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#include <linux/balloon_compaction.h>
  39
  40#include <asm/tlbflush.h>
  41
  42#define CREATE_TRACE_POINTS
  43#include <trace/events/migrate.h>
  44
  45#include "internal.h"
  46
  47/*
  48 * migrate_prep() needs to be called before we start compiling a list of pages
  49 * to be migrated using isolate_lru_page(). If scheduling work on other CPUs is
  50 * undesirable, use migrate_prep_local()
  51 */
  52int migrate_prep(void)
  53{
  54        /*
  55         * Clear the LRU lists so pages can be isolated.
  56         * Note that pages may be moved off the LRU after we have
  57         * drained them. Those pages will fail to migrate like other
  58         * pages that may be busy.
  59         */
  60        lru_add_drain_all();
  61
  62        return 0;
  63}
  64
  65/* Do the necessary work of migrate_prep but not if it involves other CPUs */
  66int migrate_prep_local(void)
  67{
  68        lru_add_drain();
  69
  70        return 0;
  71}
  72
  73/*
  74 * Add isolated pages on the list back to the LRU under page lock
  75 * to avoid leaking evictable pages back onto unevictable list.
  76 */
  77void putback_lru_pages(struct list_head *l)
  78{
  79        struct page *page;
  80        struct page *page2;
  81
  82        list_for_each_entry_safe(page, page2, l, lru) {
  83                list_del(&page->lru);
  84                dec_zone_page_state(page, NR_ISOLATED_ANON +
  85                                page_is_file_cache(page));
  86                        putback_lru_page(page);
  87        }
  88}
  89
  90/*
  91 * Put previously isolated pages back onto the appropriate lists
  92 * from where they were once taken off for compaction/migration.
  93 *
  94 * This function shall be used instead of putback_lru_pages(),
  95 * whenever the isolated pageset has been built by isolate_migratepages_range()
  96 */
  97void putback_movable_pages(struct list_head *l)
  98{
  99        struct page *page;
 100        struct page *page2;
 101
 102        list_for_each_entry_safe(page, page2, l, lru) {
 103                if (unlikely(PageHuge(page))) {
 104                        putback_active_hugepage(page);
 105                        continue;
 106                }
 107                list_del(&page->lru);
 108                dec_zone_page_state(page, NR_ISOLATED_ANON +
 109                                page_is_file_cache(page));
 110                if (unlikely(isolated_balloon_page(page)))
 111                        balloon_page_putback(page);
 112                else
 113                        putback_lru_page(page);
 114        }
 115}
 116
 117/*
 118 * Restore a potential migration pte to a working pte entry
 119 */
 120static int remove_migration_pte(struct page *new, struct vm_area_struct *vma,
 121                                 unsigned long addr, void *old)
 122{
 123        struct mm_struct *mm = vma->vm_mm;
 124        swp_entry_t entry;
 125        pmd_t *pmd;
 126        pte_t *ptep, pte;
 127        spinlock_t *ptl;
 128
 129        if (unlikely(PageHuge(new))) {
 130                ptep = huge_pte_offset(mm, addr);
 131                if (!ptep)
 132                        goto out;
 133                ptl = &mm->page_table_lock;
 134        } else {
 135                pmd = mm_find_pmd(mm, addr);
 136                if (!pmd)
 137                        goto out;
 138                if (pmd_trans_huge(*pmd))
 139                        goto out;
 140
 141                ptep = pte_offset_map(pmd, addr);
 142
 143                /*
 144                 * Peek to check is_swap_pte() before taking ptlock?  No, we
 145                 * can race mremap's move_ptes(), which skips anon_vma lock.
 146                 */
 147
 148                ptl = pte_lockptr(mm, pmd);
 149        }
 150
 151        spin_lock(ptl);
 152        pte = *ptep;
 153        if (!is_swap_pte(pte))
 154                goto unlock;
 155
 156        entry = pte_to_swp_entry(pte);
 157
 158        if (!is_migration_entry(entry) ||
 159            migration_entry_to_page(entry) != old)
 160                goto unlock;
 161
 162        get_page(new);
 163        pte = pte_mkold(mk_pte(new, vma->vm_page_prot));
 164        if (pte_swp_soft_dirty(*ptep))
 165                pte = pte_mksoft_dirty(pte);
 166        if (is_write_migration_entry(entry))
 167                pte = pte_mkwrite(pte);
 168#ifdef CONFIG_HUGETLB_PAGE
 169        if (PageHuge(new)) {
 170                pte = pte_mkhuge(pte);
 171                pte = arch_make_huge_pte(pte, vma, new, 0);
 172        }
 173#endif
 174        flush_dcache_page(new);
 175        set_pte_at(mm, addr, ptep, pte);
 176
 177        if (PageHuge(new)) {
 178                if (PageAnon(new))
 179                        hugepage_add_anon_rmap(new, vma, addr);
 180                else
 181                        page_dup_rmap(new);
 182        } else if (PageAnon(new))
 183                page_add_anon_rmap(new, vma, addr);
 184        else
 185                page_add_file_rmap(new);
 186
 187        /* No need to invalidate - it was non-present before */
 188        update_mmu_cache(vma, addr, ptep);
 189unlock:
 190        pte_unmap_unlock(ptep, ptl);
 191out:
 192        return SWAP_AGAIN;
 193}
 194
 195/*
 196 * Get rid of all migration entries and replace them by
 197 * references to the indicated page.
 198 */
 199static void remove_migration_ptes(struct page *old, struct page *new)
 200{
 201        rmap_walk(new, remove_migration_pte, old);
 202}
 203
 204/*
 205 * Something used the pte of a page under migration. We need to
 206 * get to the page and wait until migration is finished.
 207 * When we return from this function the fault will be retried.
 208 */
 209static void __migration_entry_wait(struct mm_struct *mm, pte_t *ptep,
 210                                spinlock_t *ptl)
 211{
 212        pte_t pte;
 213        swp_entry_t entry;
 214        struct page *page;
 215
 216        spin_lock(ptl);
 217        pte = *ptep;
 218        if (!is_swap_pte(pte))
 219                goto out;
 220
 221        entry = pte_to_swp_entry(pte);
 222        if (!is_migration_entry(entry))
 223                goto out;
 224
 225        page = migration_entry_to_page(entry);
 226
 227        /*
 228         * Once radix-tree replacement of page migration started, page_count
 229         * *must* be zero. And, we don't want to call wait_on_page_locked()
 230         * against a page without get_page().
 231         * So, we use get_page_unless_zero(), here. Even failed, page fault
 232         * will occur again.
 233         */
 234        if (!get_page_unless_zero(page))
 235                goto out;
 236        pte_unmap_unlock(ptep, ptl);
 237        wait_on_page_locked(page);
 238        put_page(page);
 239        return;
 240out:
 241        pte_unmap_unlock(ptep, ptl);
 242}
 243
 244void migration_entry_wait(struct mm_struct *mm, pmd_t *pmd,
 245                                unsigned long address)
 246{
 247        spinlock_t *ptl = pte_lockptr(mm, pmd);
 248        pte_t *ptep = pte_offset_map(pmd, address);
 249        __migration_entry_wait(mm, ptep, ptl);
 250}
 251
 252void migration_entry_wait_huge(struct mm_struct *mm, pte_t *pte)
 253{
 254        spinlock_t *ptl = &(mm)->page_table_lock;
 255        __migration_entry_wait(mm, pte, ptl);
 256}
 257
 258#ifdef CONFIG_BLOCK
 259/* Returns true if all buffers are successfully locked */
 260static bool buffer_migrate_lock_buffers(struct buffer_head *head,
 261                                                        enum migrate_mode mode)
 262{
 263        struct buffer_head *bh = head;
 264
 265        /* Simple case, sync compaction */
 266        if (mode != MIGRATE_ASYNC) {
 267                do {
 268                        get_bh(bh);
 269                        lock_buffer(bh);
 270                        bh = bh->b_this_page;
 271
 272                } while (bh != head);
 273
 274                return true;
 275        }
 276
 277        /* async case, we cannot block on lock_buffer so use trylock_buffer */
 278        do {
 279                get_bh(bh);
 280                if (!trylock_buffer(bh)) {
 281                        /*
 282                         * We failed to lock the buffer and cannot stall in
 283                         * async migration. Release the taken locks
 284                         */
 285                        struct buffer_head *failed_bh = bh;
 286                        put_bh(failed_bh);
 287                        bh = head;
 288                        while (bh != failed_bh) {
 289                                unlock_buffer(bh);
 290                                put_bh(bh);
 291                                bh = bh->b_this_page;
 292                        }
 293                        return false;
 294                }
 295
 296                bh = bh->b_this_page;
 297        } while (bh != head);
 298        return true;
 299}
 300#else
 301static inline bool buffer_migrate_lock_buffers(struct buffer_head *head,
 302                                                        enum migrate_mode mode)
 303{
 304        return true;
 305}
 306#endif /* CONFIG_BLOCK */
 307
 308/*
 309 * Replace the page in the mapping.
 310 *
 311 * The number of remaining references must be:
 312 * 1 for anonymous pages without a mapping
 313 * 2 for pages with a mapping
 314 * 3 for pages with a mapping and PagePrivate/PagePrivate2 set.
 315 */
 316int migrate_page_move_mapping(struct address_space *mapping,
 317                struct page *newpage, struct page *page,
 318                struct buffer_head *head, enum migrate_mode mode)
 319{
 320        int expected_count = 0;
 321        void **pslot;
 322
 323        if (!mapping) {
 324                /* Anonymous page without mapping */
 325                if (page_count(page) != 1)
 326                        return -EAGAIN;
 327                return MIGRATEPAGE_SUCCESS;
 328        }
 329
 330        spin_lock_irq(&mapping->tree_lock);
 331
 332        pslot = radix_tree_lookup_slot(&mapping->page_tree,
 333                                        page_index(page));
 334
 335        expected_count = 2 + page_has_private(page);
 336        if (page_count(page) != expected_count ||
 337                radix_tree_deref_slot_protected(pslot, &mapping->tree_lock) != page) {
 338                spin_unlock_irq(&mapping->tree_lock);
 339                return -EAGAIN;
 340        }
 341
 342        if (!page_freeze_refs(page, expected_count)) {
 343                spin_unlock_irq(&mapping->tree_lock);
 344                return -EAGAIN;
 345        }
 346
 347        /*
 348         * In the async migration case of moving a page with buffers, lock the
 349         * buffers using trylock before the mapping is moved. If the mapping
 350         * was moved, we later failed to lock the buffers and could not move
 351         * the mapping back due to an elevated page count, we would have to
 352         * block waiting on other references to be dropped.
 353         */
 354        if (mode == MIGRATE_ASYNC && head &&
 355                        !buffer_migrate_lock_buffers(head, mode)) {
 356                page_unfreeze_refs(page, expected_count);
 357                spin_unlock_irq(&mapping->tree_lock);
 358                return -EAGAIN;
 359        }
 360
 361        /*
 362         * Now we know that no one else is looking at the page.
 363         */
 364        get_page(newpage);      /* add cache reference */
 365        if (PageSwapCache(page)) {
 366                SetPageSwapCache(newpage);
 367                set_page_private(newpage, page_private(page));
 368        }
 369
 370        radix_tree_replace_slot(pslot, newpage);
 371
 372        /*
 373         * Drop cache reference from old page by unfreezing
 374         * to one less reference.
 375         * We know this isn't the last reference.
 376         */
 377        page_unfreeze_refs(page, expected_count - 1);
 378
 379        /*
 380         * If moved to a different zone then also account
 381         * the page for that zone. Other VM counters will be
 382         * taken care of when we establish references to the
 383         * new page and drop references to the old page.
 384         *
 385         * Note that anonymous pages are accounted for
 386         * via NR_FILE_PAGES and NR_ANON_PAGES if they
 387         * are mapped to swap space.
 388         */
 389        __dec_zone_page_state(page, NR_FILE_PAGES);
 390        __inc_zone_page_state(newpage, NR_FILE_PAGES);
 391        if (!PageSwapCache(page) && PageSwapBacked(page)) {
 392                __dec_zone_page_state(page, NR_SHMEM);
 393                __inc_zone_page_state(newpage, NR_SHMEM);
 394        }
 395        spin_unlock_irq(&mapping->tree_lock);
 396
 397        return MIGRATEPAGE_SUCCESS;
 398}
 399
 400/*
 401 * The expected number of remaining references is the same as that
 402 * of migrate_page_move_mapping().
 403 */
 404int migrate_huge_page_move_mapping(struct address_space *mapping,
 405                                   struct page *newpage, struct page *page)
 406{
 407        int expected_count;
 408        void **pslot;
 409
 410        if (!mapping) {
 411                if (page_count(page) != 1)
 412                        return -EAGAIN;
 413                return MIGRATEPAGE_SUCCESS;
 414        }
 415
 416        spin_lock_irq(&mapping->tree_lock);
 417
 418        pslot = radix_tree_lookup_slot(&mapping->page_tree,
 419                                        page_index(page));
 420
 421        expected_count = 2 + page_has_private(page);
 422        if (page_count(page) != expected_count ||
 423                radix_tree_deref_slot_protected(pslot, &mapping->tree_lock) != page) {
 424                spin_unlock_irq(&mapping->tree_lock);
 425                return -EAGAIN;
 426        }
 427
 428        if (!page_freeze_refs(page, expected_count)) {
 429                spin_unlock_irq(&mapping->tree_lock);
 430                return -EAGAIN;
 431        }
 432
 433        get_page(newpage);
 434
 435        radix_tree_replace_slot(pslot, newpage);
 436
 437        page_unfreeze_refs(page, expected_count - 1);
 438
 439        spin_unlock_irq(&mapping->tree_lock);
 440        return MIGRATEPAGE_SUCCESS;
 441}
 442
 443/*
 444 * Copy the page to its new location
 445 */
 446void migrate_page_copy(struct page *newpage, struct page *page)
 447{
 448        if (PageHuge(page) || PageTransHuge(page))
 449                copy_huge_page(newpage, page);
 450        else
 451                copy_highpage(newpage, page);
 452
 453        if (PageError(page))
 454                SetPageError(newpage);
 455        if (PageReferenced(page))
 456                SetPageReferenced(newpage);
 457        if (PageUptodate(page))
 458                SetPageUptodate(newpage);
 459        if (TestClearPageActive(page)) {
 460                VM_BUG_ON(PageUnevictable(page));
 461                SetPageActive(newpage);
 462        } else if (TestClearPageUnevictable(page))
 463                SetPageUnevictable(newpage);
 464        if (PageChecked(page))
 465                SetPageChecked(newpage);
 466        if (PageMappedToDisk(page))
 467                SetPageMappedToDisk(newpage);
 468
 469        if (PageDirty(page)) {
 470                clear_page_dirty_for_io(page);
 471                /*
 472                 * Want to mark the page and the radix tree as dirty, and
 473                 * redo the accounting that clear_page_dirty_for_io undid,
 474                 * but we can't use set_page_dirty because that function
 475                 * is actually a signal that all of the page has become dirty.
 476                 * Whereas only part of our page may be dirty.
 477                 */
 478                if (PageSwapBacked(page))
 479                        SetPageDirty(newpage);
 480                else
 481                        __set_page_dirty_nobuffers(newpage);
 482        }
 483
 484        mlock_migrate_page(newpage, page);
 485        ksm_migrate_page(newpage, page);
 486        /*
 487         * Please do not reorder this without considering how mm/ksm.c's
 488         * get_ksm_page() depends upon ksm_migrate_page() and PageSwapCache().
 489         */
 490        ClearPageSwapCache(page);
 491        ClearPagePrivate(page);
 492        set_page_private(page, 0);
 493
 494        /*
 495         * If any waiters have accumulated on the new page then
 496         * wake them up.
 497         */
 498        if (PageWriteback(newpage))
 499                end_page_writeback(newpage);
 500}
 501
 502/************************************************************
 503 *                    Migration functions
 504 ***********************************************************/
 505
 506/* Always fail migration. Used for mappings that are not movable */
 507int fail_migrate_page(struct address_space *mapping,
 508                        struct page *newpage, struct page *page)
 509{
 510        return -EIO;
 511}
 512EXPORT_SYMBOL(fail_migrate_page);
 513
 514/*
 515 * Common logic to directly migrate a single page suitable for
 516 * pages that do not use PagePrivate/PagePrivate2.
 517 *
 518 * Pages are locked upon entry and exit.
 519 */
 520int migrate_page(struct address_space *mapping,
 521                struct page *newpage, struct page *page,
 522                enum migrate_mode mode)
 523{
 524        int rc;
 525
 526        BUG_ON(PageWriteback(page));    /* Writeback must be complete */
 527
 528        rc = migrate_page_move_mapping(mapping, newpage, page, NULL, mode);
 529
 530        if (rc != MIGRATEPAGE_SUCCESS)
 531                return rc;
 532
 533        migrate_page_copy(newpage, page);
 534        return MIGRATEPAGE_SUCCESS;
 535}
 536EXPORT_SYMBOL(migrate_page);
 537
 538#ifdef CONFIG_BLOCK
 539/*
 540 * Migration function for pages with buffers. This function can only be used
 541 * if the underlying filesystem guarantees that no other references to "page"
 542 * exist.
 543 */
 544int buffer_migrate_page(struct address_space *mapping,
 545                struct page *newpage, struct page *page, enum migrate_mode mode)
 546{
 547        struct buffer_head *bh, *head;
 548        int rc;
 549
 550        if (!page_has_buffers(page))
 551                return migrate_page(mapping, newpage, page, mode);
 552
 553        head = page_buffers(page);
 554
 555        rc = migrate_page_move_mapping(mapping, newpage, page, head, mode);
 556
 557        if (rc != MIGRATEPAGE_SUCCESS)
 558                return rc;
 559
 560        /*
 561         * In the async case, migrate_page_move_mapping locked the buffers
 562         * with an IRQ-safe spinlock held. In the sync case, the buffers
 563         * need to be locked now
 564         */
 565        if (mode != MIGRATE_ASYNC)
 566                BUG_ON(!buffer_migrate_lock_buffers(head, mode));
 567
 568        ClearPagePrivate(page);
 569        set_page_private(newpage, page_private(page));
 570        set_page_private(page, 0);
 571        put_page(page);
 572        get_page(newpage);
 573
 574        bh = head;
 575        do {
 576                set_bh_page(bh, newpage, bh_offset(bh));
 577                bh = bh->b_this_page;
 578
 579        } while (bh != head);
 580
 581        SetPagePrivate(newpage);
 582
 583        migrate_page_copy(newpage, page);
 584
 585        bh = head;
 586        do {
 587                unlock_buffer(bh);
 588                put_bh(bh);
 589                bh = bh->b_this_page;
 590
 591        } while (bh != head);
 592
 593        return MIGRATEPAGE_SUCCESS;
 594}
 595EXPORT_SYMBOL(buffer_migrate_page);
 596#endif
 597
 598/*
 599 * Writeback a page to clean the dirty state
 600 */
 601static int writeout(struct address_space *mapping, struct page *page)
 602{
 603        struct writeback_control wbc = {
 604                .sync_mode = WB_SYNC_NONE,
 605                .nr_to_write = 1,
 606                .range_start = 0,
 607                .range_end = LLONG_MAX,
 608                .for_reclaim = 1
 609        };
 610        int rc;
 611
 612        if (!mapping->a_ops->writepage)
 613                /* No write method for the address space */
 614                return -EINVAL;
 615
 616        if (!clear_page_dirty_for_io(page))
 617                /* Someone else already triggered a write */
 618                return -EAGAIN;
 619
 620        /*
 621         * A dirty page may imply that the underlying filesystem has
 622         * the page on some queue. So the page must be clean for
 623         * migration. Writeout may mean we loose the lock and the
 624         * page state is no longer what we checked for earlier.
 625         * At this point we know that the migration attempt cannot
 626         * be successful.
 627         */
 628        remove_migration_ptes(page, page);
 629
 630        rc = mapping->a_ops->writepage(page, &wbc);
 631
 632        if (rc != AOP_WRITEPAGE_ACTIVATE)
 633                /* unlocked. Relock */
 634                lock_page(page);
 635
 636        return (rc < 0) ? -EIO : -EAGAIN;
 637}
 638
 639/*
 640 * Default handling if a filesystem does not provide a migration function.
 641 */
 642static int fallback_migrate_page(struct address_space *mapping,
 643        struct page *newpage, struct page *page, enum migrate_mode mode)
 644{
 645        if (PageDirty(page)) {
 646                /* Only writeback pages in full synchronous migration */
 647                if (mode != MIGRATE_SYNC)
 648                        return -EBUSY;
 649                return writeout(mapping, page);
 650        }
 651
 652        /*
 653         * Buffers may be managed in a filesystem specific way.
 654         * We must have no buffers or drop them.
 655         */
 656        if (page_has_private(page) &&
 657            !try_to_release_page(page, GFP_KERNEL))
 658                return -EAGAIN;
 659
 660        return migrate_page(mapping, newpage, page, mode);
 661}
 662
 663/*
 664 * Move a page to a newly allocated page
 665 * The page is locked and all ptes have been successfully removed.
 666 *
 667 * The new page will have replaced the old page if this function
 668 * is successful.
 669 *
 670 * Return value:
 671 *   < 0 - error code
 672 *  MIGRATEPAGE_SUCCESS - success
 673 */
 674static int move_to_new_page(struct page *newpage, struct page *page,
 675                                int remap_swapcache, enum migrate_mode mode)
 676{
 677        struct address_space *mapping;
 678        int rc;
 679
 680        /*
 681         * Block others from accessing the page when we get around to
 682         * establishing additional references. We are the only one
 683         * holding a reference to the new page at this point.
 684         */
 685        if (!trylock_page(newpage))
 686                BUG();
 687
 688        /* Prepare mapping for the new page.*/
 689        newpage->index = page->index;
 690        newpage->mapping = page->mapping;
 691        if (PageSwapBacked(page))
 692                SetPageSwapBacked(newpage);
 693
 694        mapping = page_mapping(page);
 695        if (!mapping)
 696                rc = migrate_page(mapping, newpage, page, mode);
 697        else if (mapping->a_ops->migratepage)
 698                /*
 699                 * Most pages have a mapping and most filesystems provide a
 700                 * migratepage callback. Anonymous pages are part of swap
 701                 * space which also has its own migratepage callback. This
 702                 * is the most common path for page migration.
 703                 */
 704                rc = mapping->a_ops->migratepage(mapping,
 705                                                newpage, page, mode);
 706        else
 707                rc = fallback_migrate_page(mapping, newpage, page, mode);
 708
 709        if (rc != MIGRATEPAGE_SUCCESS) {
 710                newpage->mapping = NULL;
 711        } else {
 712                if (remap_swapcache)
 713                        remove_migration_ptes(page, newpage);
 714                page->mapping = NULL;
 715        }
 716
 717        unlock_page(newpage);
 718
 719        return rc;
 720}
 721
 722static int __unmap_and_move(struct page *page, struct page *newpage,
 723                                int force, enum migrate_mode mode)
 724{
 725        int rc = -EAGAIN;
 726        int remap_swapcache = 1;
 727        struct mem_cgroup *mem;
 728        struct anon_vma *anon_vma = NULL;
 729
 730        if (!trylock_page(page)) {
 731                if (!force || mode == MIGRATE_ASYNC)
 732                        goto out;
 733
 734                /*
 735                 * It's not safe for direct compaction to call lock_page.
 736                 * For example, during page readahead pages are added locked
 737                 * to the LRU. Later, when the IO completes the pages are
 738                 * marked uptodate and unlocked. However, the queueing
 739                 * could be merging multiple pages for one bio (e.g.
 740                 * mpage_readpages). If an allocation happens for the
 741                 * second or third page, the process can end up locking
 742                 * the same page twice and deadlocking. Rather than
 743                 * trying to be clever about what pages can be locked,
 744                 * avoid the use of lock_page for direct compaction
 745                 * altogether.
 746                 */
 747                if (current->flags & PF_MEMALLOC)
 748                        goto out;
 749
 750                lock_page(page);
 751        }
 752
 753        /* charge against new page */
 754        mem_cgroup_prepare_migration(page, newpage, &mem);
 755
 756        if (PageWriteback(page)) {
 757                /*
 758                 * Only in the case of a full synchronous migration is it
 759                 * necessary to wait for PageWriteback. In the async case,
 760                 * the retry loop is too short and in the sync-light case,
 761                 * the overhead of stalling is too much
 762                 */
 763                if (mode != MIGRATE_SYNC) {
 764                        rc = -EBUSY;
 765                        goto uncharge;
 766                }
 767                if (!force)
 768                        goto uncharge;
 769                wait_on_page_writeback(page);
 770        }
 771        /*
 772         * By try_to_unmap(), page->mapcount goes down to 0 here. In this case,
 773         * we cannot notice that anon_vma is freed while we migrates a page.
 774         * This get_anon_vma() delays freeing anon_vma pointer until the end
 775         * of migration. File cache pages are no problem because of page_lock()
 776         * File Caches may use write_page() or lock_page() in migration, then,
 777         * just care Anon page here.
 778         */
 779        if (PageAnon(page) && !PageKsm(page)) {
 780                /*
 781                 * Only page_lock_anon_vma_read() understands the subtleties of
 782                 * getting a hold on an anon_vma from outside one of its mms.
 783                 */
 784                anon_vma = page_get_anon_vma(page);
 785                if (anon_vma) {
 786                        /*
 787                         * Anon page
 788                         */
 789                } else if (PageSwapCache(page)) {
 790                        /*
 791                         * We cannot be sure that the anon_vma of an unmapped
 792                         * swapcache page is safe to use because we don't
 793                         * know in advance if the VMA that this page belonged
 794                         * to still exists. If the VMA and others sharing the
 795                         * data have been freed, then the anon_vma could
 796                         * already be invalid.
 797                         *
 798                         * To avoid this possibility, swapcache pages get
 799                         * migrated but are not remapped when migration
 800                         * completes
 801                         */
 802                        remap_swapcache = 0;
 803                } else {
 804                        goto uncharge;
 805                }
 806        }
 807
 808        if (unlikely(balloon_page_movable(page))) {
 809                /*
 810                 * A ballooned page does not need any special attention from
 811                 * physical to virtual reverse mapping procedures.
 812                 * Skip any attempt to unmap PTEs or to remap swap cache,
 813                 * in order to avoid burning cycles at rmap level, and perform
 814                 * the page migration right away (proteced by page lock).
 815                 */
 816                rc = balloon_page_migrate(newpage, page, mode);
 817                goto uncharge;
 818        }
 819
 820        /*
 821         * Corner case handling:
 822         * 1. When a new swap-cache page is read into, it is added to the LRU
 823         * and treated as swapcache but it has no rmap yet.
 824         * Calling try_to_unmap() against a page->mapping==NULL page will
 825         * trigger a BUG.  So handle it here.
 826         * 2. An orphaned page (see truncate_complete_page) might have
 827         * fs-private metadata. The page can be picked up due to memory
 828         * offlining.  Everywhere else except page reclaim, the page is
 829         * invisible to the vm, so the page can not be migrated.  So try to
 830         * free the metadata, so the page can be freed.
 831         */
 832        if (!page->mapping) {
 833                VM_BUG_ON(PageAnon(page));
 834                if (page_has_private(page)) {
 835                        try_to_free_buffers(page);
 836                        goto uncharge;
 837                }
 838                goto skip_unmap;
 839        }
 840
 841        /* Establish migration ptes or remove ptes */
 842        try_to_unmap(page, TTU_MIGRATION|TTU_IGNORE_MLOCK|TTU_IGNORE_ACCESS);
 843
 844skip_unmap:
 845        if (!page_mapped(page))
 846                rc = move_to_new_page(newpage, page, remap_swapcache, mode);
 847
 848        if (rc && remap_swapcache)
 849                remove_migration_ptes(page, page);
 850
 851        /* Drop an anon_vma reference if we took one */
 852        if (anon_vma)
 853                put_anon_vma(anon_vma);
 854
 855uncharge:
 856        mem_cgroup_end_migration(mem, page, newpage,
 857                                 (rc == MIGRATEPAGE_SUCCESS ||
 858                                  rc == MIGRATEPAGE_BALLOON_SUCCESS));
 859        unlock_page(page);
 860out:
 861        return rc;
 862}
 863
 864/*
 865 * Obtain the lock on page, remove all ptes and migrate the page
 866 * to the newly allocated page in newpage.
 867 */
 868static int unmap_and_move(new_page_t get_new_page, unsigned long private,
 869                        struct page *page, int force, enum migrate_mode mode)
 870{
 871        int rc = 0;
 872        int *result = NULL;
 873        struct page *newpage = get_new_page(page, private, &result);
 874
 875        if (!newpage)
 876                return -ENOMEM;
 877
 878        if (page_count(page) == 1) {
 879                /* page was freed from under us. So we are done. */
 880                goto out;
 881        }
 882
 883        if (unlikely(PageTransHuge(page)))
 884                if (unlikely(split_huge_page(page)))
 885                        goto out;
 886
 887        rc = __unmap_and_move(page, newpage, force, mode);
 888
 889        if (unlikely(rc == MIGRATEPAGE_BALLOON_SUCCESS)) {
 890                /*
 891                 * A ballooned page has been migrated already.
 892                 * Now, it's the time to wrap-up counters,
 893                 * handle the page back to Buddy and return.
 894                 */
 895                dec_zone_page_state(page, NR_ISOLATED_ANON +
 896                                    page_is_file_cache(page));
 897                balloon_page_free(page);
 898                return MIGRATEPAGE_SUCCESS;
 899        }
 900out:
 901        if (rc != -EAGAIN) {
 902                /*
 903                 * A page that has been migrated has all references
 904                 * removed and will be freed. A page that has not been
 905                 * migrated will have kepts its references and be
 906                 * restored.
 907                 */
 908                list_del(&page->lru);
 909                dec_zone_page_state(page, NR_ISOLATED_ANON +
 910                                page_is_file_cache(page));
 911                putback_lru_page(page);
 912        }
 913        /*
 914         * Move the new page to the LRU. If migration was not successful
 915         * then this will free the page.
 916         */
 917        putback_lru_page(newpage);
 918        if (result) {
 919                if (rc)
 920                        *result = rc;
 921                else
 922                        *result = page_to_nid(newpage);
 923        }
 924        return rc;
 925}
 926
 927/*
 928 * Counterpart of unmap_and_move_page() for hugepage migration.
 929 *
 930 * This function doesn't wait the completion of hugepage I/O
 931 * because there is no race between I/O and migration for hugepage.
 932 * Note that currently hugepage I/O occurs only in direct I/O
 933 * where no lock is held and PG_writeback is irrelevant,
 934 * and writeback status of all subpages are counted in the reference
 935 * count of the head page (i.e. if all subpages of a 2MB hugepage are
 936 * under direct I/O, the reference of the head page is 512 and a bit more.)
 937 * This means that when we try to migrate hugepage whose subpages are
 938 * doing direct I/O, some references remain after try_to_unmap() and
 939 * hugepage migration fails without data corruption.
 940 *
 941 * There is also no race when direct I/O is issued on the page under migration,
 942 * because then pte is replaced with migration swap entry and direct I/O code
 943 * will wait in the page fault for migration to complete.
 944 */
 945static int unmap_and_move_huge_page(new_page_t get_new_page,
 946                                unsigned long private, struct page *hpage,
 947                                int force, enum migrate_mode mode)
 948{
 949        int rc = 0;
 950        int *result = NULL;
 951        struct page *new_hpage = get_new_page(hpage, private, &result);
 952        struct anon_vma *anon_vma = NULL;
 953
 954        /*
 955         * Movability of hugepages depends on architectures and hugepage size.
 956         * This check is necessary because some callers of hugepage migration
 957         * like soft offline and memory hotremove don't walk through page
 958         * tables or check whether the hugepage is pmd-based or not before
 959         * kicking migration.
 960         */
 961        if (!hugepage_migration_support(page_hstate(hpage)))
 962                return -ENOSYS;
 963
 964        if (!new_hpage)
 965                return -ENOMEM;
 966
 967        rc = -EAGAIN;
 968
 969        if (!trylock_page(hpage)) {
 970                if (!force || mode != MIGRATE_SYNC)
 971                        goto out;
 972                lock_page(hpage);
 973        }
 974
 975        if (PageAnon(hpage))
 976                anon_vma = page_get_anon_vma(hpage);
 977
 978        try_to_unmap(hpage, TTU_MIGRATION|TTU_IGNORE_MLOCK|TTU_IGNORE_ACCESS);
 979
 980        if (!page_mapped(hpage))
 981                rc = move_to_new_page(new_hpage, hpage, 1, mode);
 982
 983        if (rc)
 984                remove_migration_ptes(hpage, hpage);
 985
 986        if (anon_vma)
 987                put_anon_vma(anon_vma);
 988
 989        if (!rc)
 990                hugetlb_cgroup_migrate(hpage, new_hpage);
 991
 992        unlock_page(hpage);
 993out:
 994        if (rc != -EAGAIN)
 995                putback_active_hugepage(hpage);
 996        put_page(new_hpage);
 997        if (result) {
 998                if (rc)
 999                        *result = rc;
1000                else
1001                        *result = page_to_nid(new_hpage);
1002        }
1003        return rc;
1004}
1005
1006/*
1007 * migrate_pages - migrate the pages specified in a list, to the free pages
1008 *                 supplied as the target for the page migration
1009 *
1010 * @from:               The list of pages to be migrated.
1011 * @get_new_page:       The function used to allocate free pages to be used
1012 *                      as the target of the page migration.
1013 * @private:            Private data to be passed on to get_new_page()
1014 * @mode:               The migration mode that specifies the constraints for
1015 *                      page migration, if any.
1016 * @reason:             The reason for page migration.
1017 *
1018 * The function returns after 10 attempts or if no pages are movable any more
1019 * because the list has become empty or no retryable pages exist any more.
1020 * The caller should call putback_lru_pages() to return pages to the LRU
1021 * or free list only if ret != 0.
1022 *
1023 * Returns the number of pages that were not migrated, or an error code.
1024 */
1025int migrate_pages(struct list_head *from, new_page_t get_new_page,
1026                unsigned long private, enum migrate_mode mode, int reason)
1027{
1028        int retry = 1;
1029        int nr_failed = 0;
1030        int nr_succeeded = 0;
1031        int pass = 0;
1032        struct page *page;
1033        struct page *page2;
1034        int swapwrite = current->flags & PF_SWAPWRITE;
1035        int rc;
1036
1037        if (!swapwrite)
1038                current->flags |= PF_SWAPWRITE;
1039
1040        for(pass = 0; pass < 10 && retry; pass++) {
1041                retry = 0;
1042
1043                list_for_each_entry_safe(page, page2, from, lru) {
1044                        cond_resched();
1045
1046                        if (PageHuge(page))
1047                                rc = unmap_and_move_huge_page(get_new_page,
1048                                                private, page, pass > 2, mode);
1049                        else
1050                                rc = unmap_and_move(get_new_page, private,
1051                                                page, pass > 2, mode);
1052
1053                        switch(rc) {
1054                        case -ENOMEM:
1055                                goto out;
1056                        case -EAGAIN:
1057                                retry++;
1058                                break;
1059                        case MIGRATEPAGE_SUCCESS:
1060                                nr_succeeded++;
1061                                break;
1062                        default:
1063                                /* Permanent failure */
1064                                nr_failed++;
1065                                break;
1066                        }
1067                }
1068        }
1069        rc = nr_failed + retry;
1070out:
1071        if (nr_succeeded)
1072                count_vm_events(PGMIGRATE_SUCCESS, nr_succeeded);
1073        if (nr_failed)
1074                count_vm_events(PGMIGRATE_FAIL, nr_failed);
1075        trace_mm_migrate_pages(nr_succeeded, nr_failed, mode, reason);
1076
1077        if (!swapwrite)
1078                current->flags &= ~PF_SWAPWRITE;
1079
1080        return rc;
1081}
1082
1083#ifdef CONFIG_NUMA
1084/*
1085 * Move a list of individual pages
1086 */
1087struct page_to_node {
1088        unsigned long addr;
1089        struct page *page;
1090        int node;
1091        int status;
1092};
1093
1094static struct page *new_page_node(struct page *p, unsigned long private,
1095                int **result)
1096{
1097        struct page_to_node *pm = (struct page_to_node *)private;
1098
1099        while (pm->node != MAX_NUMNODES && pm->page != p)
1100                pm++;
1101
1102        if (pm->node == MAX_NUMNODES)
1103                return NULL;
1104
1105        *result = &pm->status;
1106
1107        if (PageHuge(p))
1108                return alloc_huge_page_node(page_hstate(compound_head(p)),
1109                                        pm->node);
1110        else
1111                return alloc_pages_exact_node(pm->node,
1112                                GFP_HIGHUSER_MOVABLE | GFP_THISNODE, 0);
1113}
1114
1115/*
1116 * Move a set of pages as indicated in the pm array. The addr
1117 * field must be set to the virtual address of the page to be moved
1118 * and the node number must contain a valid target node.
1119 * The pm array ends with node = MAX_NUMNODES.
1120 */
1121static int do_move_page_to_node_array(struct mm_struct *mm,
1122                                      struct page_to_node *pm,
1123                                      int migrate_all)
1124{
1125        int err;
1126        struct page_to_node *pp;
1127        LIST_HEAD(pagelist);
1128
1129        down_read(&mm->mmap_sem);
1130
1131        /*
1132         * Build a list of pages to migrate
1133         */
1134        for (pp = pm; pp->node != MAX_NUMNODES; pp++) {
1135                struct vm_area_struct *vma;
1136                struct page *page;
1137
1138                err = -EFAULT;
1139                vma = find_vma(mm, pp->addr);
1140                if (!vma || pp->addr < vma->vm_start || !vma_migratable(vma))
1141                        goto set_status;
1142
1143                page = follow_page(vma, pp->addr, FOLL_GET|FOLL_SPLIT);
1144
1145                err = PTR_ERR(page);
1146                if (IS_ERR(page))
1147                        goto set_status;
1148
1149                err = -ENOENT;
1150                if (!page)
1151                        goto set_status;
1152
1153                /* Use PageReserved to check for zero page */
1154                if (PageReserved(page))
1155                        goto put_and_set;
1156
1157                pp->page = page;
1158                err = page_to_nid(page);
1159
1160                if (err == pp->node)
1161                        /*
1162                         * Node already in the right place
1163                         */
1164                        goto put_and_set;
1165
1166                err = -EACCES;
1167                if (page_mapcount(page) > 1 &&
1168                                !migrate_all)
1169                        goto put_and_set;
1170
1171                if (PageHuge(page)) {
1172                        isolate_huge_page(page, &pagelist);
1173                        goto put_and_set;
1174                }
1175
1176                err = isolate_lru_page(page);
1177                if (!err) {
1178                        list_add_tail(&page->lru, &pagelist);
1179                        inc_zone_page_state(page, NR_ISOLATED_ANON +
1180                                            page_is_file_cache(page));
1181                }
1182put_and_set:
1183                /*
1184                 * Either remove the duplicate refcount from
1185                 * isolate_lru_page() or drop the page ref if it was
1186                 * not isolated.
1187                 */
1188                put_page(page);
1189set_status:
1190                pp->status = err;
1191        }
1192
1193        err = 0;
1194        if (!list_empty(&pagelist)) {
1195                err = migrate_pages(&pagelist, new_page_node,
1196                                (unsigned long)pm, MIGRATE_SYNC, MR_SYSCALL);
1197                if (err)
1198                        putback_movable_pages(&pagelist);
1199        }
1200
1201        up_read(&mm->mmap_sem);
1202        return err;
1203}
1204
1205/*
1206 * Migrate an array of page address onto an array of nodes and fill
1207 * the corresponding array of status.
1208 */
1209static int do_pages_move(struct mm_struct *mm, nodemask_t task_nodes,
1210                         unsigned long nr_pages,
1211                         const void __user * __user *pages,
1212                         const int __user *nodes,
1213                         int __user *status, int flags)
1214{
1215        struct page_to_node *pm;
1216        unsigned long chunk_nr_pages;
1217        unsigned long chunk_start;
1218        int err;
1219
1220        err = -ENOMEM;
1221        pm = (struct page_to_node *)__get_free_page(GFP_KERNEL);
1222        if (!pm)
1223                goto out;
1224
1225        migrate_prep();
1226
1227        /*
1228         * Store a chunk of page_to_node array in a page,
1229         * but keep the last one as a marker
1230         */
1231        chunk_nr_pages = (PAGE_SIZE / sizeof(struct page_to_node)) - 1;
1232
1233        for (chunk_start = 0;
1234             chunk_start < nr_pages;
1235             chunk_start += chunk_nr_pages) {
1236                int j;
1237
1238                if (chunk_start + chunk_nr_pages > nr_pages)
1239                        chunk_nr_pages = nr_pages - chunk_start;
1240
1241                /* fill the chunk pm with addrs and nodes from user-space */
1242                for (j = 0; j < chunk_nr_pages; j++) {
1243                        const void __user *p;
1244                        int node;
1245
1246                        err = -EFAULT;
1247                        if (get_user(p, pages + j + chunk_start))
1248                                goto out_pm;
1249                        pm[j].addr = (unsigned long) p;
1250
1251                        if (get_user(node, nodes + j + chunk_start))
1252                                goto out_pm;
1253
1254                        err = -ENODEV;
1255                        if (node < 0 || node >= MAX_NUMNODES)
1256                                goto out_pm;
1257
1258                        if (!node_state(node, N_MEMORY))
1259                                goto out_pm;
1260
1261                        err = -EACCES;
1262                        if (!node_isset(node, task_nodes))
1263                                goto out_pm;
1264
1265                        pm[j].node = node;
1266                }
1267
1268                /* End marker for this chunk */
1269                pm[chunk_nr_pages].node = MAX_NUMNODES;
1270
1271                /* Migrate this chunk */
1272                err = do_move_page_to_node_array(mm, pm,
1273                                                 flags & MPOL_MF_MOVE_ALL);
1274                if (err < 0)
1275                        goto out_pm;
1276
1277                /* Return status information */
1278                for (j = 0; j < chunk_nr_pages; j++)
1279                        if (put_user(pm[j].status, status + j + chunk_start)) {
1280                                err = -EFAULT;
1281                                goto out_pm;
1282                        }
1283        }
1284        err = 0;
1285
1286out_pm:
1287        free_page((unsigned long)pm);
1288out:
1289        return err;
1290}
1291
1292/*
1293 * Determine the nodes of an array of pages and store it in an array of status.
1294 */
1295static void do_pages_stat_array(struct mm_struct *mm, unsigned long nr_pages,
1296                                const void __user **pages, int *status)
1297{
1298        unsigned long i;
1299
1300        down_read(&mm->mmap_sem);
1301
1302        for (i = 0; i < nr_pages; i++) {
1303                unsigned long addr = (unsigned long)(*pages);
1304                struct vm_area_struct *vma;
1305                struct page *page;
1306                int err = -EFAULT;
1307
1308                vma = find_vma(mm, addr);
1309                if (!vma || addr < vma->vm_start)
1310                        goto set_status;
1311
1312                page = follow_page(vma, addr, 0);
1313
1314                err = PTR_ERR(page);
1315                if (IS_ERR(page))
1316                        goto set_status;
1317
1318                err = -ENOENT;
1319                /* Use PageReserved to check for zero page */
1320                if (!page || PageReserved(page))
1321                        goto set_status;
1322
1323                err = page_to_nid(page);
1324set_status:
1325                *status = err;
1326
1327                pages++;
1328                status++;
1329        }
1330
1331        up_read(&mm->mmap_sem);
1332}
1333
1334/*
1335 * Determine the nodes of a user array of pages and store it in
1336 * a user array of status.
1337 */
1338static int do_pages_stat(struct mm_struct *mm, unsigned long nr_pages,
1339                         const void __user * __user *pages,
1340                         int __user *status)
1341{
1342#define DO_PAGES_STAT_CHUNK_NR 16
1343        const void __user *chunk_pages[DO_PAGES_STAT_CHUNK_NR];
1344        int chunk_status[DO_PAGES_STAT_CHUNK_NR];
1345
1346        while (nr_pages) {
1347                unsigned long chunk_nr;
1348
1349                chunk_nr = nr_pages;
1350                if (chunk_nr > DO_PAGES_STAT_CHUNK_NR)
1351                        chunk_nr = DO_PAGES_STAT_CHUNK_NR;
1352
1353                if (copy_from_user(chunk_pages, pages, chunk_nr * sizeof(*chunk_pages)))
1354                        break;
1355
1356                do_pages_stat_array(mm, chunk_nr, chunk_pages, chunk_status);
1357
1358                if (copy_to_user(status, chunk_status, chunk_nr * sizeof(*status)))
1359                        break;
1360
1361                pages += chunk_nr;
1362                status += chunk_nr;
1363                nr_pages -= chunk_nr;
1364        }
1365        return nr_pages ? -EFAULT : 0;
1366}
1367
1368/*
1369 * Move a list of pages in the address space of the currently executing
1370 * process.
1371 */
1372SYSCALL_DEFINE6(move_pages, pid_t, pid, unsigned long, nr_pages,
1373                const void __user * __user *, pages,
1374                const int __user *, nodes,
1375                int __user *, status, int, flags)
1376{
1377        const struct cred *cred = current_cred(), *tcred;
1378        struct task_struct *task;
1379        struct mm_struct *mm;
1380        int err;
1381        nodemask_t task_nodes;
1382
1383        /* Check flags */
1384        if (flags & ~(MPOL_MF_MOVE|MPOL_MF_MOVE_ALL))
1385                return -EINVAL;
1386
1387        if ((flags & MPOL_MF_MOVE_ALL) && !capable(CAP_SYS_NICE))
1388                return -EPERM;
1389
1390        /* Find the mm_struct */
1391        rcu_read_lock();
1392        task = pid ? find_task_by_vpid(pid) : current;
1393        if (!task) {
1394                rcu_read_unlock();
1395                return -ESRCH;
1396        }
1397        get_task_struct(task);
1398
1399        /*
1400         * Check if this process has the right to modify the specified
1401         * process. The right exists if the process has administrative
1402         * capabilities, superuser privileges or the same
1403         * userid as the target process.
1404         */
1405        tcred = __task_cred(task);
1406        if (!uid_eq(cred->euid, tcred->suid) && !uid_eq(cred->euid, tcred->uid) &&
1407            !uid_eq(cred->uid,  tcred->suid) && !uid_eq(cred->uid,  tcred->uid) &&
1408            !capable(CAP_SYS_NICE)) {
1409                rcu_read_unlock();
1410                err = -EPERM;
1411                goto out;
1412        }
1413        rcu_read_unlock();
1414
1415        err = security_task_movememory(task);
1416        if (err)
1417                goto out;
1418
1419        task_nodes = cpuset_mems_allowed(task);
1420        mm = get_task_mm(task);
1421        put_task_struct(task);
1422
1423        if (!mm)
1424                return -EINVAL;
1425
1426        if (nodes)
1427                err = do_pages_move(mm, task_nodes, nr_pages, pages,
1428                                    nodes, status, flags);
1429        else
1430                err = do_pages_stat(mm, nr_pages, pages, status);
1431
1432        mmput(mm);
1433        return err;
1434
1435out:
1436        put_task_struct(task);
1437        return err;
1438}
1439
1440/*
1441 * Call migration functions in the vma_ops that may prepare
1442 * memory in a vm for migration. migration functions may perform
1443 * the migration for vmas that do not have an underlying page struct.
1444 */
1445int migrate_vmas(struct mm_struct *mm, const nodemask_t *to,
1446        const nodemask_t *from, unsigned long flags)
1447{
1448        struct vm_area_struct *vma;
1449        int err = 0;
1450
1451        for (vma = mm->mmap; vma && !err; vma = vma->vm_next) {
1452                if (vma->vm_ops && vma->vm_ops->migrate) {
1453                        err = vma->vm_ops->migrate(vma, to, from, flags);
1454                        if (err)
1455                                break;
1456                }
1457        }
1458        return err;
1459}
1460
1461#ifdef CONFIG_NUMA_BALANCING
1462/*
1463 * Returns true if this is a safe migration target node for misplaced NUMA
1464 * pages. Currently it only checks the watermarks which crude
1465 */
1466static bool migrate_balanced_pgdat(struct pglist_data *pgdat,
1467                                   unsigned long nr_migrate_pages)
1468{
1469        int z;
1470        for (z = pgdat->nr_zones - 1; z >= 0; z--) {
1471                struct zone *zone = pgdat->node_zones + z;
1472
1473                if (!populated_zone(zone))
1474                        continue;
1475
1476                if (!zone_reclaimable(zone))
1477                        continue;
1478
1479                /* Avoid waking kswapd by allocating pages_to_migrate pages. */
1480                if (!zone_watermark_ok(zone, 0,
1481                                       high_wmark_pages(zone) +
1482                                       nr_migrate_pages,
1483                                       0, 0))
1484                        continue;
1485                return true;
1486        }
1487        return false;
1488}
1489
1490static struct page *alloc_misplaced_dst_page(struct page *page,
1491                                           unsigned long data,
1492                                           int **result)
1493{
1494        int nid = (int) data;
1495        struct page *newpage;
1496
1497        newpage = alloc_pages_exact_node(nid,
1498                                         (GFP_HIGHUSER_MOVABLE | GFP_THISNODE |
1499                                          __GFP_NOMEMALLOC | __GFP_NORETRY |
1500                                          __GFP_NOWARN) &
1501                                         ~GFP_IOFS, 0);
1502        if (newpage)
1503                page_nid_xchg_last(newpage, page_nid_last(page));
1504
1505        return newpage;
1506}
1507
1508/*
1509 * page migration rate limiting control.
1510 * Do not migrate more than @pages_to_migrate in a @migrate_interval_millisecs
1511 * window of time. Default here says do not migrate more than 1280M per second.
1512 * If a node is rate-limited then PTE NUMA updates are also rate-limited. However
1513 * as it is faults that reset the window, pte updates will happen unconditionally
1514 * if there has not been a fault since @pteupdate_interval_millisecs after the
1515 * throttle window closed.
1516 */
1517static unsigned int migrate_interval_millisecs __read_mostly = 100;
1518static unsigned int pteupdate_interval_millisecs __read_mostly = 1000;
1519static unsigned int ratelimit_pages __read_mostly = 128 << (20 - PAGE_SHIFT);
1520
1521/* Returns true if NUMA migration is currently rate limited */
1522bool migrate_ratelimited(int node)
1523{
1524        pg_data_t *pgdat = NODE_DATA(node);
1525
1526        if (time_after(jiffies, pgdat->numabalancing_migrate_next_window +
1527                                msecs_to_jiffies(pteupdate_interval_millisecs)))
1528                return false;
1529
1530        if (pgdat->numabalancing_migrate_nr_pages < ratelimit_pages)
1531                return false;
1532
1533        return true;
1534}
1535
1536/* Returns true if the node is migrate rate-limited after the update */
1537bool numamigrate_update_ratelimit(pg_data_t *pgdat, unsigned long nr_pages)
1538{
1539        bool rate_limited = false;
1540
1541        /*
1542         * Rate-limit the amount of data that is being migrated to a node.
1543         * Optimal placement is no good if the memory bus is saturated and
1544         * all the time is being spent migrating!
1545         */
1546        spin_lock(&pgdat->numabalancing_migrate_lock);
1547        if (time_after(jiffies, pgdat->numabalancing_migrate_next_window)) {
1548                pgdat->numabalancing_migrate_nr_pages = 0;
1549                pgdat->numabalancing_migrate_next_window = jiffies +
1550                        msecs_to_jiffies(migrate_interval_millisecs);
1551        }
1552        if (pgdat->numabalancing_migrate_nr_pages > ratelimit_pages)
1553                rate_limited = true;
1554        else
1555                pgdat->numabalancing_migrate_nr_pages += nr_pages;
1556        spin_unlock(&pgdat->numabalancing_migrate_lock);
1557        
1558        return rate_limited;
1559}
1560
1561int numamigrate_isolate_page(pg_data_t *pgdat, struct page *page)
1562{
1563        int page_lru;
1564
1565        VM_BUG_ON(compound_order(page) && !PageTransHuge(page));
1566
1567        /* Avoid migrating to a node that is nearly full */
1568        if (!migrate_balanced_pgdat(pgdat, 1UL << compound_order(page)))
1569                return 0;
1570
1571        if (isolate_lru_page(page))
1572                return 0;
1573
1574        /*
1575         * migrate_misplaced_transhuge_page() skips page migration's usual
1576         * check on page_count(), so we must do it here, now that the page
1577         * has been isolated: a GUP pin, or any other pin, prevents migration.
1578         * The expected page count is 3: 1 for page's mapcount and 1 for the
1579         * caller's pin and 1 for the reference taken by isolate_lru_page().
1580         */
1581        if (PageTransHuge(page) && page_count(page) != 3) {
1582                putback_lru_page(page);
1583                return 0;
1584        }
1585
1586        page_lru = page_is_file_cache(page);
1587        mod_zone_page_state(page_zone(page), NR_ISOLATED_ANON + page_lru,
1588                                hpage_nr_pages(page));
1589
1590        /*
1591         * Isolating the page has taken another reference, so the
1592         * caller's reference can be safely dropped without the page
1593         * disappearing underneath us during migration.
1594         */
1595        put_page(page);
1596        return 1;
1597}
1598
1599/*
1600 * Attempt to migrate a misplaced page to the specified destination
1601 * node. Caller is expected to have an elevated reference count on
1602 * the page that will be dropped by this function before returning.
1603 */
1604int migrate_misplaced_page(struct page *page, int node)
1605{
1606        pg_data_t *pgdat = NODE_DATA(node);
1607        int isolated;
1608        int nr_remaining;
1609        LIST_HEAD(migratepages);
1610
1611        /*
1612         * Don't migrate pages that are mapped in multiple processes.
1613         * TODO: Handle false sharing detection instead of this hammer
1614         */
1615        if (page_mapcount(page) != 1)
1616                goto out;
1617
1618        /*
1619         * Rate-limit the amount of data that is being migrated to a node.
1620         * Optimal placement is no good if the memory bus is saturated and
1621         * all the time is being spent migrating!
1622         */
1623        if (numamigrate_update_ratelimit(pgdat, 1))
1624                goto out;
1625
1626        isolated = numamigrate_isolate_page(pgdat, page);
1627        if (!isolated)
1628                goto out;
1629
1630        list_add(&page->lru, &migratepages);
1631        nr_remaining = migrate_pages(&migratepages, alloc_misplaced_dst_page,
1632                                     node, MIGRATE_ASYNC, MR_NUMA_MISPLACED);
1633        if (nr_remaining) {
1634                putback_lru_pages(&migratepages);
1635                isolated = 0;
1636        } else
1637                count_vm_numa_event(NUMA_PAGE_MIGRATE);
1638        BUG_ON(!list_empty(&migratepages));
1639        return isolated;
1640
1641out:
1642        put_page(page);
1643        return 0;
1644}
1645#endif /* CONFIG_NUMA_BALANCING */
1646
1647#if defined(CONFIG_NUMA_BALANCING) && defined(CONFIG_TRANSPARENT_HUGEPAGE)
1648/*
1649 * Migrates a THP to a given target node. page must be locked and is unlocked
1650 * before returning.
1651 */
1652int migrate_misplaced_transhuge_page(struct mm_struct *mm,
1653                                struct vm_area_struct *vma,
1654                                pmd_t *pmd, pmd_t entry,
1655                                unsigned long address,
1656                                struct page *page, int node)
1657{
1658        unsigned long haddr = address & HPAGE_PMD_MASK;
1659        pg_data_t *pgdat = NODE_DATA(node);
1660        int isolated = 0;
1661        struct page *new_page = NULL;
1662        struct mem_cgroup *memcg = NULL;
1663        int page_lru = page_is_file_cache(page);
1664
1665        /*
1666         * Don't migrate pages that are mapped in multiple processes.
1667         * TODO: Handle false sharing detection instead of this hammer
1668         */
1669        if (page_mapcount(page) != 1)
1670                goto out_dropref;
1671
1672        /*
1673         * Rate-limit the amount of data that is being migrated to a node.
1674         * Optimal placement is no good if the memory bus is saturated and
1675         * all the time is being spent migrating!
1676         */
1677        if (numamigrate_update_ratelimit(pgdat, HPAGE_PMD_NR))
1678                goto out_dropref;
1679
1680        new_page = alloc_pages_node(node,
1681                (GFP_TRANSHUGE | GFP_THISNODE) & ~__GFP_WAIT, HPAGE_PMD_ORDER);
1682        if (!new_page)
1683                goto out_fail;
1684
1685        page_nid_xchg_last(new_page, page_nid_last(page));
1686
1687        isolated = numamigrate_isolate_page(pgdat, page);
1688        if (!isolated) {
1689                put_page(new_page);
1690                goto out_fail;
1691        }
1692
1693        /* Prepare a page as a migration target */
1694        __set_page_locked(new_page);
1695        SetPageSwapBacked(new_page);
1696
1697        /* anon mapping, we can simply copy page->mapping to the new page: */
1698        new_page->mapping = page->mapping;
1699        new_page->index = page->index;
1700        migrate_page_copy(new_page, page);
1701        WARN_ON(PageLRU(new_page));
1702
1703        /* Recheck the target PMD */
1704        spin_lock(&mm->page_table_lock);
1705        if (unlikely(!pmd_same(*pmd, entry))) {
1706                spin_unlock(&mm->page_table_lock);
1707
1708                /* Reverse changes made by migrate_page_copy() */
1709                if (TestClearPageActive(new_page))
1710                        SetPageActive(page);
1711                if (TestClearPageUnevictable(new_page))
1712                        SetPageUnevictable(page);
1713                mlock_migrate_page(page, new_page);
1714
1715                unlock_page(new_page);
1716                put_page(new_page);             /* Free it */
1717
1718                /* Retake the callers reference and putback on LRU */
1719                get_page(page);
1720                putback_lru_page(page);
1721                mod_zone_page_state(page_zone(page),
1722                         NR_ISOLATED_ANON + page_lru, -HPAGE_PMD_NR);
1723                goto out_fail;
1724        }
1725
1726        /*
1727         * Traditional migration needs to prepare the memcg charge
1728         * transaction early to prevent the old page from being
1729         * uncharged when installing migration entries.  Here we can
1730         * save the potential rollback and start the charge transfer
1731         * only when migration is already known to end successfully.
1732         */
1733        mem_cgroup_prepare_migration(page, new_page, &memcg);
1734
1735        entry = mk_pmd(new_page, vma->vm_page_prot);
1736        entry = pmd_mknonnuma(entry);
1737        entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
1738        entry = pmd_mkhuge(entry);
1739
1740        pmdp_clear_flush(vma, haddr, pmd);
1741        set_pmd_at(mm, haddr, pmd, entry);
1742        page_add_new_anon_rmap(new_page, vma, haddr);
1743        update_mmu_cache_pmd(vma, address, &entry);
1744        page_remove_rmap(page);
1745        /*
1746         * Finish the charge transaction under the page table lock to
1747         * prevent split_huge_page() from dividing up the charge
1748         * before it's fully transferred to the new page.
1749         */
1750        mem_cgroup_end_migration(memcg, page, new_page, true);
1751        spin_unlock(&mm->page_table_lock);
1752
1753        unlock_page(new_page);
1754        unlock_page(page);
1755        put_page(page);                 /* Drop the rmap reference */
1756        put_page(page);                 /* Drop the LRU isolation reference */
1757
1758        count_vm_events(PGMIGRATE_SUCCESS, HPAGE_PMD_NR);
1759        count_vm_numa_events(NUMA_PAGE_MIGRATE, HPAGE_PMD_NR);
1760
1761        mod_zone_page_state(page_zone(page),
1762                        NR_ISOLATED_ANON + page_lru,
1763                        -HPAGE_PMD_NR);
1764        return isolated;
1765
1766out_fail:
1767        count_vm_events(PGMIGRATE_FAIL, HPAGE_PMD_NR);
1768out_dropref:
1769        entry = pmd_mknonnuma(entry);
1770        set_pmd_at(mm, haddr, pmd, entry);
1771        update_mmu_cache_pmd(vma, address, &entry);
1772
1773        unlock_page(page);
1774        put_page(page);
1775        return 0;
1776}
1777#endif /* CONFIG_NUMA_BALANCING */
1778
1779#endif /* CONFIG_NUMA */
1780
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