return ret;
1119 out_unlock:
1120         spin_unlock(fe->ptl);
1121         return ret;
1122 }
1123
1124 /*
1125  * FOLL_FORCE can write to even unwritable pmd's, but only
1126  * after we've gone through a COW cycle and they are dirty.
1127  */
1128 static inline bool can_follow_write_pmd(pmd_t pmd, unsigned int flags)
1129 {
1130         return pmd_write(pmd) ||
1131                ((flags & FOLL_FORCE) && (flags & FOLL_COW) && pmd_dirty(pmd));
1132 }
1133
1134 struct page *follow_trans_huge_pmd(struct vm_area_struct *vma,
1135                                    unsigned long addr,
1136                                    pmd_t *pmd,
1137                                    unsigned int flags)
1138 {
1139         struct mm_struct *mm = vma->vm_mm;
1140         struct page *page = NULL;
1141
1142         assert_spin_locked(pmd_lockptr(mm, pmd));
1143
1144         if (flags & FOLL_WRITE && !can_follow_write_pmd(*pmd, flags))
1145                 goto out;
1146
1147         /* Avoid dumping huge zero page */
1148         if ((flags & FOLL_DUMP) && is_huge_zero_pmd(*pmd))
1149                 return ERR_PTR(-EFAULT);
1150
1151         /* Full NUMA hinting faults to serialise migration in fault paths */
1152         if ((flags & FOLL_NUMA) && pmd_protnone(*pmd))
1153                 goto out;
1154
1155         page = pmd_page(*pmd);
1156         VM_BUG_ON_PAGE(!PageHead(page) && !is_zone_device_page(page), page);
1157         if (flags & FOLL_TOUCH)
1158                 touch_pmd(vma, addr, pmd, flags);
1159         if ((flags & FOLL_MLOCK) && (vma->vm_flags & VM_LOCKED)) {
1160                 /*
1161                  * We don't mlock() pte-mapped THPs. This way we can avoid
1162                  * leaking mlocked pages into non-VM_LOCKED VMAs.
1163                  *
1164                  * For anon THP:
1165                  *
1166                  * In most cases the pmd is the only mapping of the page as we
1167                  * break COW for the mlock() -- see gup_flags |= FOLL_WRITE for
1168                  * writable private mappings in populate_vma_page_range().
1169                  *
1170                  * The only scenario when we have the page shared here is if we
1171                  * mlocking read-only mapping shared over fork(). We skip
1172                  * mlocking such pages.
1173                  *
1174                  * For file THP:
1175                  *
1176                  * We can expect PageDoubleMap() to be stable under page lock:
1177                  * for file pages we set it in page_add_file_rmap(), which
1178                  * requires page to be locked.
1179                  */
1180
1181                 if (PageAnon(page) && compound_mapcount(page) != 1)
1182                         goto skip_mlock;
1183                 if (PageDoubleMap(page) || !page->mapping)
1184                         goto skip_mlock;
1185                 if (!trylock_page(page))
1186                         goto skip_mlock;
1187                 lru_add_drain();
1188                 if (page->mapping && !PageDoubleMap(page))
1189                         mlock_vma_page(page);
1190                 unlock_page(page);
1191         }
1192 skip_mlock:
1193         page += (addr & ~HPAGE_PMD_MASK) >> PAGE_SHIFT;
1194         VM_BUG_ON_PAGE(!PageCompound(page) && !is_zone_device_page(page), page);
1195         if (flags & FOLL_GET)
1196                 get_page(page);
1197
1198 out:
1199         return page;
1200 }
1201
1202 /* NUMA hinting page fault entry point for trans huge pmds */
1203 int do_huge_pmd_numa_page(struct fault_env *fe, pmd_t pmd)
1204 {
1205         struct vm_area_struct *vma = fe->vma;
1206         struct anon_vma *anon_vma = NULL;
1207         struct page *page;
1208         unsigned long haddr = fe->address & HPAGE_PMD_MASK;
1209         int page_nid = -1, this_nid = numa_node_id();
1210         int target_nid, last_cpupid = -1;
1211         bool page_locked;
1212         bool migrated = false;
1213         bool was_writable;
1214         int flags = 0;
1215
1216         fe->ptl = pmd_lock(vma->vm_mm, fe->pmd);
1217         if (unlikely(!pmd_same(pmd, *fe->pmd)))
1218                 goto out_unlock;
1219
1220         /*
1221          * If there are potential migrations, wait for completion and retry
1222          * without disrupting NUMA hinting information. Do not relock and
1223          * check_same as the page may no longer be mapped.
1224          */
1225         if (unlikely(pmd_trans_migrating(*fe->pmd))) {
1226                 page = pmd_page(*fe->pmd);
1227                 if (!get_page_unless_zero(page))
1228                         goto out_unlock;
1229                 spin_unlock(fe->ptl);
1230                 wait_on_page_locked(page);
1231                 put_page(page);
1232                 goto out;
1233         }
1234
1235         page = pmd_page(pmd);
1236         BUG_ON(is_huge_zero_page(page));
1237         page_nid = page_to_nid(page);
1238         last_cpupid = page_cpupid_last(page);
1239         count_vm_numa_event(NUMA_HINT_FAULTS);
1240         if (page_nid == this_nid) {
1241                 count_vm_numa_event(NUMA_HINT_FAULTS_LOCAL);
1242                 flags |= TNF_FAULT_LOCAL;
1243         }
1244
1245         /* See similar comment in do_numa_page for explanation */
1246         if (!pmd_write(pmd))
1247                 flags |= TNF_NO_GROUP;
1248
1249         /*
1250          * Acquire the page lock to serialise THP migrations but avoid dropping
1251          * page_table_lock if at all possible
1252          */
1253         page_locked = trylock_page(page);
1254         target_nid = mpol_misplaced(page, vma, haddr);
1255         if (target_nid == -1) {
1256                 /* If the page was locked, there are no parallel migrations */
1257                 if (page_locked)
1258                         goto clear_pmdnuma;
1259         }
1260
1261         /* Migration could have started since the pmd_trans_migrating check */
1262         if (!page_locked) {
1263                 page_nid = -1;
1264                 if (!get_page_unless_zero(page))
1265                         goto out_unlock;
1266                 spin_unlock(fe->ptl);
1267                 wait_on_page_locked(page);
1268                 put_page(page);
1269                 goto out;
1270         }
1271
1272         /*
1273          * Page is misplaced. Page lock serialises migrations. Acquire anon_vma
1274          * to serialises splits
1275          */
1276         get_page(page);
1277         spin_unlock(fe->ptl);
1278         anon_vma = page_lock_anon_vma_read(page);
1279
1280         /* Confirm the PMD did not change while page_table_lock was released */
1281         spin_lock(fe->ptl);
1282         if (unlikely(!pmd_same(pmd, *fe->pmd))) {
1283                 unlock_page(page);
1284                 put_page(page);
1285                 page_nid = -1;
1286                 goto out_unlock;
1287         }
1288
1289         /* Bail if we fail to protect against THP splits for any reason */
1290         if (unlikely(!anon_vma)) {
1291                 put_page(page);
1292                 page_nid = -1;
1293                 goto clear_pmdnuma;
1294         }
1295
1296         /*
1297          * Migrate the THP to the requested node, returns with page unlocked
1298          * and access rights restored.
1299          */
1300         spin_unlock(fe->ptl);
1301         migrated = migrate_misplaced_transhuge_page(vma->vm_mm, vma,
1302                                 fe->pmd, pmd, fe->address, page, target_nid);
1303         if (migrated) {
1304                 flags |= TNF_MIGRATED;
1305                 page_nid = target_nid;
1306         } else
1307                 flags |= TNF_MIGRATE_FAIL;
1308
1309         goto out;
1310 clear_pmdnuma:
1311         BUG_ON(!PageLocked(page));
1312         was_writable = pmd_write(pmd);
1313         pmd = pmd_modify(pmd, vma->vm_page_prot);
1314         pmd = pmd_mkyoung(pmd);
1315         if (was_writable)
1316                 pmd = pmd_mkwrite(pmd);
1317         set_pmd_at(vma->vm_mm, haddr, fe->pmd, pmd);
1318         update_mmu_cache_pmd(vma, fe->address, fe->pmd);
1319         unlock_page(page);
1320 out_unlock:
1321         spin_unlock(fe->ptl);
1322
1323 out:
1324         if (anon_vma)
1325                 page_unlock_anon_vma_read(anon_vma);
1326
1327         if (page_nid != -1)
1328                 task_numa_fault(last_cpupid, page_nid, HPAGE_PMD_NR, fe->flags);
1329
1330         return 0;
1331 }
1332
1333 /*
1334  * Return true if we do MADV_FREE successfully on entire pmd page.
1335  * Otherwise, return false.
1336  */
1337 bool madvise_free_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
1338                 pmd_t *pmd, unsigned long addr, unsigned long next)
1339 {
1340         spinlock_t *ptl;
1341         pmd_t orig_pmd;
1342         struct page *page;
1343         struct mm_struct *mm = tlb->mm;
1344         bool ret = false;
1345
1346         ptl = pmd_trans_huge_lock(pmd, vma);
1347         if (!ptl)
1348                 goto out_unlocked;
1349
1350         orig_pmd = *pmd;
1351         if (is_huge_zero_pmd(orig_pmd))
1352                 goto out;
1353
1354         page = pmd_page(orig_pmd);
1355         /*
1356          * If other processes are mapping this page, we couldn't discard
1357          * the page unless they all do MADV_FREE so let's skip the page.
1358          */
1359         if (page_mapcount(page) != 1)
1360                 goto out;
1361
1362         if (!trylock_page(page))
1363                 goto out;
1364
1365         /*
1366          * If user want to discard part-pages of THP, split it so MADV_FREE
1367          * will deactivate only them.
1368          */
1369         if (next - addr != HPAGE_PMD_SIZE) {
1370                 get_page(page);
1371                 spin_unlock(ptl);
1372                 split_huge_page(page);
1373                 unlock_page(page);
1374                 put_page(page);
1375                 goto out_unlocked;
1376         }
1377
1378         if (PageDirty(page))
1379                 ClearPageDirty(page);
1380         unlock_page(page);
1381
1382         if (PageActive(page))
1383                 deactivate_page(page);
1384
1385         if (pmd_young(orig_pmd) || pmd_dirty(orig_pmd)) {
1386                 pmdp_invalidate(vma, addr, pmd);
1387                 orig_pmd = pmd_mkold(orig_pmd);
1388                 orig_pmd = pmd_mkclean(orig_pmd);
1389
1390                 set_pmd_at(mm, addr, pmd, orig_pmd);
1391                 tlb_remove_pmd_tlb_entry(tlb, pmd, addr);
1392         }
1393         ret = true;
1394 out:
1395         spin_unlock(ptl);
1396 out_unlocked:
1397         return ret;
1398 }
1399
1400 int zap_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
1401                  pmd_t *pmd, unsigned long addr)
1402 {
1403         pmd_t orig_pmd;
1404         spinlock_t *ptl;
1405
1406         ptl = __pmd_trans_huge_lock(pmd, vma);
1407         if (!ptl)
1408                 return 0;
1409         /*
1410          * For architectures like ppc64 we look at deposited pgtable
1411          * when calling pmdp_huge_get_and_clear. So do the
1412          * pgtable_trans_huge_withdraw after finishing pmdp related
1413          * operations.
1414          */
1415         orig_pmd = pmdp_huge_get_and_clear_full(tlb->mm, addr, pmd,
1416                         tlb->fullmm);
1417         tlb_remove_pmd_tlb_entry(tlb, pmd, addr);
1418         if (vma_is_dax(vma)) {
1419                 spin_unlock(ptl);
1420                 if (is_huge_zero_pmd(orig_pmd))
1421                         tlb_remove_page(tlb, pmd_page(orig_pmd));
1422         } else if (is_huge_zero_pmd(orig_pmd)) {
1423                 pte_free(tlb->mm, pgtable_trans_huge_withdraw(tlb->mm, pmd));
1424                 atomic_long_dec(&tlb->mm->nr_ptes);
1425                 spin_unlock(ptl);
1426                 tlb_remove_page(tlb, pmd_page(orig_pmd));
1427         } else {
1428                 struct page *page = pmd_page(orig_pmd);
1429                 page_remove_rmap(page, true);
1430                 VM_BUG_ON_PAGE(page_mapcount(page) < 0, page);
1431                 VM_BUG_ON_PAGE(!PageHead(page), page);
1432                 if (PageAnon(page)) {
1433                         pgtable_t pgtable;
1434                         pgtable = pgtable_trans_huge_withdraw(tlb->mm, pmd);
1435                         pte_free(tlb->mm, pgtable);
1436                         atomic_long_dec(&tlb->mm->nr_ptes);
1437                         add_mm_counter(tlb->mm, MM_ANONPAGES, -HPAGE_PMD_NR);
1438                 } else {
1439                         add_mm_counter(tlb->mm, MM_FILEPAGES, -HPAGE_PMD_NR);
1440                 }
1441                 spin_unlock(ptl);
1442                 tlb_remove_page_size(tlb, page, HPAGE_PMD_SIZE);
1443         }
1444         return 1;
1445 }
1446
1447 bool move_huge_pmd(struct vm_area_struct *vma, unsigned long old_addr,
1448                   unsigned long new_addr, unsigned long old_end,
1449                   pmd_t *old_pmd, pmd_t *new_pmd)
1450 {
1451         spinlock_t *old_ptl, *new_ptl;
1452         pmd_t pmd;
1453         struct mm_struct *mm = vma->vm_mm;
1454         bool force_flush = false;
1455
1456         if ((old_addr & ~HPAGE_PMD_MASK) ||
1457             (new_addr & ~HPAGE_PMD_MASK) ||
1458             old_end - old_addr < HPAGE_PMD_SIZE)
1459                 return false;
1460
1461         /*
1462          * The destination pmd shouldn't be established, free_pgtables()
1463          * should have release it.
1464          */
1465         if (WARN_ON(!pmd_none(*new_pmd))) {
1466                 VM_BUG_ON(pmd_trans_huge(*new_pmd));
1467                 return false;
1468         }
1469
1470         /*
1471          * We don't have to worry about the ordering of src and dst
1472          * ptlocks because exclusive mmap_sem prevents deadlock.
1473          */
1474         old_ptl = __pmd_trans_huge_lock(old_pmd, vma);
1475         if (old_ptl) {
1476                 new_ptl = pmd_lockptr(mm, new_pmd);
1477                 if (new_ptl != old_ptl)
1478                         spin_lock_nested(new_ptl, SINGLE_DEPTH_NESTING);
1479                 pmd = pmdp_huge_get_and_clear(mm, old_addr, old_pmd);
1480                 if (pmd_present(pmd))
1481                         force_flush = true;
1482                 VM_BUG_ON(!pmd_none(*new_pmd));
1483
1484                 if (pmd_move_must_withdraw(new_ptl, old_ptl) &&
1485                                 vma_is_anonymous(vma)) {
1486                         pgtable_t pgtable;
1487                         pgtable = pgtable_trans_huge_withdraw(mm, old_pmd);
1488                         pgtable_trans_huge_deposit(mm, new_pmd, pgtable);
1489                 }
1490                 set_pmd_at(mm, new_addr, new_pmd, pmd_mksoft_dirty(pmd));
1491                 if (force_flush)
1492                         flush_tlb_range(vma, old_addr, old_addr + PMD_SIZE);
1493                 if (new_ptl != old_ptl)
1494                         spin_unlock(new_ptl);
1495                 spin_unlock(old_ptl);
1496                 return true;
1497         }
1498         return false;
1499 }
1500
1501 /*
1502  * Returns
1503  *  - 0 if PMD could not be locked
1504  *  - 1 if PMD was locked but protections unchange and TLB flush unnecessary
1505  *  - HPAGE_PMD_NR is protections changed and TLB flush necessary
1506  */
1507 int change_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
1508                 unsigned long addr, pgprot_t newprot, int prot_numa)
1509 {
1510         struct mm_struct *mm = vma->vm_mm;
1511         spinlock_t *ptl;
1512         pmd_t entry;
1513         bool preserve_write;
1514         int ret;
1515
1516         ptl = __pmd_trans_huge_lock(pmd, vma);
1517         if (!ptl)
1518                 return 0;
1519
1520         preserve_write = prot_numa && pmd_write(*pmd);
1521         ret = 1;
1522
1523         /*
1524          * Avoid trapping faults against the zero page. The read-only
1525          * data is likely to be read-cached on the local CPU and
1526          * local/remote hits to the zero page are not interesting.
1527          */
1528         if (prot_numa && is_huge_zero_pmd(*pmd))
1529                 goto unlock;
1530
1531         if (prot_numa && pmd_protnone(*pmd))
1532                 goto unlock;
1533
1534         /*
1535          * In case prot_numa, we are under down_read(mmap_sem). It's critical
1536          * to not clear pmd intermittently to avoid race with MADV_DONTNEED
1537          * which is also under down_read(mmap_sem):
1538          *
1539          *      CPU0:                           CPU1:
1540          *                              change_huge_pmd(prot_numa=1)
1541          *                               pmdp_huge_get_and_clear_notify()
1542          * madvise_dontneed()
1543          *  zap_pmd_range()
1544          *   pmd_trans_huge(*pmd) == 0 (without ptl)
1545          *   // skip the pmd
1546          *                               set_pmd_at();
1547          *                               // pmd is re-established
1548          *
1549          * The race makes MADV_DONTNEED miss the huge pmd and don't clear it
1550          * which may break userspace.
1551          *
1552          * pmdp_invalidate() is required to make sure we don't miss
1553          * dirty/young flags set by hardware.
1554          */
1555         entry = *pmd;
1556         pmdp_invalidate(vma, addr, pmd);
1557
1558         /*
1559          * Recover dirty/young flags.  It relies on pmdp_invalidate to not
1560          * corrupt them.
1561          */
1562         if (pmd_dirty(*pmd))
1563                 entry = pmd_mkdirty(entry);
1564         if (pmd_young(*pmd))
1565                 entry = pmd_mkyoung(entry);
1566
1567         entry = pmd_modify(entry, newprot);
1568         if (preserve_write)
1569                 entry = pmd_mkwrite(entry);
1570         ret = HPAGE_PMD_NR;
1571         set_pmd_at(mm, addr, pmd, entry);
1572         BUG_ON(vma_is_anonymous(vma) && !preserve_write && pmd_write(entry));
1573 unlock:
1574         spin_unlock(ptl);
1575         return ret;
1576 }
1577
1578 /*
1579  * Returns page table lock pointer if a given pmd maps a thp, NULL otherwise.
1580  *
1581  * Note that if it returns page table lock pointer, this routine returns without
1582  * unlocking page table lock. So callers must unlock it.
1583  */
1584 spinlock_t *__pmd_trans_huge_lock(pmd_t *pmd, struct vm_area_struct *vma)
1585 {
1586         spinlock_t *ptl;
1587         ptl = pmd_lock(vma->vm_mm, pmd);
1588         if (likely(pmd_trans_huge(*pmd) || pmd_devmap(*pmd)))
1589                 return ptl;
1590         spin_unlock(ptl);
1591         return NULL;
1592 }
1593
1594 static void __split_huge_zero_page_pmd(struct vm_area_struct *vma,
1595                 unsigned long haddr, pmd_t *pmd)
1596 {
1597         struct mm_struct *mm = vma->vm_mm;
1598         pgtable_t pgtable;
1599         pmd_t _pmd;
1600         int i;
1601
1602         /* leave pmd empty until pte is filled */
1603         pmdp_huge_clear_flush_notify(vma, haddr, pmd);
1604
1605         pgtable = pgtable_trans_huge_withdraw(mm, pmd);
1606         pmd_populate(mm, &_pmd, pgtable);
1607
1608         for (i = 0; i < HPAGE_PMD_NR; i++, haddr += PAGE_SIZE) {
1609                 pte_t *pte, entry;
1610                 entry = pfn_pte(my_zero_pfn(haddr), vma->vm_page_prot);
1611                 entry = pte_mkspecial(entry);
1612                 pte = pte_offset_map(&_pmd, haddr);
1613                 VM_BUG_ON(!pte_none(*pte));
1614                 set_pte_at(mm, haddr, pte, entry);
1615                 pte_unmap(pte);
1616         }
1617         smp_wmb(); /* make pte visible before pmd */
1618         pmd_populate(mm, pmd, pgtable);
1619 }
1620
1621 static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
1622                 unsigned long haddr, bool freeze)
1623 {
1624         struct mm_struct *mm = vma->vm_mm;
1625         struct page *page;
1626         pgtable_t pgtable;
1627         pmd_t _pmd;
1628         bool young, write, dirty, soft_dirty;
1629         unsigned long addr;
1630         int i;
1631
1632         VM_BUG_ON(haddr & ~HPAGE_PMD_MASK);
1633         VM_BUG_ON_VMA(vma->vm_start > haddr, vma);
1634         VM_BUG_ON_VMA(vma->vm_end < haddr + HPAGE_PMD_SIZE, vma);
1635         VM_BUG_ON(!pmd_trans_huge(*pmd) && !pmd_devmap(*pmd));
1636
1637         count_vm_event(THP_SPLIT_PMD);
1638
1639         if (!vma_is_anonymous(vma)) {
1640                 _pmd = pmdp_huge_clear_flush_notify(vma, haddr, pmd);
1641                 if (vma_is_dax(vma))
1642                         return;
1643                 page = pmd_page(_pmd);
1644                 if (!PageDirty(page) && pmd_dirty(_pmd))
1645                         set_page_dirty(page);
1646                 if (!PageReferenced(page) && pmd_young(_pmd))
1647                         SetPageReferenced(page);
1648                 page_remove_rmap(page, true);
1649                 put_page(page);
1650                 add_mm_counter(mm, MM_FILEPAGES, -HPAGE_PMD_NR);
1651                 return;
1652         } else if (is_huge_zero_pmd(*pmd)) {
1653                 return __split_huge_zero_page_pmd(vma, haddr, pmd);
1654         }
1655
1656         page = pmd_page(*pmd);
1657         VM_BUG_ON_PAGE(!page_count(page), page);
1658         page_ref_add(page, HPAGE_PMD_NR - 1);
1659         write = pmd_write(*pmd);
1660         young = pmd_young(*pmd);
1661         dirty = pmd_dirty(*pmd);
1662         soft_dirty = pmd_soft_dirty(*pmd);
1663
1664         pmdp_huge_split_prepare(vma, haddr, pmd);
1665         pgtable = pgtable_trans_huge_withdraw(mm, pmd);
1666         pmd_populate(mm, &_pmd, pgtable);
1667
1668         for (i = 0, addr = haddr; i < HPAGE_PMD_NR; i++, addr += PAGE_SIZE) {
1669                 pte_t entry, *pte;
1670                 /*
1671                  * Note that NUMA hinting access restrictions are not
1672                  * transferred to avoid any possibility of altering
1673                  * permissions across VMAs.
1674                  */
1675                 if (freeze) {
1676                         swp_entry_t swp_entry;
1677                         swp_entry = make_migration_entry(page + i, write);
1678                         entry = swp_entry_to_pte(swp_entry);
1679                         if (soft_dirty)
1680                                 entry = pte_swp_mksoft_dirty(entry);
1681                 } else {
1682                         entry = mk_pte(page + i, READ_ONCE(vma->vm_page_prot));
1683                         entry = maybe_mkwrite(entry, vma);
1684                         if (!write)
1685                                 entry = pte_wrprotect(entry);
1686                         if (!young)
1687                                 entry = pte_mkold(entry);
1688                         if (soft_dirty)
1689                                 entry = pte_mksoft_dirty(entry);
1690                 }
1691                 if (dirty)
1692                         SetPageDirty(page + i);
1693                 pte = pte_offset_map(&_pmd, addr);
1694                 BUG_ON(!pte_none(*pte));
1695                 set_pte_at(mm, addr, pte, entry);
1696                 atomic_inc(&page[i]._mapcount);
1697                 pte_unmap(pte);
1698         }
1699
1700         /*
1701          * Set PG_double_map before dropping compound_mapcount to avoid
1702          * false-negative page_mapped().
1703          */
1704         if (compound_mapcount(page) > 1 && !TestSetPageDoubleMap(page)) {
1705                 for (i = 0; i < HPAGE_PMD_NR; i++)
1706                         atomic_inc(&page[i]._mapcount);
1707         }
1708
1709         if (atomic_add_negative(-1, compound_mapcount_ptr(page))) {
1710                 /* Last compound_mapcount is gone. */
1711                 __dec_node_page_state(page, NR_ANON_THPS);
1712                 if (TestClearPageDoubleMap(page)) {
1713                         /* No need in mapcount reference anymore */
1714                         for (i = 0; i < HPAGE_PMD_NR; i++)
1715                                 atomic_dec(&page[i]._mapcount);
1716                 }
1717         }
1718
1719         smp_wmb(); /* make pte visible before pmd */
1720         /*
1721          * Up to this point the pmd is present and huge and userland has the
1722          * whole access to the hugepage during the split (which happens in
1723          * place). If we overwrite the pmd with the not-huge version pointing
1724          * to the pte here (which of course we could if all CPUs were bug
1725          * free), userland could trigger a small page size TLB miss on the
1726          * small sized TLB while the hugepage TLB entry is still established in
1727          * the huge TLB. Some CPU doesn't like that.
1728          * See http://support.amd.com/us/Processor_TechDocs/41322.pdf, Erratum
1729          * 383 on page 93. Intel should be safe but is also warns that it's
1730          * only safe if the permission and cache attributes of the two entries
1731          * loaded in the two TLB is identical (which should be the case here).
1732          * But it is generally safer to never allow small and huge TLB entries
1733          * for the same virtual address to be loaded simultaneously. So instead
1734          * of doing "pmd_populate(); flush_pmd_tlb_range();" we first mark the
1735          * current pmd notpresent (atomically because here the pmd_trans_huge
1736          * and pmd_trans_splitting must remain set at all times on the pmd
1737          * until the split is complete for this pmd), then we flush the SMP TLB
1738          * and finally we write the non-huge version of the pmd entry with
1739          * pmd_populate.
1740          */
1741         pmdp_invalidate(vma, haddr, pmd);
1742         pmd_populate(mm, pmd, pgtable);
1743
1744         if (freeze) {
1745                 for (i = 0; i < HPAGE_PMD_NR; i++) {
1746                         page_remove_rmap(page + i, false);
1747                         put_page(page + i);
1748                 }
1749         }
1750 }
1751
1752 void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
1753                 unsigned long address, bool freeze, struct page *page)
1754 {
1755         spinlock_t *ptl;
1756         struct mm_struct *mm = vma->vm_mm;
1757         unsigned long haddr = address & HPAGE_PMD_MASK;
1758
1759         mmu_notifier_invalidate_range_start(mm, haddr, haddr + HPAGE_PMD_SIZE);
1760         ptl = pmd_lock(mm, pmd);
1761
1762         /*
1763          * If caller asks to setup a migration entries, we need a page to check
1764          * pmd against. Otherwise we can end up replacing wrong page.
1765          */
1766         VM_BUG_ON(freeze && !page);
1767         if (page && page != pmd_page(*pmd))
1768                 goto out;
1769
1770         if (pmd_trans_huge(*pmd)) {
1771                 page = pmd_page(*pmd);
1772                 if (PageMlocked(page))
1773                         clear_page_mlock(page);
1774         } else if (!pmd_devmap(*pmd))
1775                 goto out;
1776         __split_huge_pmd_locked(vma, pmd, haddr, freeze);
1777 out:
1778         spin_unlock(ptl);
1779         mmu_notifier_invalidate_range_end(mm, haddr, haddr + HPAGE_PMD_SIZE);
1780 }
1781
1782 void split_huge_pmd_address(struct vm_area_struct *vma, unsigned long address,
1783                 bool freeze, struct page *page)
1784 {
1785         pgd_t *pgd;
1786         pud_t *pud;
1787         pmd_t *pmd;
1788
1789         pgd = pgd_offset(vma->vm_mm, address);
1790         if (!pgd_present(*pgd))
1791                 return;
1792
1793         pud = pud_offset(pgd, address);
1794         if (!pud_present(*pud))
1795                 return;
1796
1797         pmd = pmd_offset(pud, address);
1798
1799         __split_huge_pmd(vma, pmd, address, freeze, page);
1800 }
1801
1802 void vma_adjust_trans_huge(struct vm_area_struct *vma,
1803                              unsigned long start,
1804                              unsigned long end,
1805                              long adjust_next)
1806 {
1807         /*
1808          * If the new start address isn't hpage aligned and it could
1809          * previously contain an hugepage: check if we need to split
1810          * an huge pmd.
1811          */
1812         if (start & ~HPAGE_PMD_MASK &&
1813             (start & HPAGE_PMD_MASK) >= vma->vm_start &&
1814             (start & HPAGE_PMD_MASK) + HPAGE_PMD_SIZE <= vma->vm_end)
1815                 split_huge_pmd_address(vma, start, false, NULL);
1816
1817         /*
1818          * If the new end address isn't hpage aligned and it could
1819          * previously contain an hugepage: check if we need to split
1820          * an huge pmd.
1821          */
1822         if (end & ~HPAGE_PMD_MASK &&
1823             (end & HPAGE_PMD_MASK) >= vma->vm_start &&
1824             (end & HPAGE_PMD_MASK) + HPAGE_PMD_SIZE <= vma->vm_end)
1825                 split_huge_pmd_address(vma, end, false, NULL);
1826
1827         /*
1828          * If we're also updating the vma->vm_next->vm_start, if the new
1829          * vm_next->vm_start isn't page aligned and it could previously
1830          * contain an hugepage: check if we need to split an huge pmd.
1831          */
1832         if (adjust_next > 0) {
1833                 struct vm_area_struct *next = vma->vm_next;
1834                 unsigned long nstart = next->vm_start;
1835                 nstart += adjust_next << PAGE_SHIFT;
1836                 if (nstart & ~HPAGE_PMD_MASK &&
1837                     (nstart & HPAGE_PMD_MASK) >= next->vm_start &&
1838                     (nstart & HPAGE_PMD_MASK) + HPAGE_PMD_SIZE <= next->vm_end)
1839                         split_huge_pmd_address(next, nstart, false, NULL);
1840         }
1841 }
1842
1843 static void unmap_page(struct page *page)
1844 {
1845         enum ttu_flags ttu_flags = TTU_IGNORE_MLOCK | TTU_IGNORE_ACCESS |
1846                 TTU_RMAP_LOCKED;
1847         int i, ret;
1848
1849         VM_BUG_ON_PAGE(!PageHead(page), page);
1850
1851         if (PageAnon(page))
1852                 ttu_flags |= TTU_MIGRATION;
1853
1854         /* We only need TTU_SPLIT_HUGE_PMD once */
1855         ret = try_to_unmap(page, ttu_flags | TTU_SPLIT_HUGE_PMD);
1856         for (i = 1; !ret && i < HPAGE_PMD_NR; i++) {
1857                 /* Cut short if the page is unmapped */
1858                 if (page_count(page) == 1)
1859                         return;
1860
1861                 ret = try_to_unmap(page + i, ttu_flags);
1862         }
1863         VM_BUG_ON_PAGE(ret, page + i - 1);
1864 }
1865
1866 static void remap_page(struct page *page)
1867 {
1868         int i;
1869
1870         for (i = 0; i < HPAGE_PMD_NR; i++)
1871                 remove_migration_ptes(page + i, page + i, true);
1872 }
1873
1874 static void __split_huge_page_tail(struct page *head, int tail,
1875                 struct lruvec *lruvec, struct list_head *list)
1876 {
1877         struct page *page_tail = head + tail;
1878
1879         VM_BUG_ON_PAGE(atomic_read(&page_tail->_mapcount) != -1, page_tail);
1880
1881         /*
1882          * Clone page flags before unfreezing refcount.
1883          *
1884          * After successful get_page_unless_zero() might follow flags change,
1885          * for exmaple lock_page() which set PG_waiters.
1886          */
1887         page_tail->flags &= ~PAGE_FLAGS_CHECK_AT_PREP;
1888         page_tail->flags |= (head->flags &
1889                         ((1L << PG_referenced) |
1890                          (1L << PG_swapbacked) |
1891                          (1L << PG_mlocked) |
1892                          (1L << PG_uptodate) |
1893                          (1L << PG_active) |
1894                          (1L << PG_locked) |
1895                          (1L << PG_unevictable) |
1896                          (1L << PG_dirty)));
1897
1898         /* ->mapping in first tail page is compound_mapcount */
1899         VM_BUG_ON_PAGE(tail > 2 && page_tail->mapping != TAIL_MAPPING,
1900                         page_tail);
1901         page_tail->mapping = head->mapping;
1902         page_tail->index = head->index + tail;
1903
1904         /* Page flags must be visible before we make the page non-compound. */
1905         smp_wmb();
1906
1907         /*
1908          * Clear PageTail before unfreezing page refcount.
1909          *
1910          * After successful get_page_unless_zero() might follow put_page()
1911          * which needs correct compound_head().
1912          */
1913         clear_compound_head(page_tail);
1914
1915         /* Finally unfreeze refcount. Additional reference from page cache. */
1916         page_ref_unfreeze(page_tail, 1 + (!PageAnon(head) ||
1917                                           PageSwapCache(head)));
1918
1919         if (page_is_young(head))
1920                 set_page_young(page_tail);
1921         if (page_is_idle(head))
1922                 set_page_idle(page_tail);
1923
1924         page_cpupid_xchg_last(page_tail, page_cpupid_last(head));
1925         lru_add_page_tail(head, page_tail, lruvec, list);
1926 }
1927
1928 static void __split_huge_page(struct page *page, struct list_head *list,
1929                 pgoff_t end, unsigned long flags)
1930 {
1931         struct page *head = compound_head(page);
1932         struct zone *zone = page_zone(head);
1933         struct lruvec *lruvec;
1934         int i;
1935
1936         lruvec = mem_cgroup_page_lruvec(head, zone->zone_pgdat);
1937
1938         /* complete memcg works before add pages to LRU */
1939         mem_cgroup_split_huge_fixup(head);
1940
1941         for (i = HPAGE_PMD_NR - 1; i >= 1; i--) {
1942                 __split_huge_page_tail(head, i, lruvec, list);
1943                 /* Some pages can be beyond i_size: drop them from page cache */
1944                 if (head[i].index >= end) {
1945                         __ClearPageDirty(head + i);
1946                         __delete_from_page_cache(head + i, NULL);
1947                         if (IS_ENABLED(CONFIG_SHMEM) && PageSwapBacked(head))
1948                                 shmem_uncharge(head->mapping->host, 1);
1949                         put_page(head + i);
1950                 }
1951         }
1952
1953         ClearPageCompound(head);
1954
1955         split_page_owner(head, HPAGE_PMD_ORDER);
1956
1957         /* See comment in __split_huge_page_tail() */
1958         if (PageAnon(head)) {
1959                 page_ref_inc(head);
1960         } else {
1961                 /* Additional pin to radix tree */
1962                 page_ref_add(head, 2);
1963                 spin_unlock(&head->mapping->tree_lock);
1964         }
1965
1966         spin_unlock_irqrestore(zone_lru_lock(page_zone(head)), flags);
1967
1968         remap_page(head);
1969
1970         for (i = 0; i < HPAGE_PMD_NR; i++) {
1971                 struct page *subpage = head + i;
1972                 if (subpage == page)
1973                         continue;
1974                 unlock_page(subpage);
1975
1976                 /*
1977                  * Subpages may be freed if there wasn't any mapping
1978                  * like if add_to_swap() is running on a lru page that
1979                  * had its mapping zapped. And freeing these pages
1980                  * requires taking the lru_lock so we do the put_page
1981                  * of the tail pages after the split is complete.
1982                  */
1983                 put_page(subpage);
1984         }
1985 }
1986
1987 int total_mapcount(struct page *page)
1988 {
1989         int i, compound, ret;
1990
1991         VM_BUG_ON_PAGE(PageTail(page), page);
1992
1993         if (likely(!PageCompound(page)))
1994                 return atomic_read(&page->_mapcount) + 1;
1995
1996         compound = compound_mapcount(page);
1997         if (PageHuge(page))
1998                 return compound;
1999         ret = compound;
2000         for (i = 0; i < HPAGE_PMD_NR; i++)
2001                 ret += atomic_read(&page[i]._mapcount) + 1;
2002         /* File pages has compound_mapcount included in _mapcount */
2003         if (!PageAnon(page))
2004                 return ret - compound * HPAGE_PMD_NR;
2005         if (PageDoubleMap(page))
2006                 ret -= HPAGE_PMD_NR;
2007         return ret;
2008 }
2009
2010 /*
2011  * This calculates accurately how many mappings a transparent hugepage
2012  * has (unlike page_mapcount() which isn't fully accurate). This full
2013  * accuracy is primarily needed to know if copy-on-write faults can
2014  * reuse the page and change the mapping to read-write instead of
2015  * copying them. At the same time this returns the total_mapcount too.
2016  *
2017  * The function returns the highest mapcount any one of the subpages
2018  * has. If the return value is one, even if different processes are
2019  * mapping different subpages of the transparent hugepage, they can
2020  * all reuse it, because each process is reusing a different subpage.
2021  *
2022  * The total_mapcount is instead counting all virtual mappings of the
2023  * subpages. If the total_mapcount is equal to "one", it tells the
2024  * caller all mappings belong to the same "mm" and in turn the
2025  * anon_vma of the transparent hugepage can become the vma->anon_vma
2026  * local one as no other process may be mapping any of the subpages.
2027  *
2028  * It would be more accurate to replace page_mapcount() with
2029  * page_trans_huge_mapcount(), however we only use
2030  * page_trans_huge_mapcount() in the copy-on-write faults where we
2031  * need full accuracy to avoid breaking page pinning, because
2032  * page_trans_huge_mapcount() is slower than page_mapcount().
2033  */
2034 int page_trans_huge_mapcount(struct page *page, int *total_mapcount)
2035 {
2036         int i, ret, _total_mapcount, mapcount;
2037
2038         /* hugetlbfs shouldn't call it */
2039         VM_BUG_ON_PAGE(PageHuge(page), page);
2040
2041         if (likely(!PageTransCompound(page))) {
2042                 mapcount = atomic_read(&page->_mapcount) + 1;
2043                 if (total_mapcount)
2044                         *total_mapcount = mapcount;
2045                 return mapcount;
2046         }
2047
2048         page = compound_head(page);
2049
2050         _total_mapcount = ret = 0;
2051         for (i = 0; i < HPAGE_PMD_NR; i++) {
2052                 mapcount = atomic_read(&page[i]._mapcount) + 1;
2053                 ret = max(ret, mapcount);
2054                 _total_mapcount += mapcount;
2055         }
2056         if (PageDoubleMap(page)) {
2057                 ret -= 1;
2058                 _total_mapcount -= HPAGE_PMD_NR;
2059         }
2060         mapcount = compound_mapcount(page);
2061         ret += mapcount;
2062         _total_mapcount += mapcount;
2063         if (total_mapcount)
2064                 *total_mapcount = _total_mapcount;
2065         return ret;
2066 }
2067
2068 /*
2069  * This function splits huge page into normal pages. @page can point to any
2070  * subpage of huge page to split. Split doesn't change the position of @page.
2071  *
2072  * Only caller must hold pin on the @page, otherwise split fails with -EBUSY.
2073  * The huge page must be locked.
2074  *
2075  * If @list is null, tail pages will be added to LRU list, otherwise, to @list.
2076  *
2077  * Both head page and tail pages will inherit mapping, flags, and so on from
2078  * the hugepage.
2079  *
2080  * GUP pin and PG_locked transferred to @page. Rest subpages can be freed if
2081  * they are not mapped.
2082  *
2083  * Returns 0 if the hugepage is split successfully.
2084  * Returns -EBUSY if the page is pinned or if anon_vma disappeared from under
2085  * us.
2086  */
2087 int split_huge_page_to_list(struct page *page, struct list_head *list)
2088 {
2089         struct page *head = compound_head(page);
2090         struct pglist_data *pgdata = NODE_DATA(page_to_nid(head));
2091         struct anon_vma *anon_vma = NULL;
2092         struct address_space *mapping = NULL;
2093         int count, mapcount, extra_pins, ret;
2094         bool mlocked;
2095         unsigned long flags;
2096         pgoff_t end;
2097
2098         VM_BUG_ON_PAGE(is_huge_zero_page(page), page);
2099         VM_BUG_ON_PAGE(!PageLocked(page), page);
2100         VM_BUG_ON_PAGE(!PageSwapBacked(page), page);
2101         VM_BUG_ON_PAGE(!PageCompound(page), page);
2102
2103         if (PageAnon(head)) {
2104                 /*
2105                  * The caller does not necessarily hold an mmap_sem that would
2106                  * prevent the anon_vma disappearing so we first we take a
2107                  * reference to it and then lock the anon_vma for write. This
2108                  * is similar to page_lock_anon_vma_read except the write lock
2109                  * is taken to serialise against parallel split or collapse
2110                  * operations.
2111                  */
2112                 anon_vma = page_get_anon_vma(head);
2113                 if (!anon_vma) {
2114                         ret = -EBUSY;
2115                         goto out;
2116                 }
2117                 extra_pins = 0;
2118                 end = -1;
2119                 mapping = NULL;
2120                 anon_vma_lock_write(anon_vma);
2121         } else {
2122                 mapping = head->mapping;
2123
2124                 /* Truncated ? */
2125                 if (!mapping) {
2126                         ret = -EBUSY;
2127                         goto out;
2128                 }
2129
2130                 /* Addidional pins from radix tree */
2131                 extra_pins = HPAGE_PMD_NR;
2132                 anon_vma = NULL;
2133                 i_mmap_lock_read(mapping);
2134
2135                 /*
2136                  *__split_huge_page() may need to trim off pages beyond EOF:
2137                  * but on 32-bit, i_size_read() takes an irq-unsafe seqlock,
2138                  * which cannot be nested inside the page tree lock. So note
2139                  * end now: i_size itself may be changed at any moment, but
2140                  * head page lock is good enough to serialize the trimming.
2141                  */
2142                 end = DIV_ROUND_UP(i_size_read(mapping->host), PAGE_SIZE);
2143         }
2144
2145         /*
2146          * Racy check if we can split the page, before unmap_page() will
2147          * split PMDs
2148          */
2149         if (total_mapcount(head) != page_count(head) - extra_pins - 1) {
2150                 ret = -EBUSY;
2151                 goto out_unlock;
2152         }
2153
2154         mlocked = PageMlocked(page);
2155         unmap_page(head);
2156         VM_BUG_ON_PAGE(compound_mapcount(head), head);
2157
2158         /* Make sure the page is not on per-CPU pagevec as it takes pin */
2159         if (mlocked)
2160                 lru_add_drain();
2161
2162         /* prevent PageLRU to go away from under us, and freeze lru stats */
2163         spin_lock_irqsave(zone_lru_lock(page_zone(head)), flags);
2164
2165         if (mapping) {
2166                 void **pslot;
2167
2168                 spin_lock(&mapping->tree_lock);
2169                 pslot = radix_tree_lookup_slot(&mapping->page_tree,
2170                                 page_index(head));
2171                 /*
2172                  * Check if the head page is present in radix tree.
2173                  * We assume all tail are present too, if head is there.
2174                  */
2175                 if (radix_tree_deref_slot_protected(pslot,
2176                                         &mapping->tree_lock) != head)
2177                         goto fail;
2178         }
2179
2180         /* Prevent deferred_split_scan() touching ->_refcount */
2181         spin_lock(&pgdata->split_queue_lock);
2182         count = page_count(head);
2183         mapcount = total_mapcount(head);
2184         if (!mapcount && page_ref_freeze(head, 1 + extra_pins)) {
2185                 if (!list_empty(page_deferred_list(head))) {
2186                         pgdata->split_queue_len--;
2187                         list_del(page_deferred_list(head));
2188                 }
2189                 if (mapping)
2190                         __dec_node_page_state(page, NR_SHMEM_THPS);
2191                 spin_unlock(&pgdata->split_queue_lock);
2192                 __split_huge_page(page, list, end, flags);
2193                 ret = 0;
2194         } else {
2195                 if (IS_ENABLED(CONFIG_DEBUG_VM) && mapcount) {
2196                         pr_alert("total_mapcount: %u, page_count(): %u\n",
2197                                         mapcount, count);
2198                         if (PageTail(page))
2199                                 dump_page(head, NULL);
2200                         dump_page(page, "total_mapcount(head) > 0");
2201                         BUG();
2202                 }
2203                 spin_unlock(&pgdata->split_queue_lock);
2204 fail:           if (mapping)
2205                         spin_unlock(&mapping->tree_lock);
2206                 spin_unlock_irqrestore(zone_lru_lock(page_zone(head)), flags);
2207                 remap_page(head);
2208                 ret = -EBUSY;
2209         }
2210
2211 out_unlock:
2212         if (anon_vma) {
2213                 anon_vma_unlock_write(anon_vma);
2214                 put_anon_vma(anon_vma);
2215         }
2216         if (mapping)
2217                 i_mmap_unlock_read(mapping);
2218 out:
2219         count_vm_event(!ret ? THP_SPLIT_PAGE : THP_SPLIT_PAGE_FAILED);
2220         return ret;
2221 }
2222
2223 void free_transhuge_page(struct page *page)
2224 {
2225         struct pglist_data *pgdata = NODE_DATA(page_to_nid(page));
2226         unsigned long flags;
2227
2228         spin_lock_irqsave(&pgdata->split_queue_lock, flags);
2229         if (!list_empty(page_deferred_list(page))) {
2230                 pgdata->split_queue_len--;
2231                 list_del(page_deferred_list(page));
2232         }
2233         spin_unlock_irqrestore(&pgdata->split_queue_lock, flags);
2234         free_compound_page(page);
2235 }
2236
2237 void deferred_split_huge_page(struct page *page)
2238 {
2239         struct pglist_data *pgdata = NODE_DATA(page_to_nid(page));
2240         unsigned long flags;
2241
2242         VM_BUG_ON_PAGE(!PageTransHuge(page), page);
2243
2244         spin_lock_irqsave(&pgdata->split_queue_lock, flags);
2245         if (list_empty(page_deferred_list(page))) {
2246                 count_vm_event(THP_DEFERRED_SPLIT_PAGE);
2247                 list_add_tail(page_deferred_list(page), &pgdata->split_queue);
2248                 pgdata->split_queue_len++;
2249         }
2250         spin_unlock_irqrestore(&pgdata->split_queue_lock, flags);
2251 }
2252
2253 static unsigned long deferred_split_count(struct shrinker *shrink,
2254                 struct shrink_control *sc)
2255 {
2256         struct pglist_data *pgdata = NODE_DATA(sc->nid);
2257         return ACCESS_ONCE(pgdata->split_queue_len);
2258 }
2259
2260 static unsigned long deferred_split_scan(struct shrinker *shrink,
2261                 struct shrink_control *sc)
2262 {
2263         struct pglist_data *pgdata = NODE_DATA(sc->nid);
2264         unsigned long flags;
2265         LIST_HEAD(list), *pos, *next;
2266         struct page *page;
2267         int split = 0;
2268
2269         spin_lock_irqsave(&pgdata->split_queue_lock, flags);
2270         /* Take pin on all head pages to avoid freeing them under us */
2271         list_for_each_safe(pos, next, &pgdata->split_queue) {
2272                 page = list_entry((void *)pos, struct page, mapping);
2273                 page = compound_head(page);
2274                 if (get_page_unless_zero(page)) {
2275                         list_move(page_deferred_list(page), &list);
2276                 } else {
2277                         /* We lost race with put_compound_page() */
2278                         list_del_init(page_deferred_list(page));
2279                         pgdata->split_queue_len--;
2280                 }
2281                 if (!--sc->nr_to_scan)
2282                         break;
2283         }
2284         spin_unlock_irqrestore(&pgdata->split_queue_lock, flags);
2285
2286         list_for_each_safe(pos, next, &list) {
2287                 page = list_entry((void *)pos, struct page, mapping);
2288                 if (!trylock_page(page))
2289                         goto next;
2290                 /* split_huge_page() removes page from list on success */
2291                 if (!split_huge_page(page))
2292                         split++;
2293                 unlock_page(page);
2294 next:
2295                 put_page(page);
2296         }
2297
2298         spin_lock_irqsave(&pgdata->split_queue_lock, flags);
2299         list_splice_tail(&list, &pgdata->split_queue);
2300         spin_unlock_irqrestore(&pgdata->split_queue_lock, flags);
2301
2302         /*
2303          * Stop shrinker if we didn't split any page, but the queue is empty.
2304          * This can happen if pages were freed under us.
2305          */
2306         if (!split && list_empty(&pgdata->split_queue))
2307                 return SHRINK_STOP;
2308         return split;
2309 }
2310
2311 static struct shrinker deferred_split_shrinker = {
2312         .count_objects = deferred_split_count,
2313         .scan_objects = deferred_split_scan,
2314         .seeks = DEFAULT_SEEKS,
2315         .flags = SHRINKER_NUMA_AWARE,
2316 };
2317
2318 #ifdef CONFIG_DEBUG_FS
2319 static int split_huge_pages_set(void *data, u64 val)
2320 {
2321         struct zone *zone;
2322         struct page *page;
2323         unsigned long pfn, max_zone_pfn;
2324         unsigned long total = 0, split = 0;
2325
2326         if (val != 1)
2327                 return -EINVAL;
2328
2329         for_each_populated_zone(zone) {
2330                 max_zone_pfn = zone_end_pfn(zone);
2331                 for (pfn = zone->zone_start_pfn; pfn < max_zone_pfn; pfn++) {
2332                         if (!pfn_valid(pfn))
2333                                 continue;
2334
2335                         page = pfn_to_page(pfn);
2336                         if (!get_page_unless_zero(page))
2337                                 continue;
2338
2339                         if (zone != page_zone(page))
2340                                 goto next;
2341
2342                         if (!PageHead(page) || PageHuge(page) || !PageLRU(page))
2343                                 goto next;
2344
2345                         total++;
2346                         lock_page(page);
2347                         if (!split_huge_page(page))
2348                                 split++;
2349                         unlock_page(page);
2350 next:
2351                         put_page(page);
2352                 }
2353         }
2354
2355         pr_info("%lu of %lu THP split\n", split, total);
2356
2357         return 0;
2358 }
2359 DEFINE_SIMPLE_ATTRIBUTE(split_huge_pages_fops, NULL, split_huge_pages_set,
2360                 "%llu\n");
2361
2362 static int __init split_huge_pages_debugfs(void)
2363 {
2364         void *ret;
2365
2366         ret = debugfs_create_file("split_huge_pages", 0200, NULL, NULL,
2367                         &split_huge_pages_fops);
2368         if (!ret)
2369                 pr_warn("Failed to create split_huge_pages in debugfs");
2370         return 0;
2371 }
2372 late_initcall(split_huge_pages_debugfs);
2373 #endif