/*
   * 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/module.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/gfp.h>

  #include <asm/tlbflush.h>

  #include "internal.h"

  #define lru_to_page(_head) (list_entry((_head)->prev, struct page, lru))
  
  /*

   * 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;
  }

  /*

   * Add isolated pages on the list back to the LRU under page lock
   * to avoid leaking evictable pages back onto unevictable list.

   */

  void putback_lru_pages(struct list_head *l)

  {
  	struct page *page;
  	struct page *page2;

  
  	list_for_each_entry_safe(page, page2, l, lru) {

  		list_del(&page->lru);

  		dec_zone_page_state(page, NR_ISOLATED_ANON +

  				page_is_file_cache(page));

  		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;
   	pgd_t *pgd;
   	pud_t *pud;
   	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 = &mm->page_table_lock;
  	} else {
  		pgd = pgd_offset(mm, addr);
  		if (!pgd_present(*pgd))
  			goto out;

  		pud = pud_offset(pgd, addr);
  		if (!pud_present(*pud))
  			goto out;

  		pmd = pmd_offset(pud, addr);

  		if (pmd_trans_huge(*pmd))
  			goto out;

  		if (!pmd_present(*pmd))
  			goto out;

  		ptep = pte_offset_map(pmd, addr);

  		if (!is_swap_pte(*ptep)) {
  			pte_unmap(ptep);
  			goto out;
  		}
  
  		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 (is_write_migration_entry(entry))
  		pte = pte_mkwrite(pte);

  #ifdef CONFIG_HUGETLB_PAGE

  	if (PageHuge(new))
  		pte = pte_mkhuge(pte);

  #endif

  	flush_cache_page(vma, addr, pte_pfn(pte));

  	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;

  }
  
  /*

   * 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)
  {

  	rmap_walk(new, remove_migration_pte, old);

  }
  
  /*

   * 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.
   *
   * This function is called from do_swap_page().
   */
  void migration_entry_wait(struct mm_struct *mm, pmd_t *pmd,
  				unsigned long address)
  {
  	pte_t *ptep, pte;
  	spinlock_t *ptl;
  	swp_entry_t entry;
  	struct page *page;
  
  	ptep = pte_offset_map_lock(mm, pmd, address, &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);
  }

  /*

   * 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.

   */

  static int migrate_page_move_mapping(struct address_space *mapping,
  		struct page *newpage, struct page *page)

  {

  	int expected_count;

  	void **pslot;

  	if (!mapping) {

  		/* Anonymous page without mapping */

  		if (page_count(page) != 1)
  			return -EAGAIN;
  		return 0;
  	}

  	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;
  	}

  	/*
  	 * 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);

  	page_unfreeze_refs(page, expected_count);

  	/*
  	 * Drop cache reference from old page.
  	 * We know this isn't the last reference.
  	 */

  	__put_page(page);

  	/*
  	 * 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 0;
  }

  
  /*

   * 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 0;
  	}
  
  	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);
  
  	__put_page(page);
  
  	spin_unlock_irq(&mapping->tree_lock);
  	return 0;
  }
  
  /*

   * Copy the page to its new location
   */

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

  {

  	if (PageHuge(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(PageUnevictable(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.

  		 */
  		__set_page_dirty_nobuffers(newpage);

   	}

  	mlock_migrate_page(newpage, page);

  	ksm_migrate_page(newpage, page);

  	ClearPageSwapCache(page);

  	ClearPagePrivate(page);
  	set_page_private(page, 0);
  	page->mapping = NULL;
  
  	/*
  	 * If any waiters have accumulated on the new page then
  	 * wake them up.
  	 */
  	if (PageWriteback(newpage))
  		end_page_writeback(newpage);
  }

  /************************************************************
   *                    Migration functions
   ***********************************************************/
  
  /* Always fail migration. Used for mappings that are not movable */

  int fail_migrate_page(struct address_space *mapping,
  			struct page *newpage, struct page *page)

  {
  	return -EIO;
  }
  EXPORT_SYMBOL(fail_migrate_page);

  /*
   * 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)

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

  	rc = migrate_page_move_mapping(mapping, newpage, page);

  
  	if (rc)
  		return rc;
  
  	migrate_page_copy(newpage, page);

  	return 0;
  }
  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)

  {

  	struct buffer_head *bh, *head;
  	int rc;

  	if (!page_has_buffers(page))

  		return migrate_page(mapping, newpage, page);

  
  	head = page_buffers(page);

  	rc = migrate_page_move_mapping(mapping, newpage, page);

  
  	if (rc)
  		return rc;
  
  	bh = head;
  	do {
  		get_bh(bh);
  		lock_buffer(bh);
  		bh = bh->b_this_page;
  
  	} while (bh != head);
  
  	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 0;
  }
  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)
  {
  	if (PageDirty(page))
  		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);
  }

  /*

   * 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
   *  == 0 - success

   */

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

  					int remap_swapcache, bool sync)

  {
  	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);

  	else {

  		/*

  		 * Do not writeback pages if !sync and migratepage is
  		 * not pointing to migrate_page() which is nonblocking
  		 * (swapcache/tmpfs uses migratepage = migrate_page).

  		 */

  		if (PageDirty(page) && !sync &&
  		    mapping->a_ops->migratepage != migrate_page)
  			rc = -EBUSY;
  		else if (mapping->a_ops->migratepage)
  			/*
  			 * Most pages have a mapping and most filesystems
  			 * should provide a migration function. Anonymous
  			 * pages are part of swap space which also has its
  			 * own migration function. This is the most common
  			 * path for page migration.
  			 */
  			rc = mapping->a_ops->migratepage(mapping,
  							newpage, page);
  		else
  			rc = fallback_migrate_page(mapping, newpage, page);
  	}

  	if (rc) {

  		newpage->mapping = NULL;

  	} else {
  		if (remap_swapcache)
  			remove_migration_ptes(page, newpage);
  	}

  
  	unlock_page(newpage);
  
  	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, unsigned long private,

  			struct page *page, int force, bool offlining, bool sync)

  {
  	int rc = 0;

  	int *result = NULL;
  	struct page *newpage = get_new_page(page, private, &result);

  	int remap_swapcache = 1;

  	int charge = 0;

  	struct mem_cgroup *mem;

  	struct anon_vma *anon_vma = NULL;

  
  	if (!newpage)
  		return -ENOMEM;

  	if (page_count(page) == 1) {

  		/* page was freed from under us. So we are done. */

  		goto move_newpage;

  	}

  	if (unlikely(PageTransHuge(page)))
  		if (unlikely(split_huge_page(page)))
  			goto move_newpage;

  	/* prepare cgroup just returns 0 or -ENOMEM */

  	rc = -EAGAIN;

  	if (!trylock_page(page)) {

  		if (!force || !sync)

  			goto move_newpage;

  
  		/*
  		 * 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 move_newpage;

  		lock_page(page);
  	}

  	/*
  	 * Only memory hotplug's offline_pages() caller has locked out KSM,
  	 * and can safely migrate a KSM page.  The other cases have skipped
  	 * PageKsm along with PageReserved - but it is only now when we have
  	 * the page lock that we can be certain it will not go KSM beneath us
  	 * (KSM will not upgrade a page from PageAnon to PageKsm when it sees
  	 * its pagecount raised, but only here do we take the page lock which
  	 * serializes that).
  	 */
  	if (PageKsm(page) && !offlining) {
  		rc = -EBUSY;
  		goto unlock;
  	}

  	/* charge against new page */

  	charge = mem_cgroup_prepare_migration(page, newpage, &mem, GFP_KERNEL);

  	if (charge == -ENOMEM) {
  		rc = -ENOMEM;
  		goto unlock;
  	}
  	BUG_ON(charge);

  	if (PageWriteback(page)) {

  		/*
  		 * For !sync, there is no point retrying as the retry loop
  		 * is expected to be too short for PageWriteback to be cleared
  		 */
  		if (!sync) {
  			rc = -EBUSY;
  			goto uncharge;
  		}
  		if (!force)

  			goto uncharge;

  		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)) {

  		/*
  		 * Only page_lock_anon_vma() 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
  			 */
  			remap_swapcache = 0;
  		} else {

  			goto uncharge;

  		}

  	}

  	/*

  	 * 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(PageAnon(page));
  		if (page_has_private(page)) {

  			try_to_free_buffers(page);

  			goto uncharge;

  		}

  		goto skip_unmap;

  	}

  	/* Establish migration ptes or remove ptes */

  	try_to_unmap(page, TTU_MIGRATION|TTU_IGNORE_MLOCK|TTU_IGNORE_ACCESS);

  skip_unmap:

  	if (!page_mapped(page))

  		rc = move_to_new_page(newpage, page, remap_swapcache, sync);

  	if (rc && remap_swapcache)

  		remove_migration_ptes(page, page);

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

  	if (anon_vma)

  		put_anon_vma(anon_vma);

  uncharge:
  	if (!charge)

  		mem_cgroup_end_migration(mem, page, newpage, rc == 0);

  unlock:
  	unlock_page(page);

  move_newpage:

  	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);

  	}

  	/*
  	 * Move the new page to the LRU. If migration was not successful
  	 * then this will free the page.
  	 */

  	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,
  				unsigned long private, struct page *hpage,

  				int force, bool offlining, bool sync)

  {
  	int rc = 0;
  	int *result = NULL;
  	struct page *new_hpage = get_new_page(hpage, private, &result);

  	struct anon_vma *anon_vma = NULL;
  
  	if (!new_hpage)
  		return -ENOMEM;
  
  	rc = -EAGAIN;
  
  	if (!trylock_page(hpage)) {

  		if (!force || !sync)

  			goto out;
  		lock_page(hpage);
  	}

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

  
  	try_to_unmap(hpage, TTU_MIGRATION|TTU_IGNORE_MLOCK|TTU_IGNORE_ACCESS);
  
  	if (!page_mapped(hpage))

  		rc = move_to_new_page(new_hpage, hpage, 1, sync);

  
  	if (rc)
  		remove_migration_ptes(hpage, hpage);

  	if (anon_vma)

  		put_anon_vma(anon_vma);

  out:
  	unlock_page(hpage);
  
  	if (rc != -EAGAIN) {
  		list_del(&hpage->lru);
  		put_page(hpage);
  	}
  
  	put_page(new_hpage);
  
  	if (result) {
  		if (rc)
  			*result = rc;
  		else
  			*result = page_to_nid(new_hpage);
  	}
  	return rc;
  }
  
  /*

   * migrate_pages
   *

   * The function takes one list of pages to migrate and a function
   * that determines from the page to be migrated and the private data
   * the target of the move and allocates the page.

   *
   * The function returns after 10 attempts or if no pages
   * are movable anymore because to has become empty

   * or no retryable pages exist anymore.
   * Caller should call putback_lru_pages to return pages to the LRU

   * or free list only if ret != 0.

   *

   * Return: Number of pages not migrated or error code.

   */

  int migrate_pages(struct list_head *from,

  		new_page_t get_new_page, unsigned long private, bool offlining,

  		bool sync)

  {

  	int retry = 1;

  	int nr_failed = 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();

  			rc = unmap_and_move(get_new_page, private,

  						page, pass > 2, offlining,
  						sync);

  			switch(rc) {

  			case -ENOMEM:
  				goto out;

  			case -EAGAIN:

  				retry++;

  				break;
  			case 0:

  				break;
  			default:

  				/* Permanent failure */

  				nr_failed++;

  				break;

  			}

  		}
  	}

  	rc = 0;
  out:

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

  	if (rc)
  		return rc;

  	return nr_failed + retry;

  }

  int migrate_huge_pages(struct list_head *from,

  		new_page_t get_new_page, unsigned long private, bool offlining,

  		bool sync)

  {
  	int retry = 1;
  	int nr_failed = 0;
  	int pass = 0;
  	struct page *page;
  	struct page *page2;
  	int rc;
  
  	for (pass = 0; pass < 10 && retry; pass++) {
  		retry = 0;
  
  		list_for_each_entry_safe(page, page2, from, lru) {
  			cond_resched();
  
  			rc = unmap_and_move_huge_page(get_new_page,

  					private, page, pass > 2, offlining,
  					sync);

  
  			switch(rc) {
  			case -ENOMEM:
  				goto out;
  			case -EAGAIN:
  				retry++;
  				break;
  			case 0:
  				break;
  			default:
  				/* Permanent failure */
  				nr_failed++;
  				break;
  			}
  		}
  	}
  	rc = 0;
  out:

  	if (rc)
  		return rc;
  
  	return nr_failed + retry;
  }

  #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;

  	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) || PageKsm(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;

  		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,

  				(unsigned long)pm, 0, true);

  		if (err)
  			putback_lru_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, struct task_struct *task,
  			 unsigned long nr_pages,
  			 const void __user * __user *pages,
  			 const int __user *nodes,
  			 int __user *status, int flags)
  {

  	struct page_to_node *pm;

  	nodemask_t task_nodes;

  	unsigned long chunk_nr_pages;
  	unsigned long chunk_start;
  	int err;

  
  	task_nodes = cpuset_mems_allowed(task);

  	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_HIGH_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) || PageKsm(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;

  
  	/* 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;
  	}
  	mm = get_task_mm(task);

  	rcu_read_unlock();

  
  	if (!mm)
  		return -EINVAL;
  
  	/*
  	 * 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.
  	 */

  	rcu_read_lock();
  	tcred = __task_cred(task);

  	if (cred->euid != tcred->suid && cred->euid != tcred->uid &&
  	    cred->uid  != tcred->suid && 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;

  	if (nodes) {
  		err = do_pages_move(mm, task, nr_pages, pages, nodes, status,
  				    flags);
  	} else {

  		err = do_pages_stat(mm, nr_pages, pages, status);

  	}

  out:

  	mmput(mm);
  	return err;
  }

  /*
   * Call migration functions in the vma_ops that may prepare
   * memory in a vm for migration. migration functions may perform
   * the migration for vmas that do not have an underlying page struct.
   */
  int migrate_vmas(struct mm_struct *mm, const nodemask_t *to,
  	const nodemask_t *from, unsigned long flags)
  {
   	struct vm_area_struct *vma;
   	int err = 0;

  	for (vma = mm->mmap; vma && !err; vma = vma->vm_next) {

   		if (vma->vm_ops && vma->vm_ops->migrate) {
   			err = vma->vm_ops->migrate(vma, to, from, flags);
   			if (err)
   				break;
   		}
   	}
   	return err;
  }

  #endif