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0001 /*
0002  * Memory Migration functionality - linux/mm/migrate.c
0003  *
0004  * Copyright (C) 2006 Silicon Graphics, Inc., Christoph Lameter
0005  *
0006  * Page migration was first developed in the context of the memory hotplug
0007  * project. The main authors of the migration code are:
0008  *
0009  * IWAMOTO Toshihiro <iwamoto@valinux.co.jp>
0010  * Hirokazu Takahashi <taka@valinux.co.jp>
0011  * Dave Hansen <haveblue@us.ibm.com>
0012  * Christoph Lameter
0013  */
0014 
0015 #include <linux/migrate.h>
0016 #include <linux/export.h>
0017 #include <linux/swap.h>
0018 #include <linux/swapops.h>
0019 #include <linux/pagemap.h>
0020 #include <linux/buffer_head.h>
0021 #include <linux/mm_inline.h>
0022 #include <linux/nsproxy.h>
0023 #include <linux/pagevec.h>
0024 #include <linux/ksm.h>
0025 #include <linux/rmap.h>
0026 #include <linux/topology.h>
0027 #include <linux/cpu.h>
0028 #include <linux/cpuset.h>
0029 #include <linux/writeback.h>
0030 #include <linux/mempolicy.h>
0031 #include <linux/vmalloc.h>
0032 #include <linux/security.h>
0033 #include <linux/backing-dev.h>
0034 #include <linux/compaction.h>
0035 #include <linux/syscalls.h>
0036 #include <linux/hugetlb.h>
0037 #include <linux/hugetlb_cgroup.h>
0038 #include <linux/gfp.h>
0039 #include <linux/balloon_compaction.h>
0040 #include <linux/mmu_notifier.h>
0041 #include <linux/page_idle.h>
0042 #include <linux/page_owner.h>
0043 
0044 #include <asm/tlbflush.h>
0045 
0046 #define CREATE_TRACE_POINTS
0047 #include <trace/events/migrate.h>
0048 
0049 #include "internal.h"
0050 
0051 /*
0052  * migrate_prep() needs to be called before we start compiling a list of pages
0053  * to be migrated using isolate_lru_page(). If scheduling work on other CPUs is
0054  * undesirable, use migrate_prep_local()
0055  */
0056 int migrate_prep(void)
0057 {
0058     /*
0059      * Clear the LRU lists so pages can be isolated.
0060      * Note that pages may be moved off the LRU after we have
0061      * drained them. Those pages will fail to migrate like other
0062      * pages that may be busy.
0063      */
0064     lru_add_drain_all();
0065 
0066     return 0;
0067 }
0068 
0069 /* Do the necessary work of migrate_prep but not if it involves other CPUs */
0070 int migrate_prep_local(void)
0071 {
0072     lru_add_drain();
0073 
0074     return 0;
0075 }
0076 
0077 bool isolate_movable_page(struct page *page, isolate_mode_t mode)
0078 {
0079     struct address_space *mapping;
0080 
0081     /*
0082      * Avoid burning cycles with pages that are yet under __free_pages(),
0083      * or just got freed under us.
0084      *
0085      * In case we 'win' a race for a movable page being freed under us and
0086      * raise its refcount preventing __free_pages() from doing its job
0087      * the put_page() at the end of this block will take care of
0088      * release this page, thus avoiding a nasty leakage.
0089      */
0090     if (unlikely(!get_page_unless_zero(page)))
0091         goto out;
0092 
0093     /*
0094      * Check PageMovable before holding a PG_lock because page's owner
0095      * assumes anybody doesn't touch PG_lock of newly allocated page
0096      * so unconditionally grapping the lock ruins page's owner side.
0097      */
0098     if (unlikely(!__PageMovable(page)))
0099         goto out_putpage;
0100     /*
0101      * As movable pages are not isolated from LRU lists, concurrent
0102      * compaction threads can race against page migration functions
0103      * as well as race against the releasing a page.
0104      *
0105      * In order to avoid having an already isolated movable page
0106      * being (wrongly) re-isolated while it is under migration,
0107      * or to avoid attempting to isolate pages being released,
0108      * lets be sure we have the page lock
0109      * before proceeding with the movable page isolation steps.
0110      */
0111     if (unlikely(!trylock_page(page)))
0112         goto out_putpage;
0113 
0114     if (!PageMovable(page) || PageIsolated(page))
0115         goto out_no_isolated;
0116 
0117     mapping = page_mapping(page);
0118     VM_BUG_ON_PAGE(!mapping, page);
0119 
0120     if (!mapping->a_ops->isolate_page(page, mode))
0121         goto out_no_isolated;
0122 
0123     /* Driver shouldn't use PG_isolated bit of page->flags */
0124     WARN_ON_ONCE(PageIsolated(page));
0125     __SetPageIsolated(page);
0126     unlock_page(page);
0127 
0128     return true;
0129 
0130 out_no_isolated:
0131     unlock_page(page);
0132 out_putpage:
0133     put_page(page);
0134 out:
0135     return false;
0136 }
0137 
0138 /* It should be called on page which is PG_movable */
0139 void putback_movable_page(struct page *page)
0140 {
0141     struct address_space *mapping;
0142 
0143     VM_BUG_ON_PAGE(!PageLocked(page), page);
0144     VM_BUG_ON_PAGE(!PageMovable(page), page);
0145     VM_BUG_ON_PAGE(!PageIsolated(page), page);
0146 
0147     mapping = page_mapping(page);
0148     mapping->a_ops->putback_page(page);
0149     __ClearPageIsolated(page);
0150 }
0151 
0152 /*
0153  * Put previously isolated pages back onto the appropriate lists
0154  * from where they were once taken off for compaction/migration.
0155  *
0156  * This function shall be used whenever the isolated pageset has been
0157  * built from lru, balloon, hugetlbfs page. See isolate_migratepages_range()
0158  * and isolate_huge_page().
0159  */
0160 void putback_movable_pages(struct list_head *l)
0161 {
0162     struct page *page;
0163     struct page *page2;
0164 
0165     list_for_each_entry_safe(page, page2, l, lru) {
0166         if (unlikely(PageHuge(page))) {
0167             putback_active_hugepage(page);
0168             continue;
0169         }
0170         list_del(&page->lru);
0171         /*
0172          * We isolated non-lru movable page so here we can use
0173          * __PageMovable because LRU page's mapping cannot have
0174          * PAGE_MAPPING_MOVABLE.
0175          */
0176         if (unlikely(__PageMovable(page))) {
0177             VM_BUG_ON_PAGE(!PageIsolated(page), page);
0178             lock_page(page);
0179             if (PageMovable(page))
0180                 putback_movable_page(page);
0181             else
0182                 __ClearPageIsolated(page);
0183             unlock_page(page);
0184             put_page(page);
0185         } else {
0186             putback_lru_page(page);
0187             dec_node_page_state(page, NR_ISOLATED_ANON +
0188                     page_is_file_cache(page));
0189         }
0190     }
0191 }
0192 
0193 /*
0194  * Restore a potential migration pte to a working pte entry
0195  */
0196 static int remove_migration_pte(struct page *new, struct vm_area_struct *vma,
0197                  unsigned long addr, void *old)
0198 {
0199     struct mm_struct *mm = vma->vm_mm;
0200     swp_entry_t entry;
0201     pmd_t *pmd;
0202     pte_t *ptep, pte;
0203     spinlock_t *ptl;
0204 
0205     if (unlikely(PageHuge(new))) {
0206         ptep = huge_pte_offset(mm, addr);
0207         if (!ptep)
0208             goto out;
0209         ptl = huge_pte_lockptr(hstate_vma(vma), mm, ptep);
0210     } else {
0211         pmd = mm_find_pmd(mm, addr);
0212         if (!pmd)
0213             goto out;
0214 
0215         ptep = pte_offset_map(pmd, addr);
0216 
0217         /*
0218          * Peek to check is_swap_pte() before taking ptlock?  No, we
0219          * can race mremap's move_ptes(), which skips anon_vma lock.
0220          */
0221 
0222         ptl = pte_lockptr(mm, pmd);
0223     }
0224 
0225     spin_lock(ptl);
0226     pte = *ptep;
0227     if (!is_swap_pte(pte))
0228         goto unlock;
0229 
0230     entry = pte_to_swp_entry(pte);
0231 
0232     if (!is_migration_entry(entry) ||
0233         migration_entry_to_page(entry) != old)
0234         goto unlock;
0235 
0236     get_page(new);
0237     pte = pte_mkold(mk_pte(new, READ_ONCE(vma->vm_page_prot)));
0238     if (pte_swp_soft_dirty(*ptep))
0239         pte = pte_mksoft_dirty(pte);
0240 
0241     /* Recheck VMA as permissions can change since migration started  */
0242     if (is_write_migration_entry(entry))
0243         pte = maybe_mkwrite(pte, vma);
0244 
0245 #ifdef CONFIG_HUGETLB_PAGE
0246     if (PageHuge(new)) {
0247         pte = pte_mkhuge(pte);
0248         pte = arch_make_huge_pte(pte, vma, new, 0);
0249     }
0250 #endif
0251     flush_dcache_page(new);
0252     set_pte_at(mm, addr, ptep, pte);
0253 
0254     if (PageHuge(new)) {
0255         if (PageAnon(new))
0256             hugepage_add_anon_rmap(new, vma, addr);
0257         else
0258             page_dup_rmap(new, true);
0259     } else if (PageAnon(new))
0260         page_add_anon_rmap(new, vma, addr, false);
0261     else
0262         page_add_file_rmap(new, false);
0263 
0264     if (vma->vm_flags & VM_LOCKED && !PageTransCompound(new))
0265         mlock_vma_page(new);
0266 
0267     /* No need to invalidate - it was non-present before */
0268     update_mmu_cache(vma, addr, ptep);
0269 unlock:
0270     pte_unmap_unlock(ptep, ptl);
0271 out:
0272     return SWAP_AGAIN;
0273 }
0274 
0275 /*
0276  * Get rid of all migration entries and replace them by
0277  * references to the indicated page.
0278  */
0279 void remove_migration_ptes(struct page *old, struct page *new, bool locked)
0280 {
0281     struct rmap_walk_control rwc = {
0282         .rmap_one = remove_migration_pte,
0283         .arg = old,
0284     };
0285 
0286     if (locked)
0287         rmap_walk_locked(new, &rwc);
0288     else
0289         rmap_walk(new, &rwc);
0290 }
0291 
0292 /*
0293  * Something used the pte of a page under migration. We need to
0294  * get to the page and wait until migration is finished.
0295  * When we return from this function the fault will be retried.
0296  */
0297 void __migration_entry_wait(struct mm_struct *mm, pte_t *ptep,
0298                 spinlock_t *ptl)
0299 {
0300     pte_t pte;
0301     swp_entry_t entry;
0302     struct page *page;
0303 
0304     spin_lock(ptl);
0305     pte = *ptep;
0306     if (!is_swap_pte(pte))
0307         goto out;
0308 
0309     entry = pte_to_swp_entry(pte);
0310     if (!is_migration_entry(entry))
0311         goto out;
0312 
0313     page = migration_entry_to_page(entry);
0314 
0315     /*
0316      * Once radix-tree replacement of page migration started, page_count
0317      * *must* be zero. And, we don't want to call wait_on_page_locked()
0318      * against a page without get_page().
0319      * So, we use get_page_unless_zero(), here. Even failed, page fault
0320      * will occur again.
0321      */
0322     if (!get_page_unless_zero(page))
0323         goto out;
0324     pte_unmap_unlock(ptep, ptl);
0325     wait_on_page_locked(page);
0326     put_page(page);
0327     return;
0328 out:
0329     pte_unmap_unlock(ptep, ptl);
0330 }
0331 
0332 void migration_entry_wait(struct mm_struct *mm, pmd_t *pmd,
0333                 unsigned long address)
0334 {
0335     spinlock_t *ptl = pte_lockptr(mm, pmd);
0336     pte_t *ptep = pte_offset_map(pmd, address);
0337     __migration_entry_wait(mm, ptep, ptl);
0338 }
0339 
0340 void migration_entry_wait_huge(struct vm_area_struct *vma,
0341         struct mm_struct *mm, pte_t *pte)
0342 {
0343     spinlock_t *ptl = huge_pte_lockptr(hstate_vma(vma), mm, pte);
0344     __migration_entry_wait(mm, pte, ptl);
0345 }
0346 
0347 #ifdef CONFIG_BLOCK
0348 /* Returns true if all buffers are successfully locked */
0349 static bool buffer_migrate_lock_buffers(struct buffer_head *head,
0350                             enum migrate_mode mode)
0351 {
0352     struct buffer_head *bh = head;
0353 
0354     /* Simple case, sync compaction */
0355     if (mode != MIGRATE_ASYNC) {
0356         do {
0357             get_bh(bh);
0358             lock_buffer(bh);
0359             bh = bh->b_this_page;
0360 
0361         } while (bh != head);
0362 
0363         return true;
0364     }
0365 
0366     /* async case, we cannot block on lock_buffer so use trylock_buffer */
0367     do {
0368         get_bh(bh);
0369         if (!trylock_buffer(bh)) {
0370             /*
0371              * We failed to lock the buffer and cannot stall in
0372              * async migration. Release the taken locks
0373              */
0374             struct buffer_head *failed_bh = bh;
0375             put_bh(failed_bh);
0376             bh = head;
0377             while (bh != failed_bh) {
0378                 unlock_buffer(bh);
0379                 put_bh(bh);
0380                 bh = bh->b_this_page;
0381             }
0382             return false;
0383         }
0384 
0385         bh = bh->b_this_page;
0386     } while (bh != head);
0387     return true;
0388 }
0389 #else
0390 static inline bool buffer_migrate_lock_buffers(struct buffer_head *head,
0391                             enum migrate_mode mode)
0392 {
0393     return true;
0394 }
0395 #endif /* CONFIG_BLOCK */
0396 
0397 /*
0398  * Replace the page in the mapping.
0399  *
0400  * The number of remaining references must be:
0401  * 1 for anonymous pages without a mapping
0402  * 2 for pages with a mapping
0403  * 3 for pages with a mapping and PagePrivate/PagePrivate2 set.
0404  */
0405 int migrate_page_move_mapping(struct address_space *mapping,
0406         struct page *newpage, struct page *page,
0407         struct buffer_head *head, enum migrate_mode mode,
0408         int extra_count)
0409 {
0410     struct zone *oldzone, *newzone;
0411     int dirty;
0412     int expected_count = 1 + extra_count;
0413     void **pslot;
0414 
0415     if (!mapping) {
0416         /* Anonymous page without mapping */
0417         if (page_count(page) != expected_count)
0418             return -EAGAIN;
0419 
0420         /* No turning back from here */
0421         newpage->index = page->index;
0422         newpage->mapping = page->mapping;
0423         if (PageSwapBacked(page))
0424             __SetPageSwapBacked(newpage);
0425 
0426         return MIGRATEPAGE_SUCCESS;
0427     }
0428 
0429     oldzone = page_zone(page);
0430     newzone = page_zone(newpage);
0431 
0432     spin_lock_irq(&mapping->tree_lock);
0433 
0434     pslot = radix_tree_lookup_slot(&mapping->page_tree,
0435                     page_index(page));
0436 
0437     expected_count += 1 + page_has_private(page);
0438     if (page_count(page) != expected_count ||
0439         radix_tree_deref_slot_protected(pslot, &mapping->tree_lock) != page) {
0440         spin_unlock_irq(&mapping->tree_lock);
0441         return -EAGAIN;
0442     }
0443 
0444     if (!page_ref_freeze(page, expected_count)) {
0445         spin_unlock_irq(&mapping->tree_lock);
0446         return -EAGAIN;
0447     }
0448 
0449     /*
0450      * In the async migration case of moving a page with buffers, lock the
0451      * buffers using trylock before the mapping is moved. If the mapping
0452      * was moved, we later failed to lock the buffers and could not move
0453      * the mapping back due to an elevated page count, we would have to
0454      * block waiting on other references to be dropped.
0455      */
0456     if (mode == MIGRATE_ASYNC && head &&
0457             !buffer_migrate_lock_buffers(head, mode)) {
0458         page_ref_unfreeze(page, expected_count);
0459         spin_unlock_irq(&mapping->tree_lock);
0460         return -EAGAIN;
0461     }
0462 
0463     /*
0464      * Now we know that no one else is looking at the page:
0465      * no turning back from here.
0466      */
0467     newpage->index = page->index;
0468     newpage->mapping = page->mapping;
0469     get_page(newpage);  /* add cache reference */
0470     if (PageSwapBacked(page)) {
0471         __SetPageSwapBacked(newpage);
0472         if (PageSwapCache(page)) {
0473             SetPageSwapCache(newpage);
0474             set_page_private(newpage, page_private(page));
0475         }
0476     } else {
0477         VM_BUG_ON_PAGE(PageSwapCache(page), page);
0478     }
0479 
0480     /* Move dirty while page refs frozen and newpage not yet exposed */
0481     dirty = PageDirty(page);
0482     if (dirty) {
0483         ClearPageDirty(page);
0484         SetPageDirty(newpage);
0485     }
0486 
0487     radix_tree_replace_slot(&mapping->page_tree, pslot, newpage);
0488 
0489     /*
0490      * Drop cache reference from old page by unfreezing
0491      * to one less reference.
0492      * We know this isn't the last reference.
0493      */
0494     page_ref_unfreeze(page, expected_count - 1);
0495 
0496     spin_unlock(&mapping->tree_lock);
0497     /* Leave irq disabled to prevent preemption while updating stats */
0498 
0499     /*
0500      * If moved to a different zone then also account
0501      * the page for that zone. Other VM counters will be
0502      * taken care of when we establish references to the
0503      * new page and drop references to the old page.
0504      *
0505      * Note that anonymous pages are accounted for
0506      * via NR_FILE_PAGES and NR_ANON_MAPPED if they
0507      * are mapped to swap space.
0508      */
0509     if (newzone != oldzone) {
0510         __dec_node_state(oldzone->zone_pgdat, NR_FILE_PAGES);
0511         __inc_node_state(newzone->zone_pgdat, NR_FILE_PAGES);
0512         if (PageSwapBacked(page) && !PageSwapCache(page)) {
0513             __dec_node_state(oldzone->zone_pgdat, NR_SHMEM);
0514             __inc_node_state(newzone->zone_pgdat, NR_SHMEM);
0515         }
0516         if (dirty && mapping_cap_account_dirty(mapping)) {
0517             __dec_node_state(oldzone->zone_pgdat, NR_FILE_DIRTY);
0518             __dec_zone_state(oldzone, NR_ZONE_WRITE_PENDING);
0519             __inc_node_state(newzone->zone_pgdat, NR_FILE_DIRTY);
0520             __inc_zone_state(newzone, NR_ZONE_WRITE_PENDING);
0521         }
0522     }
0523     local_irq_enable();
0524 
0525     return MIGRATEPAGE_SUCCESS;
0526 }
0527 EXPORT_SYMBOL(migrate_page_move_mapping);
0528 
0529 /*
0530  * The expected number of remaining references is the same as that
0531  * of migrate_page_move_mapping().
0532  */
0533 int migrate_huge_page_move_mapping(struct address_space *mapping,
0534                    struct page *newpage, struct page *page)
0535 {
0536     int expected_count;
0537     void **pslot;
0538 
0539     spin_lock_irq(&mapping->tree_lock);
0540 
0541     pslot = radix_tree_lookup_slot(&mapping->page_tree,
0542                     page_index(page));
0543 
0544     expected_count = 2 + page_has_private(page);
0545     if (page_count(page) != expected_count ||
0546         radix_tree_deref_slot_protected(pslot, &mapping->tree_lock) != page) {
0547         spin_unlock_irq(&mapping->tree_lock);
0548         return -EAGAIN;
0549     }
0550 
0551     if (!page_ref_freeze(page, expected_count)) {
0552         spin_unlock_irq(&mapping->tree_lock);
0553         return -EAGAIN;
0554     }
0555 
0556     newpage->index = page->index;
0557     newpage->mapping = page->mapping;
0558 
0559     get_page(newpage);
0560 
0561     radix_tree_replace_slot(&mapping->page_tree, pslot, newpage);
0562 
0563     page_ref_unfreeze(page, expected_count - 1);
0564 
0565     spin_unlock_irq(&mapping->tree_lock);
0566 
0567     return MIGRATEPAGE_SUCCESS;
0568 }
0569 
0570 /*
0571  * Gigantic pages are so large that we do not guarantee that page++ pointer
0572  * arithmetic will work across the entire page.  We need something more
0573  * specialized.
0574  */
0575 static void __copy_gigantic_page(struct page *dst, struct page *src,
0576                 int nr_pages)
0577 {
0578     int i;
0579     struct page *dst_base = dst;
0580     struct page *src_base = src;
0581 
0582     for (i = 0; i < nr_pages; ) {
0583         cond_resched();
0584         copy_highpage(dst, src);
0585 
0586         i++;
0587         dst = mem_map_next(dst, dst_base, i);
0588         src = mem_map_next(src, src_base, i);
0589     }
0590 }
0591 
0592 static void copy_huge_page(struct page *dst, struct page *src)
0593 {
0594     int i;
0595     int nr_pages;
0596 
0597     if (PageHuge(src)) {
0598         /* hugetlbfs page */
0599         struct hstate *h = page_hstate(src);
0600         nr_pages = pages_per_huge_page(h);
0601 
0602         if (unlikely(nr_pages > MAX_ORDER_NR_PAGES)) {
0603             __copy_gigantic_page(dst, src, nr_pages);
0604             return;
0605         }
0606     } else {
0607         /* thp page */
0608         BUG_ON(!PageTransHuge(src));
0609         nr_pages = hpage_nr_pages(src);
0610     }
0611 
0612     for (i = 0; i < nr_pages; i++) {
0613         cond_resched();
0614         copy_highpage(dst + i, src + i);
0615     }
0616 }
0617 
0618 /*
0619  * Copy the page to its new location
0620  */
0621 void migrate_page_copy(struct page *newpage, struct page *page)
0622 {
0623     int cpupid;
0624 
0625     if (PageHuge(page) || PageTransHuge(page))
0626         copy_huge_page(newpage, page);
0627     else
0628         copy_highpage(newpage, page);
0629 
0630     if (PageError(page))
0631         SetPageError(newpage);
0632     if (PageReferenced(page))
0633         SetPageReferenced(newpage);
0634     if (PageUptodate(page))
0635         SetPageUptodate(newpage);
0636     if (TestClearPageActive(page)) {
0637         VM_BUG_ON_PAGE(PageUnevictable(page), page);
0638         SetPageActive(newpage);
0639     } else if (TestClearPageUnevictable(page))
0640         SetPageUnevictable(newpage);
0641     if (PageChecked(page))
0642         SetPageChecked(newpage);
0643     if (PageMappedToDisk(page))
0644         SetPageMappedToDisk(newpage);
0645 
0646     /* Move dirty on pages not done by migrate_page_move_mapping() */
0647     if (PageDirty(page))
0648         SetPageDirty(newpage);
0649 
0650     if (page_is_young(page))
0651         set_page_young(newpage);
0652     if (page_is_idle(page))
0653         set_page_idle(newpage);
0654 
0655     /*
0656      * Copy NUMA information to the new page, to prevent over-eager
0657      * future migrations of this same page.
0658      */
0659     cpupid = page_cpupid_xchg_last(page, -1);
0660     page_cpupid_xchg_last(newpage, cpupid);
0661 
0662     ksm_migrate_page(newpage, page);
0663     /*
0664      * Please do not reorder this without considering how mm/ksm.c's
0665      * get_ksm_page() depends upon ksm_migrate_page() and PageSwapCache().
0666      */
0667     if (PageSwapCache(page))
0668         ClearPageSwapCache(page);
0669     ClearPagePrivate(page);
0670     set_page_private(page, 0);
0671 
0672     /*
0673      * If any waiters have accumulated on the new page then
0674      * wake them up.
0675      */
0676     if (PageWriteback(newpage))
0677         end_page_writeback(newpage);
0678 
0679     copy_page_owner(page, newpage);
0680 
0681     mem_cgroup_migrate(page, newpage);
0682 }
0683 EXPORT_SYMBOL(migrate_page_copy);
0684 
0685 /************************************************************
0686  *                    Migration functions
0687  ***********************************************************/
0688 
0689 /*
0690  * Common logic to directly migrate a single LRU page suitable for
0691  * pages that do not use PagePrivate/PagePrivate2.
0692  *
0693  * Pages are locked upon entry and exit.
0694  */
0695 int migrate_page(struct address_space *mapping,
0696         struct page *newpage, struct page *page,
0697         enum migrate_mode mode)
0698 {
0699     int rc;
0700 
0701     BUG_ON(PageWriteback(page));    /* Writeback must be complete */
0702 
0703     rc = migrate_page_move_mapping(mapping, newpage, page, NULL, mode, 0);
0704 
0705     if (rc != MIGRATEPAGE_SUCCESS)
0706         return rc;
0707 
0708     migrate_page_copy(newpage, page);
0709     return MIGRATEPAGE_SUCCESS;
0710 }
0711 EXPORT_SYMBOL(migrate_page);
0712 
0713 #ifdef CONFIG_BLOCK
0714 /*
0715  * Migration function for pages with buffers. This function can only be used
0716  * if the underlying filesystem guarantees that no other references to "page"
0717  * exist.
0718  */
0719 int buffer_migrate_page(struct address_space *mapping,
0720         struct page *newpage, struct page *page, enum migrate_mode mode)
0721 {
0722     struct buffer_head *bh, *head;
0723     int rc;
0724 
0725     if (!page_has_buffers(page))
0726         return migrate_page(mapping, newpage, page, mode);
0727 
0728     head = page_buffers(page);
0729 
0730     rc = migrate_page_move_mapping(mapping, newpage, page, head, mode, 0);
0731 
0732     if (rc != MIGRATEPAGE_SUCCESS)
0733         return rc;
0734 
0735     /*
0736      * In the async case, migrate_page_move_mapping locked the buffers
0737      * with an IRQ-safe spinlock held. In the sync case, the buffers
0738      * need to be locked now
0739      */
0740     if (mode != MIGRATE_ASYNC)
0741         BUG_ON(!buffer_migrate_lock_buffers(head, mode));
0742 
0743     ClearPagePrivate(page);
0744     set_page_private(newpage, page_private(page));
0745     set_page_private(page, 0);
0746     put_page(page);
0747     get_page(newpage);
0748 
0749     bh = head;
0750     do {
0751         set_bh_page(bh, newpage, bh_offset(bh));
0752         bh = bh->b_this_page;
0753 
0754     } while (bh != head);
0755 
0756     SetPagePrivate(newpage);
0757 
0758     migrate_page_copy(newpage, page);
0759 
0760     bh = head;
0761     do {
0762         unlock_buffer(bh);
0763         put_bh(bh);
0764         bh = bh->b_this_page;
0765 
0766     } while (bh != head);
0767 
0768     return MIGRATEPAGE_SUCCESS;
0769 }
0770 EXPORT_SYMBOL(buffer_migrate_page);
0771 #endif
0772 
0773 /*
0774  * Writeback a page to clean the dirty state
0775  */
0776 static int writeout(struct address_space *mapping, struct page *page)
0777 {
0778     struct writeback_control wbc = {
0779         .sync_mode = WB_SYNC_NONE,
0780         .nr_to_write = 1,
0781         .range_start = 0,
0782         .range_end = LLONG_MAX,
0783         .for_reclaim = 1
0784     };
0785     int rc;
0786 
0787     if (!mapping->a_ops->writepage)
0788         /* No write method for the address space */
0789         return -EINVAL;
0790 
0791     if (!clear_page_dirty_for_io(page))
0792         /* Someone else already triggered a write */
0793         return -EAGAIN;
0794 
0795     /*
0796      * A dirty page may imply that the underlying filesystem has
0797      * the page on some queue. So the page must be clean for
0798      * migration. Writeout may mean we loose the lock and the
0799      * page state is no longer what we checked for earlier.
0800      * At this point we know that the migration attempt cannot
0801      * be successful.
0802      */
0803     remove_migration_ptes(page, page, false);
0804 
0805     rc = mapping->a_ops->writepage(page, &wbc);
0806 
0807     if (rc != AOP_WRITEPAGE_ACTIVATE)
0808         /* unlocked. Relock */
0809         lock_page(page);
0810 
0811     return (rc < 0) ? -EIO : -EAGAIN;
0812 }
0813 
0814 /*
0815  * Default handling if a filesystem does not provide a migration function.
0816  */
0817 static int fallback_migrate_page(struct address_space *mapping,
0818     struct page *newpage, struct page *page, enum migrate_mode mode)
0819 {
0820     if (PageDirty(page)) {
0821         /* Only writeback pages in full synchronous migration */
0822         if (mode != MIGRATE_SYNC)
0823             return -EBUSY;
0824         return writeout(mapping, page);
0825     }
0826 
0827     /*
0828      * Buffers may be managed in a filesystem specific way.
0829      * We must have no buffers or drop them.
0830      */
0831     if (page_has_private(page) &&
0832         !try_to_release_page(page, GFP_KERNEL))
0833         return -EAGAIN;
0834 
0835     return migrate_page(mapping, newpage, page, mode);
0836 }
0837 
0838 /*
0839  * Move a page to a newly allocated page
0840  * The page is locked and all ptes have been successfully removed.
0841  *
0842  * The new page will have replaced the old page if this function
0843  * is successful.
0844  *
0845  * Return value:
0846  *   < 0 - error code
0847  *  MIGRATEPAGE_SUCCESS - success
0848  */
0849 static int move_to_new_page(struct page *newpage, struct page *page,
0850                 enum migrate_mode mode)
0851 {
0852     struct address_space *mapping;
0853     int rc = -EAGAIN;
0854     bool is_lru = !__PageMovable(page);
0855 
0856     VM_BUG_ON_PAGE(!PageLocked(page), page);
0857     VM_BUG_ON_PAGE(!PageLocked(newpage), newpage);
0858 
0859     mapping = page_mapping(page);
0860 
0861     if (likely(is_lru)) {
0862         if (!mapping)
0863             rc = migrate_page(mapping, newpage, page, mode);
0864         else if (mapping->a_ops->migratepage)
0865             /*
0866              * Most pages have a mapping and most filesystems
0867              * provide a migratepage callback. Anonymous pages
0868              * are part of swap space which also has its own
0869              * migratepage callback. This is the most common path
0870              * for page migration.
0871              */
0872             rc = mapping->a_ops->migratepage(mapping, newpage,
0873                             page, mode);
0874         else
0875             rc = fallback_migrate_page(mapping, newpage,
0876                             page, mode);
0877     } else {
0878         /*
0879          * In case of non-lru page, it could be released after
0880          * isolation step. In that case, we shouldn't try migration.
0881          */
0882         VM_BUG_ON_PAGE(!PageIsolated(page), page);
0883         if (!PageMovable(page)) {
0884             rc = MIGRATEPAGE_SUCCESS;
0885             __ClearPageIsolated(page);
0886             goto out;
0887         }
0888 
0889         rc = mapping->a_ops->migratepage(mapping, newpage,
0890                         page, mode);
0891         WARN_ON_ONCE(rc == MIGRATEPAGE_SUCCESS &&
0892             !PageIsolated(page));
0893     }
0894 
0895     /*
0896      * When successful, old pagecache page->mapping must be cleared before
0897      * page is freed; but stats require that PageAnon be left as PageAnon.
0898      */
0899     if (rc == MIGRATEPAGE_SUCCESS) {
0900         if (__PageMovable(page)) {
0901             VM_BUG_ON_PAGE(!PageIsolated(page), page);
0902 
0903             /*
0904              * We clear PG_movable under page_lock so any compactor
0905              * cannot try to migrate this page.
0906              */
0907             __ClearPageIsolated(page);
0908         }
0909 
0910         /*
0911          * Anonymous and movable page->mapping will be cleard by
0912          * free_pages_prepare so don't reset it here for keeping
0913          * the type to work PageAnon, for example.
0914          */
0915         if (!PageMappingFlags(page))
0916             page->mapping = NULL;
0917     }
0918 out:
0919     return rc;
0920 }
0921 
0922 static int __unmap_and_move(struct page *page, struct page *newpage,
0923                 int force, enum migrate_mode mode)
0924 {
0925     int rc = -EAGAIN;
0926     int page_was_mapped = 0;
0927     struct anon_vma *anon_vma = NULL;
0928     bool is_lru = !__PageMovable(page);
0929 
0930     if (!trylock_page(page)) {
0931         if (!force || mode == MIGRATE_ASYNC)
0932             goto out;
0933 
0934         /*
0935          * It's not safe for direct compaction to call lock_page.
0936          * For example, during page readahead pages are added locked
0937          * to the LRU. Later, when the IO completes the pages are
0938          * marked uptodate and unlocked. However, the queueing
0939          * could be merging multiple pages for one bio (e.g.
0940          * mpage_readpages). If an allocation happens for the
0941          * second or third page, the process can end up locking
0942          * the same page twice and deadlocking. Rather than
0943          * trying to be clever about what pages can be locked,
0944          * avoid the use of lock_page for direct compaction
0945          * altogether.
0946          */
0947         if (current->flags & PF_MEMALLOC)
0948             goto out;
0949 
0950         lock_page(page);
0951     }
0952 
0953     if (PageWriteback(page)) {
0954         /*
0955          * Only in the case of a full synchronous migration is it
0956          * necessary to wait for PageWriteback. In the async case,
0957          * the retry loop is too short and in the sync-light case,
0958          * the overhead of stalling is too much
0959          */
0960         if (mode != MIGRATE_SYNC) {
0961             rc = -EBUSY;
0962             goto out_unlock;
0963         }
0964         if (!force)
0965             goto out_unlock;
0966         wait_on_page_writeback(page);
0967     }
0968 
0969     /*
0970      * By try_to_unmap(), page->mapcount goes down to 0 here. In this case,
0971      * we cannot notice that anon_vma is freed while we migrates a page.
0972      * This get_anon_vma() delays freeing anon_vma pointer until the end
0973      * of migration. File cache pages are no problem because of page_lock()
0974      * File Caches may use write_page() or lock_page() in migration, then,
0975      * just care Anon page here.
0976      *
0977      * Only page_get_anon_vma() understands the subtleties of
0978      * getting a hold on an anon_vma from outside one of its mms.
0979      * But if we cannot get anon_vma, then we won't need it anyway,
0980      * because that implies that the anon page is no longer mapped
0981      * (and cannot be remapped so long as we hold the page lock).
0982      */
0983     if (PageAnon(page) && !PageKsm(page))
0984         anon_vma = page_get_anon_vma(page);
0985 
0986     /*
0987      * Block others from accessing the new page when we get around to
0988      * establishing additional references. We are usually the only one
0989      * holding a reference to newpage at this point. We used to have a BUG
0990      * here if trylock_page(newpage) fails, but would like to allow for
0991      * cases where there might be a race with the previous use of newpage.
0992      * This is much like races on refcount of oldpage: just don't BUG().
0993      */
0994     if (unlikely(!trylock_page(newpage)))
0995         goto out_unlock;
0996 
0997     if (unlikely(!is_lru)) {
0998         rc = move_to_new_page(newpage, page, mode);
0999         goto out_unlock_both;
1000     }
1001 
1002     /*
1003      * Corner case handling:
1004      * 1. When a new swap-cache page is read into, it is added to the LRU
1005      * and treated as swapcache but it has no rmap yet.
1006      * Calling try_to_unmap() against a page->mapping==NULL page will
1007      * trigger a BUG.  So handle it here.
1008      * 2. An orphaned page (see truncate_complete_page) might have
1009      * fs-private metadata. The page can be picked up due to memory
1010      * offlining.  Everywhere else except page reclaim, the page is
1011      * invisible to the vm, so the page can not be migrated.  So try to
1012      * free the metadata, so the page can be freed.
1013      */
1014     if (!page->mapping) {
1015         VM_BUG_ON_PAGE(PageAnon(page), page);
1016         if (page_has_private(page)) {
1017             try_to_free_buffers(page);
1018             goto out_unlock_both;
1019         }
1020     } else if (page_mapped(page)) {
1021         /* Establish migration ptes */
1022         VM_BUG_ON_PAGE(PageAnon(page) && !PageKsm(page) && !anon_vma,
1023                 page);
1024         try_to_unmap(page,
1025             TTU_MIGRATION|TTU_IGNORE_MLOCK|TTU_IGNORE_ACCESS);
1026         page_was_mapped = 1;
1027     }
1028 
1029     if (!page_mapped(page))
1030         rc = move_to_new_page(newpage, page, mode);
1031 
1032     if (page_was_mapped)
1033         remove_migration_ptes(page,
1034             rc == MIGRATEPAGE_SUCCESS ? newpage : page, false);
1035 
1036 out_unlock_both:
1037     unlock_page(newpage);
1038 out_unlock:
1039     /* Drop an anon_vma reference if we took one */
1040     if (anon_vma)
1041         put_anon_vma(anon_vma);
1042     unlock_page(page);
1043 out:
1044     /*
1045      * If migration is successful, decrease refcount of the newpage
1046      * which will not free the page because new page owner increased
1047      * refcounter. As well, if it is LRU page, add the page to LRU
1048      * list in here.
1049      */
1050     if (rc == MIGRATEPAGE_SUCCESS) {
1051         if (unlikely(__PageMovable(newpage)))
1052             put_page(newpage);
1053         else
1054             putback_lru_page(newpage);
1055     }
1056 
1057     return rc;
1058 }
1059 
1060 /*
1061  * gcc 4.7 and 4.8 on arm get an ICEs when inlining unmap_and_move().  Work
1062  * around it.
1063  */
1064 #if (GCC_VERSION >= 40700 && GCC_VERSION < 40900) && defined(CONFIG_ARM)
1065 #define ICE_noinline noinline
1066 #else
1067 #define ICE_noinline
1068 #endif
1069 
1070 /*
1071  * Obtain the lock on page, remove all ptes and migrate the page
1072  * to the newly allocated page in newpage.
1073  */
1074 static ICE_noinline int unmap_and_move(new_page_t get_new_page,
1075                    free_page_t put_new_page,
1076                    unsigned long private, struct page *page,
1077                    int force, enum migrate_mode mode,
1078                    enum migrate_reason reason)
1079 {
1080     int rc = MIGRATEPAGE_SUCCESS;
1081     int *result = NULL;
1082     struct page *newpage;
1083 
1084     newpage = get_new_page(page, private, &result);
1085     if (!newpage)
1086         return -ENOMEM;
1087 
1088     if (page_count(page) == 1) {
1089         /* page was freed from under us. So we are done. */
1090         ClearPageActive(page);
1091         ClearPageUnevictable(page);
1092         if (unlikely(__PageMovable(page))) {
1093             lock_page(page);
1094             if (!PageMovable(page))
1095                 __ClearPageIsolated(page);
1096             unlock_page(page);
1097         }
1098         if (put_new_page)
1099             put_new_page(newpage, private);
1100         else
1101             put_page(newpage);
1102         goto out;
1103     }
1104 
1105     if (unlikely(PageTransHuge(page))) {
1106         lock_page(page);
1107         rc = split_huge_page(page);
1108         unlock_page(page);
1109         if (rc)
1110             goto out;
1111     }
1112 
1113     rc = __unmap_and_move(page, newpage, force, mode);
1114     if (rc == MIGRATEPAGE_SUCCESS)
1115         set_page_owner_migrate_reason(newpage, reason);
1116 
1117 out:
1118     if (rc != -EAGAIN) {
1119         /*
1120          * A page that has been migrated has all references
1121          * removed and will be freed. A page that has not been
1122          * migrated will have kepts its references and be
1123          * restored.
1124          */
1125         list_del(&page->lru);
1126 
1127         /*
1128          * Compaction can migrate also non-LRU pages which are
1129          * not accounted to NR_ISOLATED_*. They can be recognized
1130          * as __PageMovable
1131          */
1132         if (likely(!__PageMovable(page)))
1133             dec_node_page_state(page, NR_ISOLATED_ANON +
1134                     page_is_file_cache(page));
1135     }
1136 
1137     /*
1138      * If migration is successful, releases reference grabbed during
1139      * isolation. Otherwise, restore the page to right list unless
1140      * we want to retry.
1141      */
1142     if (rc == MIGRATEPAGE_SUCCESS) {
1143         put_page(page);
1144         if (reason == MR_MEMORY_FAILURE) {
1145             /*
1146              * Set PG_HWPoison on just freed page
1147              * intentionally. Although it's rather weird,
1148              * it's how HWPoison flag works at the moment.
1149              */
1150             if (!test_set_page_hwpoison(page))
1151                 num_poisoned_pages_inc();
1152         }
1153     } else {
1154         if (rc != -EAGAIN) {
1155             if (likely(!__PageMovable(page))) {
1156                 putback_lru_page(page);
1157                 goto put_new;
1158             }
1159 
1160             lock_page(page);
1161             if (PageMovable(page))
1162                 putback_movable_page(page);
1163             else
1164                 __ClearPageIsolated(page);
1165             unlock_page(page);
1166             put_page(page);
1167         }
1168 put_new:
1169         if (put_new_page)
1170             put_new_page(newpage, private);
1171         else
1172             put_page(newpage);
1173     }
1174 
1175     if (result) {
1176         if (rc)
1177             *result = rc;
1178         else
1179             *result = page_to_nid(newpage);
1180     }
1181     return rc;
1182 }
1183 
1184 /*
1185  * Counterpart of unmap_and_move_page() for hugepage migration.
1186  *
1187  * This function doesn't wait the completion of hugepage I/O
1188  * because there is no race between I/O and migration for hugepage.
1189  * Note that currently hugepage I/O occurs only in direct I/O
1190  * where no lock is held and PG_writeback is irrelevant,
1191  * and writeback status of all subpages are counted in the reference
1192  * count of the head page (i.e. if all subpages of a 2MB hugepage are
1193  * under direct I/O, the reference of the head page is 512 and a bit more.)
1194  * This means that when we try to migrate hugepage whose subpages are
1195  * doing direct I/O, some references remain after try_to_unmap() and
1196  * hugepage migration fails without data corruption.
1197  *
1198  * There is also no race when direct I/O is issued on the page under migration,
1199  * because then pte is replaced with migration swap entry and direct I/O code
1200  * will wait in the page fault for migration to complete.
1201  */
1202 static int unmap_and_move_huge_page(new_page_t get_new_page,
1203                 free_page_t put_new_page, unsigned long private,
1204                 struct page *hpage, int force,
1205                 enum migrate_mode mode, int reason)
1206 {
1207     int rc = -EAGAIN;
1208     int *result = NULL;
1209     int page_was_mapped = 0;
1210     struct page *new_hpage;
1211     struct anon_vma *anon_vma = NULL;
1212 
1213     /*
1214      * Movability of hugepages depends on architectures and hugepage size.
1215      * This check is necessary because some callers of hugepage migration
1216      * like soft offline and memory hotremove don't walk through page
1217      * tables or check whether the hugepage is pmd-based or not before
1218      * kicking migration.
1219      */
1220     if (!hugepage_migration_supported(page_hstate(hpage))) {
1221         putback_active_hugepage(hpage);
1222         return -ENOSYS;
1223     }
1224 
1225     new_hpage = get_new_page(hpage, private, &result);
1226     if (!new_hpage)
1227         return -ENOMEM;
1228 
1229     if (!trylock_page(hpage)) {
1230         if (!force || mode != MIGRATE_SYNC)
1231             goto out;
1232         lock_page(hpage);
1233     }
1234 
1235     if (PageAnon(hpage))
1236         anon_vma = page_get_anon_vma(hpage);
1237 
1238     if (unlikely(!trylock_page(new_hpage)))
1239         goto put_anon;
1240 
1241     if (page_mapped(hpage)) {
1242         try_to_unmap(hpage,
1243             TTU_MIGRATION|TTU_IGNORE_MLOCK|TTU_IGNORE_ACCESS);
1244         page_was_mapped = 1;
1245     }
1246 
1247     if (!page_mapped(hpage))
1248         rc = move_to_new_page(new_hpage, hpage, mode);
1249 
1250     if (page_was_mapped)
1251         remove_migration_ptes(hpage,
1252             rc == MIGRATEPAGE_SUCCESS ? new_hpage : hpage, false);
1253 
1254     unlock_page(new_hpage);
1255 
1256 put_anon:
1257     if (anon_vma)
1258         put_anon_vma(anon_vma);
1259 
1260     if (rc == MIGRATEPAGE_SUCCESS) {
1261         hugetlb_cgroup_migrate(hpage, new_hpage);
1262         put_new_page = NULL;
1263         set_page_owner_migrate_reason(new_hpage, reason);
1264     }
1265 
1266     unlock_page(hpage);
1267 out:
1268     if (rc != -EAGAIN)
1269         putback_active_hugepage(hpage);
1270 
1271     /*
1272      * If migration was not successful and there's a freeing callback, use
1273      * it.  Otherwise, put_page() will drop the reference grabbed during
1274      * isolation.
1275      */
1276     if (put_new_page)
1277         put_new_page(new_hpage, private);
1278     else
1279         putback_active_hugepage(new_hpage);
1280 
1281     if (result) {
1282         if (rc)
1283             *result = rc;
1284         else
1285             *result = page_to_nid(new_hpage);
1286     }
1287     return rc;
1288 }
1289 
1290 /*
1291  * migrate_pages - migrate the pages specified in a list, to the free pages
1292  *         supplied as the target for the page migration
1293  *
1294  * @from:       The list of pages to be migrated.
1295  * @get_new_page:   The function used to allocate free pages to be used
1296  *          as the target of the page migration.
1297  * @put_new_page:   The function used to free target pages if migration
1298  *          fails, or NULL if no special handling is necessary.
1299  * @private:        Private data to be passed on to get_new_page()
1300  * @mode:       The migration mode that specifies the constraints for
1301  *          page migration, if any.
1302  * @reason:     The reason for page migration.
1303  *
1304  * The function returns after 10 attempts or if no pages are movable any more
1305  * because the list has become empty or no retryable pages exist any more.
1306  * The caller should call putback_movable_pages() to return pages to the LRU
1307  * or free list only if ret != 0.
1308  *
1309  * Returns the number of pages that were not migrated, or an error code.
1310  */
1311 int migrate_pages(struct list_head *from, new_page_t get_new_page,
1312         free_page_t put_new_page, unsigned long private,
1313         enum migrate_mode mode, int reason)
1314 {
1315     int retry = 1;
1316     int nr_failed = 0;
1317     int nr_succeeded = 0;
1318     int pass = 0;
1319     struct page *page;
1320     struct page *page2;
1321     int swapwrite = current->flags & PF_SWAPWRITE;
1322     int rc;
1323 
1324     if (!swapwrite)
1325         current->flags |= PF_SWAPWRITE;
1326 
1327     for(pass = 0; pass < 10 && retry; pass++) {
1328         retry = 0;
1329 
1330         list_for_each_entry_safe(page, page2, from, lru) {
1331             cond_resched();
1332 
1333             if (PageHuge(page))
1334                 rc = unmap_and_move_huge_page(get_new_page,
1335                         put_new_page, private, page,
1336                         pass > 2, mode, reason);
1337             else
1338                 rc = unmap_and_move(get_new_page, put_new_page,
1339                         private, page, pass > 2, mode,
1340                         reason);
1341 
1342             switch(rc) {
1343             case -ENOMEM:
1344                 nr_failed++;
1345                 goto out;
1346             case -EAGAIN:
1347                 retry++;
1348                 break;
1349             case MIGRATEPAGE_SUCCESS:
1350                 nr_succeeded++;
1351                 break;
1352             default:
1353                 /*
1354                  * Permanent failure (-EBUSY, -ENOSYS, etc.):
1355                  * unlike -EAGAIN case, the failed page is
1356                  * removed from migration page list and not
1357                  * retried in the next outer loop.
1358                  */
1359                 nr_failed++;
1360                 break;
1361             }
1362         }
1363     }
1364     nr_failed += retry;
1365     rc = nr_failed;
1366 out:
1367     if (nr_succeeded)
1368         count_vm_events(PGMIGRATE_SUCCESS, nr_succeeded);
1369     if (nr_failed)
1370         count_vm_events(PGMIGRATE_FAIL, nr_failed);
1371     trace_mm_migrate_pages(nr_succeeded, nr_failed, mode, reason);
1372 
1373     if (!swapwrite)
1374         current->flags &= ~PF_SWAPWRITE;
1375 
1376     return rc;
1377 }
1378 
1379 #ifdef CONFIG_NUMA
1380 /*
1381  * Move a list of individual pages
1382  */
1383 struct page_to_node {
1384     unsigned long addr;
1385     struct page *page;
1386     int node;
1387     int status;
1388 };
1389 
1390 static struct page *new_page_node(struct page *p, unsigned long private,
1391         int **result)
1392 {
1393     struct page_to_node *pm = (struct page_to_node *)private;
1394 
1395     while (pm->node != MAX_NUMNODES && pm->page != p)
1396         pm++;
1397 
1398     if (pm->node == MAX_NUMNODES)
1399         return NULL;
1400 
1401     *result = &pm->status;
1402 
1403     if (PageHuge(p))
1404         return alloc_huge_page_node(page_hstate(compound_head(p)),
1405                     pm->node);
1406     else
1407         return __alloc_pages_node(pm->node,
1408                 GFP_HIGHUSER_MOVABLE | __GFP_THISNODE, 0);
1409 }
1410 
1411 /*
1412  * Move a set of pages as indicated in the pm array. The addr
1413  * field must be set to the virtual address of the page to be moved
1414  * and the node number must contain a valid target node.
1415  * The pm array ends with node = MAX_NUMNODES.
1416  */
1417 static int do_move_page_to_node_array(struct mm_struct *mm,
1418                       struct page_to_node *pm,
1419                       int migrate_all)
1420 {
1421     int err;
1422     struct page_to_node *pp;
1423     LIST_HEAD(pagelist);
1424 
1425     down_read(&mm->mmap_sem);
1426 
1427     /*
1428      * Build a list of pages to migrate
1429      */
1430     for (pp = pm; pp->node != MAX_NUMNODES; pp++) {
1431         struct vm_area_struct *vma;
1432         struct page *page;
1433 
1434         err = -EFAULT;
1435         vma = find_vma(mm, pp->addr);
1436         if (!vma || pp->addr < vma->vm_start || !vma_migratable(vma))
1437             goto set_status;
1438 
1439         /* FOLL_DUMP to ignore special (like zero) pages */
1440         page = follow_page(vma, pp->addr,
1441                 FOLL_GET | FOLL_SPLIT | FOLL_DUMP);
1442 
1443         err = PTR_ERR(page);
1444         if (IS_ERR(page))
1445             goto set_status;
1446 
1447         err = -ENOENT;
1448         if (!page)
1449             goto set_status;
1450 
1451         pp->page = page;
1452         err = page_to_nid(page);
1453 
1454         if (err == pp->node)
1455             /*
1456              * Node already in the right place
1457              */
1458             goto put_and_set;
1459 
1460         err = -EACCES;
1461         if (page_mapcount(page) > 1 &&
1462                 !migrate_all)
1463             goto put_and_set;
1464 
1465         if (PageHuge(page)) {
1466             if (PageHead(page))
1467                 isolate_huge_page(page, &pagelist);
1468             goto put_and_set;
1469         }
1470 
1471         err = isolate_lru_page(page);
1472         if (!err) {
1473             list_add_tail(&page->lru, &pagelist);
1474             inc_node_page_state(page, NR_ISOLATED_ANON +
1475                         page_is_file_cache(page));
1476         }
1477 put_and_set:
1478         /*
1479          * Either remove the duplicate refcount from
1480          * isolate_lru_page() or drop the page ref if it was
1481          * not isolated.
1482          */
1483         put_page(page);
1484 set_status:
1485         pp->status = err;
1486     }
1487 
1488     err = 0;
1489     if (!list_empty(&pagelist)) {
1490         err = migrate_pages(&pagelist, new_page_node, NULL,
1491                 (unsigned long)pm, MIGRATE_SYNC, MR_SYSCALL);
1492         if (err)
1493             putback_movable_pages(&pagelist);
1494     }
1495 
1496     up_read(&mm->mmap_sem);
1497     return err;
1498 }
1499 
1500 /*
1501  * Migrate an array of page address onto an array of nodes and fill
1502  * the corresponding array of status.
1503  */
1504 static int do_pages_move(struct mm_struct *mm, nodemask_t task_nodes,
1505              unsigned long nr_pages,
1506              const void __user * __user *pages,
1507              const int __user *nodes,
1508              int __user *status, int flags)
1509 {
1510     struct page_to_node *pm;
1511     unsigned long chunk_nr_pages;
1512     unsigned long chunk_start;
1513     int err;
1514 
1515     err = -ENOMEM;
1516     pm = (struct page_to_node *)__get_free_page(GFP_KERNEL);
1517     if (!pm)
1518         goto out;
1519 
1520     migrate_prep();
1521 
1522     /*
1523      * Store a chunk of page_to_node array in a page,
1524      * but keep the last one as a marker
1525      */
1526     chunk_nr_pages = (PAGE_SIZE / sizeof(struct page_to_node)) - 1;
1527 
1528     for (chunk_start = 0;
1529          chunk_start < nr_pages;
1530          chunk_start += chunk_nr_pages) {
1531         int j;
1532 
1533         if (chunk_start + chunk_nr_pages > nr_pages)
1534             chunk_nr_pages = nr_pages - chunk_start;
1535 
1536         /* fill the chunk pm with addrs and nodes from user-space */
1537         for (j = 0; j < chunk_nr_pages; j++) {
1538             const void __user *p;
1539             int node;
1540 
1541             err = -EFAULT;
1542             if (get_user(p, pages + j + chunk_start))
1543                 goto out_pm;
1544             pm[j].addr = (unsigned long) p;
1545 
1546             if (get_user(node, nodes + j + chunk_start))
1547                 goto out_pm;
1548 
1549             err = -ENODEV;
1550             if (node < 0 || node >= MAX_NUMNODES)
1551                 goto out_pm;
1552 
1553             if (!node_state(node, N_MEMORY))
1554                 goto out_pm;
1555 
1556             err = -EACCES;
1557             if (!node_isset(node, task_nodes))
1558                 goto out_pm;
1559 
1560             pm[j].node = node;
1561         }
1562 
1563         /* End marker for this chunk */
1564         pm[chunk_nr_pages].node = MAX_NUMNODES;
1565 
1566         /* Migrate this chunk */
1567         err = do_move_page_to_node_array(mm, pm,
1568                          flags & MPOL_MF_MOVE_ALL);
1569         if (err < 0)
1570             goto out_pm;
1571 
1572         /* Return status information */
1573         for (j = 0; j < chunk_nr_pages; j++)
1574             if (put_user(pm[j].status, status + j + chunk_start)) {
1575                 err = -EFAULT;
1576                 goto out_pm;
1577             }
1578     }
1579     err = 0;
1580 
1581 out_pm:
1582     free_page((unsigned long)pm);
1583 out:
1584     return err;
1585 }
1586 
1587 /*
1588  * Determine the nodes of an array of pages and store it in an array of status.
1589  */
1590 static void do_pages_stat_array(struct mm_struct *mm, unsigned long nr_pages,
1591                 const void __user **pages, int *status)
1592 {
1593     unsigned long i;
1594 
1595     down_read(&mm->mmap_sem);
1596 
1597     for (i = 0; i < nr_pages; i++) {
1598         unsigned long addr = (unsigned long)(*pages);
1599         struct vm_area_struct *vma;
1600         struct page *page;
1601         int err = -EFAULT;
1602 
1603         vma = find_vma(mm, addr);
1604         if (!vma || addr < vma->vm_start)
1605             goto set_status;
1606 
1607         /* FOLL_DUMP to ignore special (like zero) pages */
1608         page = follow_page(vma, addr, FOLL_DUMP);
1609 
1610         err = PTR_ERR(page);
1611         if (IS_ERR(page))
1612             goto set_status;
1613 
1614         err = page ? page_to_nid(page) : -ENOENT;
1615 set_status:
1616         *status = err;
1617 
1618         pages++;
1619         status++;
1620     }
1621 
1622     up_read(&mm->mmap_sem);
1623 }
1624 
1625 /*
1626  * Determine the nodes of a user array of pages and store it in
1627  * a user array of status.
1628  */
1629 static int do_pages_stat(struct mm_struct *mm, unsigned long nr_pages,
1630              const void __user * __user *pages,
1631              int __user *status)
1632 {
1633 #define DO_PAGES_STAT_CHUNK_NR 16
1634     const void __user *chunk_pages[DO_PAGES_STAT_CHUNK_NR];
1635     int chunk_status[DO_PAGES_STAT_CHUNK_NR];
1636 
1637     while (nr_pages) {
1638         unsigned long chunk_nr;
1639 
1640         chunk_nr = nr_pages;
1641         if (chunk_nr > DO_PAGES_STAT_CHUNK_NR)
1642             chunk_nr = DO_PAGES_STAT_CHUNK_NR;
1643 
1644         if (copy_from_user(chunk_pages, pages, chunk_nr * sizeof(*chunk_pages)))
1645             break;
1646 
1647         do_pages_stat_array(mm, chunk_nr, chunk_pages, chunk_status);
1648 
1649         if (copy_to_user(status, chunk_status, chunk_nr * sizeof(*status)))
1650             break;
1651 
1652         pages += chunk_nr;
1653         status += chunk_nr;
1654         nr_pages -= chunk_nr;
1655     }
1656     return nr_pages ? -EFAULT : 0;
1657 }
1658 
1659 /*
1660  * Move a list of pages in the address space of the currently executing
1661  * process.
1662  */
1663 SYSCALL_DEFINE6(move_pages, pid_t, pid, unsigned long, nr_pages,
1664         const void __user * __user *, pages,
1665         const int __user *, nodes,
1666         int __user *, status, int, flags)
1667 {
1668     const struct cred *cred = current_cred(), *tcred;
1669     struct task_struct *task;
1670     struct mm_struct *mm;
1671     int err;
1672     nodemask_t task_nodes;
1673 
1674     /* Check flags */
1675     if (flags & ~(MPOL_MF_MOVE|MPOL_MF_MOVE_ALL))
1676         return -EINVAL;
1677 
1678     if ((flags & MPOL_MF_MOVE_ALL) && !capable(CAP_SYS_NICE))
1679         return -EPERM;
1680 
1681     /* Find the mm_struct */
1682     rcu_read_lock();
1683     task = pid ? find_task_by_vpid(pid) : current;
1684     if (!task) {
1685         rcu_read_unlock();
1686         return -ESRCH;
1687     }
1688     get_task_struct(task);
1689 
1690     /*
1691      * Check if this process has the right to modify the specified
1692      * process. The right exists if the process has administrative
1693      * capabilities, superuser privileges or the same
1694      * userid as the target process.
1695      */
1696     tcred = __task_cred(task);
1697     if (!uid_eq(cred->euid, tcred->suid) && !uid_eq(cred->euid, tcred->uid) &&
1698         !uid_eq(cred->uid,  tcred->suid) && !uid_eq(cred->uid,  tcred->uid) &&
1699         !capable(CAP_SYS_NICE)) {
1700         rcu_read_unlock();
1701         err = -EPERM;
1702         goto out;
1703     }
1704     rcu_read_unlock();
1705 
1706     err = security_task_movememory(task);
1707     if (err)
1708         goto out;
1709 
1710     task_nodes = cpuset_mems_allowed(task);
1711     mm = get_task_mm(task);
1712     put_task_struct(task);
1713 
1714     if (!mm)
1715         return -EINVAL;
1716 
1717     if (nodes)
1718         err = do_pages_move(mm, task_nodes, nr_pages, pages,
1719                     nodes, status, flags);
1720     else
1721         err = do_pages_stat(mm, nr_pages, pages, status);
1722 
1723     mmput(mm);
1724     return err;
1725 
1726 out:
1727     put_task_struct(task);
1728     return err;
1729 }
1730 
1731 #ifdef CONFIG_NUMA_BALANCING
1732 /*
1733  * Returns true if this is a safe migration target node for misplaced NUMA
1734  * pages. Currently it only checks the watermarks which crude
1735  */
1736 static bool migrate_balanced_pgdat(struct pglist_data *pgdat,
1737                    unsigned long nr_migrate_pages)
1738 {
1739     int z;
1740 
1741     if (!pgdat_reclaimable(pgdat))
1742         return false;
1743 
1744     for (z = pgdat->nr_zones - 1; z >= 0; z--) {
1745         struct zone *zone = pgdat->node_zones + z;
1746 
1747         if (!populated_zone(zone))
1748             continue;
1749 
1750         /* Avoid waking kswapd by allocating pages_to_migrate pages. */
1751         if (!zone_watermark_ok(zone, 0,
1752                        high_wmark_pages(zone) +
1753                        nr_migrate_pages,
1754                        0, 0))
1755             continue;
1756         return true;
1757     }
1758     return false;
1759 }
1760 
1761 static struct page *alloc_misplaced_dst_page(struct page *page,
1762                        unsigned long data,
1763                        int **result)
1764 {
1765     int nid = (int) data;
1766     struct page *newpage;
1767 
1768     newpage = __alloc_pages_node(nid,
1769                      (GFP_HIGHUSER_MOVABLE |
1770                       __GFP_THISNODE | __GFP_NOMEMALLOC |
1771                       __GFP_NORETRY | __GFP_NOWARN) &
1772                      ~__GFP_RECLAIM, 0);
1773 
1774     return newpage;
1775 }
1776 
1777 /*
1778  * page migration rate limiting control.
1779  * Do not migrate more than @pages_to_migrate in a @migrate_interval_millisecs
1780  * window of time. Default here says do not migrate more than 1280M per second.
1781  */
1782 static unsigned int migrate_interval_millisecs __read_mostly = 100;
1783 static unsigned int ratelimit_pages __read_mostly = 128 << (20 - PAGE_SHIFT);
1784 
1785 /* Returns true if the node is migrate rate-limited after the update */
1786 static bool numamigrate_update_ratelimit(pg_data_t *pgdat,
1787                     unsigned long nr_pages)
1788 {
1789     /*
1790      * Rate-limit the amount of data that is being migrated to a node.
1791      * Optimal placement is no good if the memory bus is saturated and
1792      * all the time is being spent migrating!
1793      */
1794     if (time_after(jiffies, pgdat->numabalancing_migrate_next_window)) {
1795         spin_lock(&pgdat->numabalancing_migrate_lock);
1796         pgdat->numabalancing_migrate_nr_pages = 0;
1797         pgdat->numabalancing_migrate_next_window = jiffies +
1798             msecs_to_jiffies(migrate_interval_millisecs);
1799         spin_unlock(&pgdat->numabalancing_migrate_lock);
1800     }
1801     if (pgdat->numabalancing_migrate_nr_pages > ratelimit_pages) {
1802         trace_mm_numa_migrate_ratelimit(current, pgdat->node_id,
1803                                 nr_pages);
1804         return true;
1805     }
1806 
1807     /*
1808      * This is an unlocked non-atomic update so errors are possible.
1809      * The consequences are failing to migrate when we potentiall should
1810      * have which is not severe enough to warrant locking. If it is ever
1811      * a problem, it can be converted to a per-cpu counter.
1812      */
1813     pgdat->numabalancing_migrate_nr_pages += nr_pages;
1814     return false;
1815 }
1816 
1817 static int numamigrate_isolate_page(pg_data_t *pgdat, struct page *page)
1818 {
1819     int page_lru;
1820 
1821     VM_BUG_ON_PAGE(compound_order(page) && !PageTransHuge(page), page);
1822 
1823     /* Avoid migrating to a node that is nearly full */
1824     if (!migrate_balanced_pgdat(pgdat, 1UL << compound_order(page)))
1825         return 0;
1826 
1827     if (isolate_lru_page(page))
1828         return 0;
1829 
1830     /*
1831      * migrate_misplaced_transhuge_page() skips page migration's usual
1832      * check on page_count(), so we must do it here, now that the page
1833      * has been isolated: a GUP pin, or any other pin, prevents migration.
1834      * The expected page count is 3: 1 for page's mapcount and 1 for the
1835      * caller's pin and 1 for the reference taken by isolate_lru_page().
1836      */
1837     if (PageTransHuge(page) && page_count(page) != 3) {
1838         putback_lru_page(page);
1839         return 0;
1840     }
1841 
1842     page_lru = page_is_file_cache(page);
1843     mod_node_page_state(page_pgdat(page), NR_ISOLATED_ANON + page_lru,
1844                 hpage_nr_pages(page));
1845 
1846     /*
1847      * Isolating the page has taken another reference, so the
1848      * caller's reference can be safely dropped without the page
1849      * disappearing underneath us during migration.
1850      */
1851     put_page(page);
1852     return 1;
1853 }
1854 
1855 bool pmd_trans_migrating(pmd_t pmd)
1856 {
1857     struct page *page = pmd_page(pmd);
1858     return PageLocked(page);
1859 }
1860 
1861 /*
1862  * Attempt to migrate a misplaced page to the specified destination
1863  * node. Caller is expected to have an elevated reference count on
1864  * the page that will be dropped by this function before returning.
1865  */
1866 int migrate_misplaced_page(struct page *page, struct vm_area_struct *vma,
1867                int node)
1868 {
1869     pg_data_t *pgdat = NODE_DATA(node);
1870     int isolated;
1871     int nr_remaining;
1872     LIST_HEAD(migratepages);
1873 
1874     /*
1875      * Don't migrate file pages that are mapped in multiple processes
1876      * with execute permissions as they are probably shared libraries.
1877      */
1878     if (page_mapcount(page) != 1 && page_is_file_cache(page) &&
1879         (vma->vm_flags & VM_EXEC))
1880         goto out;
1881 
1882     /*
1883      * Rate-limit the amount of data that is being migrated to a node.
1884      * Optimal placement is no good if the memory bus is saturated and
1885      * all the time is being spent migrating!
1886      */
1887     if (numamigrate_update_ratelimit(pgdat, 1))
1888         goto out;
1889 
1890     isolated = numamigrate_isolate_page(pgdat, page);
1891     if (!isolated)
1892         goto out;
1893 
1894     list_add(&page->lru, &migratepages);
1895     nr_remaining = migrate_pages(&migratepages, alloc_misplaced_dst_page,
1896                      NULL, node, MIGRATE_ASYNC,
1897                      MR_NUMA_MISPLACED);
1898     if (nr_remaining) {
1899         if (!list_empty(&migratepages)) {
1900             list_del(&page->lru);
1901             dec_node_page_state(page, NR_ISOLATED_ANON +
1902                     page_is_file_cache(page));
1903             putback_lru_page(page);
1904         }
1905         isolated = 0;
1906     } else
1907         count_vm_numa_event(NUMA_PAGE_MIGRATE);
1908     BUG_ON(!list_empty(&migratepages));
1909     return isolated;
1910 
1911 out:
1912     put_page(page);
1913     return 0;
1914 }
1915 #endif /* CONFIG_NUMA_BALANCING */
1916 
1917 #if defined(CONFIG_NUMA_BALANCING) && defined(CONFIG_TRANSPARENT_HUGEPAGE)
1918 /*
1919  * Migrates a THP to a given target node. page must be locked and is unlocked
1920  * before returning.
1921  */
1922 int migrate_misplaced_transhuge_page(struct mm_struct *mm,
1923                 struct vm_area_struct *vma,
1924                 pmd_t *pmd, pmd_t entry,
1925                 unsigned long address,
1926                 struct page *page, int node)
1927 {
1928     spinlock_t *ptl;
1929     pg_data_t *pgdat = NODE_DATA(node);
1930     int isolated = 0;
1931     struct page *new_page = NULL;
1932     int page_lru = page_is_file_cache(page);
1933     unsigned long mmun_start = address & HPAGE_PMD_MASK;
1934     unsigned long mmun_end = mmun_start + HPAGE_PMD_SIZE;
1935     pmd_t orig_entry;
1936 
1937     /*
1938      * Rate-limit the amount of data that is being migrated to a node.
1939      * Optimal placement is no good if the memory bus is saturated and
1940      * all the time is being spent migrating!
1941      */
1942     if (numamigrate_update_ratelimit(pgdat, HPAGE_PMD_NR))
1943         goto out_dropref;
1944 
1945     new_page = alloc_pages_node(node,
1946         (GFP_TRANSHUGE_LIGHT | __GFP_THISNODE),
1947         HPAGE_PMD_ORDER);
1948     if (!new_page)
1949         goto out_fail;
1950     prep_transhuge_page(new_page);
1951 
1952     isolated = numamigrate_isolate_page(pgdat, page);
1953     if (!isolated) {
1954         put_page(new_page);
1955         goto out_fail;
1956     }
1957     /*
1958      * We are not sure a pending tlb flush here is for a huge page
1959      * mapping or not. Hence use the tlb range variant
1960      */
1961     if (mm_tlb_flush_pending(mm))
1962         flush_tlb_range(vma, mmun_start, mmun_end);
1963 
1964     /* Prepare a page as a migration target */
1965     __SetPageLocked(new_page);
1966     __SetPageSwapBacked(new_page);
1967 
1968     /* anon mapping, we can simply copy page->mapping to the new page: */
1969     new_page->mapping = page->mapping;
1970     new_page->index = page->index;
1971     migrate_page_copy(new_page, page);
1972     WARN_ON(PageLRU(new_page));
1973 
1974     /* Recheck the target PMD */
1975     mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
1976     ptl = pmd_lock(mm, pmd);
1977     if (unlikely(!pmd_same(*pmd, entry) || page_count(page) != 2)) {
1978 fail_putback:
1979         spin_unlock(ptl);
1980         mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
1981 
1982         /* Reverse changes made by migrate_page_copy() */
1983         if (TestClearPageActive(new_page))
1984             SetPageActive(page);
1985         if (TestClearPageUnevictable(new_page))
1986             SetPageUnevictable(page);
1987 
1988         unlock_page(new_page);
1989         put_page(new_page);     /* Free it */
1990 
1991         /* Retake the callers reference and putback on LRU */
1992         get_page(page);
1993         putback_lru_page(page);
1994         mod_node_page_state(page_pgdat(page),
1995              NR_ISOLATED_ANON + page_lru, -HPAGE_PMD_NR);
1996 
1997         goto out_unlock;
1998     }
1999 
2000     orig_entry = *pmd;
2001     entry = mk_huge_pmd(new_page, vma->vm_page_prot);
2002     entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
2003 
2004     /*
2005      * Clear the old entry under pagetable lock and establish the new PTE.
2006      * Any parallel GUP will either observe the old page blocking on the
2007      * page lock, block on the page table lock or observe the new page.
2008      * The SetPageUptodate on the new page and page_add_new_anon_rmap
2009      * guarantee the copy is visible before the pagetable update.
2010      */
2011     flush_cache_range(vma, mmun_start, mmun_end);
2012     page_add_anon_rmap(new_page, vma, mmun_start, true);
2013     pmdp_huge_clear_flush_notify(vma, mmun_start, pmd);
2014     set_pmd_at(mm, mmun_start, pmd, entry);
2015     update_mmu_cache_pmd(vma, address, &entry);
2016 
2017     if (page_count(page) != 2) {
2018         set_pmd_at(mm, mmun_start, pmd, orig_entry);
2019         flush_pmd_tlb_range(vma, mmun_start, mmun_end);
2020         mmu_notifier_invalidate_range(mm, mmun_start, mmun_end);
2021         update_mmu_cache_pmd(vma, address, &entry);
2022         page_remove_rmap(new_page, true);
2023         goto fail_putback;
2024     }
2025 
2026     mlock_migrate_page(new_page, page);
2027     page_remove_rmap(page, true);
2028     set_page_owner_migrate_reason(new_page, MR_NUMA_MISPLACED);
2029 
2030     spin_unlock(ptl);
2031     mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
2032 
2033     /* Take an "isolate" reference and put new page on the LRU. */
2034     get_page(new_page);
2035     putback_lru_page(new_page);
2036 
2037     unlock_page(new_page);
2038     unlock_page(page);
2039     put_page(page);         /* Drop the rmap reference */
2040     put_page(page);         /* Drop the LRU isolation reference */
2041 
2042     count_vm_events(PGMIGRATE_SUCCESS, HPAGE_PMD_NR);
2043     count_vm_numa_events(NUMA_PAGE_MIGRATE, HPAGE_PMD_NR);
2044 
2045     mod_node_page_state(page_pgdat(page),
2046             NR_ISOLATED_ANON + page_lru,
2047             -HPAGE_PMD_NR);
2048     return isolated;
2049 
2050 out_fail:
2051     count_vm_events(PGMIGRATE_FAIL, HPAGE_PMD_NR);
2052 out_dropref:
2053     ptl = pmd_lock(mm, pmd);
2054     if (pmd_same(*pmd, entry)) {
2055         entry = pmd_modify(entry, vma->vm_page_prot);
2056         set_pmd_at(mm, mmun_start, pmd, entry);
2057         update_mmu_cache_pmd(vma, address, &entry);
2058     }
2059     spin_unlock(ptl);
2060 
2061 out_unlock:
2062     unlock_page(page);
2063     put_page(page);
2064     return 0;
2065 }
2066 #endif /* CONFIG_NUMA_BALANCING */
2067 
2068 #endif /* CONFIG_NUMA */