linux/mm/migrate.c
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   1/*
   2 * Memory Migration functionality - linux/mm/migration.c
   3 *
   4 * Copyright (C) 2006 Silicon Graphics, Inc., Christoph Lameter
   5 *
   6 * Page migration was first developed in the context of the memory hotplug
   7 * project. The main authors of the migration code are:
   8 *
   9 * IWAMOTO Toshihiro <iwamoto@valinux.co.jp>
  10 * Hirokazu Takahashi <taka@valinux.co.jp>
  11 * Dave Hansen <haveblue@us.ibm.com>
  12 * Christoph Lameter
  13 */
  14
  15#include <linux/migrate.h>
  16#include <linux/export.h>
  17#include <linux/swap.h>
  18#include <linux/swapops.h>
  19#include <linux/pagemap.h>
  20#include <linux/buffer_head.h>
  21#include <linux/mm_inline.h>
  22#include <linux/nsproxy.h>
  23#include <linux/pagevec.h>
  24#include <linux/ksm.h>
  25#include <linux/rmap.h>
  26#include <linux/topology.h>
  27#include <linux/cpu.h>
  28#include <linux/cpuset.h>
  29#include <linux/writeback.h>
  30#include <linux/mempolicy.h>
  31#include <linux/vmalloc.h>
  32#include <linux/security.h>
  33#include <linux/memcontrol.h>
  34#include <linux/syscalls.h>
  35#include <linux/hugetlb.h>
  36#include <linux/hugetlb_cgroup.h>
  37#include <linux/gfp.h>
  38
  39#include <asm/tlbflush.h>
  40
  41#include "internal.h"
  42
  43/*
  44 * migrate_prep() needs to be called before we start compiling a list of pages
  45 * to be migrated using isolate_lru_page(). If scheduling work on other CPUs is
  46 * undesirable, use migrate_prep_local()
  47 */
  48int migrate_prep(void)
  49{
  50        /*
  51         * Clear the LRU lists so pages can be isolated.
  52         * Note that pages may be moved off the LRU after we have
  53         * drained them. Those pages will fail to migrate like other
  54         * pages that may be busy.
  55         */
  56        lru_add_drain_all();
  57
  58        return 0;
  59}
  60
  61/* Do the necessary work of migrate_prep but not if it involves other CPUs */
  62int migrate_prep_local(void)
  63{
  64        lru_add_drain();
  65
  66        return 0;
  67}
  68
  69/*
  70 * Add isolated pages on the list back to the LRU under page lock
  71 * to avoid leaking evictable pages back onto unevictable list.
  72 */
  73void putback_lru_pages(struct list_head *l)
  74{
  75        struct page *page;
  76        struct page *page2;
  77
  78        list_for_each_entry_safe(page, page2, l, lru) {
  79                list_del(&page->lru);
  80                dec_zone_page_state(page, NR_ISOLATED_ANON +
  81                                page_is_file_cache(page));
  82                putback_lru_page(page);
  83        }
  84}
  85
  86/*
  87 * Restore a potential migration pte to a working pte entry
  88 */
  89static int remove_migration_pte(struct page *new, struct vm_area_struct *vma,
  90                                 unsigned long addr, void *old)
  91{
  92        struct mm_struct *mm = vma->vm_mm;
  93        swp_entry_t entry;
  94        pgd_t *pgd;
  95        pud_t *pud;
  96        pmd_t *pmd;
  97        pte_t *ptep, pte;
  98        spinlock_t *ptl;
  99
 100        if (unlikely(PageHuge(new))) {
 101                ptep = huge_pte_offset(mm, addr);
 102                if (!ptep)
 103                        goto out;
 104                ptl = &mm->page_table_lock;
 105        } else {
 106                pgd = pgd_offset(mm, addr);
 107                if (!pgd_present(*pgd))
 108                        goto out;
 109
 110                pud = pud_offset(pgd, addr);
 111                if (!pud_present(*pud))
 112                        goto out;
 113
 114                pmd = pmd_offset(pud, addr);
 115                if (pmd_trans_huge(*pmd))
 116                        goto out;
 117                if (!pmd_present(*pmd))
 118                        goto out;
 119
 120                ptep = pte_offset_map(pmd, addr);
 121
 122                /*
 123                 * Peek to check is_swap_pte() before taking ptlock?  No, we
 124                 * can race mremap's move_ptes(), which skips anon_vma lock.
 125                 */
 126
 127                ptl = pte_lockptr(mm, pmd);
 128        }
 129
 130        spin_lock(ptl);
 131        pte = *ptep;
 132        if (!is_swap_pte(pte))
 133                goto unlock;
 134
 135        entry = pte_to_swp_entry(pte);
 136
 137        if (!is_migration_entry(entry) ||
 138            migration_entry_to_page(entry) != old)
 139                goto unlock;
 140
 141        get_page(new);
 142        pte = pte_mkold(mk_pte(new, vma->vm_page_prot));
 143        if (is_write_migration_entry(entry))
 144                pte = pte_mkwrite(pte);
 145#ifdef CONFIG_HUGETLB_PAGE
 146        if (PageHuge(new))
 147                pte = pte_mkhuge(pte);
 148#endif
 149        flush_cache_page(vma, addr, pte_pfn(pte));
 150        set_pte_at(mm, addr, ptep, pte);
 151
 152        if (PageHuge(new)) {
 153                if (PageAnon(new))
 154                        hugepage_add_anon_rmap(new, vma, addr);
 155                else
 156                        page_dup_rmap(new);
 157        } else if (PageAnon(new))
 158                page_add_anon_rmap(new, vma, addr);
 159        else
 160                page_add_file_rmap(new);
 161
 162        /* No need to invalidate - it was non-present before */
 163        update_mmu_cache(vma, addr, ptep);
 164unlock:
 165        pte_unmap_unlock(ptep, ptl);
 166out:
 167        return SWAP_AGAIN;
 168}
 169
 170/*
 171 * Get rid of all migration entries and replace them by
 172 * references to the indicated page.
 173 */
 174static void remove_migration_ptes(struct page *old, struct page *new)
 175{
 176        rmap_walk(new, remove_migration_pte, old);
 177}
 178
 179/*
 180 * Something used the pte of a page under migration. We need to
 181 * get to the page and wait until migration is finished.
 182 * When we return from this function the fault will be retried.
 183 */
 184void migration_entry_wait(struct mm_struct *mm, pmd_t *pmd,
 185                                unsigned long address)
 186{
 187        pte_t *ptep, pte;
 188        spinlock_t *ptl;
 189        swp_entry_t entry;
 190        struct page *page;
 191
 192        ptep = pte_offset_map_lock(mm, pmd, address, &ptl);
 193        pte = *ptep;
 194        if (!is_swap_pte(pte))
 195                goto out;
 196
 197        entry = pte_to_swp_entry(pte);
 198        if (!is_migration_entry(entry))
 199                goto out;
 200
 201        page = migration_entry_to_page(entry);
 202
 203        /*
 204         * Once radix-tree replacement of page migration started, page_count
 205         * *must* be zero. And, we don't want to call wait_on_page_locked()
 206         * against a page without get_page().
 207         * So, we use get_page_unless_zero(), here. Even failed, page fault
 208         * will occur again.
 209         */
 210        if (!get_page_unless_zero(page))
 211                goto out;
 212        pte_unmap_unlock(ptep, ptl);
 213        wait_on_page_locked(page);
 214        put_page(page);
 215        return;
 216out:
 217        pte_unmap_unlock(ptep, ptl);
 218}
 219
 220#ifdef CONFIG_BLOCK
 221/* Returns true if all buffers are successfully locked */
 222static bool buffer_migrate_lock_buffers(struct buffer_head *head,
 223                                                        enum migrate_mode mode)
 224{
 225        struct buffer_head *bh = head;
 226
 227        /* Simple case, sync compaction */
 228        if (mode != MIGRATE_ASYNC) {
 229                do {
 230                        get_bh(bh);
 231                        lock_buffer(bh);
 232                        bh = bh->b_this_page;
 233
 234                } while (bh != head);
 235
 236                return true;
 237        }
 238
 239        /* async case, we cannot block on lock_buffer so use trylock_buffer */
 240        do {
 241                get_bh(bh);
 242                if (!trylock_buffer(bh)) {
 243                        /*
 244                         * We failed to lock the buffer and cannot stall in
 245                         * async migration. Release the taken locks
 246                         */
 247                        struct buffer_head *failed_bh = bh;
 248                        put_bh(failed_bh);
 249                        bh = head;
 250                        while (bh != failed_bh) {
 251                                unlock_buffer(bh);
 252                                put_bh(bh);
 253                                bh = bh->b_this_page;
 254                        }
 255                        return false;
 256                }
 257
 258                bh = bh->b_this_page;
 259        } while (bh != head);
 260        return true;
 261}
 262#else
 263static inline bool buffer_migrate_lock_buffers(struct buffer_head *head,
 264                                                        enum migrate_mode mode)
 265{
 266        return true;
 267}
 268#endif /* CONFIG_BLOCK */
 269
 270/*
 271 * Replace the page in the mapping.
 272 *
 273 * The number of remaining references must be:
 274 * 1 for anonymous pages without a mapping
 275 * 2 for pages with a mapping
 276 * 3 for pages with a mapping and PagePrivate/PagePrivate2 set.
 277 */
 278static int migrate_page_move_mapping(struct address_space *mapping,
 279                struct page *newpage, struct page *page,
 280                struct buffer_head *head, enum migrate_mode mode)
 281{
 282        int expected_count;
 283        void **pslot;
 284
 285        if (!mapping) {
 286                /* Anonymous page without mapping */
 287                if (page_count(page) != 1)
 288                        return -EAGAIN;
 289                return 0;
 290        }
 291
 292        spin_lock_irq(&mapping->tree_lock);
 293
 294        pslot = radix_tree_lookup_slot(&mapping->page_tree,
 295                                        page_index(page));
 296
 297        expected_count = 2 + page_has_private(page);
 298        if (page_count(page) != expected_count ||
 299                radix_tree_deref_slot_protected(pslot, &mapping->tree_lock) != page) {
 300                spin_unlock_irq(&mapping->tree_lock);
 301                return -EAGAIN;
 302        }
 303
 304        if (!page_freeze_refs(page, expected_count)) {
 305                spin_unlock_irq(&mapping->tree_lock);
 306                return -EAGAIN;
 307        }
 308
 309        /*
 310         * In the async migration case of moving a page with buffers, lock the
 311         * buffers using trylock before the mapping is moved. If the mapping
 312         * was moved, we later failed to lock the buffers and could not move
 313         * the mapping back due to an elevated page count, we would have to
 314         * block waiting on other references to be dropped.
 315         */
 316        if (mode == MIGRATE_ASYNC && head &&
 317                        !buffer_migrate_lock_buffers(head, mode)) {
 318                page_unfreeze_refs(page, expected_count);
 319                spin_unlock_irq(&mapping->tree_lock);
 320                return -EAGAIN;
 321        }
 322
 323        /*
 324         * Now we know that no one else is looking at the page.
 325         */
 326        get_page(newpage);      /* add cache reference */
 327        if (PageSwapCache(page)) {
 328                SetPageSwapCache(newpage);
 329                set_page_private(newpage, page_private(page));
 330        }
 331
 332        radix_tree_replace_slot(pslot, newpage);
 333
 334        /*
 335         * Drop cache reference from old page by unfreezing
 336         * to one less reference.
 337         * We know this isn't the last reference.
 338         */
 339        page_unfreeze_refs(page, expected_count - 1);
 340
 341        /*
 342         * If moved to a different zone then also account
 343         * the page for that zone. Other VM counters will be
 344         * taken care of when we establish references to the
 345         * new page and drop references to the old page.
 346         *
 347         * Note that anonymous pages are accounted for
 348         * via NR_FILE_PAGES and NR_ANON_PAGES if they
 349         * are mapped to swap space.
 350         */
 351        __dec_zone_page_state(page, NR_FILE_PAGES);
 352        __inc_zone_page_state(newpage, NR_FILE_PAGES);
 353        if (!PageSwapCache(page) && PageSwapBacked(page)) {
 354                __dec_zone_page_state(page, NR_SHMEM);
 355                __inc_zone_page_state(newpage, NR_SHMEM);
 356        }
 357        spin_unlock_irq(&mapping->tree_lock);
 358
 359        return 0;
 360}
 361
 362/*
 363 * The expected number of remaining references is the same as that
 364 * of migrate_page_move_mapping().
 365 */
 366int migrate_huge_page_move_mapping(struct address_space *mapping,
 367                                   struct page *newpage, struct page *page)
 368{
 369        int expected_count;
 370        void **pslot;
 371
 372        if (!mapping) {
 373                if (page_count(page) != 1)
 374                        return -EAGAIN;
 375                return 0;
 376        }
 377
 378        spin_lock_irq(&mapping->tree_lock);
 379
 380        pslot = radix_tree_lookup_slot(&mapping->page_tree,
 381                                        page_index(page));
 382
 383        expected_count = 2 + page_has_private(page);
 384        if (page_count(page) != expected_count ||
 385                radix_tree_deref_slot_protected(pslot, &mapping->tree_lock) != page) {
 386                spin_unlock_irq(&mapping->tree_lock);
 387                return -EAGAIN;
 388        }
 389
 390        if (!page_freeze_refs(page, expected_count)) {
 391                spin_unlock_irq(&mapping->tree_lock);
 392                return -EAGAIN;
 393        }
 394
 395        get_page(newpage);
 396
 397        radix_tree_replace_slot(pslot, newpage);
 398
 399        page_unfreeze_refs(page, expected_count - 1);
 400
 401        spin_unlock_irq(&mapping->tree_lock);
 402        return 0;
 403}
 404
 405/*
 406 * Copy the page to its new location
 407 */
 408void migrate_page_copy(struct page *newpage, struct page *page)
 409{
 410        if (PageHuge(page))
 411                copy_huge_page(newpage, page);
 412        else
 413                copy_highpage(newpage, page);
 414
 415        if (PageError(page))
 416                SetPageError(newpage);
 417        if (PageReferenced(page))
 418                SetPageReferenced(newpage);
 419        if (PageUptodate(page))
 420                SetPageUptodate(newpage);
 421        if (TestClearPageActive(page)) {
 422                VM_BUG_ON(PageUnevictable(page));
 423                SetPageActive(newpage);
 424        } else if (TestClearPageUnevictable(page))
 425                SetPageUnevictable(newpage);
 426        if (PageChecked(page))
 427                SetPageChecked(newpage);
 428        if (PageMappedToDisk(page))
 429                SetPageMappedToDisk(newpage);
 430
 431        if (PageDirty(page)) {
 432                clear_page_dirty_for_io(page);
 433                /*
 434                 * Want to mark the page and the radix tree as dirty, and
 435                 * redo the accounting that clear_page_dirty_for_io undid,
 436                 * but we can't use set_page_dirty because that function
 437                 * is actually a signal that all of the page has become dirty.
 438                 * Whereas only part of our page may be dirty.
 439                 */
 440                if (PageSwapBacked(page))
 441                        SetPageDirty(newpage);
 442                else
 443                        __set_page_dirty_nobuffers(newpage);
 444        }
 445
 446        mlock_migrate_page(newpage, page);
 447        ksm_migrate_page(newpage, page);
 448
 449        ClearPageSwapCache(page);
 450        ClearPagePrivate(page);
 451        set_page_private(page, 0);
 452
 453        /*
 454         * If any waiters have accumulated on the new page then
 455         * wake them up.
 456         */
 457        if (PageWriteback(newpage))
 458                end_page_writeback(newpage);
 459}
 460
 461/************************************************************
 462 *                    Migration functions
 463 ***********************************************************/
 464
 465/* Always fail migration. Used for mappings that are not movable */
 466int fail_migrate_page(struct address_space *mapping,
 467                        struct page *newpage, struct page *page)
 468{
 469        return -EIO;
 470}
 471EXPORT_SYMBOL(fail_migrate_page);
 472
 473/*
 474 * Common logic to directly migrate a single page suitable for
 475 * pages that do not use PagePrivate/PagePrivate2.
 476 *
 477 * Pages are locked upon entry and exit.
 478 */
 479int migrate_page(struct address_space *mapping,
 480                struct page *newpage, struct page *page,
 481                enum migrate_mode mode)
 482{
 483        int rc;
 484
 485        BUG_ON(PageWriteback(page));    /* Writeback must be complete */
 486
 487        rc = migrate_page_move_mapping(mapping, newpage, page, NULL, mode);
 488
 489        if (rc)
 490                return rc;
 491
 492        migrate_page_copy(newpage, page);
 493        return 0;
 494}
 495EXPORT_SYMBOL(migrate_page);
 496
 497#ifdef CONFIG_BLOCK
 498/*
 499 * Migration function for pages with buffers. This function can only be used
 500 * if the underlying filesystem guarantees that no other references to "page"
 501 * exist.
 502 */
 503int buffer_migrate_page(struct address_space *mapping,
 504                struct page *newpage, struct page *page, enum migrate_mode mode)
 505{
 506        struct buffer_head *bh, *head;
 507        int rc;
 508
 509        if (!page_has_buffers(page))
 510                return migrate_page(mapping, newpage, page, mode);
 511
 512        head = page_buffers(page);
 513
 514        rc = migrate_page_move_mapping(mapping, newpage, page, head, mode);
 515
 516        if (rc)
 517                return rc;
 518
 519        /*
 520         * In the async case, migrate_page_move_mapping locked the buffers
 521         * with an IRQ-safe spinlock held. In the sync case, the buffers
 522         * need to be locked now
 523         */
 524        if (mode != MIGRATE_ASYNC)
 525                BUG_ON(!buffer_migrate_lock_buffers(head, mode));
 526
 527        ClearPagePrivate(page);
 528        set_page_private(newpage, page_private(page));
 529        set_page_private(page, 0);
 530        put_page(page);
 531        get_page(newpage);
 532
 533        bh = head;
 534        do {
 535                set_bh_page(bh, newpage, bh_offset(bh));
 536                bh = bh->b_this_page;
 537
 538        } while (bh != head);
 539
 540        SetPagePrivate(newpage);
 541
 542        migrate_page_copy(newpage, page);
 543
 544        bh = head;
 545        do {
 546                unlock_buffer(bh);
 547                put_bh(bh);
 548                bh = bh->b_this_page;
 549
 550        } while (bh != head);
 551
 552        return 0;
 553}
 554EXPORT_SYMBOL(buffer_migrate_page);
 555#endif
 556
 557/*
 558 * Writeback a page to clean the dirty state
 559 */
 560static int writeout(struct address_space *mapping, struct page *page)
 561{
 562        struct writeback_control wbc = {
 563                .sync_mode = WB_SYNC_NONE,
 564                .nr_to_write = 1,
 565                .range_start = 0,
 566                .range_end = LLONG_MAX,
 567                .for_reclaim = 1
 568        };
 569        int rc;
 570
 571        if (!mapping->a_ops->writepage)
 572                /* No write method for the address space */
 573                return -EINVAL;
 574
 575        if (!clear_page_dirty_for_io(page))
 576                /* Someone else already triggered a write */
 577                return -EAGAIN;
 578
 579        /*
 580         * A dirty page may imply that the underlying filesystem has
 581         * the page on some queue. So the page must be clean for
 582         * migration. Writeout may mean we loose the lock and the
 583         * page state is no longer what we checked for earlier.
 584         * At this point we know that the migration attempt cannot
 585         * be successful.
 586         */
 587        remove_migration_ptes(page, page);
 588
 589        rc = mapping->a_ops->writepage(page, &wbc);
 590
 591        if (rc != AOP_WRITEPAGE_ACTIVATE)
 592                /* unlocked. Relock */
 593                lock_page(page);
 594
 595        return (rc < 0) ? -EIO : -EAGAIN;
 596}
 597
 598/*
 599 * Default handling if a filesystem does not provide a migration function.
 600 */
 601static int fallback_migrate_page(struct address_space *mapping,
 602        struct page *newpage, struct page *page, enum migrate_mode mode)
 603{
 604        if (PageDirty(page)) {
 605                /* Only writeback pages in full synchronous migration */
 606                if (mode != MIGRATE_SYNC)
 607                        return -EBUSY;
 608                return writeout(mapping, page);
 609        }
 610
 611        /*
 612         * Buffers may be managed in a filesystem specific way.
 613         * We must have no buffers or drop them.
 614         */
 615        if (page_has_private(page) &&
 616            !try_to_release_page(page, GFP_KERNEL))
 617                return -EAGAIN;
 618
 619        return migrate_page(mapping, newpage, page, mode);
 620}
 621
 622/*
 623 * Move a page to a newly allocated page
 624 * The page is locked and all ptes have been successfully removed.
 625 *
 626 * The new page will have replaced the old page if this function
 627 * is successful.
 628 *
 629 * Return value:
 630 *   < 0 - error code
 631 *  == 0 - success
 632 */
 633static int move_to_new_page(struct page *newpage, struct page *page,
 634                                int remap_swapcache, enum migrate_mode mode)
 635{
 636        struct address_space *mapping;
 637        int rc;
 638
 639        /*
 640         * Block others from accessing the page when we get around to
 641         * establishing additional references. We are the only one
 642         * holding a reference to the new page at this point.
 643         */
 644        if (!trylock_page(newpage))
 645                BUG();
 646
 647        /* Prepare mapping for the new page.*/
 648        newpage->index = page->index;
 649        newpage->mapping = page->mapping;
 650        if (PageSwapBacked(page))
 651                SetPageSwapBacked(newpage);
 652
 653        mapping = page_mapping(page);
 654        if (!mapping)
 655                rc = migrate_page(mapping, newpage, page, mode);
 656        else if (mapping->a_ops->migratepage)
 657                /*
 658                 * Most pages have a mapping and most filesystems provide a
 659                 * migratepage callback. Anonymous pages are part of swap
 660                 * space which also has its own migratepage callback. This
 661                 * is the most common path for page migration.
 662                 */
 663                rc = mapping->a_ops->migratepage(mapping,
 664                                                newpage, page, mode);
 665        else
 666                rc = fallback_migrate_page(mapping, newpage, page, mode);
 667
 668        if (rc) {
 669                newpage->mapping = NULL;
 670        } else {
 671                if (remap_swapcache)
 672                        remove_migration_ptes(page, newpage);
 673                page->mapping = NULL;
 674        }
 675
 676        unlock_page(newpage);
 677
 678        return rc;
 679}
 680
 681static int __unmap_and_move(struct page *page, struct page *newpage,
 682                        int force, bool offlining, enum migrate_mode mode)
 683{
 684        int rc = -EAGAIN;
 685        int remap_swapcache = 1;
 686        struct mem_cgroup *mem;
 687        struct anon_vma *anon_vma = NULL;
 688
 689        if (!trylock_page(page)) {
 690                if (!force || mode == MIGRATE_ASYNC)
 691                        goto out;
 692
 693                /*
 694                 * It's not safe for direct compaction to call lock_page.
 695                 * For example, during page readahead pages are added locked
 696                 * to the LRU. Later, when the IO completes the pages are
 697                 * marked uptodate and unlocked. However, the queueing
 698                 * could be merging multiple pages for one bio (e.g.
 699                 * mpage_readpages). If an allocation happens for the
 700                 * second or third page, the process can end up locking
 701                 * the same page twice and deadlocking. Rather than
 702                 * trying to be clever about what pages can be locked,
 703                 * avoid the use of lock_page for direct compaction
 704                 * altogether.
 705                 */
 706                if (current->flags & PF_MEMALLOC)
 707                        goto out;
 708
 709                lock_page(page);
 710        }
 711
 712        /*
 713         * Only memory hotplug's offline_pages() caller has locked out KSM,
 714         * and can safely migrate a KSM page.  The other cases have skipped
 715         * PageKsm along with PageReserved - but it is only now when we have
 716         * the page lock that we can be certain it will not go KSM beneath us
 717         * (KSM will not upgrade a page from PageAnon to PageKsm when it sees
 718         * its pagecount raised, but only here do we take the page lock which
 719         * serializes that).
 720         */
 721        if (PageKsm(page) && !offlining) {
 722                rc = -EBUSY;
 723                goto unlock;
 724        }
 725
 726        /* charge against new page */
 727        mem_cgroup_prepare_migration(page, newpage, &mem);
 728
 729        if (PageWriteback(page)) {
 730                /*
 731                 * Only in the case of a full syncronous migration is it
 732                 * necessary to wait for PageWriteback. In the async case,
 733                 * the retry loop is too short and in the sync-light case,
 734                 * the overhead of stalling is too much
 735                 */
 736                if (mode != MIGRATE_SYNC) {
 737                        rc = -EBUSY;
 738                        goto uncharge;
 739                }
 740                if (!force)
 741                        goto uncharge;
 742                wait_on_page_writeback(page);
 743        }
 744        /*
 745         * By try_to_unmap(), page->mapcount goes down to 0 here. In this case,
 746         * we cannot notice that anon_vma is freed while we migrates a page.
 747         * This get_anon_vma() delays freeing anon_vma pointer until the end
 748         * of migration. File cache pages are no problem because of page_lock()
 749         * File Caches may use write_page() or lock_page() in migration, then,
 750         * just care Anon page here.
 751         */
 752        if (PageAnon(page)) {
 753                /*
 754                 * Only page_lock_anon_vma() understands the subtleties of
 755                 * getting a hold on an anon_vma from outside one of its mms.
 756                 */
 757                anon_vma = page_get_anon_vma(page);
 758                if (anon_vma) {
 759                        /*
 760                         * Anon page
 761                         */
 762                } else if (PageSwapCache(page)) {
 763                        /*
 764                         * We cannot be sure that the anon_vma of an unmapped
 765                         * swapcache page is safe to use because we don't
 766                         * know in advance if the VMA that this page belonged
 767                         * to still exists. If the VMA and others sharing the
 768                         * data have been freed, then the anon_vma could
 769                         * already be invalid.
 770                         *
 771                         * To avoid this possibility, swapcache pages get
 772                         * migrated but are not remapped when migration
 773                         * completes
 774                         */
 775                        remap_swapcache = 0;
 776                } else {
 777                        goto uncharge;
 778                }
 779        }
 780
 781        /*
 782         * Corner case handling:
 783         * 1. When a new swap-cache page is read into, it is added to the LRU
 784         * and treated as swapcache but it has no rmap yet.
 785         * Calling try_to_unmap() against a page->mapping==NULL page will
 786         * trigger a BUG.  So handle it here.
 787         * 2. An orphaned page (see truncate_complete_page) might have
 788         * fs-private metadata. The page can be picked up due to memory
 789         * offlining.  Everywhere else except page reclaim, the page is
 790         * invisible to the vm, so the page can not be migrated.  So try to
 791         * free the metadata, so the page can be freed.
 792         */
 793        if (!page->mapping) {
 794                VM_BUG_ON(PageAnon(page));
 795                if (page_has_private(page)) {
 796                        try_to_free_buffers(page);
 797                        goto uncharge;
 798                }
 799                goto skip_unmap;
 800        }
 801
 802        /* Establish migration ptes or remove ptes */
 803        try_to_unmap(page, TTU_MIGRATION|TTU_IGNORE_MLOCK|TTU_IGNORE_ACCESS);
 804
 805skip_unmap:
 806        if (!page_mapped(page))
 807                rc = move_to_new_page(newpage, page, remap_swapcache, mode);
 808
 809        if (rc && remap_swapcache)
 810                remove_migration_ptes(page, page);
 811
 812        /* Drop an anon_vma reference if we took one */
 813        if (anon_vma)
 814                put_anon_vma(anon_vma);
 815
 816uncharge:
 817        mem_cgroup_end_migration(mem, page, newpage, rc == 0);
 818unlock:
 819        unlock_page(page);
 820out:
 821        return rc;
 822}
 823
 824/*
 825 * Obtain the lock on page, remove all ptes and migrate the page
 826 * to the newly allocated page in newpage.
 827 */
 828static int unmap_and_move(new_page_t get_new_page, unsigned long private,
 829                        struct page *page, int force, bool offlining,
 830                        enum migrate_mode mode)
 831{
 832        int rc = 0;
 833        int *result = NULL;
 834        struct page *newpage = get_new_page(page, private, &result);
 835
 836        if (!newpage)
 837                return -ENOMEM;
 838
 839        if (page_count(page) == 1) {
 840                /* page was freed from under us. So we are done. */
 841                goto out;
 842        }
 843
 844        if (unlikely(PageTransHuge(page)))
 845                if (unlikely(split_huge_page(page)))
 846                        goto out;
 847
 848        rc = __unmap_and_move(page, newpage, force, offlining, mode);
 849out:
 850        if (rc != -EAGAIN) {
 851                /*
 852                 * A page that has been migrated has all references
 853                 * removed and will be freed. A page that has not been
 854                 * migrated will have kepts its references and be
 855                 * restored.
 856                 */
 857                list_del(&page->lru);
 858                dec_zone_page_state(page, NR_ISOLATED_ANON +
 859                                page_is_file_cache(page));
 860                putback_lru_page(page);
 861        }
 862        /*
 863         * Move the new page to the LRU. If migration was not successful
 864         * then this will free the page.
 865         */
 866        putback_lru_page(newpage);
 867        if (result) {
 868                if (rc)
 869                        *result = rc;
 870                else
 871                        *result = page_to_nid(newpage);
 872        }
 873        return rc;
 874}
 875
 876/*
 877 * Counterpart of unmap_and_move_page() for hugepage migration.
 878 *
 879 * This function doesn't wait the completion of hugepage I/O
 880 * because there is no race between I/O and migration for hugepage.
 881 * Note that currently hugepage I/O occurs only in direct I/O
 882 * where no lock is held and PG_writeback is irrelevant,
 883 * and writeback status of all subpages are counted in the reference
 884 * count of the head page (i.e. if all subpages of a 2MB hugepage are
 885 * under direct I/O, the reference of the head page is 512 and a bit more.)
 886 * This means that when we try to migrate hugepage whose subpages are
 887 * doing direct I/O, some references remain after try_to_unmap() and
 888 * hugepage migration fails without data corruption.
 889 *
 890 * There is also no race when direct I/O is issued on the page under migration,
 891 * because then pte is replaced with migration swap entry and direct I/O code
 892 * will wait in the page fault for migration to complete.
 893 */
 894static int unmap_and_move_huge_page(new_page_t get_new_page,
 895                                unsigned long private, struct page *hpage,
 896                                int force, bool offlining,
 897                                enum migrate_mode mode)
 898{
 899        int rc = 0;
 900        int *result = NULL;
 901        struct page *new_hpage = get_new_page(hpage, private, &result);
 902        struct anon_vma *anon_vma = NULL;
 903
 904        if (!new_hpage)
 905                return -ENOMEM;
 906
 907        rc = -EAGAIN;
 908
 909        if (!trylock_page(hpage)) {
 910                if (!force || mode != MIGRATE_SYNC)
 911                        goto out;
 912                lock_page(hpage);
 913        }
 914
 915        if (PageAnon(hpage))
 916                anon_vma = page_get_anon_vma(hpage);
 917
 918        try_to_unmap(hpage, TTU_MIGRATION|TTU_IGNORE_MLOCK|TTU_IGNORE_ACCESS);
 919
 920        if (!page_mapped(hpage))
 921                rc = move_to_new_page(new_hpage, hpage, 1, mode);
 922
 923        if (rc)
 924                remove_migration_ptes(hpage, hpage);
 925
 926        if (anon_vma)
 927                put_anon_vma(anon_vma);
 928
 929        if (!rc)
 930                hugetlb_cgroup_migrate(hpage, new_hpage);
 931
 932        unlock_page(hpage);
 933out:
 934        put_page(new_hpage);
 935        if (result) {
 936                if (rc)
 937                        *result = rc;
 938                else
 939                        *result = page_to_nid(new_hpage);
 940        }
 941        return rc;
 942}
 943
 944/*
 945 * migrate_pages
 946 *
 947 * The function takes one list of pages to migrate and a function
 948 * that determines from the page to be migrated and the private data
 949 * the target of the move and allocates the page.
 950 *
 951 * The function returns after 10 attempts or if no pages
 952 * are movable anymore because to has become empty
 953 * or no retryable pages exist anymore.
 954 * Caller should call putback_lru_pages to return pages to the LRU
 955 * or free list only if ret != 0.
 956 *
 957 * Return: Number of pages not migrated or error code.
 958 */
 959int migrate_pages(struct list_head *from,
 960                new_page_t get_new_page, unsigned long private, bool offlining,
 961                enum migrate_mode mode)
 962{
 963        int retry = 1;
 964        int nr_failed = 0;
 965        int pass = 0;
 966        struct page *page;
 967        struct page *page2;
 968        int swapwrite = current->flags & PF_SWAPWRITE;
 969        int rc;
 970
 971        if (!swapwrite)
 972                current->flags |= PF_SWAPWRITE;
 973
 974        for(pass = 0; pass < 10 && retry; pass++) {
 975                retry = 0;
 976
 977                list_for_each_entry_safe(page, page2, from, lru) {
 978                        cond_resched();
 979
 980                        rc = unmap_and_move(get_new_page, private,
 981                                                page, pass > 2, offlining,
 982                                                mode);
 983
 984                        switch(rc) {
 985                        case -ENOMEM:
 986                                goto out;
 987                        case -EAGAIN:
 988                                retry++;
 989                                break;
 990                        case 0:
 991                                break;
 992                        default:
 993                                /* Permanent failure */
 994                                nr_failed++;
 995                                break;
 996                        }
 997                }
 998        }
 999        rc = 0;
1000out:
1001        if (!swapwrite)
1002                current->flags &= ~PF_SWAPWRITE;
1003
1004        if (rc)
1005                return rc;
1006
1007        return nr_failed + retry;
1008}
1009
1010int migrate_huge_page(struct page *hpage, new_page_t get_new_page,
1011                      unsigned long private, bool offlining,
1012                      enum migrate_mode mode)
1013{
1014        int pass, rc;
1015
1016        for (pass = 0; pass < 10; pass++) {
1017                rc = unmap_and_move_huge_page(get_new_page,
1018                                              private, hpage, pass > 2, offlining,
1019                                              mode);
1020                switch (rc) {
1021                case -ENOMEM:
1022                        goto out;
1023                case -EAGAIN:
1024                        /* try again */
1025                        cond_resched();
1026                        break;
1027                case 0:
1028                        goto out;
1029                default:
1030                        rc = -EIO;
1031                        goto out;
1032                }
1033        }
1034out:
1035        return rc;
1036}
1037
1038#ifdef CONFIG_NUMA
1039/*
1040 * Move a list of individual pages
1041 */
1042struct page_to_node {
1043        unsigned long addr;
1044        struct page *page;
1045        int node;
1046        int status;
1047};
1048
1049static struct page *new_page_node(struct page *p, unsigned long private,
1050                int **result)
1051{
1052        struct page_to_node *pm = (struct page_to_node *)private;
1053
1054        while (pm->node != MAX_NUMNODES && pm->page != p)
1055                pm++;
1056
1057        if (pm->node == MAX_NUMNODES)
1058                return NULL;
1059
1060        *result = &pm->status;
1061
1062        return alloc_pages_exact_node(pm->node,
1063                                GFP_HIGHUSER_MOVABLE | GFP_THISNODE, 0);
1064}
1065
1066/*
1067 * Move a set of pages as indicated in the pm array. The addr
1068 * field must be set to the virtual address of the page to be moved
1069 * and the node number must contain a valid target node.
1070 * The pm array ends with node = MAX_NUMNODES.
1071 */
1072static int do_move_page_to_node_array(struct mm_struct *mm,
1073                                      struct page_to_node *pm,
1074                                      int migrate_all)
1075{
1076        int err;
1077        struct page_to_node *pp;
1078        LIST_HEAD(pagelist);
1079
1080        down_read(&mm->mmap_sem);
1081
1082        /*
1083         * Build a list of pages to migrate
1084         */
1085        for (pp = pm; pp->node != MAX_NUMNODES; pp++) {
1086                struct vm_area_struct *vma;
1087                struct page *page;
1088
1089                err = -EFAULT;
1090                vma = find_vma(mm, pp->addr);
1091                if (!vma || pp->addr < vma->vm_start || !vma_migratable(vma))
1092                        goto set_status;
1093
1094                page = follow_page(vma, pp->addr, FOLL_GET|FOLL_SPLIT);
1095
1096                err = PTR_ERR(page);
1097                if (IS_ERR(page))
1098                        goto set_status;
1099
1100                err = -ENOENT;
1101                if (!page)
1102                        goto set_status;
1103
1104                /* Use PageReserved to check for zero page */
1105                if (PageReserved(page) || PageKsm(page))
1106                        goto put_and_set;
1107
1108                pp->page = page;
1109                err = page_to_nid(page);
1110
1111                if (err == pp->node)
1112                        /*
1113                         * Node already in the right place
1114                         */
1115                        goto put_and_set;
1116
1117                err = -EACCES;
1118                if (page_mapcount(page) > 1 &&
1119                                !migrate_all)
1120                        goto put_and_set;
1121
1122                err = isolate_lru_page(page);
1123                if (!err) {
1124                        list_add_tail(&page->lru, &pagelist);
1125                        inc_zone_page_state(page, NR_ISOLATED_ANON +
1126                                            page_is_file_cache(page));
1127                }
1128put_and_set:
1129                /*
1130                 * Either remove the duplicate refcount from
1131                 * isolate_lru_page() or drop the page ref if it was
1132                 * not isolated.
1133                 */
1134                put_page(page);
1135set_status:
1136                pp->status = err;
1137        }
1138
1139        err = 0;
1140        if (!list_empty(&pagelist)) {
1141                err = migrate_pages(&pagelist, new_page_node,
1142                                (unsigned long)pm, 0, MIGRATE_SYNC);
1143                if (err)
1144                        putback_lru_pages(&pagelist);
1145        }
1146
1147        up_read(&mm->mmap_sem);
1148        return err;
1149}
1150
1151/*
1152 * Migrate an array of page address onto an array of nodes and fill
1153 * the corresponding array of status.
1154 */
1155static int do_pages_move(struct mm_struct *mm, nodemask_t task_nodes,
1156                         unsigned long nr_pages,
1157                         const void __user * __user *pages,
1158                         const int __user *nodes,
1159                         int __user *status, int flags)
1160{
1161        struct page_to_node *pm;
1162        unsigned long chunk_nr_pages;
1163        unsigned long chunk_start;
1164        int err;
1165
1166        err = -ENOMEM;
1167        pm = (struct page_to_node *)__get_free_page(GFP_KERNEL);
1168        if (!pm)
1169                goto out;
1170
1171        migrate_prep();
1172
1173        /*
1174         * Store a chunk of page_to_node array in a page,
1175         * but keep the last one as a marker
1176         */
1177        chunk_nr_pages = (PAGE_SIZE / sizeof(struct page_to_node)) - 1;
1178
1179        for (chunk_start = 0;
1180             chunk_start < nr_pages;
1181             chunk_start += chunk_nr_pages) {
1182                int j;
1183
1184                if (chunk_start + chunk_nr_pages > nr_pages)
1185                        chunk_nr_pages = nr_pages - chunk_start;
1186
1187                /* fill the chunk pm with addrs and nodes from user-space */
1188                for (j = 0; j < chunk_nr_pages; j++) {
1189                        const void __user *p;
1190                        int node;
1191
1192                        err = -EFAULT;
1193                        if (get_user(p, pages + j + chunk_start))
1194                                goto out_pm;
1195                        pm[j].addr = (unsigned long) p;
1196
1197                        if (get_user(node, nodes + j + chunk_start))
1198                                goto out_pm;
1199
1200                        err = -ENODEV;
1201                        if (node < 0 || node >= MAX_NUMNODES)
1202                                goto out_pm;
1203
1204                        if (!node_state(node, N_HIGH_MEMORY))
1205                                goto out_pm;
1206
1207                        err = -EACCES;
1208                        if (!node_isset(node, task_nodes))
1209                                goto out_pm;
1210
1211                        pm[j].node = node;
1212                }
1213
1214                /* End marker for this chunk */
1215                pm[chunk_nr_pages].node = MAX_NUMNODES;
1216
1217                /* Migrate this chunk */
1218                err = do_move_page_to_node_array(mm, pm,
1219                                                 flags & MPOL_MF_MOVE_ALL);
1220                if (err < 0)
1221                        goto out_pm;
1222
1223                /* Return status information */
1224                for (j = 0; j < chunk_nr_pages; j++)
1225                        if (put_user(pm[j].status, status + j + chunk_start)) {
1226                                err = -EFAULT;
1227                                goto out_pm;
1228                        }
1229        }
1230        err = 0;
1231
1232out_pm:
1233        free_page((unsigned long)pm);
1234out:
1235        return err;
1236}
1237
1238/*
1239 * Determine the nodes of an array of pages and store it in an array of status.
1240 */
1241static void do_pages_stat_array(struct mm_struct *mm, unsigned long nr_pages,
1242                                const void __user **pages, int *status)
1243{
1244        unsigned long i;
1245
1246        down_read(&mm->mmap_sem);
1247
1248        for (i = 0; i < nr_pages; i++) {
1249                unsigned long addr = (unsigned long)(*pages);
1250                struct vm_area_struct *vma;
1251                struct page *page;
1252                int err = -EFAULT;
1253
1254                vma = find_vma(mm, addr);
1255                if (!vma || addr < vma->vm_start)
1256                        goto set_status;
1257
1258                page = follow_page(vma, addr, 0);
1259
1260                err = PTR_ERR(page);
1261                if (IS_ERR(page))
1262                        goto set_status;
1263
1264                err = -ENOENT;
1265                /* Use PageReserved to check for zero page */
1266                if (!page || PageReserved(page) || PageKsm(page))
1267                        goto set_status;
1268
1269                err = page_to_nid(page);
1270set_status:
1271                *status = err;
1272
1273                pages++;
1274                status++;
1275        }
1276
1277        up_read(&mm->mmap_sem);
1278}
1279
1280/*
1281 * Determine the nodes of a user array of pages and store it in
1282 * a user array of status.
1283 */
1284static int do_pages_stat(struct mm_struct *mm, unsigned long nr_pages,
1285                         const void __user * __user *pages,
1286                         int __user *status)
1287{
1288#define DO_PAGES_STAT_CHUNK_NR 16
1289        const void __user *chunk_pages[DO_PAGES_STAT_CHUNK_NR];
1290        int chunk_status[DO_PAGES_STAT_CHUNK_NR];
1291
1292        while (nr_pages) {
1293                unsigned long chunk_nr;
1294
1295                chunk_nr = nr_pages;
1296                if (chunk_nr > DO_PAGES_STAT_CHUNK_NR)
1297                        chunk_nr = DO_PAGES_STAT_CHUNK_NR;
1298
1299                if (copy_from_user(chunk_pages, pages, chunk_nr * sizeof(*chunk_pages)))
1300                        break;
1301
1302                do_pages_stat_array(mm, chunk_nr, chunk_pages, chunk_status);
1303
1304                if (copy_to_user(status, chunk_status, chunk_nr * sizeof(*status)))
1305                        break;
1306
1307                pages += chunk_nr;
1308                status += chunk_nr;
1309                nr_pages -= chunk_nr;
1310        }
1311        return nr_pages ? -EFAULT : 0;
1312}
1313
1314/*
1315 * Move a list of pages in the address space of the currently executing
1316 * process.
1317 */
1318SYSCALL_DEFINE6(move_pages, pid_t, pid, unsigned long, nr_pages,
1319                const void __user * __user *, pages,
1320                const int __user *, nodes,
1321                int __user *, status, int, flags)
1322{
1323        const struct cred *cred = current_cred(), *tcred;
1324        struct task_struct *task;
1325        struct mm_struct *mm;
1326        int err;
1327        nodemask_t task_nodes;
1328
1329        /* Check flags */
1330        if (flags & ~(MPOL_MF_MOVE|MPOL_MF_MOVE_ALL))
1331                return -EINVAL;
1332
1333        if ((flags & MPOL_MF_MOVE_ALL) && !capable(CAP_SYS_NICE))
1334                return -EPERM;
1335
1336        /* Find the mm_struct */
1337        rcu_read_lock();
1338        task = pid ? find_task_by_vpid(pid) : current;
1339        if (!task) {
1340                rcu_read_unlock();
1341                return -ESRCH;
1342        }
1343        get_task_struct(task);
1344
1345        /*
1346         * Check if this process has the right to modify the specified
1347         * process. The right exists if the process has administrative
1348         * capabilities, superuser privileges or the same
1349         * userid as the target process.
1350         */
1351        tcred = __task_cred(task);
1352        if (!uid_eq(cred->euid, tcred->suid) && !uid_eq(cred->euid, tcred->uid) &&
1353            !uid_eq(cred->uid,  tcred->suid) && !uid_eq(cred->uid,  tcred->uid) &&
1354            !capable(CAP_SYS_NICE)) {
1355                rcu_read_unlock();
1356                err = -EPERM;
1357                goto out;
1358        }
1359        rcu_read_unlock();
1360
1361        err = security_task_movememory(task);
1362        if (err)
1363                goto out;
1364
1365        task_nodes = cpuset_mems_allowed(task);
1366        mm = get_task_mm(task);
1367        put_task_struct(task);
1368
1369        if (!mm)
1370                return -EINVAL;
1371
1372        if (nodes)
1373                err = do_pages_move(mm, task_nodes, nr_pages, pages,
1374                                    nodes, status, flags);
1375        else
1376                err = do_pages_stat(mm, nr_pages, pages, status);
1377
1378        mmput(mm);
1379        return err;
1380
1381out:
1382        put_task_struct(task);
1383        return err;
1384}
1385
1386/*
1387 * Call migration functions in the vma_ops that may prepare
1388 * memory in a vm for migration. migration functions may perform
1389 * the migration for vmas that do not have an underlying page struct.
1390 */
1391int migrate_vmas(struct mm_struct *mm, const nodemask_t *to,
1392        const nodemask_t *from, unsigned long flags)
1393{
1394        struct vm_area_struct *vma;
1395        int err = 0;
1396
1397        for (vma = mm->mmap; vma && !err; vma = vma->vm_next) {
1398                if (vma->vm_ops && vma->vm_ops->migrate) {
1399                        err = vma->vm_ops->migrate(vma, to, from, flags);
1400                        if (err)
1401                                break;
1402                }
1403        }
1404        return err;
1405}
1406#endif
1407
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