/*
   * Memory Migration functionality - linux/mm/migration.c
   *
   * Copyright (C) 2006 Silicon Graphics, Inc., Christoph Lameter
   *
   * Page migration was first developed in the context of the memory hotplug
   * project. The main authors of the migration code are:
   *
   * IWAMOTO Toshihiro <iwamoto@valinux.co.jp>
   * Hirokazu Takahashi <taka@valinux.co.jp>
   * Dave Hansen <haveblue@us.ibm.com>

   * Christoph Lameter

   */
  
  #include <linux/migrate.h>

  #include <linux/export.h>

  #include <linux/swap.h>

  #include <linux/swapops.h>

  #include <linux/pagemap.h>

  #include <linux/buffer_head.h>

  #include <linux/mm_inline.h>

  #include <linux/nsproxy.h>

  #include <linux/pagevec.h>

  #include <linux/ksm.h>

  #include <linux/rmap.h>
  #include <linux/topology.h>
  #include <linux/cpu.h>
  #include <linux/cpuset.h>

  #include <linux/writeback.h>

  #include <linux/mempolicy.h>
  #include <linux/vmalloc.h>

  #include <linux/security.h>

  #include <linux/memcontrol.h>

  #include <linux/syscalls.h>

  #include <linux/hugetlb.h>

  #include <linux/hugetlb_cgroup.h>

  #include <linux/gfp.h>

  #include <linux/balloon_compaction.h>

  #include <linux/mmu_notifier.h>

  #include <asm/tlbflush.h>

  #define CREATE_TRACE_POINTS
  #include <trace/events/migrate.h>

  #include "internal.h"

  /*

   * migrate_prep() needs to be called before we start compiling a list of pages

   * to be migrated using isolate_lru_page(). If scheduling work on other CPUs is
   * undesirable, use migrate_prep_local()

   */
  int migrate_prep(void)
  {

  	/*
  	 * Clear the LRU lists so pages can be isolated.
  	 * Note that pages may be moved off the LRU after we have
  	 * drained them. Those pages will fail to migrate like other
  	 * pages that may be busy.
  	 */
  	lru_add_drain_all();
  
  	return 0;
  }

  /* Do the necessary work of migrate_prep but not if it involves other CPUs */
  int migrate_prep_local(void)
  {
  	lru_add_drain();
  
  	return 0;
  }

  /*

   * Put previously isolated pages back onto the appropriate lists
   * from where they were once taken off for compaction/migration.
   *

   * This function shall be used whenever the isolated pageset has been
   * built from lru, balloon, hugetlbfs page. See isolate_migratepages_range()
   * and isolate_huge_page().

   */
  void putback_movable_pages(struct list_head *l)
  {
  	struct page *page;
  	struct page *page2;
  
  	list_for_each_entry_safe(page, page2, l, lru) {

  		if (unlikely(PageHuge(page))) {
  			putback_active_hugepage(page);
  			continue;
  		}

  		list_del(&page->lru);
  		dec_zone_page_state(page, NR_ISOLATED_ANON +
  				page_is_file_cache(page));

  		if (unlikely(isolated_balloon_page(page)))

  			balloon_page_putback(page);
  		else
  			putback_lru_page(page);

  	}

  }

  /*
   * Restore a potential migration pte to a working pte entry
   */

  static int remove_migration_pte(struct page *new, struct vm_area_struct *vma,
  				 unsigned long addr, void *old)

  {
  	struct mm_struct *mm = vma->vm_mm;
  	swp_entry_t entry;

   	pmd_t *pmd;
  	pte_t *ptep, pte;
   	spinlock_t *ptl;

  	if (unlikely(PageHuge(new))) {
  		ptep = huge_pte_offset(mm, addr);
  		if (!ptep)
  			goto out;

  		ptl = huge_pte_lockptr(hstate_vma(vma), mm, ptep);

  	} else {

  		pmd = mm_find_pmd(mm, addr);
  		if (!pmd)

  			goto out;

  		ptep = pte_offset_map(pmd, addr);

  		/*
  		 * Peek to check is_swap_pte() before taking ptlock?  No, we
  		 * can race mremap's move_ptes(), which skips anon_vma lock.
  		 */

  
  		ptl = pte_lockptr(mm, pmd);
  	}

   	spin_lock(ptl);
  	pte = *ptep;
  	if (!is_swap_pte(pte))

  		goto unlock;

  
  	entry = pte_to_swp_entry(pte);

  	if (!is_migration_entry(entry) ||
  	    migration_entry_to_page(entry) != old)
  		goto unlock;

  	get_page(new);
  	pte = pte_mkold(mk_pte(new, vma->vm_page_prot));

  	if (pte_swp_soft_dirty(*ptep))
  		pte = pte_mksoft_dirty(pte);

  
  	/* Recheck VMA as permissions can change since migration started  */

  	if (is_write_migration_entry(entry))

  		pte = maybe_mkwrite(pte, vma);

  #ifdef CONFIG_HUGETLB_PAGE

  	if (PageHuge(new)) {

  		pte = pte_mkhuge(pte);

  		pte = arch_make_huge_pte(pte, vma, new, 0);
  	}

  #endif

  	flush_dcache_page(new);

  	set_pte_at(mm, addr, ptep, pte);

  	if (PageHuge(new)) {
  		if (PageAnon(new))
  			hugepage_add_anon_rmap(new, vma, addr);
  		else
  			page_dup_rmap(new);
  	} else if (PageAnon(new))

  		page_add_anon_rmap(new, vma, addr);
  	else
  		page_add_file_rmap(new);
  
  	/* No need to invalidate - it was non-present before */

  	update_mmu_cache(vma, addr, ptep);

  unlock:

  	pte_unmap_unlock(ptep, ptl);

  out:
  	return SWAP_AGAIN;

  }
  
  /*

   * Congratulations to trinity for discovering this bug.
   * mm/fremap.c's remap_file_pages() accepts any range within a single vma to
   * convert that vma to VM_NONLINEAR; and generic_file_remap_pages() will then
   * replace the specified range by file ptes throughout (maybe populated after).
   * If page migration finds a page within that range, while it's still located
   * by vma_interval_tree rather than lost to i_mmap_nonlinear list, no problem:
   * zap_pte() clears the temporary migration entry before mmap_sem is dropped.
   * But if the migrating page is in a part of the vma outside the range to be
   * remapped, then it will not be cleared, and remove_migration_ptes() needs to
   * deal with it.  Fortunately, this part of the vma is of course still linear,
   * so we just need to use linear location on the nonlinear list.
   */
  static int remove_linear_migration_ptes_from_nonlinear(struct page *page,
  		struct address_space *mapping, void *arg)
  {
  	struct vm_area_struct *vma;
  	/* hugetlbfs does not support remap_pages, so no huge pgoff worries */
  	pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
  	unsigned long addr;
  
  	list_for_each_entry(vma,
  		&mapping->i_mmap_nonlinear, shared.nonlinear) {
  
  		addr = vma->vm_start + ((pgoff - vma->vm_pgoff) << PAGE_SHIFT);
  		if (addr >= vma->vm_start && addr < vma->vm_end)
  			remove_migration_pte(page, vma, addr, arg);
  	}
  	return SWAP_AGAIN;
  }
  
  /*

   * Get rid of all migration entries and replace them by
   * references to the indicated page.
   */
  static void remove_migration_ptes(struct page *old, struct page *new)
  {

  	struct rmap_walk_control rwc = {
  		.rmap_one = remove_migration_pte,
  		.arg = old,

  		.file_nonlinear = remove_linear_migration_ptes_from_nonlinear,

  	};
  
  	rmap_walk(new, &rwc);

  }
  
  /*

   * Something used the pte of a page under migration. We need to
   * get to the page and wait until migration is finished.
   * When we return from this function the fault will be retried.

   */

  static void __migration_entry_wait(struct mm_struct *mm, pte_t *ptep,
  				spinlock_t *ptl)

  {

  	pte_t pte;

  	swp_entry_t entry;
  	struct page *page;

  	spin_lock(ptl);

  	pte = *ptep;
  	if (!is_swap_pte(pte))
  		goto out;
  
  	entry = pte_to_swp_entry(pte);
  	if (!is_migration_entry(entry))
  		goto out;
  
  	page = migration_entry_to_page(entry);

  	/*
  	 * Once radix-tree replacement of page migration started, page_count
  	 * *must* be zero. And, we don't want to call wait_on_page_locked()
  	 * against a page without get_page().
  	 * So, we use get_page_unless_zero(), here. Even failed, page fault
  	 * will occur again.
  	 */
  	if (!get_page_unless_zero(page))
  		goto out;

  	pte_unmap_unlock(ptep, ptl);
  	wait_on_page_locked(page);
  	put_page(page);
  	return;
  out:
  	pte_unmap_unlock(ptep, ptl);
  }

  void migration_entry_wait(struct mm_struct *mm, pmd_t *pmd,
  				unsigned long address)
  {
  	spinlock_t *ptl = pte_lockptr(mm, pmd);
  	pte_t *ptep = pte_offset_map(pmd, address);
  	__migration_entry_wait(mm, ptep, ptl);
  }

  void migration_entry_wait_huge(struct vm_area_struct *vma,
  		struct mm_struct *mm, pte_t *pte)

  {

  	spinlock_t *ptl = huge_pte_lockptr(hstate_vma(vma), mm, pte);

  	__migration_entry_wait(mm, pte, ptl);
  }

  #ifdef CONFIG_BLOCK
  /* Returns true if all buffers are successfully locked */

  static bool buffer_migrate_lock_buffers(struct buffer_head *head,
  							enum migrate_mode mode)

  {
  	struct buffer_head *bh = head;
  
  	/* Simple case, sync compaction */

  	if (mode != MIGRATE_ASYNC) {

  		do {
  			get_bh(bh);
  			lock_buffer(bh);
  			bh = bh->b_this_page;
  
  		} while (bh != head);
  
  		return true;
  	}
  
  	/* async case, we cannot block on lock_buffer so use trylock_buffer */
  	do {
  		get_bh(bh);
  		if (!trylock_buffer(bh)) {
  			/*
  			 * We failed to lock the buffer and cannot stall in
  			 * async migration. Release the taken locks
  			 */
  			struct buffer_head *failed_bh = bh;
  			put_bh(failed_bh);
  			bh = head;
  			while (bh != failed_bh) {
  				unlock_buffer(bh);
  				put_bh(bh);
  				bh = bh->b_this_page;
  			}
  			return false;
  		}
  
  		bh = bh->b_this_page;
  	} while (bh != head);
  	return true;
  }
  #else
  static inline bool buffer_migrate_lock_buffers(struct buffer_head *head,

  							enum migrate_mode mode)

  {
  	return true;
  }
  #endif /* CONFIG_BLOCK */

  /*

   * Replace the page in the mapping.

   *
   * The number of remaining references must be:
   * 1 for anonymous pages without a mapping
   * 2 for pages with a mapping

   * 3 for pages with a mapping and PagePrivate/PagePrivate2 set.

   */

  int migrate_page_move_mapping(struct address_space *mapping,

  		struct page *newpage, struct page *page,

  		struct buffer_head *head, enum migrate_mode mode,
  		int extra_count)

  {

  	int expected_count = 1 + extra_count;

  	void **pslot;

  	if (!mapping) {

  		/* Anonymous page without mapping */

  		if (page_count(page) != expected_count)

  			return -EAGAIN;

  		return MIGRATEPAGE_SUCCESS;

  	}

  	spin_lock_irq(&mapping->tree_lock);

  	pslot = radix_tree_lookup_slot(&mapping->page_tree,
   					page_index(page));

  	expected_count += 1 + page_has_private(page);

  	if (page_count(page) != expected_count ||

  		radix_tree_deref_slot_protected(pslot, &mapping->tree_lock) != page) {

  		spin_unlock_irq(&mapping->tree_lock);

  		return -EAGAIN;

  	}

  	if (!page_freeze_refs(page, expected_count)) {

  		spin_unlock_irq(&mapping->tree_lock);

  		return -EAGAIN;
  	}

  	/*

  	 * In the async migration case of moving a page with buffers, lock the
  	 * buffers using trylock before the mapping is moved. If the mapping
  	 * was moved, we later failed to lock the buffers and could not move
  	 * the mapping back due to an elevated page count, we would have to
  	 * block waiting on other references to be dropped.
  	 */

  	if (mode == MIGRATE_ASYNC && head &&
  			!buffer_migrate_lock_buffers(head, mode)) {

  		page_unfreeze_refs(page, expected_count);
  		spin_unlock_irq(&mapping->tree_lock);
  		return -EAGAIN;
  	}
  
  	/*

  	 * Now we know that no one else is looking at the page.

  	 */

  	get_page(newpage);	/* add cache reference */

  	if (PageSwapCache(page)) {
  		SetPageSwapCache(newpage);
  		set_page_private(newpage, page_private(page));
  	}

  	radix_tree_replace_slot(pslot, newpage);
  
  	/*

  	 * Drop cache reference from old page by unfreezing
  	 * to one less reference.

  	 * We know this isn't the last reference.
  	 */

  	page_unfreeze_refs(page, expected_count - 1);

  	/*
  	 * If moved to a different zone then also account
  	 * the page for that zone. Other VM counters will be
  	 * taken care of when we establish references to the
  	 * new page and drop references to the old page.
  	 *
  	 * Note that anonymous pages are accounted for
  	 * via NR_FILE_PAGES and NR_ANON_PAGES if they
  	 * are mapped to swap space.
  	 */
  	__dec_zone_page_state(page, NR_FILE_PAGES);
  	__inc_zone_page_state(newpage, NR_FILE_PAGES);

  	if (!PageSwapCache(page) && PageSwapBacked(page)) {

  		__dec_zone_page_state(page, NR_SHMEM);
  		__inc_zone_page_state(newpage, NR_SHMEM);
  	}

  	spin_unlock_irq(&mapping->tree_lock);

  	return MIGRATEPAGE_SUCCESS;

  }

  
  /*

   * The expected number of remaining references is the same as that
   * of migrate_page_move_mapping().
   */
  int migrate_huge_page_move_mapping(struct address_space *mapping,
  				   struct page *newpage, struct page *page)
  {
  	int expected_count;
  	void **pslot;
  
  	if (!mapping) {
  		if (page_count(page) != 1)
  			return -EAGAIN;

  		return MIGRATEPAGE_SUCCESS;

  	}
  
  	spin_lock_irq(&mapping->tree_lock);
  
  	pslot = radix_tree_lookup_slot(&mapping->page_tree,
  					page_index(page));
  
  	expected_count = 2 + page_has_private(page);
  	if (page_count(page) != expected_count ||

  		radix_tree_deref_slot_protected(pslot, &mapping->tree_lock) != page) {

  		spin_unlock_irq(&mapping->tree_lock);
  		return -EAGAIN;
  	}
  
  	if (!page_freeze_refs(page, expected_count)) {
  		spin_unlock_irq(&mapping->tree_lock);
  		return -EAGAIN;
  	}
  
  	get_page(newpage);
  
  	radix_tree_replace_slot(pslot, newpage);

  	page_unfreeze_refs(page, expected_count - 1);

  
  	spin_unlock_irq(&mapping->tree_lock);

  	return MIGRATEPAGE_SUCCESS;

  }
  
  /*

   * Gigantic pages are so large that we do not guarantee that page++ pointer
   * arithmetic will work across the entire page.  We need something more
   * specialized.
   */
  static void __copy_gigantic_page(struct page *dst, struct page *src,
  				int nr_pages)
  {
  	int i;
  	struct page *dst_base = dst;
  	struct page *src_base = src;
  
  	for (i = 0; i < nr_pages; ) {
  		cond_resched();
  		copy_highpage(dst, src);
  
  		i++;
  		dst = mem_map_next(dst, dst_base, i);
  		src = mem_map_next(src, src_base, i);
  	}
  }
  
  static void copy_huge_page(struct page *dst, struct page *src)
  {
  	int i;
  	int nr_pages;
  
  	if (PageHuge(src)) {
  		/* hugetlbfs page */
  		struct hstate *h = page_hstate(src);
  		nr_pages = pages_per_huge_page(h);
  
  		if (unlikely(nr_pages > MAX_ORDER_NR_PAGES)) {
  			__copy_gigantic_page(dst, src, nr_pages);
  			return;
  		}
  	} else {
  		/* thp page */
  		BUG_ON(!PageTransHuge(src));
  		nr_pages = hpage_nr_pages(src);
  	}
  
  	for (i = 0; i < nr_pages; i++) {
  		cond_resched();
  		copy_highpage(dst + i, src + i);
  	}
  }
  
  /*

   * Copy the page to its new location
   */

  void migrate_page_copy(struct page *newpage, struct page *page)

  {

  	int cpupid;

  	if (PageHuge(page) || PageTransHuge(page))

  		copy_huge_page(newpage, page);
  	else
  		copy_highpage(newpage, page);

  
  	if (PageError(page))
  		SetPageError(newpage);
  	if (PageReferenced(page))
  		SetPageReferenced(newpage);
  	if (PageUptodate(page))
  		SetPageUptodate(newpage);

  	if (TestClearPageActive(page)) {

  		VM_BUG_ON_PAGE(PageUnevictable(page), page);

  		SetPageActive(newpage);

  	} else if (TestClearPageUnevictable(page))
  		SetPageUnevictable(newpage);

  	if (PageChecked(page))
  		SetPageChecked(newpage);
  	if (PageMappedToDisk(page))
  		SetPageMappedToDisk(newpage);
  
  	if (PageDirty(page)) {
  		clear_page_dirty_for_io(page);

  		/*
  		 * Want to mark the page and the radix tree as dirty, and
  		 * redo the accounting that clear_page_dirty_for_io undid,
  		 * but we can't use set_page_dirty because that function
  		 * is actually a signal that all of the page has become dirty.

  		 * Whereas only part of our page may be dirty.

  		 */

  		if (PageSwapBacked(page))
  			SetPageDirty(newpage);
  		else
  			__set_page_dirty_nobuffers(newpage);

   	}

  	/*
  	 * Copy NUMA information to the new page, to prevent over-eager
  	 * future migrations of this same page.
  	 */
  	cpupid = page_cpupid_xchg_last(page, -1);
  	page_cpupid_xchg_last(newpage, cpupid);

  	mlock_migrate_page(newpage, page);

  	ksm_migrate_page(newpage, page);

  	/*
  	 * Please do not reorder this without considering how mm/ksm.c's
  	 * get_ksm_page() depends upon ksm_migrate_page() and PageSwapCache().
  	 */

  	ClearPageSwapCache(page);

  	ClearPagePrivate(page);
  	set_page_private(page, 0);

  
  	/*
  	 * If any waiters have accumulated on the new page then
  	 * wake them up.
  	 */
  	if (PageWriteback(newpage))
  		end_page_writeback(newpage);
  }

  /************************************************************
   *                    Migration functions
   ***********************************************************/

  /*
   * Common logic to directly migrate a single page suitable for

   * pages that do not use PagePrivate/PagePrivate2.

   *
   * Pages are locked upon entry and exit.
   */

  int migrate_page(struct address_space *mapping,

  		struct page *newpage, struct page *page,
  		enum migrate_mode mode)

  {
  	int rc;
  
  	BUG_ON(PageWriteback(page));	/* Writeback must be complete */

  	rc = migrate_page_move_mapping(mapping, newpage, page, NULL, mode, 0);

  	if (rc != MIGRATEPAGE_SUCCESS)

  		return rc;
  
  	migrate_page_copy(newpage, page);

  	return MIGRATEPAGE_SUCCESS;

  }
  EXPORT_SYMBOL(migrate_page);

  #ifdef CONFIG_BLOCK

  /*

   * Migration function for pages with buffers. This function can only be used
   * if the underlying filesystem guarantees that no other references to "page"
   * exist.
   */

  int buffer_migrate_page(struct address_space *mapping,

  		struct page *newpage, struct page *page, enum migrate_mode mode)

  {

  	struct buffer_head *bh, *head;
  	int rc;

  	if (!page_has_buffers(page))

  		return migrate_page(mapping, newpage, page, mode);

  
  	head = page_buffers(page);

  	rc = migrate_page_move_mapping(mapping, newpage, page, head, mode, 0);

  	if (rc != MIGRATEPAGE_SUCCESS)

  		return rc;

  	/*
  	 * In the async case, migrate_page_move_mapping locked the buffers
  	 * with an IRQ-safe spinlock held. In the sync case, the buffers
  	 * need to be locked now
  	 */

  	if (mode != MIGRATE_ASYNC)
  		BUG_ON(!buffer_migrate_lock_buffers(head, mode));

  
  	ClearPagePrivate(page);
  	set_page_private(newpage, page_private(page));
  	set_page_private(page, 0);
  	put_page(page);
  	get_page(newpage);
  
  	bh = head;
  	do {
  		set_bh_page(bh, newpage, bh_offset(bh));
  		bh = bh->b_this_page;
  
  	} while (bh != head);
  
  	SetPagePrivate(newpage);
  
  	migrate_page_copy(newpage, page);
  
  	bh = head;
  	do {
  		unlock_buffer(bh);
   		put_bh(bh);
  		bh = bh->b_this_page;
  
  	} while (bh != head);

  	return MIGRATEPAGE_SUCCESS;

  }
  EXPORT_SYMBOL(buffer_migrate_page);

  #endif

  /*
   * Writeback a page to clean the dirty state
   */
  static int writeout(struct address_space *mapping, struct page *page)

  {

  	struct writeback_control wbc = {
  		.sync_mode = WB_SYNC_NONE,
  		.nr_to_write = 1,
  		.range_start = 0,
  		.range_end = LLONG_MAX,

  		.for_reclaim = 1
  	};
  	int rc;
  
  	if (!mapping->a_ops->writepage)
  		/* No write method for the address space */
  		return -EINVAL;
  
  	if (!clear_page_dirty_for_io(page))
  		/* Someone else already triggered a write */
  		return -EAGAIN;

  	/*

  	 * A dirty page may imply that the underlying filesystem has
  	 * the page on some queue. So the page must be clean for
  	 * migration. Writeout may mean we loose the lock and the
  	 * page state is no longer what we checked for earlier.
  	 * At this point we know that the migration attempt cannot
  	 * be successful.

  	 */

  	remove_migration_ptes(page, page);

  	rc = mapping->a_ops->writepage(page, &wbc);

  	if (rc != AOP_WRITEPAGE_ACTIVATE)
  		/* unlocked. Relock */
  		lock_page(page);

  	return (rc < 0) ? -EIO : -EAGAIN;

  }
  
  /*
   * Default handling if a filesystem does not provide a migration function.
   */
  static int fallback_migrate_page(struct address_space *mapping,

  	struct page *newpage, struct page *page, enum migrate_mode mode)

  {

  	if (PageDirty(page)) {

  		/* Only writeback pages in full synchronous migration */
  		if (mode != MIGRATE_SYNC)

  			return -EBUSY;

  		return writeout(mapping, page);

  	}

  
  	/*
  	 * Buffers may be managed in a filesystem specific way.
  	 * We must have no buffers or drop them.
  	 */

  	if (page_has_private(page) &&

  	    !try_to_release_page(page, GFP_KERNEL))
  		return -EAGAIN;

  	return migrate_page(mapping, newpage, page, mode);

  }

  /*

   * Move a page to a newly allocated page
   * The page is locked and all ptes have been successfully removed.
   *
   * The new page will have replaced the old page if this function
   * is successful.

   *
   * Return value:
   *   < 0 - error code

   *  MIGRATEPAGE_SUCCESS - success

   */

  static int move_to_new_page(struct page *newpage, struct page *page,

  				int page_was_mapped, enum migrate_mode mode)

  {
  	struct address_space *mapping;
  	int rc;
  
  	/*
  	 * Block others from accessing the page when we get around to
  	 * establishing additional references. We are the only one
  	 * holding a reference to the new page at this point.
  	 */

  	if (!trylock_page(newpage))

  		BUG();
  
  	/* Prepare mapping for the new page.*/
  	newpage->index = page->index;
  	newpage->mapping = page->mapping;

  	if (PageSwapBacked(page))
  		SetPageSwapBacked(newpage);

  
  	mapping = page_mapping(page);
  	if (!mapping)

  		rc = migrate_page(mapping, newpage, page, mode);

  	else if (mapping->a_ops->migratepage)

  		/*

  		 * Most pages have a mapping and most filesystems provide a
  		 * migratepage callback. Anonymous pages are part of swap
  		 * space which also has its own migratepage callback. This
  		 * is the most common path for page migration.

  		 */

  		rc = mapping->a_ops->migratepage(mapping,

  						newpage, page, mode);

  	else

  		rc = fallback_migrate_page(mapping, newpage, page, mode);

  	if (rc != MIGRATEPAGE_SUCCESS) {

  		newpage->mapping = NULL;

  	} else {

  		mem_cgroup_migrate(page, newpage, false);

  		if (page_was_mapped)

  			remove_migration_ptes(page, newpage);

  		page->mapping = NULL;

  	}

  
  	unlock_page(newpage);
  
  	return rc;
  }

  static int __unmap_and_move(struct page *page, struct page *newpage,

  				int force, enum migrate_mode mode)

  {

  	int rc = -EAGAIN;

  	int page_was_mapped = 0;

  	struct anon_vma *anon_vma = NULL;

  	if (!trylock_page(page)) {

  		if (!force || mode == MIGRATE_ASYNC)

  			goto out;

  
  		/*
  		 * It's not safe for direct compaction to call lock_page.
  		 * For example, during page readahead pages are added locked
  		 * to the LRU. Later, when the IO completes the pages are
  		 * marked uptodate and unlocked. However, the queueing
  		 * could be merging multiple pages for one bio (e.g.
  		 * mpage_readpages). If an allocation happens for the
  		 * second or third page, the process can end up locking
  		 * the same page twice and deadlocking. Rather than
  		 * trying to be clever about what pages can be locked,
  		 * avoid the use of lock_page for direct compaction
  		 * altogether.
  		 */
  		if (current->flags & PF_MEMALLOC)

  			goto out;

  		lock_page(page);
  	}
  
  	if (PageWriteback(page)) {

  		/*

  		 * Only in the case of a full synchronous migration is it

  		 * necessary to wait for PageWriteback. In the async case,
  		 * the retry loop is too short and in the sync-light case,
  		 * the overhead of stalling is too much

  		 */

  		if (mode != MIGRATE_SYNC) {

  			rc = -EBUSY;

  			goto out_unlock;

  		}
  		if (!force)

  			goto out_unlock;

  		wait_on_page_writeback(page);
  	}

  	/*

  	 * By try_to_unmap(), page->mapcount goes down to 0 here. In this case,
  	 * we cannot notice that anon_vma is freed while we migrates a page.

  	 * This get_anon_vma() delays freeing anon_vma pointer until the end

  	 * of migration. File cache pages are no problem because of page_lock()

  	 * File Caches may use write_page() or lock_page() in migration, then,
  	 * just care Anon page here.

  	 */

  	if (PageAnon(page) && !PageKsm(page)) {

  		/*

  		 * Only page_lock_anon_vma_read() understands the subtleties of

  		 * getting a hold on an anon_vma from outside one of its mms.
  		 */

  		anon_vma = page_get_anon_vma(page);

  		if (anon_vma) {
  			/*

  			 * Anon page

  			 */

  		} else if (PageSwapCache(page)) {

  			/*
  			 * We cannot be sure that the anon_vma of an unmapped
  			 * swapcache page is safe to use because we don't
  			 * know in advance if the VMA that this page belonged
  			 * to still exists. If the VMA and others sharing the
  			 * data have been freed, then the anon_vma could
  			 * already be invalid.
  			 *
  			 * To avoid this possibility, swapcache pages get
  			 * migrated but are not remapped when migration
  			 * completes
  			 */

  		} else {

  			goto out_unlock;

  		}

  	}

  	if (unlikely(isolated_balloon_page(page))) {

  		/*
  		 * A ballooned page does not need any special attention from
  		 * physical to virtual reverse mapping procedures.
  		 * Skip any attempt to unmap PTEs or to remap swap cache,
  		 * in order to avoid burning cycles at rmap level, and perform
  		 * the page migration right away (proteced by page lock).
  		 */
  		rc = balloon_page_migrate(newpage, page, mode);

  		goto out_unlock;

  	}

  	/*

  	 * Corner case handling:
  	 * 1. When a new swap-cache page is read into, it is added to the LRU
  	 * and treated as swapcache but it has no rmap yet.
  	 * Calling try_to_unmap() against a page->mapping==NULL page will
  	 * trigger a BUG.  So handle it here.
  	 * 2. An orphaned page (see truncate_complete_page) might have
  	 * fs-private metadata. The page can be picked up due to memory
  	 * offlining.  Everywhere else except page reclaim, the page is
  	 * invisible to the vm, so the page can not be migrated.  So try to
  	 * free the metadata, so the page can be freed.

  	 */

  	if (!page->mapping) {

  		VM_BUG_ON_PAGE(PageAnon(page), page);

  		if (page_has_private(page)) {

  			try_to_free_buffers(page);

  			goto out_unlock;

  		}

  		goto skip_unmap;

  	}

  	/* Establish migration ptes or remove ptes */

  	if (page_mapped(page)) {
  		try_to_unmap(page,
  			TTU_MIGRATION|TTU_IGNORE_MLOCK|TTU_IGNORE_ACCESS);
  		page_was_mapped = 1;
  	}

  skip_unmap:

  	if (!page_mapped(page))

  		rc = move_to_new_page(newpage, page, page_was_mapped, mode);

  	if (rc && page_was_mapped)

  		remove_migration_ptes(page, page);

  
  	/* Drop an anon_vma reference if we took one */

  	if (anon_vma)

  		put_anon_vma(anon_vma);

  out_unlock:

  	unlock_page(page);

  out:
  	return rc;
  }

  /*
   * Obtain the lock on page, remove all ptes and migrate the page
   * to the newly allocated page in newpage.
   */

  static int unmap_and_move(new_page_t get_new_page, free_page_t put_new_page,
  			unsigned long private, struct page *page, int force,
  			enum migrate_mode mode)

  {
  	int rc = 0;
  	int *result = NULL;
  	struct page *newpage = get_new_page(page, private, &result);
  
  	if (!newpage)
  		return -ENOMEM;
  
  	if (page_count(page) == 1) {
  		/* page was freed from under us. So we are done. */
  		goto out;
  	}
  
  	if (unlikely(PageTransHuge(page)))
  		if (unlikely(split_huge_page(page)))
  			goto out;

  	rc = __unmap_and_move(page, newpage, force, mode);

  out:

  	if (rc != -EAGAIN) {

  		/*
  		 * A page that has been migrated has all references
  		 * removed and will be freed. A page that has not been
  		 * migrated will have kepts its references and be
  		 * restored.
  		 */
  		list_del(&page->lru);

  		dec_zone_page_state(page, NR_ISOLATED_ANON +

  				page_is_file_cache(page));

  		putback_lru_page(page);

  	}

  	/*

  	 * If migration was not successful and there's a freeing callback, use
  	 * it.  Otherwise, putback_lru_page() will drop the reference grabbed
  	 * during isolation.

  	 */

  	if (rc != MIGRATEPAGE_SUCCESS && put_new_page) {
  		ClearPageSwapBacked(newpage);

  		put_new_page(newpage, private);

  	} else if (unlikely(__is_movable_balloon_page(newpage))) {
  		/* drop our reference, page already in the balloon */
  		put_page(newpage);

  	} else

  		putback_lru_page(newpage);

  	if (result) {
  		if (rc)
  			*result = rc;
  		else
  			*result = page_to_nid(newpage);
  	}

  	return rc;
  }
  
  /*

   * Counterpart of unmap_and_move_page() for hugepage migration.
   *
   * This function doesn't wait the completion of hugepage I/O
   * because there is no race between I/O and migration for hugepage.
   * Note that currently hugepage I/O occurs only in direct I/O
   * where no lock is held and PG_writeback is irrelevant,
   * and writeback status of all subpages are counted in the reference
   * count of the head page (i.e. if all subpages of a 2MB hugepage are
   * under direct I/O, the reference of the head page is 512 and a bit more.)
   * This means that when we try to migrate hugepage whose subpages are
   * doing direct I/O, some references remain after try_to_unmap() and
   * hugepage migration fails without data corruption.
   *
   * There is also no race when direct I/O is issued on the page under migration,
   * because then pte is replaced with migration swap entry and direct I/O code
   * will wait in the page fault for migration to complete.
   */
  static int unmap_and_move_huge_page(new_page_t get_new_page,

  				free_page_t put_new_page, unsigned long private,
  				struct page *hpage, int force,
  				enum migrate_mode mode)

  {
  	int rc = 0;
  	int *result = NULL;

  	int page_was_mapped = 0;

  	struct page *new_hpage;

  	struct anon_vma *anon_vma = NULL;

  	/*
  	 * Movability of hugepages depends on architectures and hugepage size.
  	 * This check is necessary because some callers of hugepage migration
  	 * like soft offline and memory hotremove don't walk through page
  	 * tables or check whether the hugepage is pmd-based or not before
  	 * kicking migration.
  	 */

  	if (!hugepage_migration_supported(page_hstate(hpage))) {

  		putback_active_hugepage(hpage);

  		return -ENOSYS;

  	}

  	new_hpage = get_new_page(hpage, private, &result);

  	if (!new_hpage)
  		return -ENOMEM;
  
  	rc = -EAGAIN;
  
  	if (!trylock_page(hpage)) {

  		if (!force || mode != MIGRATE_SYNC)

  			goto out;
  		lock_page(hpage);
  	}

  	if (PageAnon(hpage))
  		anon_vma = page_get_anon_vma(hpage);

  	if (page_mapped(hpage)) {
  		try_to_unmap(hpage,
  			TTU_MIGRATION|TTU_IGNORE_MLOCK|TTU_IGNORE_ACCESS);
  		page_was_mapped = 1;
  	}

  
  	if (!page_mapped(hpage))

  		rc = move_to_new_page(new_hpage, hpage, page_was_mapped, mode);

  	if (rc != MIGRATEPAGE_SUCCESS && page_was_mapped)

  		remove_migration_ptes(hpage, hpage);

  	if (anon_vma)

  		put_anon_vma(anon_vma);

  	if (rc == MIGRATEPAGE_SUCCESS)

  		hugetlb_cgroup_migrate(hpage, new_hpage);

  	unlock_page(hpage);

  out:

  	if (rc != -EAGAIN)
  		putback_active_hugepage(hpage);

  
  	/*
  	 * If migration was not successful and there's a freeing callback, use
  	 * it.  Otherwise, put_page() will drop the reference grabbed during
  	 * isolation.
  	 */
  	if (rc != MIGRATEPAGE_SUCCESS && put_new_page)
  		put_new_page(new_hpage, private);
  	else
  		put_page(new_hpage);

  	if (result) {
  		if (rc)
  			*result = rc;
  		else
  			*result = page_to_nid(new_hpage);
  	}
  	return rc;
  }
  
  /*

   * migrate_pages - migrate the pages specified in a list, to the free pages
   *		   supplied as the target for the page migration

   *

   * @from:		The list of pages to be migrated.
   * @get_new_page:	The function used to allocate free pages to be used
   *			as the target of the page migration.

   * @put_new_page:	The function used to free target pages if migration
   *			fails, or NULL if no special handling is necessary.

   * @private:		Private data to be passed on to get_new_page()
   * @mode:		The migration mode that specifies the constraints for
   *			page migration, if any.
   * @reason:		The reason for page migration.

   *

   * The function returns after 10 attempts or if no pages are movable any more
   * because the list has become empty or no retryable pages exist any more.
   * The caller should call putback_lru_pages() to return pages to the LRU

   * or free list only if ret != 0.

   *

   * Returns the number of pages that were not migrated, or an error code.

   */

  int migrate_pages(struct list_head *from, new_page_t get_new_page,

  		free_page_t put_new_page, unsigned long private,
  		enum migrate_mode mode, int reason)

  {

  	int retry = 1;

  	int nr_failed = 0;

  	int nr_succeeded = 0;

  	int pass = 0;
  	struct page *page;
  	struct page *page2;
  	int swapwrite = current->flags & PF_SWAPWRITE;
  	int rc;
  
  	if (!swapwrite)
  		current->flags |= PF_SWAPWRITE;

  	for(pass = 0; pass < 10 && retry; pass++) {
  		retry = 0;

  		list_for_each_entry_safe(page, page2, from, lru) {

  			cond_resched();

  			if (PageHuge(page))
  				rc = unmap_and_move_huge_page(get_new_page,

  						put_new_page, private, page,
  						pass > 2, mode);

  			else

  				rc = unmap_and_move(get_new_page, put_new_page,
  						private, page, pass > 2, mode);

  			switch(rc) {

  			case -ENOMEM:
  				goto out;

  			case -EAGAIN:

  				retry++;

  				break;

  			case MIGRATEPAGE_SUCCESS:

  				nr_succeeded++;

  				break;
  			default:

  				/*
  				 * Permanent failure (-EBUSY, -ENOSYS, etc.):
  				 * unlike -EAGAIN case, the failed page is
  				 * removed from migration page list and not
  				 * retried in the next outer loop.
  				 */

  				nr_failed++;

  				break;

  			}

  		}
  	}

  	rc = nr_failed + retry;

  out:

  	if (nr_succeeded)
  		count_vm_events(PGMIGRATE_SUCCESS, nr_succeeded);
  	if (nr_failed)
  		count_vm_events(PGMIGRATE_FAIL, nr_failed);

  	trace_mm_migrate_pages(nr_succeeded, nr_failed, mode, reason);

  	if (!swapwrite)
  		current->flags &= ~PF_SWAPWRITE;

  	return rc;

  }

  #ifdef CONFIG_NUMA
  /*
   * Move a list of individual pages
   */
  struct page_to_node {
  	unsigned long addr;
  	struct page *page;
  	int node;
  	int status;
  };
  
  static struct page *new_page_node(struct page *p, unsigned long private,
  		int **result)
  {
  	struct page_to_node *pm = (struct page_to_node *)private;
  
  	while (pm->node != MAX_NUMNODES && pm->page != p)
  		pm++;
  
  	if (pm->node == MAX_NUMNODES)
  		return NULL;
  
  	*result = &pm->status;

  	if (PageHuge(p))
  		return alloc_huge_page_node(page_hstate(compound_head(p)),
  					pm->node);
  	else
  		return alloc_pages_exact_node(pm->node,

  				GFP_HIGHUSER_MOVABLE | __GFP_THISNODE, 0);

  }
  
  /*
   * Move a set of pages as indicated in the pm array. The addr
   * field must be set to the virtual address of the page to be moved
   * and the node number must contain a valid target node.

   * The pm array ends with node = MAX_NUMNODES.

   */

  static int do_move_page_to_node_array(struct mm_struct *mm,
  				      struct page_to_node *pm,
  				      int migrate_all)

  {
  	int err;
  	struct page_to_node *pp;
  	LIST_HEAD(pagelist);
  
  	down_read(&mm->mmap_sem);
  
  	/*
  	 * Build a list of pages to migrate
  	 */

  	for (pp = pm; pp->node != MAX_NUMNODES; pp++) {
  		struct vm_area_struct *vma;
  		struct page *page;

  		err = -EFAULT;
  		vma = find_vma(mm, pp->addr);

  		if (!vma || pp->addr < vma->vm_start || !vma_migratable(vma))

  			goto set_status;

  		page = follow_page(vma, pp->addr, FOLL_GET|FOLL_SPLIT);

  
  		err = PTR_ERR(page);
  		if (IS_ERR(page))
  			goto set_status;

  		err = -ENOENT;
  		if (!page)
  			goto set_status;

  		/* Use PageReserved to check for zero page */

  		if (PageReserved(page))

  			goto put_and_set;
  
  		pp->page = page;
  		err = page_to_nid(page);
  
  		if (err == pp->node)
  			/*
  			 * Node already in the right place
  			 */
  			goto put_and_set;
  
  		err = -EACCES;
  		if (page_mapcount(page) > 1 &&
  				!migrate_all)
  			goto put_and_set;

  		if (PageHuge(page)) {
  			isolate_huge_page(page, &pagelist);
  			goto put_and_set;
  		}

  		err = isolate_lru_page(page);

  		if (!err) {

  			list_add_tail(&page->lru, &pagelist);

  			inc_zone_page_state(page, NR_ISOLATED_ANON +
  					    page_is_file_cache(page));
  		}

  put_and_set:
  		/*
  		 * Either remove the duplicate refcount from
  		 * isolate_lru_page() or drop the page ref if it was
  		 * not isolated.
  		 */
  		put_page(page);
  set_status:
  		pp->status = err;
  	}

  	err = 0;

  	if (!list_empty(&pagelist)) {

  		err = migrate_pages(&pagelist, new_page_node, NULL,

  				(unsigned long)pm, MIGRATE_SYNC, MR_SYSCALL);

  		if (err)

  			putback_movable_pages(&pagelist);

  	}

  
  	up_read(&mm->mmap_sem);
  	return err;
  }
  
  /*

   * Migrate an array of page address onto an array of nodes and fill
   * the corresponding array of status.
   */

  static int do_pages_move(struct mm_struct *mm, nodemask_t task_nodes,

  			 unsigned long nr_pages,
  			 const void __user * __user *pages,
  			 const int __user *nodes,
  			 int __user *status, int flags)
  {

  	struct page_to_node *pm;

  	unsigned long chunk_nr_pages;
  	unsigned long chunk_start;
  	int err;

  	err = -ENOMEM;
  	pm = (struct page_to_node *)__get_free_page(GFP_KERNEL);
  	if (!pm)

  		goto out;

  
  	migrate_prep();

  	/*

  	 * Store a chunk of page_to_node array in a page,
  	 * but keep the last one as a marker

  	 */

  	chunk_nr_pages = (PAGE_SIZE / sizeof(struct page_to_node)) - 1;

  	for (chunk_start = 0;
  	     chunk_start < nr_pages;
  	     chunk_start += chunk_nr_pages) {
  		int j;

  		if (chunk_start + chunk_nr_pages > nr_pages)
  			chunk_nr_pages = nr_pages - chunk_start;
  
  		/* fill the chunk pm with addrs and nodes from user-space */
  		for (j = 0; j < chunk_nr_pages; j++) {
  			const void __user *p;

  			int node;

  			err = -EFAULT;
  			if (get_user(p, pages + j + chunk_start))
  				goto out_pm;
  			pm[j].addr = (unsigned long) p;
  
  			if (get_user(node, nodes + j + chunk_start))

  				goto out_pm;
  
  			err = -ENODEV;

  			if (node < 0 || node >= MAX_NUMNODES)
  				goto out_pm;

  			if (!node_state(node, N_MEMORY))

  				goto out_pm;
  
  			err = -EACCES;
  			if (!node_isset(node, task_nodes))
  				goto out_pm;

  			pm[j].node = node;
  		}
  
  		/* End marker for this chunk */
  		pm[chunk_nr_pages].node = MAX_NUMNODES;
  
  		/* Migrate this chunk */
  		err = do_move_page_to_node_array(mm, pm,
  						 flags & MPOL_MF_MOVE_ALL);
  		if (err < 0)
  			goto out_pm;

  		/* Return status information */

  		for (j = 0; j < chunk_nr_pages; j++)
  			if (put_user(pm[j].status, status + j + chunk_start)) {

  				err = -EFAULT;

  				goto out_pm;
  			}
  	}
  	err = 0;

  
  out_pm:

  	free_page((unsigned long)pm);

  out:
  	return err;
  }
  
  /*

   * Determine the nodes of an array of pages and store it in an array of status.

   */

  static void do_pages_stat_array(struct mm_struct *mm, unsigned long nr_pages,
  				const void __user **pages, int *status)

  {

  	unsigned long i;

  	down_read(&mm->mmap_sem);

  	for (i = 0; i < nr_pages; i++) {

  		unsigned long addr = (unsigned long)(*pages);

  		struct vm_area_struct *vma;
  		struct page *page;

  		int err = -EFAULT;

  
  		vma = find_vma(mm, addr);

  		if (!vma || addr < vma->vm_start)

  			goto set_status;

  		page = follow_page(vma, addr, 0);

  
  		err = PTR_ERR(page);
  		if (IS_ERR(page))
  			goto set_status;

  		err = -ENOENT;
  		/* Use PageReserved to check for zero page */

  		if (!page || PageReserved(page))

  			goto set_status;
  
  		err = page_to_nid(page);
  set_status:

  		*status = err;
  
  		pages++;
  		status++;
  	}
  
  	up_read(&mm->mmap_sem);
  }
  
  /*
   * Determine the nodes of a user array of pages and store it in
   * a user array of status.
   */
  static int do_pages_stat(struct mm_struct *mm, unsigned long nr_pages,
  			 const void __user * __user *pages,
  			 int __user *status)
  {
  #define DO_PAGES_STAT_CHUNK_NR 16
  	const void __user *chunk_pages[DO_PAGES_STAT_CHUNK_NR];
  	int chunk_status[DO_PAGES_STAT_CHUNK_NR];

  	while (nr_pages) {
  		unsigned long chunk_nr;

  		chunk_nr = nr_pages;
  		if (chunk_nr > DO_PAGES_STAT_CHUNK_NR)
  			chunk_nr = DO_PAGES_STAT_CHUNK_NR;
  
  		if (copy_from_user(chunk_pages, pages, chunk_nr * sizeof(*chunk_pages)))
  			break;

  
  		do_pages_stat_array(mm, chunk_nr, chunk_pages, chunk_status);

  		if (copy_to_user(status, chunk_status, chunk_nr * sizeof(*status)))
  			break;

  		pages += chunk_nr;
  		status += chunk_nr;
  		nr_pages -= chunk_nr;
  	}
  	return nr_pages ? -EFAULT : 0;

  }
  
  /*
   * Move a list of pages in the address space of the currently executing
   * process.
   */

  SYSCALL_DEFINE6(move_pages, pid_t, pid, unsigned long, nr_pages,
  		const void __user * __user *, pages,
  		const int __user *, nodes,
  		int __user *, status, int, flags)

  {

  	const struct cred *cred = current_cred(), *tcred;

  	struct task_struct *task;

  	struct mm_struct *mm;

  	int err;

  	nodemask_t task_nodes;

  
  	/* Check flags */
  	if (flags & ~(MPOL_MF_MOVE|MPOL_MF_MOVE_ALL))
  		return -EINVAL;
  
  	if ((flags & MPOL_MF_MOVE_ALL) && !capable(CAP_SYS_NICE))
  		return -EPERM;
  
  	/* Find the mm_struct */

  	rcu_read_lock();

  	task = pid ? find_task_by_vpid(pid) : current;

  	if (!task) {

  		rcu_read_unlock();

  		return -ESRCH;
  	}

  	get_task_struct(task);

  
  	/*
  	 * Check if this process has the right to modify the specified
  	 * process. The right exists if the process has administrative
  	 * capabilities, superuser privileges or the same
  	 * userid as the target process.
  	 */

  	tcred = __task_cred(task);

  	if (!uid_eq(cred->euid, tcred->suid) && !uid_eq(cred->euid, tcred->uid) &&
  	    !uid_eq(cred->uid,  tcred->suid) && !uid_eq(cred->uid,  tcred->uid) &&

  	    !capable(CAP_SYS_NICE)) {

  		rcu_read_unlock();

  		err = -EPERM;

  		goto out;

  	}

  	rcu_read_unlock();

   	err = security_task_movememory(task);
   	if (err)

  		goto out;

  	task_nodes = cpuset_mems_allowed(task);
  	mm = get_task_mm(task);
  	put_task_struct(task);

  	if (!mm)
  		return -EINVAL;
  
  	if (nodes)
  		err = do_pages_move(mm, task_nodes, nr_pages, pages,
  				    nodes, status, flags);
  	else
  		err = do_pages_stat(mm, nr_pages, pages, status);

  	mmput(mm);
  	return err;

  
  out:
  	put_task_struct(task);
  	return err;

  }

  #ifdef CONFIG_NUMA_BALANCING
  /*
   * Returns true if this is a safe migration target node for misplaced NUMA
   * pages. Currently it only checks the watermarks which crude
   */
  static bool migrate_balanced_pgdat(struct pglist_data *pgdat,

  				   unsigned long nr_migrate_pages)

  {
  	int z;
  	for (z = pgdat->nr_zones - 1; z >= 0; z--) {
  		struct zone *zone = pgdat->node_zones + z;
  
  		if (!populated_zone(zone))
  			continue;

  		if (!zone_reclaimable(zone))

  			continue;
  
  		/* Avoid waking kswapd by allocating pages_to_migrate pages. */
  		if (!zone_watermark_ok(zone, 0,
  				       high_wmark_pages(zone) +
  				       nr_migrate_pages,
  				       0, 0))
  			continue;
  		return true;
  	}
  	return false;
  }
  
  static struct page *alloc_misplaced_dst_page(struct page *page,
  					   unsigned long data,
  					   int **result)
  {
  	int nid = (int) data;
  	struct page *newpage;
  
  	newpage = alloc_pages_exact_node(nid,

  					 (GFP_HIGHUSER_MOVABLE |
  					  __GFP_THISNODE | __GFP_NOMEMALLOC |
  					  __GFP_NORETRY | __GFP_NOWARN) &

  					 ~GFP_IOFS, 0);

  	return newpage;
  }
  
  /*

   * page migration rate limiting control.
   * Do not migrate more than @pages_to_migrate in a @migrate_interval_millisecs
   * window of time. Default here says do not migrate more than 1280M per second.

   * If a node is rate-limited then PTE NUMA updates are also rate-limited. However
   * as it is faults that reset the window, pte updates will happen unconditionally
   * if there has not been a fault since @pteupdate_interval_millisecs after the
   * throttle window closed.

   */
  static unsigned int migrate_interval_millisecs __read_mostly = 100;

  static unsigned int pteupdate_interval_millisecs __read_mostly = 1000;

  static unsigned int ratelimit_pages __read_mostly = 128 << (20 - PAGE_SHIFT);

  /* Returns true if NUMA migration is currently rate limited */
  bool migrate_ratelimited(int node)
  {
  	pg_data_t *pgdat = NODE_DATA(node);
  
  	if (time_after(jiffies, pgdat->numabalancing_migrate_next_window +
  				msecs_to_jiffies(pteupdate_interval_millisecs)))
  		return false;
  
  	if (pgdat->numabalancing_migrate_nr_pages < ratelimit_pages)
  		return false;
  
  	return true;
  }

  /* Returns true if the node is migrate rate-limited after the update */

  static bool numamigrate_update_ratelimit(pg_data_t *pgdat,
  					unsigned long nr_pages)

  {

  	/*
  	 * Rate-limit the amount of data that is being migrated to a node.
  	 * Optimal placement is no good if the memory bus is saturated and
  	 * all the time is being spent migrating!
  	 */

  	if (time_after(jiffies, pgdat->numabalancing_migrate_next_window)) {

  		spin_lock(&pgdat->numabalancing_migrate_lock);

  		pgdat->numabalancing_migrate_nr_pages = 0;
  		pgdat->numabalancing_migrate_next_window = jiffies +
  			msecs_to_jiffies(migrate_interval_millisecs);

  		spin_unlock(&pgdat->numabalancing_migrate_lock);

  	}

  	if (pgdat->numabalancing_migrate_nr_pages > ratelimit_pages) {
  		trace_mm_numa_migrate_ratelimit(current, pgdat->node_id,
  								nr_pages);

  		return true;

  	}

  
  	/*
  	 * This is an unlocked non-atomic update so errors are possible.
  	 * The consequences are failing to migrate when we potentiall should
  	 * have which is not severe enough to warrant locking. If it is ever
  	 * a problem, it can be converted to a per-cpu counter.
  	 */
  	pgdat->numabalancing_migrate_nr_pages += nr_pages;
  	return false;

  }

  static int numamigrate_isolate_page(pg_data_t *pgdat, struct page *page)

  {

  	int page_lru;

  	VM_BUG_ON_PAGE(compound_order(page) && !PageTransHuge(page), page);

  	/* Avoid migrating to a node that is nearly full */

  	if (!migrate_balanced_pgdat(pgdat, 1UL << compound_order(page)))
  		return 0;

  	if (isolate_lru_page(page))
  		return 0;

  	/*
  	 * migrate_misplaced_transhuge_page() skips page migration's usual
  	 * check on page_count(), so we must do it here, now that the page
  	 * has been isolated: a GUP pin, or any other pin, prevents migration.
  	 * The expected page count is 3: 1 for page's mapcount and 1 for the
  	 * caller's pin and 1 for the reference taken by isolate_lru_page().
  	 */
  	if (PageTransHuge(page) && page_count(page) != 3) {
  		putback_lru_page(page);
  		return 0;

  	}

  	page_lru = page_is_file_cache(page);
  	mod_zone_page_state(page_zone(page), NR_ISOLATED_ANON + page_lru,
  				hpage_nr_pages(page));

  	/*

  	 * Isolating the page has taken another reference, so the
  	 * caller's reference can be safely dropped without the page
  	 * disappearing underneath us during migration.

  	 */
  	put_page(page);

  	return 1;

  }

  bool pmd_trans_migrating(pmd_t pmd)
  {
  	struct page *page = pmd_page(pmd);
  	return PageLocked(page);
  }
  
  void wait_migrate_huge_page(struct anon_vma *anon_vma, pmd_t *pmd)
  {
  	struct page *page = pmd_page(*pmd);
  	wait_on_page_locked(page);
  }

  /*
   * Attempt to migrate a misplaced page to the specified destination
   * node. Caller is expected to have an elevated reference count on
   * the page that will be dropped by this function before returning.
   */

  int migrate_misplaced_page(struct page *page, struct vm_area_struct *vma,
  			   int node)

  {
  	pg_data_t *pgdat = NODE_DATA(node);

  	int isolated;

  	int nr_remaining;
  	LIST_HEAD(migratepages);
  
  	/*

  	 * Don't migrate file pages that are mapped in multiple processes
  	 * with execute permissions as they are probably shared libraries.

  	 */

  	if (page_mapcount(page) != 1 && page_is_file_cache(page) &&
  	    (vma->vm_flags & VM_EXEC))

  		goto out;

  
  	/*
  	 * Rate-limit the amount of data that is being migrated to a node.
  	 * Optimal placement is no good if the memory bus is saturated and
  	 * all the time is being spent migrating!
  	 */

  	if (numamigrate_update_ratelimit(pgdat, 1))

  		goto out;

  
  	isolated = numamigrate_isolate_page(pgdat, page);
  	if (!isolated)
  		goto out;
  
  	list_add(&page->lru, &migratepages);

  	nr_remaining = migrate_pages(&migratepages, alloc_misplaced_dst_page,

  				     NULL, node, MIGRATE_ASYNC,
  				     MR_NUMA_MISPLACED);