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                 int ret;
 665                 pgtable = pte_alloc_one(vma->vm_mm, haddr);
 666                 if (unlikely(!pgtable))
 667                         return VM_FAULT_OOM;
 668                 zero_page = mm_get_huge_zero_page(vma->vm_mm);
 669                 if (unlikely(!zero_page)) {
 670                         pte_free(vma->vm_mm, pgtable);
 671                         count_vm_event(THP_FAULT_FALLBACK);
 672                         return VM_FAULT_FALLBACK;
 673                 }
 674                 fe->ptl = pmd_lock(vma->vm_mm, fe->pmd);
 675                 ret = 0;
 676                 if (pmd_none(*fe->pmd)) {
 677                         if (userfaultfd_missing(vma)) {
 678                                 spin_unlock(fe->ptl);
 679                                 pte_free(vma->vm_mm, pgtable);
 680                                 ret = handle_userfault(fe, VM_UFFD_MISSING);
 681                                 VM_BUG_ON(ret & VM_FAULT_FALLBACK);
 682                         } else {
 683                                 set_huge_zero_page(pgtable, vma->vm_mm, vma,
 684                                                    haddr, fe->pmd, zero_page);
 685                                 spin_unlock(fe->ptl);
 686                         }
 687                 } else {
 688                         spin_unlock(fe->ptl);
 689                         pte_free(vma->vm_mm, pgtable);
 690                 }
 691                 return ret;
 692         }
 693         gfp = alloc_hugepage_direct_gfpmask(vma);
 694         page = alloc_hugepage_vma(gfp, vma, haddr, HPAGE_PMD_ORDER);
 695         if (unlikely(!page)) {
 696                 count_vm_event(THP_FAULT_FALLBACK);
 697                 return VM_FAULT_FALLBACK;
 698         }
 699         prep_transhuge_page(page);
 700         return __do_huge_pmd_anonymous_page(fe, page, gfp);
 701 }
 702
 703 static void insert_pfn_pmd(struct vm_area_struct *vma, unsigned long addr,
 704                 pmd_t *pmd, pfn_t pfn, pgprot_t prot, bool write)
 705 {
 706         struct mm_struct *mm = vma->vm_mm;
 707         pmd_t entry;
 708         spinlock_t *ptl;
 709
 710         ptl = pmd_lock(mm, pmd);
 711         entry = pmd_mkhuge(pfn_t_pmd(pfn, prot));
 712         if (pfn_t_devmap(pfn))
 713                 entry = pmd_mkdevmap(entry);
 714         if (write) {
 715                 entry = pmd_mkyoung(pmd_mkdirty(entry));
 716                 entry = maybe_pmd_mkwrite(entry, vma);
 717         }
 718         set_pmd_at(mm, addr, pmd, entry);
 719         update_mmu_cache_pmd(vma, addr, pmd);
 720         spin_unlock(ptl);
 721 }
 722
 723 int vmf_insert_pfn_pmd(struct vm_area_struct *vma, unsigned long addr,
 724                         pmd_t *pmd, pfn_t pfn, bool write)
 725 {
 726         pgprot_t pgprot = vma->vm_page_prot;
 727         /*
 728          * If we had pmd_special, we could avoid all these restrictions,
 729          * but we need to be consistent with PTEs and architectures that
 730          * can't support a 'special' bit.
 731          */
 732         BUG_ON(!(vma->vm_flags & (VM_PFNMAP|VM_MIXEDMAP)));
 733         BUG_ON((vma->vm_flags & (VM_PFNMAP|VM_MIXEDMAP)) ==
 734                                                 (VM_PFNMAP|VM_MIXEDMAP));
 735         BUG_ON((vma->vm_flags & VM_PFNMAP) && is_cow_mapping(vma->vm_flags));
 736         BUG_ON(!pfn_t_devmap(pfn));
 737
 738         if (addr < vma->vm_start || addr >= vma->vm_end)
 739                 return VM_FAULT_SIGBUS;
 740         if (track_pfn_insert(vma, &pgprot, pfn))
 741                 return VM_FAULT_SIGBUS;
 742         insert_pfn_pmd(vma, addr, pmd, pfn, pgprot, write);
 743         return VM_FAULT_NOPAGE;
 744 }
 745 EXPORT_SYMBOL_GPL(vmf_insert_pfn_pmd);
 746
 747 static void touch_pmd(struct vm_area_struct *vma, unsigned long addr,
 748                 pmd_t *pmd, int flags)
 749 {
 750         pmd_t _pmd;
 751
 752         _pmd = pmd_mkyoung(*pmd);
 753         if (flags & FOLL_WRITE)
 754                 _pmd = pmd_mkdirty(_pmd);
 755         if (pmdp_set_access_flags(vma, addr & HPAGE_PMD_MASK,
 756                                 pmd, _pmd, flags & FOLL_WRITE))
 757                 update_mmu_cache_pmd(vma, addr, pmd);
 758 }
 759
 760 struct page *follow_devmap_pmd(struct vm_area_struct *vma, unsigned long addr,
 761                 pmd_t *pmd, int flags)
 762 {
 763         unsigned long pfn = pmd_pfn(*pmd);
 764         struct mm_struct *mm = vma->vm_mm;
 765         struct dev_pagemap *pgmap;
 766         struct page *page;
 767
 768         assert_spin_locked(pmd_lockptr(mm, pmd));
 769
 770         /*
 771          * When we COW a devmap PMD entry, we split it into PTEs, so we should
 772          * not be in this function with `flags & FOLL_COW` set.
 773          */
 774         WARN_ONCE(flags & FOLL_COW, "mm: In follow_devmap_pmd with FOLL_COW set");
 775
 776         if (flags & FOLL_WRITE && !pmd_write(*pmd))
 777                 return NULL;
 778
 779         if (pmd_present(*pmd) && pmd_devmap(*pmd))
 780                 /* pass */;
 781         else
 782                 return NULL;
 783
 784         if (flags & FOLL_TOUCH)
 785                 touch_pmd(vma, addr, pmd, flags);
 786
 787         /*
 788          * device mapped pages can only be returned if the
 789          * caller will manage the page reference count.
 790          */
 791         if (!(flags & FOLL_GET))
 792                 return ERR_PTR(-EEXIST);
 793
 794         pfn += (addr & ~PMD_MASK) >> PAGE_SHIFT;
 795         pgmap = get_dev_pagemap(pfn, NULL);
 796         if (!pgmap)
 797                 return ERR_PTR(-EFAULT);
 798         page = pfn_to_page(pfn);
 799         get_page(page);
 800         put_dev_pagemap(pgmap);
 801
 802         return page;
 803 }
 804
 805 int copy_huge_pmd(struct mm_struct *dst_mm, struct mm_struct *src_mm,
 806                   pmd_t *dst_pmd, pmd_t *src_pmd, unsigned long addr,
 807                   struct vm_area_struct *vma)
 808 {
 809         spinlock_t *dst_ptl, *src_ptl;
 810         struct page *src_page;
 811         pmd_t pmd;
 812         pgtable_t pgtable = NULL;
 813         int ret = -ENOMEM;
 814
 815         /* Skip if can be re-fill on fault */
 816         if (!vma_is_anonymous(vma))
 817                 return 0;
 818
 819         pgtable = pte_alloc_one(dst_mm, addr);
 820         if (unlikely(!pgtable))
 821                 goto out;
 822
 823         dst_ptl = pmd_lock(dst_mm, dst_pmd);
 824         src_ptl = pmd_lockptr(src_mm, src_pmd);
 825         spin_lock_nested(src_ptl, SINGLE_DEPTH_NESTING);
 826
 827         ret = -EAGAIN;
 828         pmd = *src_pmd;
 829         if (unlikely(!pmd_trans_huge(pmd))) {
 830                 pte_free(dst_mm, pgtable);
 831                 goto out_unlock;
 832         }
 833         /*
 834          * When page table lock is held, the huge zero pmd should not be
 835          * under splitting since we don't split the page itself, only pmd to
 836          * a page table.
 837          */
 838         if (is_huge_zero_pmd(pmd)) {
 839                 struct page *zero_page;
 840                 /*
 841                  * get_huge_zero_page() will never allocate a new page here,
 842                  * since we already have a zero page to copy. It just takes a
 843                  * reference.
 844                  */
 845                 zero_page = mm_get_huge_zero_page(dst_mm);
 846                 set_huge_zero_page(pgtable, dst_mm, vma, addr, dst_pmd,
 847                                 zero_page);
 848                 ret = 0;
 849                 goto out_unlock;
 850         }
 851
 852         src_page = pmd_page(pmd);
 853         VM_BUG_ON_PAGE(!PageHead(src_page), src_page);
 854         get_page(src_page);
 855         page_dup_rmap(src_page, true);
 856         add_mm_counter(dst_mm, MM_ANONPAGES, HPAGE_PMD_NR);
 857         atomic_long_inc(&dst_mm->nr_ptes);
 858         pgtable_trans_huge_deposit(dst_mm, dst_pmd, pgtable);
 859
 860         pmdp_set_wrprotect(src_mm, addr, src_pmd);
 861         pmd = pmd_mkold(pmd_wrprotect(pmd));
 862         set_pmd_at(dst_mm, addr, dst_pmd, pmd);
 863
 864         ret = 0;
 865 out_unlock:
 866         spin_unlock(src_ptl);
 867         spin_unlock(dst_ptl);
 868 out:
 869         return ret;
 870 }
 871
 872 void huge_pmd_set_accessed(struct fault_env *fe, pmd_t orig_pmd)
 873 {
 874         pmd_t entry;
 875         unsigned long haddr;
 876         bool write = fe->flags & FAULT_FLAG_WRITE;
 877
 878         fe->ptl = pmd_lock(fe->vma->vm_mm, fe->pmd);
 879         if (unlikely(!pmd_same(*fe->pmd, orig_pmd)))
 880                 goto unlock;
 881
 882         entry = pmd_mkyoung(orig_pmd);
 883         if (write)
 884                 entry = pmd_mkdirty(entry);
 885         haddr = fe->address & HPAGE_PMD_MASK;
 886         if (pmdp_set_access_flags(fe->vma, haddr, fe->pmd, entry, write))
 887                 update_mmu_cache_pmd(fe->vma, fe->address, fe->pmd);
 888
 889 unlock:
 890         spin_unlock(fe->ptl);
 891 }
 892
 893 static int do_huge_pmd_wp_page_fallback(struct fault_env *fe, pmd_t orig_pmd,
 894                 struct page *page)
 895 {
 896         struct vm_area_struct *vma = fe->vma;
 897         unsigned long haddr = fe->address & HPAGE_PMD_MASK;
 898         struct mem_cgroup *memcg;
 899         pgtable_t pgtable;
 900         pmd_t _pmd;
 901         int ret = 0, i;
 902         struct page **pages;
 903         unsigned long mmun_start;       /* For mmu_notifiers */
 904         unsigned long mmun_end;         /* For mmu_notifiers */
 905
 906         pages = kmalloc(sizeof(struct page *) * HPAGE_PMD_NR,
 907                         GFP_KERNEL);
 908         if (unlikely(!pages)) {
 909                 ret |= VM_FAULT_OOM;
 910                 goto out;
 911         }
 912
 913         for (i = 0; i < HPAGE_PMD_NR; i++) {
 914                 pages[i] = alloc_page_vma_node(GFP_HIGHUSER_MOVABLE |
 915                                                __GFP_OTHER_NODE, vma,
 916                                                fe->address, page_to_nid(page));
 917                 if (unlikely(!pages[i] ||
 918                              mem_cgroup_try_charge(pages[i], vma->vm_mm,
 919                                      GFP_KERNEL, &memcg, false))) {
 920                         if (pages[i])
 921                                 put_page(pages[i]);
 922                         while (--i >= 0) {
 923                                 memcg = (void *)page_private(pages[i]);
 924                                 set_page_private(pages[i], 0);
 925                                 mem_cgroup_cancel_charge(pages[i], memcg,
 926                                                 false);
 927                                 put_page(pages[i]);
 928                         }
 929                         kfree(pages);
 930                         ret |= VM_FAULT_OOM;
 931                         goto out;
 932                 }
 933                 set_page_private(pages[i], (unsigned long)memcg);
 934         }
 935
 936         for (i = 0; i < HPAGE_PMD_NR; i++) {
 937                 copy_user_highpage(pages[i], page + i,
 938                                    haddr + PAGE_SIZE * i, vma);
 939                 __SetPageUptodate(pages[i]);
 940                 cond_resched();
 941         }
 942
 943         mmun_start = haddr;
 944         mmun_end   = haddr + HPAGE_PMD_SIZE;
 945         mmu_notifier_invalidate_range_start(vma->vm_mm, mmun_start, mmun_end);
 946
 947         fe->ptl = pmd_lock(vma->vm_mm, fe->pmd);
 948         if (unlikely(!pmd_same(*fe->pmd, orig_pmd)))
 949                 goto out_free_pages;
 950         VM_BUG_ON_PAGE(!PageHead(page), page);
 951
 952         pmdp_huge_clear_flush_notify(vma, haddr, fe->pmd);
 953         /* leave pmd empty until pte is filled */
 954
 955         pgtable = pgtable_trans_huge_withdraw(vma->vm_mm, fe->pmd);
 956         pmd_populate(vma->vm_mm, &_pmd, pgtable);
 957
 958         for (i = 0; i < HPAGE_PMD_NR; i++, haddr += PAGE_SIZE) {
 959                 pte_t entry;
 960                 entry = mk_pte(pages[i], vma->vm_page_prot);
 961                 entry = maybe_mkwrite(pte_mkdirty(entry), vma);
 962                 memcg = (void *)page_private(pages[i]);
 963                 set_page_private(pages[i], 0);
 964                 page_add_new_anon_rmap(pages[i], fe->vma, haddr, false);
 965                 mem_cgroup_commit_charge(pages[i], memcg, false, false);
 966                 lru_cache_add_active_or_unevictable(pages[i], vma);
 967                 fe->pte = pte_offset_map(&_pmd, haddr);
 968                 VM_BUG_ON(!pte_none(*fe->pte));
 969                 set_pte_at(vma->vm_mm, haddr, fe->pte, entry);
 970                 pte_unmap(fe->pte);
 971         }
 972         kfree(pages);
 973
 974         smp_wmb(); /* make pte visible before pmd */
 975         pmd_populate(vma->vm_mm, fe->pmd, pgtable);
 976         page_remove_rmap(page, true);
 977         spin_unlock(fe->ptl);
 978
 979         mmu_notifier_invalidate_range_end(vma->vm_mm, mmun_start, mmun_end);
 980
 981         ret |= VM_FAULT_WRITE;
 982         put_page(page);
 983
 984 out:
 985         return ret;
 986
 987 out_free_pages:
 988         spin_unlock(fe->ptl);
 989         mmu_notifier_invalidate_range_end(vma->vm_mm, mmun_start, mmun_end);
 990         for (i = 0; i < HPAGE_PMD_NR; i++) {
 991                 memcg = (void *)page_private(pages[i]);
 992                 set_page_private(pages[i], 0);
 993                 mem_cgroup_cancel_charge(pages[i], memcg, false);
 994                 put_page(pages[i]);
 995         }
 996         kfree(pages);
 997         goto out;
 998 }
 999
1000 int do_huge_pmd_wp_page(struct fault_env *fe, pmd_t orig_pmd)
1001 {
1002         struct vm_area_struct *vma = fe->vma;
1003         struct page *page = NULL, *new_page;
1004         struct mem_cgroup *memcg;
1005         unsigned long haddr = fe->address & HPAGE_PMD_MASK;
1006         unsigned long mmun_start;       /* For mmu_notifiers */
1007         unsigned long mmun_end;         /* For mmu_notifiers */
1008         gfp_t huge_gfp;                 /* for allocation and charge */
1009         int ret = 0;
1010
1011         fe->ptl = pmd_lockptr(vma->vm_mm, fe->pmd);
1012         VM_BUG_ON_VMA(!vma->anon_vma, vma);
1013         if (is_huge_zero_pmd(orig_pmd))
1014                 goto alloc;
1015         spin_lock(fe->ptl);
1016         if (unlikely(!pmd_same(*fe->pmd, orig_pmd)))
1017                 goto out_unlock;
1018
1019         page = pmd_page(orig_pmd);
1020         VM_BUG_ON_PAGE(!PageCompound(page) || !PageHead(page), page);
1021         /*
1022          * We can only reuse the page if nobody else maps the huge page or it's
1023          * part.
1024          */
1025         if (!trylock_page(page)) {
1026                 get_page(page);
1027                 spin_unlock(fe->ptl);
1028                 lock_page(page);
1029                 spin_lock(fe->ptl);
1030                 if (unlikely(!pmd_same(*fe->pmd, orig_pmd))) {
1031                         unlock_page(page);
1032                         put_page(page);
1033                         goto out_unlock;
1034                 }
1035                 put_page(page);
1036         }
1037
1038         if (page_trans_huge_mapcount(page, NULL) == 1) {
1039                 pmd_t entry;
1040                 entry = pmd_mkyoung(orig_pmd);
1041                 entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
1042                 if (pmdp_set_access_flags(vma, haddr, fe->pmd, entry,  1))
1043                         update_mmu_cache_pmd(vma, fe->address, fe->pmd);
1044                 ret |= VM_FAULT_WRITE;
1045                 unlock_page(page);
1046                 goto out_unlock;
1047         }
1048         unlock_page(page);
1049         get_page(page);
1050         spin_unlock(fe->ptl);
1051 alloc:
1052         if (transparent_hugepage_enabled(vma) &&
1053             !transparent_hugepage_debug_cow()) {
1054                 huge_gfp = alloc_hugepage_direct_gfpmask(vma);
1055                 new_page = alloc_hugepage_vma(huge_gfp, vma, haddr, HPAGE_PMD_ORDER);
1056         } else
1057                 new_page = NULL;
1058
1059         if (likely(new_page)) {
1060                 prep_transhuge_page(new_page);
1061         } else {
1062                 if (!page) {
1063                         split_huge_pmd(vma, fe->pmd, fe->address);
1064                         ret |= VM_FAULT_FALLBACK;
1065                 } else {
1066                         ret = do_huge_pmd_wp_page_fallback(fe, orig_pmd, page);
1067                         if (ret & VM_FAULT_OOM) {
1068                                 split_huge_pmd(vma, fe->pmd, fe->address);
1069                                 ret |= VM_FAULT_FALLBACK;
1070                         }
1071                         put_page(page);
1072                 }
1073                 count_vm_event(THP_FAULT_FALLBACK);
1074                 goto out;
1075         }
1076
1077         if (unlikely(mem_cgroup_try_charge(new_page, vma->vm_mm,
1078                                 huge_gfp | __GFP_NORETRY, &memcg, true))) {
1079                 put_page(new_page);
1080                 split_huge_pmd(vma, fe->pmd, fe->address);
1081                 if (page)
1082                         put_page(page);
1083                 ret |= VM_FAULT_FALLBACK;
1084                 count_vm_event(THP_FAULT_FALLBACK);
1085                 goto out;
1086         }
1087
1088         count_vm_event(THP_FAULT_ALLOC);
1089
1090         if (!page)
1091                 clear_huge_page(new_page, haddr, HPAGE_PMD_NR);
1092         else
1093                 copy_user_huge_page(new_page, page, haddr, vma, HPAGE_PMD_NR);
1094         __SetPageUptodate(new_page);
1095
1096         mmun_start = haddr;
1097         mmun_end   = haddr + HPAGE_PMD_SIZE;
1098         mmu_notifier_invalidate_range_start(vma->vm_mm, mmun_start, mmun_end);
1099
1100         spin_lock(fe->ptl);
1101         if (page)
1102                 put_page(page);
1103         if (unlikely(!pmd_same(*fe->pmd, orig_pmd))) {
1104                 spin_unlock(fe->ptl);
1105                 mem_cgroup_cancel_charge(new_page, memcg, true);
1106                 put_page(new_page);
1107                 goto out_mn;
1108         } else {
1109                 pmd_t entry;
1110                 entry = mk_huge_pmd(new_page, vma->vm_page_prot);
1111                 entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
1112                 pmdp_huge_clear_flush_notify(vma, haddr, fe->pmd);
1113                 page_add_new_anon_rmap(new_page, vma, haddr, true);
1114                 mem_cgroup_commit_charge(new_page, memcg, false, true);
1115                 lru_cache_add_active_or_unevictable(new_page, vma);
1116                 set_pmd_at(vma->vm_mm, haddr, fe->pmd, entry);
1117                 update_mmu_cache_pmd(vma, fe->address, fe->pmd);
1118                 if (!page) {
1119                         add_mm_counter(vma->vm_mm, MM_ANONPAGES, HPAGE_PMD_NR);
1120                 } else {
1121                         VM_BUG_ON_PAGE(!PageHead(page), page);
1122                         page_remove_rmap(page, true);
1123                         put_page(page);
1124                 }
1125                 ret |= VM_FAULT_WRITE;
1126         }
1127         spin_unlock(fe->ptl);
1128 out_mn:
1129         mmu_notifier_invalidate_range_end(vma->vm_mm, mmun_start, mmun_end);
1130 out:
1131         return ret;
1132 out_unlock:
1133         spin_unlock(fe->ptl);
1134         return ret;
1135 }
1136
1137 /*
1138  * FOLL_FORCE can write to even unwritable pmd's, but only
1139  * after we've gone through a COW cycle and they are dirty.
1140  */
1141 static inline bool can_follow_write_pmd(pmd_t pmd, unsigned int flags)
1142 {
1143         return pmd_write(pmd) ||
1144                ((flags & FOLL_FORCE) && (flags & FOLL_COW) && pmd_dirty(pmd));
1145 }
1146
1147 struct page *follow_trans_huge_pmd(struct vm_area_struct *vma,
1148                                    unsigned long addr,
1149                                    pmd_t *pmd,
1150                                    unsigned int flags)
1151 {
1152         struct mm_struct *mm = vma->vm_mm;
1153         struct page *page = NULL;
1154
1155         assert_spin_locked(pmd_lockptr(mm, pmd));
1156
1157         if (flags & FOLL_WRITE && !can_follow_write_pmd(*pmd, flags))
1158                 goto out;
1159
1160         /* Avoid dumping huge zero page */
1161         if ((flags & FOLL_DUMP) && is_huge_zero_pmd(*pmd))
1162                 return ERR_PTR(-EFAULT);
1163
1164         /* Full NUMA hinting faults to serialise migration in fault paths */
1165         if ((flags & FOLL_NUMA) && pmd_protnone(*pmd))
1166                 goto out;
1167
1168         page = pmd_page(*pmd);
1169         VM_BUG_ON_PAGE(!PageHead(page) && !is_zone_device_page(page), page);
1170         if (flags & FOLL_TOUCH)
1171                 touch_pmd(vma, addr, pmd, flags);
1172         if ((flags & FOLL_MLOCK) && (vma->vm_flags & VM_LOCKED)) {
1173                 /*
1174                  * We don't mlock() pte-mapped THPs. This way we can avoid
1175                  * leaking mlocked pages into non-VM_LOCKED VMAs.
1176                  *
1177                  * For anon THP:
1178                  *
1179                  * In most cases the pmd is the only mapping of the page as we
1180                  * break COW for the mlock() -- see gup_flags |= FOLL_WRITE for
1181                  * writable private mappings in populate_vma_page_range().
1182                  *
1183                  * The only scenario when we have the page shared here is if we
1184                  * mlocking read-only mapping shared over fork(). We skip
1185                  * mlocking such pages.
1186                  *
1187                  * For file THP:
1188                  *
1189                  * We can expect PageDoubleMap() to be stable under page lock:
1190                  * for file pages we set it in page_add_file_rmap(), which
1191                  * requires page to be locked.
1192                  */
1193
1194                 if (PageAnon(page) && compound_mapcount(page) != 1)
1195                         goto skip_mlock;
1196                 if (PageDoubleMap(page) || !page->mapping)
1197                         goto skip_mlock;
1198                 if (!trylock_page(page))
1199                         goto skip_mlock;
1200                 lru_add_drain();
1201                 if (page->mapping && !PageDoubleMap(page))
1202                         mlock_vma_page(page);
1203                 unlock_page(page);
1204         }
1205 skip_mlock:
1206         page += (addr & ~HPAGE_PMD_MASK) >> PAGE_SHIFT;
1207         VM_BUG_ON_PAGE(!PageCompound(page) && !is_zone_device_page(page), page);
1208         if (flags & FOLL_GET)
1209                 get_page(page);
1210
1211 out:
1212         return page;
1213 }
1214
1215 /* NUMA hinting page fault entry point for trans huge pmds */
1216 int do_huge_pmd_numa_page(struct fault_env *fe, pmd_t pmd)
1217 {
1218         struct vm_area_struct *vma = fe->vma;
1219         struct anon_vma *anon_vma = NULL;
1220         struct page *page;
1221         unsigned long haddr = fe->address & HPAGE_PMD_MASK;
1222         int page_nid = -1, this_nid = numa_node_id();
1223         int target_nid, last_cpupid = -1;
1224         bool page_locked;
1225         bool migrated = false;
1226         bool was_writable;
1227         int flags = 0;
1228
1229         fe->ptl = pmd_lock(vma->vm_mm, fe->pmd);
1230         if (unlikely(!pmd_same(pmd, *fe->pmd)))
1231                 goto out_unlock;
1232
1233         /*
1234          * If there are potential migrations, wait for completion and retry
1235          * without disrupting NUMA hinting information. Do not relock and
1236          * check_same as the page may no longer be mapped.
1237          */
1238         if (unlikely(pmd_trans_migrating(*fe->pmd))) {
1239                 page = pmd_page(*fe->pmd);
1240                 if (!get_page_unless_zero(page))
1241                         goto out_unlock;
1242                 spin_unlock(fe->ptl);
1243                 wait_on_page_locked(page);
1244                 put_page(page);
1245                 goto out;
1246         }
1247
1248         page = pmd_page(pmd);
1249         BUG_ON(is_huge_zero_page(page));
1250         page_nid = page_to_nid(page);
1251         last_cpupid = page_cpupid_last(page);
1252         count_vm_numa_event(NUMA_HINT_FAULTS);
1253         if (page_nid == this_nid) {
1254                 count_vm_numa_event(NUMA_HINT_FAULTS_LOCAL);
1255                 flags |= TNF_FAULT_LOCAL;
1256         }
1257
1258         /* See similar comment in do_numa_page for explanation */
1259         if (!pmd_write(pmd))
1260                 flags |= TNF_NO_GROUP;
1261
1262         /*
1263          * Acquire the page lock to serialise THP migrations but avoid dropping
1264          * page_table_lock if at all possible
1265          */
1266         page_locked = trylock_page(page);
1267         target_nid = mpol_misplaced(page, vma, haddr);
1268         if (target_nid == -1) {
1269                 /* If the page was locked, there are no parallel migrations */
1270                 if (page_locked)
1271                         goto clear_pmdnuma;
1272         }
1273
1274         /* Migration could have started since the pmd_trans_migrating check */
1275         if (!page_locked) {
1276                 page_nid = -1;
1277                 if (!get_page_unless_zero(page))
1278                         goto out_unlock;
1279                 spin_unlock(fe->ptl);
1280                 wait_on_page_locked(page);
1281                 put_page(page);
1282                 goto out;
1283         }
1284
1285         /*
1286          * Page is misplaced. Page lock serialises migrations. Acquire anon_vma
1287          * to serialises splits
1288          */
1289         get_page(page);
1290         spin_unlock(fe->ptl);
1291         anon_vma = page_lock_anon_vma_read(page);
1292
1293         /* Confirm the PMD did not change while page_table_lock was released */
1294         spin_lock(fe->ptl);
1295         if (unlikely(!pmd_same(pmd, *fe->pmd))) {
1296                 unlock_page(page);
1297                 put_page(page);
1298                 page_nid = -1;
1299                 goto out_unlock;
1300         }
1301
1302         /* Bail if we fail to protect against THP splits for any reason */
1303         if (unlikely(!anon_vma)) {
1304                 put_page(page);
1305                 page_nid = -1;
1306                 goto clear_pmdnuma;
1307         }
1308
1309         /*
1310          * Migrate the THP to the requested node, returns with page unlocked
1311          * and access rights restored.
1312          */
1313         spin_unlock(fe->ptl);
1314         migrated = migrate_misplaced_transhuge_page(vma->vm_mm, vma,
1315                                 fe->pmd, pmd, fe->address, page, target_nid);
1316         if (migrated) {
1317                 flags |= TNF_MIGRATED;
1318                 page_nid = target_nid;
1319         } else
1320                 flags |= TNF_MIGRATE_FAIL;
1321
1322         goto out;
1323 clear_pmdnuma:
1324         BUG_ON(!PageLocked(page));
1325         was_writable = pmd_write(pmd);
1326         pmd = pmd_modify(pmd, vma->vm_page_prot);
1327         pmd = pmd_mkyoung(pmd);
1328         if (was_writable)
1329                 pmd = pmd_mkwrite(pmd);
1330         set_pmd_at(vma->vm_mm, haddr, fe->pmd, pmd);
1331         update_mmu_cache_pmd(vma, fe->address, fe->pmd);
1332         unlock_page(page);
1333 out_unlock:
1334         spin_unlock(fe->ptl);
1335
1336 out:
1337         if (anon_vma)
1338                 page_unlock_anon_vma_read(anon_vma);
1339
1340         if (page_nid != -1)
1341                 task_numa_fault(last_cpupid, page_nid, HPAGE_PMD_NR, fe->flags);
1342
1343         return 0;
1344 }
1345
1346 /*
1347  * Return true if we do MADV_FREE successfully on entire pmd page.
1348  * Otherwise, return false.
1349  */
1350 bool madvise_free_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
1351                 pmd_t *pmd, unsigned long addr, unsigned long next)
1352 {
1353         spinlock_t *ptl;
1354         pmd_t orig_pmd;
1355         struct page *page;
1356         struct mm_struct *mm = tlb->mm;
1357         bool ret = false;
1358
1359         ptl = pmd_trans_huge_lock(pmd, vma);
1360         if (!ptl)
1361                 goto out_unlocked;
1362
1363         orig_pmd = *pmd;
1364         if (is_huge_zero_pmd(orig_pmd))
1365                 goto out;
1366
1367         page = pmd_page(orig_pmd);
1368         /*
1369          * If other processes are mapping this page, we couldn't discard
1370          * the page unless they all do MADV_FREE so let's skip the page.
1371          */
1372         if (total_mapcount(page) != 1)
1373                 goto out;
1374
1375         if (!trylock_page(page))
1376                 goto out;
1377
1378         /*
1379          * If user want to discard part-pages of THP, split it so MADV_FREE
1380          * will deactivate only them.
1381          */
1382         if (next - addr != HPAGE_PMD_SIZE) {
1383                 get_page(page);
1384                 spin_unlock(ptl);
1385                 split_huge_page(page);
1386                 unlock_page(page);
1387                 put_page(page);
1388                 goto out_unlocked;
1389         }
1390
1391         if (PageDirty(page))
1392                 ClearPageDirty(page);
1393         unlock_page(page);
1394
1395         if (PageActive(page))
1396                 deactivate_page(page);
1397
1398         if (pmd_young(orig_pmd) || pmd_dirty(orig_pmd)) {
1399                 pmdp_invalidate(vma, addr, pmd);
1400                 orig_pmd = pmd_mkold(orig_pmd);
1401                 orig_pmd = pmd_mkclean(orig_pmd);
1402
1403                 set_pmd_at(mm, addr, pmd, orig_pmd);
1404                 tlb_remove_pmd_tlb_entry(tlb, pmd, addr);
1405         }
1406         ret = true;
1407 out:
1408         spin_unlock(ptl);
1409 out_unlocked:
1410         return ret;
1411 }
1412
1413 int zap_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
1414                  pmd_t *pmd, unsigned long addr)
1415 {
1416         pmd_t orig_pmd;
1417         spinlock_t *ptl;
1418
1419         ptl = __pmd_trans_huge_lock(pmd, vma);
1420         if (!ptl)
1421                 return 0;
1422         /*
1423          * For architectures like ppc64 we look at deposited pgtable
1424          * when calling pmdp_huge_get_and_clear. So do the
1425          * pgtable_trans_huge_withdraw after finishing pmdp related
1426          * operations.
1427          */
1428         orig_pmd = pmdp_huge_get_and_clear_full(tlb->mm, addr, pmd,
1429                         tlb->fullmm);
1430         tlb_remove_pmd_tlb_entry(tlb, pmd, addr);
1431         if (vma_is_dax(vma)) {
1432                 spin_unlock(ptl);
1433                 if (is_huge_zero_pmd(orig_pmd))
1434                         tlb_remove_page(tlb, pmd_page(orig_pmd));
1435         } else if (is_huge_zero_pmd(orig_pmd)) {
1436                 pte_free(tlb->mm, pgtable_trans_huge_withdraw(tlb->mm, pmd));
1437                 atomic_long_dec(&tlb->mm->nr_ptes);
1438                 spin_unlock(ptl);
1439                 tlb_remove_page(tlb, pmd_page(orig_pmd));
1440         } else {
1441                 struct page *page = pmd_page(orig_pmd);
1442                 page_remove_rmap(page, true);
1443                 VM_BUG_ON_PAGE(page_mapcount(page) < 0, page);
1444                 VM_BUG_ON_PAGE(!PageHead(page), page);
1445                 if (PageAnon(page)) {
1446                         pgtable_t pgtable;
1447                         pgtable = pgtable_trans_huge_withdraw(tlb->mm, pmd);
1448                         pte_free(tlb->mm, pgtable);
1449                         atomic_long_dec(&tlb->mm->nr_ptes);
1450                         add_mm_counter(tlb->mm, MM_ANONPAGES, -HPAGE_PMD_NR);
1451                 } else {
1452                         add_mm_counter(tlb->mm, MM_FILEPAGES, -HPAGE_PMD_NR);
1453                 }
1454                 spin_unlock(ptl);
1455                 tlb_remove_page_size(tlb, page, HPAGE_PMD_SIZE);
1456         }
1457         return 1;
1458 }
1459
1460 bool move_huge_pmd(struct vm_area_struct *vma, unsigned long old_addr,
1461                   unsigned long new_addr, unsigned long old_end,
1462                   pmd_t *old_pmd, pmd_t *new_pmd)
1463 {
1464         spinlock_t *old_ptl, *new_ptl;
1465         pmd_t pmd;
1466         struct mm_struct *mm = vma->vm_mm;
1467         bool force_flush = false;
1468
1469         if ((old_addr & ~HPAGE_PMD_MASK) ||
1470             (new_addr & ~HPAGE_PMD_MASK) ||
1471             old_end - old_addr < HPAGE_PMD_SIZE)
1472                 return false;
1473
1474         /*
1475          * The destination pmd shouldn't be established, free_pgtables()
1476          * should have release it.
1477          */
1478         if (WARN_ON(!pmd_none(*new_pmd))) {
1479                 VM_BUG_ON(pmd_trans_huge(*new_pmd));
1480                 return false;
1481         }
1482
1483         /*
1484          * We don't have to worry about the ordering of src and dst
1485          * ptlocks because exclusive mmap_sem prevents deadlock.
1486          */
1487         old_ptl = __pmd_trans_huge_lock(old_pmd, vma);
1488         if (old_ptl) {
1489                 new_ptl = pmd_lockptr(mm, new_pmd);
1490                 if (new_ptl != old_ptl)
1491                         spin_lock_nested(new_ptl, SINGLE_DEPTH_NESTING);
1492                 pmd = pmdp_huge_get_and_clear(mm, old_addr, old_pmd);
1493                 if (pmd_present(pmd))
1494                         force_flush = true;
1495                 VM_BUG_ON(!pmd_none(*new_pmd));
1496
1497                 if (pmd_move_must_withdraw(new_ptl, old_ptl) &&
1498                                 vma_is_anonymous(vma)) {
1499                         pgtable_t pgtable;
1500                         pgtable = pgtable_trans_huge_withdraw(mm, old_pmd);
1501                         pgtable_trans_huge_deposit(mm, new_pmd, pgtable);
1502                 }
1503                 set_pmd_at(mm, new_addr, new_pmd, pmd_mksoft_dirty(pmd));
1504                 if (force_flush)
1505                         flush_tlb_range(vma, old_addr, old_addr + PMD_SIZE);
1506                 if (new_ptl != old_ptl)
1507                         spin_unlock(new_ptl);
1508                 spin_unlock(old_ptl);
1509                 return true;
1510         }
1511         return false;
1512 }
1513
1514 /*
1515  * Returns
1516  *  - 0 if PMD could not be locked
1517  *  - 1 if PMD was locked but protections unchange and TLB flush unnecessary
1518  *  - HPAGE_PMD_NR is protections changed and TLB flush necessary
1519  */
1520 int change_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
1521                 unsigned long addr, pgprot_t newprot, int prot_numa)
1522 {
1523         struct mm_struct *mm = vma->vm_mm;
1524         spinlock_t *ptl;
1525         pmd_t entry;
1526         bool preserve_write;
1527         int ret;
1528
1529         ptl = __pmd_trans_huge_lock(pmd, vma);
1530         if (!ptl)
1531                 return 0;
1532
1533         preserve_write = prot_numa && pmd_write(*pmd);
1534         ret = 1;
1535
1536         /*
1537          * Avoid trapping faults against the zero page. The read-only
1538          * data is likely to be read-cached on the local CPU and
1539          * local/remote hits to the zero page are not interesting.
1540          */
1541         if (prot_numa && is_huge_zero_pmd(*pmd))
1542                 goto unlock;
1543
1544         if (prot_numa && pmd_protnone(*pmd))
1545                 goto unlock;
1546
1547         /*
1548          * In case prot_numa, we are under down_read(mmap_sem). It's critical
1549          * to not clear pmd intermittently to avoid race with MADV_DONTNEED
1550          * which is also under down_read(mmap_sem):
1551          *
1552          *      CPU0:                           CPU1:
1553          *                              change_huge_pmd(prot_numa=1)
1554          *                               pmdp_huge_get_and_clear_notify()
1555          * madvise_dontneed()
1556          *  zap_pmd_range()
1557          *   pmd_trans_huge(*pmd) == 0 (without ptl)
1558          *   // skip the pmd
1559          *                               set_pmd_at();
1560          *                               // pmd is re-established
1561          *
1562          * The race makes MADV_DONTNEED miss the huge pmd and don't clear it
1563          * which may break userspace.
1564          *
1565          * pmdp_invalidate() is required to make sure we don't miss
1566          * dirty/young flags set by hardware.
1567          */
1568         entry = *pmd;
1569         pmdp_invalidate(vma, addr, pmd);
1570
1571         /*
1572          * Recover dirty/young flags.  It relies on pmdp_invalidate to not
1573          * corrupt them.
1574          */
1575         if (pmd_dirty(*pmd))
1576                 entry = pmd_mkdirty(entry);
1577         if (pmd_young(*pmd))
1578                 entry = pmd_mkyoung(entry);
1579
1580         entry = pmd_modify(entry, newprot);
1581         if (preserve_write)
1582                 entry = pmd_mkwrite(entry);
1583         ret = HPAGE_PMD_NR;
1584         set_pmd_at(mm, addr, pmd, entry);
1585         BUG_ON(vma_is_anonymous(vma) && !preserve_write && pmd_write(entry));
1586 unlock:
1587         spin_unlock(ptl);
1588         return ret;
1589 }
1590
1591 /*
1592  * Returns page table lock pointer if a given pmd maps a thp, NULL otherwise.
1593  *
1594  * Note that if it returns page table lock pointer, this routine returns without
1595  * unlocking page table lock. So callers must unlock it.
1596  */
1597 spinlock_t *__pmd_trans_huge_lock(pmd_t *pmd, struct vm_area_struct *vma)
1598 {
1599         spinlock_t *ptl;
1600         ptl = pmd_lock(vma->vm_mm, pmd);
1601         if (likely(pmd_trans_huge(*pmd) || pmd_devmap(*pmd)))
1602                 return ptl;
1603         spin_unlock(ptl);
1604         return NULL;
1605 }
1606
1607 static void __split_huge_zero_page_pmd(struct vm_area_struct *vma,
1608                 unsigned long haddr, pmd_t *pmd)
1609 {
1610         struct mm_struct *mm = vma->vm_mm;
1611         pgtable_t pgtable;
1612         pmd_t _pmd;
1613         int i;
1614
1615         /* leave pmd empty until pte is filled */
1616         pmdp_huge_clear_flush_notify(vma, haddr, pmd);
1617
1618         pgtable = pgtable_trans_huge_withdraw(mm, pmd);
1619         pmd_populate(mm, &_pmd, pgtable);
1620
1621         for (i = 0; i < HPAGE_PMD_NR; i++, haddr += PAGE_SIZE) {
1622                 pte_t *pte, entry;
1623                 entry = pfn_pte(my_zero_pfn(haddr), vma->vm_page_prot);
1624                 entry = pte_mkspecial(entry);
1625                 pte = pte_offset_map(&_pmd, haddr);
1626                 VM_BUG_ON(!pte_none(*pte));
1627                 set_pte_at(mm, haddr, pte, entry);
1628                 pte_unmap(pte);
1629         }
1630         smp_wmb(); /* make pte visible before pmd */
1631         pmd_populate(mm, pmd, pgtable);
1632 }
1633
1634 static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
1635                 unsigned long haddr, bool freeze)
1636 {
1637         struct mm_struct *mm = vma->vm_mm;
1638         struct page *page;
1639         pgtable_t pgtable;
1640         pmd_t _pmd;
1641         bool young, write, dirty, soft_dirty;
1642         unsigned long addr;
1643         int i;
1644
1645         VM_BUG_ON(haddr & ~HPAGE_PMD_MASK);
1646         VM_BUG_ON_VMA(vma->vm_start > haddr, vma);
1647         VM_BUG_ON_VMA(vma->vm_end < haddr + HPAGE_PMD_SIZE, vma);
1648         VM_BUG_ON(!pmd_trans_huge(*pmd) && !pmd_devmap(*pmd));
1649
1650         count_vm_event(THP_SPLIT_PMD);
1651
1652         if (!vma_is_anonymous(vma)) {
1653                 _pmd = pmdp_huge_clear_flush_notify(vma, haddr, pmd);
1654                 if (vma_is_dax(vma))
1655                         return;
1656                 page = pmd_page(_pmd);
1657                 if (!PageDirty(page) && pmd_dirty(_pmd))
1658                         set_page_dirty(page);
1659                 if (!PageReferenced(page) && pmd_young(_pmd))
1660                         SetPageReferenced(page);
1661                 page_remove_rmap(page, true);
1662                 put_page(page);
1663                 add_mm_counter(mm, MM_FILEPAGES, -HPAGE_PMD_NR);
1664                 return;
1665         } else if (is_huge_zero_pmd(*pmd)) {
1666                 return __split_huge_zero_page_pmd(vma, haddr, pmd);
1667         }
1668
1669         page = pmd_page(*pmd);
1670         VM_BUG_ON_PAGE(!page_count(page), page);
1671         page_ref_add(page, HPAGE_PMD_NR - 1);
1672         write = pmd_write(*pmd);
1673         young = pmd_young(*pmd);
1674         dirty = pmd_dirty(*pmd);
1675         soft_dirty = pmd_soft_dirty(*pmd);
1676
1677         pmdp_huge_split_prepare(vma, haddr, pmd);
1678         pgtable = pgtable_trans_huge_withdraw(mm, pmd);
1679         pmd_populate(mm, &_pmd, pgtable);
1680
1681         for (i = 0, addr = haddr; i < HPAGE_PMD_NR; i++, addr += PAGE_SIZE) {
1682                 pte_t entry, *pte;
1683                 /*
1684                  * Note that NUMA hinting access restrictions are not
1685                  * transferred to avoid any possibility of altering
1686                  * permissions across VMAs.
1687                  */
1688                 if (freeze) {
1689                         swp_entry_t swp_entry;
1690                         swp_entry = make_migration_entry(page + i, write);
1691                         entry = swp_entry_to_pte(swp_entry);
1692                         if (soft_dirty)
1693                                 entry = pte_swp_mksoft_dirty(entry);
1694                 } else {
1695                         entry = mk_pte(page + i, READ_ONCE(vma->vm_page_prot));
1696                         entry = maybe_mkwrite(entry, vma);
1697                         if (!write)
1698                                 entry = pte_wrprotect(entry);
1699                         if (!young)
1700                                 entry = pte_mkold(entry);
1701                         if (soft_dirty)
1702                                 entry = pte_mksoft_dirty(entry);
1703                 }
1704                 if (dirty)
1705                         SetPageDirty(page + i);
1706                 pte = pte_offset_map(&_pmd, addr);
1707                 BUG_ON(!pte_none(*pte));
1708                 set_pte_at(mm, addr, pte, entry);
1709                 atomic_inc(&page[i]._mapcount);
1710                 pte_unmap(pte);
1711         }
1712
1713         /*
1714          * Set PG_double_map before dropping compound_mapcount to avoid
1715          * false-negative page_mapped().
1716          */
1717         if (compound_mapcount(page) > 1 && !TestSetPageDoubleMap(page)) {
1718                 for (i = 0; i < HPAGE_PMD_NR; i++)
1719                         atomic_inc(&page[i]._mapcount);
1720         }
1721
1722         if (atomic_add_negative(-1, compound_mapcount_ptr(page))) {
1723                 /* Last compound_mapcount is gone. */
1724                 __dec_node_page_state(page, NR_ANON_THPS);
1725                 if (TestClearPageDoubleMap(page)) {
1726                         /* No need in mapcount reference anymore */
1727                         for (i = 0; i < HPAGE_PMD_NR; i++)
1728                                 atomic_dec(&page[i]._mapcount);
1729                 }
1730         }
1731
1732         smp_wmb(); /* make pte visible before pmd */
1733         /*
1734          * Up to this point the pmd is present and huge and userland has the
1735          * whole access to the hugepage during the split (which happens in
1736          * place). If we overwrite the pmd with the not-huge version pointing
1737          * to the pte here (which of course we could if all CPUs were bug
1738          * free), userland could trigger a small page size TLB miss on the
1739          * small sized TLB while the hugepage TLB entry is still established in
1740          * the huge TLB. Some CPU doesn't like that.
1741          * See http://support.amd.com/us/Processor_TechDocs/41322.pdf, Erratum
1742          * 383 on page 93. Intel should be safe but is also warns that it's
1743          * only safe if the permission and cache attributes of the two entries
1744          * loaded in the two TLB is identical (which should be the case here).
1745          * But it is generally safer to never allow small and huge TLB entries
1746          * for the same virtual address to be loaded simultaneously. So instead
1747          * of doing "pmd_populate(); flush_pmd_tlb_range();" we first mark the
1748          * current pmd notpresent (atomically because here the pmd_trans_huge
1749          * and pmd_trans_splitting must remain set at all times on the pmd
1750          * until the split is complete for this pmd), then we flush the SMP TLB
1751          * and finally we write the non-huge version of the pmd entry with
1752          * pmd_populate.
1753          */
1754         pmdp_invalidate(vma, haddr, pmd);
1755         pmd_populate(mm, pmd, pgtable);
1756
1757         if (freeze) {
1758                 for (i = 0; i < HPAGE_PMD_NR; i++) {
1759                         page_remove_rmap(page + i, false);
1760                         put_page(page + i);
1761                 }
1762         }
1763 }
1764
1765 void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
1766                 unsigned long address, bool freeze, struct page *page)
1767 {
1768         spinlock_t *ptl;
1769         struct mm_struct *mm = vma->vm_mm;
1770         unsigned long haddr = address & HPAGE_PMD_MASK;
1771         bool do_unlock_page = false;
1772         pmd_t _pmd;
1773
1774         mmu_notifier_invalidate_range_start(mm, haddr, haddr + HPAGE_PMD_SIZE);
1775         ptl = pmd_lock(mm, pmd);
1776
1777         /*
1778          * If caller asks to setup a migration entries, we need a page to check
1779          * pmd against. Otherwise we can end up replacing wrong page.
1780          */
1781         VM_BUG_ON(freeze && !page);
1782         if (page) {
1783                 VM_WARN_ON_ONCE(!PageLocked(page));
1784                 if (page != pmd_page(*pmd))
1785                         goto out;
1786         }
1787
1788 repeat:
1789         if (pmd_trans_huge(*pmd)) {
1790                 if (!page) {
1791                         page = pmd_page(*pmd);
1792                         /*
1793                          * An anonymous page must be locked, to ensure that a
1794                          * concurrent reuse_swap_page() sees stable mapcount;
1795                          * but reuse_swap_page() is not used on shmem or file,
1796                          * and page lock must not be taken when zap_pmd_range()
1797                          * calls __split_huge_pmd() while i_mmap_lock is held.
1798                          */
1799                         if (PageAnon(page)) {
1800                                 if (unlikely(!trylock_page(page))) {
1801                                         get_page(page);
1802                                         _pmd = *pmd;
1803                                         spin_unlock(ptl);
1804                                         lock_page(page);
1805                                         spin_lock(ptl);
1806                                         if (unlikely(!pmd_same(*pmd, _pmd))) {
1807                                                 unlock_page(page);
1808                                                 put_page(page);
1809                                                 page = NULL;
1810                                                 goto repeat;
1811                                         }
1812                                         put_page(page);
1813                                 }
1814                                 do_unlock_page = true;
1815                         }
1816                 }
1817                 if (PageMlocked(page))
1818                         clear_page_mlock(page);
1819         } else if (!pmd_devmap(*pmd))
1820                 goto out;
1821         __split_huge_pmd_locked(vma, pmd, haddr, freeze);
1822 out:
1823         spin_unlock(ptl);
1824         if (do_unlock_page)
1825                 unlock_page(page);
1826         mmu_notifier_invalidate_range_end(mm, haddr, haddr + HPAGE_PMD_SIZE);
1827 }
1828
1829 void split_huge_pmd_address(struct vm_area_struct *vma, unsigned long address,
1830                 bool freeze, struct page *page)
1831 {
1832         pgd_t *pgd;
1833         pud_t *pud;
1834         pmd_t *pmd;
1835
1836         pgd = pgd_offset(vma->vm_mm, address);
1837         if (!pgd_present(*pgd))
1838                 return;
1839
1840         pud = pud_offset(pgd, address);
1841         if (!pud_present(*pud))
1842                 return;
1843
1844         pmd = pmd_offset(pud, address);
1845
1846         __split_huge_pmd(vma, pmd, address, freeze, page);
1847 }
1848
1849 void vma_adjust_trans_huge(struct vm_area_struct *vma,
1850                              unsigned long start,
1851                              unsigned long end,
1852                              long adjust_next)
1853 {
1854         /*
1855          * If the new start address isn't hpage aligned and it could
1856          * previously contain an hugepage: check if we need to split
1857          * an huge pmd.
1858          */
1859         if (start & ~HPAGE_PMD_MASK &&
1860             (start & HPAGE_PMD_MASK) >= vma->vm_start &&
1861             (start & HPAGE_PMD_MASK) + HPAGE_PMD_SIZE <= vma->vm_end)
1862                 split_huge_pmd_address(vma, start, false, NULL);
1863
1864         /*
1865          * If the new end address isn't hpage aligned and it could
1866          * previously contain an hugepage: check if we need to split
1867          * an huge pmd.
1868          */
1869         if (end & ~HPAGE_PMD_MASK &&
1870             (end & HPAGE_PMD_MASK) >= vma->vm_start &&
1871             (end & HPAGE_PMD_MASK) + HPAGE_PMD_SIZE <= vma->vm_end)
1872                 split_huge_pmd_address(vma, end, false, NULL);
1873
1874         /*
1875          * If we're also updating the vma->vm_next->vm_start, if the new
1876          * vm_next->vm_start isn't page aligned and it could previously
1877          * contain an hugepage: check if we need to split an huge pmd.
1878          */
1879         if (adjust_next > 0) {
1880                 struct vm_area_struct *next = vma->vm_next;
1881                 unsigned long nstart = next->vm_start;
1882                 nstart += adjust_next << PAGE_SHIFT;
1883                 if (nstart & ~HPAGE_PMD_MASK &&
1884                     (nstart & HPAGE_PMD_MASK) >= next->vm_start &&
1885                     (nstart & HPAGE_PMD_MASK) + HPAGE_PMD_SIZE <= next->vm_end)
1886                         split_huge_pmd_address(next, nstart, false, NULL);
1887         }
1888 }
1889
1890 static void unmap_page(struct page *page)
1891 {
1892         enum ttu_flags ttu_flags = TTU_IGNORE_MLOCK | TTU_IGNORE_ACCESS |
1893                 TTU_RMAP_LOCKED;
1894         int i;
1895
1896         VM_BUG_ON_PAGE(!PageHead(page), page);
1897
1898         if (PageAnon(page))
1899                 ttu_flags |= TTU_MIGRATION;
1900
1901         /* We only need TTU_SPLIT_HUGE_PMD once */
1902         try_to_unmap(page, ttu_flags | TTU_SPLIT_HUGE_PMD);
1903         for (i = 1; i < HPAGE_PMD_NR; i++) {
1904                 /* Cut short if the page is unmapped */
1905                 if (page_count(page) == 1)
1906                         return;
1907
1908                 try_to_unmap(page + i, ttu_flags);
1909         }
1910
1911         VM_WARN_ON_ONCE_PAGE(page_mapped(page), page);
1912 }
1913
1914 static void remap_page(struct page *page)
1915 {
1916         int i;
1917
1918         for (i = 0; i < HPAGE_PMD_NR; i++)
1919                 remove_migration_ptes(page + i, page + i, true);
1920 }
1921
1922 static void __split_huge_page_tail(struct page *head, int tail,
1923                 struct lruvec *lruvec, struct list_head *list)
1924 {
1925         struct page *page_tail = head + tail;
1926
1927         VM_BUG_ON_PAGE(atomic_read(&page_tail->_mapcount) != -1, page_tail);
1928
1929         /*
1930          * Clone page flags before unfreezing refcount.
1931          *
1932          * After successful get_page_unless_zero() might follow flags change,
1933          * for exmaple lock_page() which set PG_waiters.
1934          */
1935         page_tail->flags &= ~PAGE_FLAGS_CHECK_AT_PREP;
1936         page_tail->flags |= (head->flags &
1937                         ((1L << PG_referenced) |
1938                          (1L << PG_swapbacked) |
1939                          (1L << PG_mlocked) |
1940                          (1L << PG_uptodate) |
1941                          (1L << PG_active) |
1942                          (1L << PG_locked) |
1943                          (1L << PG_unevictable) |
1944                          (1L << PG_dirty)));
1945
1946         /* ->mapping in first tail page is compound_mapcount */
1947         VM_BUG_ON_PAGE(tail > 2 && page_tail->mapping != TAIL_MAPPING,
1948                         page_tail);
1949         page_tail->mapping = head->mapping;
1950         page_tail->index = head->index + tail;
1951
1952         /* Page flags must be visible before we make the page non-compound. */
1953         smp_wmb();
1954
1955         /*
1956          * Clear PageTail before unfreezing page refcount.
1957          *
1958          * After successful get_page_unless_zero() might follow put_page()
1959          * which needs correct compound_head().
1960          */
1961         clear_compound_head(page_tail);
1962
1963         /* Finally unfreeze refcount. Additional reference from page cache. */
1964         page_ref_unfreeze(page_tail, 1 + (!PageAnon(head) ||
1965                                           PageSwapCache(head)));
1966
1967         if (page_is_young(head))
1968                 set_page_young(page_tail);
1969         if (page_is_idle(head))
1970                 set_page_idle(page_tail);
1971
1972         page_cpupid_xchg_last(page_tail, page_cpupid_last(head));
1973         lru_add_page_tail(head, page_tail, lruvec, list);
1974 }
1975
1976 static void __split_huge_page(struct page *page, struct list_head *list,
1977                 pgoff_t end, unsigned long flags)
1978 {
1979         struct page *head = compound_head(page);
1980         struct zone *zone = page_zone(head);
1981         struct lruvec *lruvec;
1982         int i;
1983
1984         lruvec = mem_cgroup_page_lruvec(head, zone->zone_pgdat);
1985
1986         /* complete memcg works before add pages to LRU */
1987         mem_cgroup_split_huge_fixup(head);
1988
1989         for (i = HPAGE_PMD_NR - 1; i >= 1; i--) {
1990                 __split_huge_page_tail(head, i, lruvec, list);
1991                 /* Some pages can be beyond i_size: drop them from page cache */
1992                 if (head[i].index >= end) {
1993                         __ClearPageDirty(head + i);
1994                         __delete_from_page_cache(head + i, NULL);
1995                         if (IS_ENABLED(CONFIG_SHMEM) && PageSwapBacked(head))
1996                                 shmem_uncharge(head->mapping->host, 1);
1997                         put_page(head + i);
1998                 }
1999         }
2000
2001         ClearPageCompound(head);
2002
2003         split_page_owner(head, HPAGE_PMD_ORDER);
2004
2005         /* See comment in __split_huge_page_tail() */
2006         if (PageAnon(head)) {
2007                 page_ref_inc(head);
2008         } else {
2009                 /* Additional pin to radix tree */
2010                 page_ref_add(head, 2);
2011                 spin_unlock(&head->mapping->tree_lock);
2012         }
2013
2014         spin_unlock_irqrestore(zone_lru_lock(page_zone(head)), flags);
2015
2016         remap_page(head);
2017
2018         for (i = 0; i < HPAGE_PMD_NR; i++) {
2019                 struct page *subpage = head + i;
2020                 if (subpage == page)
2021                         continue;
2022                 unlock_page(subpage);
2023
2024                 /*
2025                  * Subpages may be freed if there wasn't any mapping
2026                  * like if add_to_swap() is running on a lru page that
2027                  * had its mapping zapped. And freeing these pages
2028                  * requires taking the lru_lock so we do the put_page
2029                  * of the tail pages after the split is complete.
2030                  */
2031                 put_page(subpage);
2032         }
2033 }
2034
2035 int total_mapcount(struct page *page)
2036 {
2037         int i, compound, ret;
2038
2039         VM_BUG_ON_PAGE(PageTail(page), page);
2040
2041         if (likely(!PageCompound(page)))
2042                 return atomic_read(&page->_mapcount) + 1;
2043
2044         compound = compound_mapcount(page);
2045         if (PageHuge(page))
2046                 return compound;
2047         ret = compound;
2048         for (i = 0; i < HPAGE_PMD_NR; i++)
2049                 ret += atomic_read(&page[i]._mapcount) + 1;
2050         /* File pages has compound_mapcount included in _mapcount */
2051         if (!PageAnon(page))
2052                 return ret - compound * HPAGE_PMD_NR;
2053         if (PageDoubleMap(page))
2054                 ret -= HPAGE_PMD_NR;
2055         return ret;
2056 }
2057
2058 /*
2059  * This calculates accurately how many mappings a transparent hugepage
2060  * has (unlike page_mapcount() which isn't fully accurate). This full
2061  * accuracy is primarily needed to know if copy-on-write faults can
2062  * reuse the page and change the mapping to read-write instead of
2063  * copying them. At the same time this returns the total_mapcount too.
2064  *
2065  * The function returns the highest mapcount any one of the subpages
2066  * has. If the return value is one, even if different processes are
2067  * mapping different subpages of the transparent hugepage, they can
2068  * all reuse it, because each process is reusing a different subpage.
2069  *
2070  * The total_mapcount is instead counting all virtual mappings of the
2071  * subpages. If the total_mapcount is equal to "one", it tells the
2072  * caller all mappings belong to the same "mm" and in turn the
2073  * anon_vma of the transparent hugepage can become the vma->anon_vma
2074  * local one as no other process may be mapping any of the subpages.
2075  *
2076  * It would be more accurate to replace page_mapcount() with
2077  * page_trans_huge_mapcount(), however we only use
2078  * page_trans_huge_mapcount() in the copy-on-write faults where we
2079  * need full accuracy to avoid breaking page pinning, because
2080  * page_trans_huge_mapcount() is slower than page_mapcount().
2081  */
2082 int page_trans_huge_mapcount(struct page *page, int *total_mapcount)
2083 {
2084         int i, ret, _total_mapcount, mapcount;
2085
2086         /* hugetlbfs shouldn't call it */
2087         VM_BUG_ON_PAGE(PageHuge(page), page);
2088
2089         if (likely(!PageTransCompound(page))) {
2090                 mapcount = atomic_read(&page->_mapcount) + 1;
2091                 if (total_mapcount)
2092                         *total_mapcount = mapcount;
2093                 return mapcount;
2094         }
2095
2096         page = compound_head(page);
2097
2098         _total_mapcount = ret = 0;
2099         for (i = 0; i < HPAGE_PMD_NR; i++) {
2100                 mapcount = atomic_read(&page[i]._mapcount) + 1;
2101                 ret = max(ret, mapcount);
2102                 _total_mapcount += mapcount;
2103         }
2104         if (PageDoubleMap(page)) {
2105                 ret -= 1;
2106                 _total_mapcount -= HPAGE_PMD_NR;
2107         }
2108         mapcount = compound_mapcount(page);
2109         ret += mapcount;
2110         _total_mapcount += mapcount;
2111         if (total_mapcount)
2112                 *total_mapcount = _total_mapcount;
2113         return ret;
2114 }
2115
2116 /*
2117  * This function splits huge page into normal pages. @page can point to any
2118  * subpage of huge page to split. Split doesn't change the position of @page.
2119  *
2120  * Only caller must hold pin on the @page, otherwise split fails with -EBUSY.
2121  * The huge page must be locked.
2122  *
2123  * If @list is null, tail pages will be added to LRU list, otherwise, to @list.
2124  *
2125  * Both head page and tail pages will inherit mapping, flags, and so on from
2126  * the hugepage.
2127  *
2128  * GUP pin and PG_locked transferred to @page. Rest subpages can be freed if
2129  * they are not mapped.
2130  *
2131  * Returns 0 if the hugepage is split successfully.
2132  * Returns -EBUSY if the page is pinned or if anon_vma disappeared from under
2133  * us.
2134  */
2135 int split_huge_page_to_list(struct page *page, struct list_head *list)
2136 {
2137         struct page *head = compound_head(page);
2138         struct pglist_data *pgdata = NODE_DATA(page_to_nid(head));
2139         struct anon_vma *anon_vma = NULL;
2140         struct address_space *mapping = NULL;
2141         int extra_pins, ret;
2142         bool mlocked;
2143         unsigned long flags;
2144         pgoff_t end;
2145
2146         VM_BUG_ON_PAGE(is_huge_zero_page(head), head);
2147         VM_BUG_ON_PAGE(!PageLocked(page), page);
2148         VM_BUG_ON_PAGE(!PageSwapBacked(page), page);
2149         VM_BUG_ON_PAGE(!PageCompound(page), page);
2150
2151         if (PageAnon(head)) {
2152                 /*
2153                  * The caller does not necessarily hold an mmap_sem that would
2154                  * prevent the anon_vma disappearing so we first we take a
2155                  * reference to it and then lock the anon_vma for write. This
2156                  * is similar to page_lock_anon_vma_read except the write lock
2157                  * is taken to serialise against parallel split or collapse
2158                  * operations.
2159                  */
2160                 anon_vma = page_get_anon_vma(head);
2161                 if (!anon_vma) {
2162                         ret = -EBUSY;
2163                         goto out;
2164                 }
2165                 extra_pins = 0;
2166                 end = -1;
2167                 mapping = NULL;
2168                 anon_vma_lock_write(anon_vma);
2169         } else {
2170                 mapping = head->mapping;
2171
2172                 /* Truncated ? */
2173                 if (!mapping) {
2174                         ret = -EBUSY;
2175                         goto out;
2176                 }
2177
2178                 /* Addidional pins from radix tree */
2179                 extra_pins = HPAGE_PMD_NR;
2180                 anon_vma = NULL;
2181                 i_mmap_lock_read(mapping);
2182
2183                 /*
2184                  *__split_huge_page() may need to trim off pages beyond EOF:
2185                  * but on 32-bit, i_size_read() takes an irq-unsafe seqlock,
2186                  * which cannot be nested inside the page tree lock. So note
2187                  * end now: i_size itself may be changed at any moment, but
2188                  * head page lock is good enough to serialize the trimming.
2189                  */
2190                 end = DIV_ROUND_UP(i_size_read(mapping->host), PAGE_SIZE);
2191         }
2192
2193         /*
2194          * Racy check if we can split the page, before unmap_page() will
2195          * split PMDs
2196          */
2197         if (total_mapcount(head) != page_count(head) - extra_pins - 1) {
2198                 ret = -EBUSY;
2199                 goto out_unlock;
2200         }
2201
2202         mlocked = PageMlocked(page);
2203         unmap_page(head);
2204
2205         /* Make sure the page is not on per-CPU pagevec as it takes pin */
2206         if (mlocked)
2207                 lru_add_drain();
2208
2209         /* prevent PageLRU to go away from under us, and freeze lru stats */
2210         spin_lock_irqsave(zone_lru_lock(page_zone(head)), flags);
2211
2212         if (mapping) {
2213                 void **pslot;
2214
2215                 spin_lock(&mapping->tree_lock);
2216                 pslot = radix_tree_lookup_slot(&mapping->page_tree,
2217                                 page_index(head));
2218                 /*
2219                  * Check if the head page is present in radix tree.
2220                  * We assume all tail are present too, if head is there.
2221                  */
2222                 if (radix_tree_deref_slot_protected(pslot,
2223                                         &mapping->tree_lock) != head)
2224                         goto fail;
2225         }
2226
2227         /* Prevent deferred_split_scan() touching ->_refcount */
2228         spin_lock(&pgdata->split_queue_lock);
2229         if (page_ref_freeze(head, 1 + extra_pins)) {
2230                 if (!list_empty(page_deferred_list(head))) {
2231                         pgdata->split_queue_len--;
2232                         list_del(page_deferred_list(head));
2233                 }
2234                 if (mapping)
2235                         __dec_node_page_state(page, NR_SHMEM_THPS);
2236                 spin_unlock(&pgdata->split_queue_lock);
2237                 __split_huge_page(page, list, end, flags);
2238                 ret = 0;
2239         } else {
2240                 spin_unlock(&pgdata->split_queue_lock);
2241 fail:
2242                 if (mapping)
2243                         spin_unlock(&mapping->tree_lock);
2244                 spin_unlock_irqrestore(zone_lru_lock(page_zone(head)), flags);
2245                 remap_page(head);
2246                 ret = -EBUSY;
2247         }
2248
2249 out_unlock:
2250         if (anon_vma) {
2251                 anon_vma_unlock_write(anon_vma);
2252                 put_anon_vma(anon_vma);
2253         }
2254         if (mapping)
2255                 i_mmap_unlock_read(mapping);
2256 out:
2257         count_vm_event(!ret ? THP_SPLIT_PAGE : THP_SPLIT_PAGE_FAILED);
2258         return ret;
2259 }
2260
2261 void free_transhuge_page(struct page *page)
2262 {
2263         struct pglist_data *pgdata = NODE_DATA(page_to_nid(page));
2264         unsigned long flags;
2265
2266         spin_lock_irqsave(&pgdata->split_queue_lock, flags);
2267         if (!list_empty(page_deferred_list(page))) {
2268                 pgdata->split_queue_len--;
2269                 list_del(page_deferred_list(page));
2270         }
2271         spin_unlock_irqrestore(&pgdata->split_queue_lock, flags);
2272         free_compound_page(page);
2273 }
2274
2275 void deferred_split_huge_page(struct page *page)
2276 {
2277         struct pglist_data *pgdata = NODE_DATA(page_to_nid(page));
2278         unsigned long flags;
2279
2280         VM_BUG_ON_PAGE(!PageTransHuge(page), page);
2281
2282         spin_lock_irqsave(&pgdata->split_queue_lock, flags);
2283         if (list_empty(page_deferred_list(page))) {
2284                 count_vm_event(THP_DEFERRED_SPLIT_PAGE);
2285                 list_add_tail(page_deferred_list(page), &pgdata->split_queue);
2286                 pgdata->split_queue_len++;
2287         }
2288         spin_unlock_irqrestore(&pgdata->split_queue_lock, flags);
2289 }
2290
2291 static unsigned long deferred_split_count(struct shrinker *shrink,
2292                 struct shrink_control *sc)
2293 {
2294         struct pglist_data *pgdata = NODE_DATA(sc->nid);
2295         return ACCESS_ONCE(pgdata->split_queue_len);
2296 }
2297
2298 static unsigned long deferred_split_scan(struct shrinker *shrink,
2299                 struct shrink_control *sc)
2300 {
2301         struct pglist_data *pgdata = NODE_DATA(sc->nid);
2302         unsigned long flags;
2303         LIST_HEAD(list), *pos, *next;
2304         struct page *page;
2305         int split = 0;
2306
2307         spin_lock_irqsave(&pgdata->split_queue_lock, flags);
2308         /* Take pin on all head pages to avoid freeing them under us */
2309         list_for_each_safe(pos, next, &pgdata->split_queue) {
2310                 page = list_entry((void *)pos, struct page, mapping);
2311                 page = compound_head(page);
2312                 if (get_page_unless_zero(page)) {
2313                         list_move(page_deferred_list(page), &list);
2314                 } else {
2315                         /* We lost race with put_compound_page() */
2316                         list_del_init(page_deferred_list(page));
2317                         pgdata->split_queue_len--;
2318                 }
2319                 if (!--sc->nr_to_scan)
2320                         break;
2321         }
2322         spin_unlock_irqrestore(&pgdata->split_queue_lock, flags);
2323
2324         list_for_each_safe(pos, next, &list) {
2325                 page = list_entry((void *)pos, struct page, mapping);
2326                 if (!trylock_page(page))
2327                         goto next;
2328                 /* split_huge_page() removes page from list on success */
2329                 if (!split_huge_page(page))
2330                         split++;
2331                 unlock_page(page);
2332 next:
2333                 put_page(page);
2334         }
2335
2336         spin_lock_irqsave(&pgdata->split_queue_lock, flags);
2337         list_splice_tail(&list, &pgdata->split_queue);
2338         spin_unlock_irqrestore(&pgdata->split_queue_lock, flags);
2339
2340         /*
2341          * Stop shrinker if we didn't split any page, but the queue is empty.
2342          * This can happen if pages were freed under us.
2343          */
2344         if (!split && list_empty(&pgdata->split_queue))
2345                 return SHRINK_STOP;
2346         return split;
2347 }
2348
2349 static struct shrinker deferred_split_shrinker = {
2350         .count_objects = deferred_split_count,
2351         .scan_objects = deferred_split_scan,
2352         .seeks = DEFAULT_SEEKS,
2353         .flags = SHRINKER_NUMA_AWARE,
2354 };
2355
2356 #ifdef CONFIG_DEBUG_FS
2357 static int split_huge_pages_set(void *data, u64 val)
2358 {
2359         struct zone *zone;
2360         struct page *page;
2361         unsigned long pfn, max_zone_pfn;
2362         unsigned long total = 0, split = 0;
2363
2364         if (val != 1)
2365                 return -EINVAL;
2366
2367         for_each_populated_zone(zone) {
2368                 max_zone_pfn = zone_end_pfn(zone);
2369                 for (pfn = zone->zone_start_pfn; pfn < max_zone_pfn; pfn++) {
2370                         if (!pfn_valid(pfn))
2371                                 continue;
2372
2373                         page = pfn_to_page(pfn);
2374                         if (!get_page_unless_zero(page))
2375                                 continue;
2376
2377                         if (zone != page_zone(page))
2378                                 goto next;
2379
2380                         if (!PageHead(page) || PageHuge(page) || !PageLRU(page))
2381                                 goto next;
2382
2383                         total++;
2384                         lock_page(page);
2385                         if (!split_huge_page(page))
2386                                 split++;
2387                         unlock_page(page);
2388 next:
2389                         put_page(page);
2390                 }
2391         }
2392
2393         pr_info("%lu of %lu THP split\n", split, total);
2394
2395         return 0;
2396 }
2397 DEFINE_SIMPLE_ATTRIBUTE(split_huge_pages_fops, NULL, split_huge_pages_set,
2398                 "%llu\n");
2399
2400 static int __init split_huge_pages_debugfs(void)
2401 {
2402         void *ret;
2403
2404         ret = debugfs_create_file("split_huge_pages", 0200, NULL, NULL,
2405                         &split_huge_pages_fops);
2406         if (!ret)
2407                 pr_warn("Failed to create split_huge_pages in debugfs");
2408         return 0;
2409 }
2410 late_initcall(split_huge_pages_debugfs);
2411 #endif