Root/mm/migrate.c

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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