/*
   * mm/rmap.c - physical to virtual reverse mappings
   *
   * Copyright 2001, Rik van Riel <riel@conectiva.com.br>
   * Released under the General Public License (GPL).
   *
   * Simple, low overhead reverse mapping scheme.
   * Please try to keep this thing as modular as possible.
   *
   * Provides methods for unmapping each kind of mapped page:
   * the anon methods track anonymous pages, and
   * the file methods track pages belonging to an inode.
   *
   * Original design by Rik van Riel <riel@conectiva.com.br> 2001
   * File methods by Dave McCracken <dmccr@us.ibm.com> 2003, 2004
   * Anonymous methods by Andrea Arcangeli <andrea@suse.de> 2004
   * Contributions by Hugh Dickins <hugh@veritas.com> 2003, 2004
   */
  
  /*
   * Lock ordering in mm:
   *

   * inode->i_mutex	(while writing or truncating, not reading or faulting)

   *   inode->i_alloc_sem (vmtruncate_range)
   *   mm->mmap_sem
   *     page->flags PG_locked (lock_page)
   *       mapping->i_mmap_lock
   *         anon_vma->lock
   *           mm->page_table_lock or pte_lock
   *             zone->lru_lock (in mark_page_accessed, isolate_lru_page)
   *             swap_lock (in swap_duplicate, swap_info_get)
   *               mmlist_lock (in mmput, drain_mmlist and others)
   *               mapping->private_lock (in __set_page_dirty_buffers)
   *               inode_lock (in set_page_dirty's __mark_inode_dirty)
   *                 sb_lock (within inode_lock in fs/fs-writeback.c)
   *                 mapping->tree_lock (widely used, in set_page_dirty,
   *                           in arch-dependent flush_dcache_mmap_lock,
   *                           within inode_lock in __sync_single_inode)

   */
  
  #include <linux/mm.h>
  #include <linux/pagemap.h>
  #include <linux/swap.h>
  #include <linux/swapops.h>
  #include <linux/slab.h>
  #include <linux/init.h>
  #include <linux/rmap.h>
  #include <linux/rcupdate.h>

  #include <linux/module.h>

  #include <linux/kallsyms.h>

  #include <linux/memcontrol.h>

  #include <linux/mmu_notifier.h>

  
  #include <asm/tlbflush.h>

  #include "internal.h"

  static struct kmem_cache *anon_vma_cachep;
  
  static inline struct anon_vma *anon_vma_alloc(void)
  {
  	return kmem_cache_alloc(anon_vma_cachep, GFP_KERNEL);
  }
  
  static inline void anon_vma_free(struct anon_vma *anon_vma)
  {
  	kmem_cache_free(anon_vma_cachep, anon_vma);
  }

  /**
   * anon_vma_prepare - attach an anon_vma to a memory region
   * @vma: the memory region in question
   *
   * This makes sure the memory mapping described by 'vma' has
   * an 'anon_vma' attached to it, so that we can associate the
   * anonymous pages mapped into it with that anon_vma.
   *
   * The common case will be that we already have one, but if
   * if not we either need to find an adjacent mapping that we
   * can re-use the anon_vma from (very common when the only
   * reason for splitting a vma has been mprotect()), or we
   * allocate a new one.
   *
   * Anon-vma allocations are very subtle, because we may have
   * optimistically looked up an anon_vma in page_lock_anon_vma()
   * and that may actually touch the spinlock even in the newly
   * allocated vma (it depends on RCU to make sure that the
   * anon_vma isn't actually destroyed).
   *
   * As a result, we need to do proper anon_vma locking even
   * for the new allocation. At the same time, we do not want
   * to do any locking for the common case of already having
   * an anon_vma.
   *
   * This must be called with the mmap_sem held for reading.
   */

  int anon_vma_prepare(struct vm_area_struct *vma)
  {
  	struct anon_vma *anon_vma = vma->anon_vma;
  
  	might_sleep();
  	if (unlikely(!anon_vma)) {
  		struct mm_struct *mm = vma->vm_mm;

  		struct anon_vma *allocated;

  
  		anon_vma = find_mergeable_anon_vma(vma);

  		allocated = NULL;
  		if (!anon_vma) {

  			anon_vma = anon_vma_alloc();
  			if (unlikely(!anon_vma))
  				return -ENOMEM;
  			allocated = anon_vma;

  		}

  		spin_lock(&anon_vma->lock);

  
  		/* page_table_lock to protect against threads */
  		spin_lock(&mm->page_table_lock);
  		if (likely(!vma->anon_vma)) {
  			vma->anon_vma = anon_vma;

  			list_add_tail(&vma->anon_vma_node, &anon_vma->head);

  			allocated = NULL;
  		}
  		spin_unlock(&mm->page_table_lock);

  		spin_unlock(&anon_vma->lock);

  		if (unlikely(allocated))
  			anon_vma_free(allocated);
  	}
  	return 0;
  }
  
  void __anon_vma_merge(struct vm_area_struct *vma, struct vm_area_struct *next)
  {
  	BUG_ON(vma->anon_vma != next->anon_vma);
  	list_del(&next->anon_vma_node);
  }
  
  void __anon_vma_link(struct vm_area_struct *vma)
  {
  	struct anon_vma *anon_vma = vma->anon_vma;

  	if (anon_vma)

  		list_add_tail(&vma->anon_vma_node, &anon_vma->head);

  }
  
  void anon_vma_link(struct vm_area_struct *vma)
  {
  	struct anon_vma *anon_vma = vma->anon_vma;
  
  	if (anon_vma) {
  		spin_lock(&anon_vma->lock);

  		list_add_tail(&vma->anon_vma_node, &anon_vma->head);

  		spin_unlock(&anon_vma->lock);
  	}
  }
  
  void anon_vma_unlink(struct vm_area_struct *vma)
  {
  	struct anon_vma *anon_vma = vma->anon_vma;
  	int empty;
  
  	if (!anon_vma)
  		return;
  
  	spin_lock(&anon_vma->lock);

  	list_del(&vma->anon_vma_node);
  
  	/* We must garbage collect the anon_vma if it's empty */
  	empty = list_empty(&anon_vma->head);
  	spin_unlock(&anon_vma->lock);
  
  	if (empty)
  		anon_vma_free(anon_vma);
  }

  static void anon_vma_ctor(void *data)

  {

  	struct anon_vma *anon_vma = data;

  	spin_lock_init(&anon_vma->lock);
  	INIT_LIST_HEAD(&anon_vma->head);

  }
  
  void __init anon_vma_init(void)
  {
  	anon_vma_cachep = kmem_cache_create("anon_vma", sizeof(struct anon_vma),

  			0, SLAB_DESTROY_BY_RCU|SLAB_PANIC, anon_vma_ctor);

  }
  
  /*
   * Getting a lock on a stable anon_vma from a page off the LRU is
   * tricky: page_lock_anon_vma rely on RCU to guard against the races.
   */

  struct anon_vma *page_lock_anon_vma(struct page *page)

  {

  	struct anon_vma *anon_vma;

  	unsigned long anon_mapping;
  
  	rcu_read_lock();
  	anon_mapping = (unsigned long) page->mapping;
  	if (!(anon_mapping & PAGE_MAPPING_ANON))
  		goto out;
  	if (!page_mapped(page))
  		goto out;
  
  	anon_vma = (struct anon_vma *) (anon_mapping - PAGE_MAPPING_ANON);
  	spin_lock(&anon_vma->lock);

  	return anon_vma;

  out:
  	rcu_read_unlock();

  	return NULL;
  }

  void page_unlock_anon_vma(struct anon_vma *anon_vma)

  {
  	spin_unlock(&anon_vma->lock);
  	rcu_read_unlock();

  }
  
  /*

   * At what user virtual address is page expected in @vma?
   * Returns virtual address or -EFAULT if page's index/offset is not
   * within the range mapped the @vma.

   */
  static inline unsigned long
  vma_address(struct page *page, struct vm_area_struct *vma)
  {
  	pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
  	unsigned long address;
  
  	address = vma->vm_start + ((pgoff - vma->vm_pgoff) << PAGE_SHIFT);
  	if (unlikely(address < vma->vm_start || address >= vma->vm_end)) {

  		/* page should be within @vma mapping range */

  		return -EFAULT;
  	}
  	return address;
  }
  
  /*
   * At what user virtual address is page expected in vma? checking that the

   * page matches the vma: currently only used on anon pages, by unuse_vma;

   */
  unsigned long page_address_in_vma(struct page *page, struct vm_area_struct *vma)
  {
  	if (PageAnon(page)) {
  		if ((void *)vma->anon_vma !=
  		    (void *)page->mapping - PAGE_MAPPING_ANON)
  			return -EFAULT;
  	} else if (page->mapping && !(vma->vm_flags & VM_NONLINEAR)) {

  		if (!vma->vm_file ||
  		    vma->vm_file->f_mapping != page->mapping)

  			return -EFAULT;
  	} else
  		return -EFAULT;
  	return vma_address(page, vma);
  }
  
  /*

   * Check that @page is mapped at @address into @mm.
   *

   * If @sync is false, page_check_address may perform a racy check to avoid
   * the page table lock when the pte is not present (helpful when reclaiming
   * highly shared pages).
   *

   * On success returns with pte mapped and locked.

   */

  pte_t *page_check_address(struct page *page, struct mm_struct *mm,

  			  unsigned long address, spinlock_t **ptlp, int sync)

  {
  	pgd_t *pgd;
  	pud_t *pud;
  	pmd_t *pmd;
  	pte_t *pte;

  	spinlock_t *ptl;

  	pgd = pgd_offset(mm, address);

  	if (!pgd_present(*pgd))
  		return NULL;
  
  	pud = pud_offset(pgd, address);
  	if (!pud_present(*pud))
  		return NULL;
  
  	pmd = pmd_offset(pud, address);
  	if (!pmd_present(*pmd))
  		return NULL;
  
  	pte = pte_offset_map(pmd, address);
  	/* Make a quick check before getting the lock */

  	if (!sync && !pte_present(*pte)) {

  		pte_unmap(pte);
  		return NULL;
  	}

  	ptl = pte_lockptr(mm, pmd);

  	spin_lock(ptl);
  	if (pte_present(*pte) && page_to_pfn(page) == pte_pfn(*pte)) {
  		*ptlp = ptl;
  		return pte;

  	}

  	pte_unmap_unlock(pte, ptl);
  	return NULL;

  }

  /**
   * page_mapped_in_vma - check whether a page is really mapped in a VMA
   * @page: the page to test
   * @vma: the VMA to test
   *
   * Returns 1 if the page is mapped into the page tables of the VMA, 0
   * if the page is not mapped into the page tables of this VMA.  Only
   * valid for normal file or anonymous VMAs.
   */
  static int page_mapped_in_vma(struct page *page, struct vm_area_struct *vma)
  {
  	unsigned long address;
  	pte_t *pte;
  	spinlock_t *ptl;
  
  	address = vma_address(page, vma);
  	if (address == -EFAULT)		/* out of vma range */
  		return 0;
  	pte = page_check_address(page, vma->vm_mm, address, &ptl, 1);
  	if (!pte)			/* the page is not in this mm */
  		return 0;
  	pte_unmap_unlock(pte, ptl);
  
  	return 1;
  }

  /*

   * Subfunctions of page_referenced: page_referenced_one called
   * repeatedly from either page_referenced_anon or page_referenced_file.
   */
  static int page_referenced_one(struct page *page,

  	struct vm_area_struct *vma, unsigned int *mapcount)

  {
  	struct mm_struct *mm = vma->vm_mm;
  	unsigned long address;

  	pte_t *pte;

  	spinlock_t *ptl;

  	int referenced = 0;

  	address = vma_address(page, vma);
  	if (address == -EFAULT)
  		goto out;

  	pte = page_check_address(page, mm, address, &ptl, 0);

  	if (!pte)
  		goto out;

  	/*
  	 * Don't want to elevate referenced for mlocked page that gets this far,
  	 * in order that it progresses to try_to_unmap and is moved to the
  	 * unevictable list.
  	 */

  	if (vma->vm_flags & VM_LOCKED) {

  		*mapcount = 1;	/* break early from loop */

  		goto out_unmap;
  	}
  
  	if (ptep_clear_flush_young_notify(vma, address, pte))

  		referenced++;

  	/* Pretend the page is referenced if the task has the
  	   swap token and is in the middle of a page fault. */

  	if (mm != current->mm && has_swap_token(mm) &&

  			rwsem_is_locked(&mm->mmap_sem))
  		referenced++;

  out_unmap:

  	(*mapcount)--;
  	pte_unmap_unlock(pte, ptl);

  out:
  	return referenced;
  }

  static int page_referenced_anon(struct page *page,
  				struct mem_cgroup *mem_cont)

  {
  	unsigned int mapcount;
  	struct anon_vma *anon_vma;
  	struct vm_area_struct *vma;
  	int referenced = 0;
  
  	anon_vma = page_lock_anon_vma(page);
  	if (!anon_vma)
  		return referenced;
  
  	mapcount = page_mapcount(page);
  	list_for_each_entry(vma, &anon_vma->head, anon_vma_node) {

  		/*
  		 * If we are reclaiming on behalf of a cgroup, skip
  		 * counting on behalf of references from different
  		 * cgroups
  		 */

  		if (mem_cont && !mm_match_cgroup(vma->vm_mm, mem_cont))

  			continue;

  		referenced += page_referenced_one(page, vma, &mapcount);

  		if (!mapcount)
  			break;
  	}

  
  	page_unlock_anon_vma(anon_vma);

  	return referenced;
  }
  
  /**
   * page_referenced_file - referenced check for object-based rmap
   * @page: the page we're checking references on.

   * @mem_cont: target memory controller

   *
   * For an object-based mapped page, find all the places it is mapped and
   * check/clear the referenced flag.  This is done by following the page->mapping
   * pointer, then walking the chain of vmas it holds.  It returns the number
   * of references it found.
   *
   * This function is only called from page_referenced for object-based pages.
   */

  static int page_referenced_file(struct page *page,
  				struct mem_cgroup *mem_cont)

  {
  	unsigned int mapcount;
  	struct address_space *mapping = page->mapping;
  	pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
  	struct vm_area_struct *vma;
  	struct prio_tree_iter iter;
  	int referenced = 0;
  
  	/*
  	 * The caller's checks on page->mapping and !PageAnon have made
  	 * sure that this is a file page: the check for page->mapping
  	 * excludes the case just before it gets set on an anon page.
  	 */
  	BUG_ON(PageAnon(page));
  
  	/*
  	 * The page lock not only makes sure that page->mapping cannot
  	 * suddenly be NULLified by truncation, it makes sure that the
  	 * structure at mapping cannot be freed and reused yet,
  	 * so we can safely take mapping->i_mmap_lock.
  	 */
  	BUG_ON(!PageLocked(page));
  
  	spin_lock(&mapping->i_mmap_lock);
  
  	/*
  	 * i_mmap_lock does not stabilize mapcount at all, but mapcount
  	 * is more likely to be accurate if we note it after spinning.
  	 */
  	mapcount = page_mapcount(page);
  
  	vma_prio_tree_foreach(vma, &iter, &mapping->i_mmap, pgoff, pgoff) {

  		/*
  		 * If we are reclaiming on behalf of a cgroup, skip
  		 * counting on behalf of references from different
  		 * cgroups
  		 */

  		if (mem_cont && !mm_match_cgroup(vma->vm_mm, mem_cont))

  			continue;

  		referenced += page_referenced_one(page, vma, &mapcount);

  		if (!mapcount)
  			break;
  	}
  
  	spin_unlock(&mapping->i_mmap_lock);
  	return referenced;
  }
  
  /**
   * page_referenced - test if the page was referenced
   * @page: the page to test
   * @is_locked: caller holds lock on the page

   * @mem_cont: target memory controller

   *
   * Quick test_and_clear_referenced for all mappings to a page,
   * returns the number of ptes which referenced the page.
   */

  int page_referenced(struct page *page, int is_locked,
  			struct mem_cgroup *mem_cont)

  {
  	int referenced = 0;

  	if (TestClearPageReferenced(page))
  		referenced++;
  
  	if (page_mapped(page) && page->mapping) {
  		if (PageAnon(page))

  			referenced += page_referenced_anon(page, mem_cont);

  		else if (is_locked)

  			referenced += page_referenced_file(page, mem_cont);

  		else if (!trylock_page(page))

  			referenced++;
  		else {
  			if (page->mapping)

  				referenced +=
  					page_referenced_file(page, mem_cont);

  			unlock_page(page);
  		}
  	}

  
  	if (page_test_and_clear_young(page))
  		referenced++;

  	return referenced;
  }

  static int page_mkclean_one(struct page *page, struct vm_area_struct *vma)
  {
  	struct mm_struct *mm = vma->vm_mm;
  	unsigned long address;

  	pte_t *pte;

  	spinlock_t *ptl;
  	int ret = 0;
  
  	address = vma_address(page, vma);
  	if (address == -EFAULT)
  		goto out;

  	pte = page_check_address(page, mm, address, &ptl, 1);

  	if (!pte)
  		goto out;

  	if (pte_dirty(*pte) || pte_write(*pte)) {
  		pte_t entry;

  		flush_cache_page(vma, address, pte_pfn(*pte));

  		entry = ptep_clear_flush_notify(vma, address, pte);

  		entry = pte_wrprotect(entry);
  		entry = pte_mkclean(entry);

  		set_pte_at(mm, address, pte, entry);

  		ret = 1;
  	}

  	pte_unmap_unlock(pte, ptl);
  out:
  	return ret;
  }
  
  static int page_mkclean_file(struct address_space *mapping, struct page *page)
  {
  	pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
  	struct vm_area_struct *vma;
  	struct prio_tree_iter iter;
  	int ret = 0;
  
  	BUG_ON(PageAnon(page));
  
  	spin_lock(&mapping->i_mmap_lock);
  	vma_prio_tree_foreach(vma, &iter, &mapping->i_mmap, pgoff, pgoff) {
  		if (vma->vm_flags & VM_SHARED)
  			ret += page_mkclean_one(page, vma);
  	}
  	spin_unlock(&mapping->i_mmap_lock);
  	return ret;
  }
  
  int page_mkclean(struct page *page)
  {
  	int ret = 0;
  
  	BUG_ON(!PageLocked(page));
  
  	if (page_mapped(page)) {
  		struct address_space *mapping = page_mapping(page);

  		if (mapping) {

  			ret = page_mkclean_file(mapping, page);

  			if (page_test_dirty(page)) {
  				page_clear_dirty(page);
  				ret = 1;
  			}

  		}

  	}
  
  	return ret;
  }

  EXPORT_SYMBOL_GPL(page_mkclean);

  /**

   * __page_set_anon_rmap - setup new anonymous rmap

   * @page:	the page to add the mapping to
   * @vma:	the vm area in which the mapping is added
   * @address:	the user virtual address mapped
   */
  static void __page_set_anon_rmap(struct page *page,
  	struct vm_area_struct *vma, unsigned long address)
  {
  	struct anon_vma *anon_vma = vma->anon_vma;
  
  	BUG_ON(!anon_vma);
  	anon_vma = (void *) anon_vma + PAGE_MAPPING_ANON;
  	page->mapping = (struct address_space *) anon_vma;
  
  	page->index = linear_page_index(vma, address);

  	/*
  	 * nr_mapped state can be updated without turning off
  	 * interrupts because it is not modified via interrupt.
  	 */

  	__inc_zone_page_state(page, NR_ANON_PAGES);

  }
  
  /**

   * __page_check_anon_rmap - sanity check anonymous rmap addition

   * @page:	the page to add the mapping to
   * @vma:	the vm area in which the mapping is added
   * @address:	the user virtual address mapped
   */
  static void __page_check_anon_rmap(struct page *page,
  	struct vm_area_struct *vma, unsigned long address)
  {
  #ifdef CONFIG_DEBUG_VM
  	/*
  	 * The page's anon-rmap details (mapping and index) are guaranteed to
  	 * be set up correctly at this point.
  	 *
  	 * We have exclusion against page_add_anon_rmap because the caller
  	 * always holds the page locked, except if called from page_dup_rmap,
  	 * in which case the page is already known to be setup.
  	 *
  	 * We have exclusion against page_add_new_anon_rmap because those pages
  	 * are initially only visible via the pagetables, and the pte is locked
  	 * over the call to page_add_new_anon_rmap.
  	 */
  	struct anon_vma *anon_vma = vma->anon_vma;
  	anon_vma = (void *) anon_vma + PAGE_MAPPING_ANON;
  	BUG_ON(page->mapping != (struct address_space *)anon_vma);
  	BUG_ON(page->index != linear_page_index(vma, address));
  #endif
  }
  
  /**

   * page_add_anon_rmap - add pte mapping to an anonymous page
   * @page:	the page to add the mapping to
   * @vma:	the vm area in which the mapping is added
   * @address:	the user virtual address mapped
   *

   * The caller needs to hold the pte lock and the page must be locked.

   */
  void page_add_anon_rmap(struct page *page,
  	struct vm_area_struct *vma, unsigned long address)
  {

  	VM_BUG_ON(!PageLocked(page));
  	VM_BUG_ON(address < vma->vm_start || address >= vma->vm_end);

  	if (atomic_inc_and_test(&page->_mapcount))
  		__page_set_anon_rmap(page, vma, address);

  	else

  		__page_check_anon_rmap(page, vma, address);

  }

  /**

   * page_add_new_anon_rmap - add pte mapping to a new anonymous page
   * @page:	the page to add the mapping to
   * @vma:	the vm area in which the mapping is added
   * @address:	the user virtual address mapped
   *
   * Same as page_add_anon_rmap but must only be called on *new* pages.
   * This means the inc-and-test can be bypassed.

   * Page does not have to be locked.

   */
  void page_add_new_anon_rmap(struct page *page,
  	struct vm_area_struct *vma, unsigned long address)
  {

  	BUG_ON(address < vma->vm_start || address >= vma->vm_end);

  	atomic_set(&page->_mapcount, 0); /* elevate count by 1 (starts at -1) */
  	__page_set_anon_rmap(page, vma, address);
  }

  /**
   * page_add_file_rmap - add pte mapping to a file page
   * @page: the page to add the mapping to
   *

   * The caller needs to hold the pte lock.

   */
  void page_add_file_rmap(struct page *page)
  {

  	if (atomic_inc_and_test(&page->_mapcount))

  		__inc_zone_page_state(page, NR_FILE_MAPPED);

  }

  #ifdef CONFIG_DEBUG_VM
  /**
   * page_dup_rmap - duplicate pte mapping to a page
   * @page:	the page to add the mapping to

   * @vma:	the vm area being duplicated
   * @address:	the user virtual address mapped

   *
   * For copy_page_range only: minimal extract from page_add_file_rmap /
   * page_add_anon_rmap, avoiding unnecessary tests (already checked) so it's
   * quicker.
   *
   * The caller needs to hold the pte lock.
   */
  void page_dup_rmap(struct page *page, struct vm_area_struct *vma, unsigned long address)
  {
  	BUG_ON(page_mapcount(page) == 0);
  	if (PageAnon(page))
  		__page_check_anon_rmap(page, vma, address);
  	atomic_inc(&page->_mapcount);
  }
  #endif

  /**
   * page_remove_rmap - take down pte mapping from a page
   * @page: page to remove mapping from

   * @vma: the vm area in which the mapping is removed

   *

   * The caller needs to hold the pte lock.

   */

  void page_remove_rmap(struct page *page, struct vm_area_struct *vma)

  {

  	if (atomic_add_negative(-1, &page->_mapcount)) {

  		if (unlikely(page_mapcount(page) < 0)) {

  			printk (KERN_EMERG "Eeek! page_mapcount(page) went negative! (%d)
  ", page_mapcount(page));

  			printk (KERN_EMERG "  page pfn = %lx
  ", page_to_pfn(page));

  			printk (KERN_EMERG "  page->flags = %lx
  ", page->flags);
  			printk (KERN_EMERG "  page->count = %x
  ", page_count(page));
  			printk (KERN_EMERG "  page->mapping = %p
  ", page->mapping);

  			print_symbol (KERN_EMERG "  vma->vm_ops = %s
  ", (unsigned long)vma->vm_ops);

  			if (vma->vm_ops) {

  				print_symbol (KERN_EMERG "  vma->vm_ops->fault = %s
  ", (unsigned long)vma->vm_ops->fault);
  			}

  			if (vma->vm_file && vma->vm_file->f_op)
  				print_symbol (KERN_EMERG "  vma->vm_file->f_op->mmap = %s
  ", (unsigned long)vma->vm_file->f_op->mmap);

  			BUG();

  		}

  		/*

  		 * Now that the last pte has gone, s390 must transfer dirty
  		 * flag from storage key to struct page.  We can usually skip
  		 * this if the page is anon, so about to be freed; but perhaps
  		 * not if it's in swapcache - there might be another pte slot
  		 * containing the swap entry, but page not yet written to swap.

  		 */

  		if ((!PageAnon(page) || PageSwapCache(page)) &&
  		    page_test_dirty(page)) {

  			page_clear_dirty(page);

  			set_page_dirty(page);

  		}

  		if (PageAnon(page))
  			mem_cgroup_uncharge_page(page);

  		__dec_zone_page_state(page,

  			PageAnon(page) ? NR_ANON_PAGES : NR_FILE_MAPPED);
  		/*
  		 * It would be tidy to reset the PageAnon mapping here,
  		 * but that might overwrite a racing page_add_anon_rmap
  		 * which increments mapcount after us but sets mapping
  		 * before us: so leave the reset to free_hot_cold_page,
  		 * and remember that it's only reliable while mapped.
  		 * Leaving it set also helps swapoff to reinstate ptes
  		 * faster for those pages still in swapcache.
  		 */

  	}
  }
  
  /*
   * Subfunctions of try_to_unmap: try_to_unmap_one called
   * repeatedly from either try_to_unmap_anon or try_to_unmap_file.
   */

  static int try_to_unmap_one(struct page *page, struct vm_area_struct *vma,

  				int migration)

  {
  	struct mm_struct *mm = vma->vm_mm;
  	unsigned long address;

  	pte_t *pte;
  	pte_t pteval;

  	spinlock_t *ptl;

  	int ret = SWAP_AGAIN;

  	address = vma_address(page, vma);
  	if (address == -EFAULT)
  		goto out;

  	pte = page_check_address(page, mm, address, &ptl, 0);

  	if (!pte)

  		goto out;

  
  	/*
  	 * If the page is mlock()d, we cannot swap it out.
  	 * If it's recently referenced (perhaps page_referenced
  	 * skipped over this mm) then we should reactivate it.
  	 */

  	if (!migration) {
  		if (vma->vm_flags & VM_LOCKED) {
  			ret = SWAP_MLOCK;
  			goto out_unmap;
  		}
  		if (ptep_clear_flush_young_notify(vma, address, pte)) {
  			ret = SWAP_FAIL;
  			goto out_unmap;
  		}
    	}

  	/* Nuke the page table entry. */
  	flush_cache_page(vma, address, page_to_pfn(page));

  	pteval = ptep_clear_flush_notify(vma, address, pte);

  
  	/* Move the dirty bit to the physical page now the pte is gone. */
  	if (pte_dirty(pteval))
  		set_page_dirty(page);

  	/* Update high watermark before we lower rss */
  	update_hiwater_rss(mm);

  	if (PageAnon(page)) {

  		swp_entry_t entry = { .val = page_private(page) };

  
  		if (PageSwapCache(page)) {
  			/*
  			 * Store the swap location in the pte.
  			 * See handle_pte_fault() ...
  			 */
  			swap_duplicate(entry);
  			if (list_empty(&mm->mmlist)) {
  				spin_lock(&mmlist_lock);
  				if (list_empty(&mm->mmlist))
  					list_add(&mm->mmlist, &init_mm.mmlist);
  				spin_unlock(&mmlist_lock);
  			}

  			dec_mm_counter(mm, anon_rss);

  #ifdef CONFIG_MIGRATION

  		} else {
  			/*
  			 * Store the pfn of the page in a special migration
  			 * pte. do_swap_page() will wait until the migration
  			 * pte is removed and then restart fault handling.
  			 */
  			BUG_ON(!migration);
  			entry = make_migration_entry(page, pte_write(pteval));

  #endif

  		}
  		set_pte_at(mm, address, pte, swp_entry_to_pte(entry));
  		BUG_ON(pte_file(*pte));

  	} else

  #ifdef CONFIG_MIGRATION
  	if (migration) {
  		/* Establish migration entry for a file page */
  		swp_entry_t entry;
  		entry = make_migration_entry(page, pte_write(pteval));
  		set_pte_at(mm, address, pte, swp_entry_to_pte(entry));
  	} else
  #endif

  		dec_mm_counter(mm, file_rss);

  	page_remove_rmap(page, vma);

  	page_cache_release(page);
  
  out_unmap:

  	pte_unmap_unlock(pte, ptl);

  out:
  	return ret;
  }
  
  /*
   * objrmap doesn't work for nonlinear VMAs because the assumption that
   * offset-into-file correlates with offset-into-virtual-addresses does not hold.
   * Consequently, given a particular page and its ->index, we cannot locate the
   * ptes which are mapping that page without an exhaustive linear search.
   *
   * So what this code does is a mini "virtual scan" of each nonlinear VMA which
   * maps the file to which the target page belongs.  The ->vm_private_data field
   * holds the current cursor into that scan.  Successive searches will circulate
   * around the vma's virtual address space.
   *
   * So as more replacement pressure is applied to the pages in a nonlinear VMA,
   * more scanning pressure is placed against them as well.   Eventually pages
   * will become fully unmapped and are eligible for eviction.
   *
   * For very sparsely populated VMAs this is a little inefficient - chances are
   * there there won't be many ptes located within the scan cluster.  In this case
   * maybe we could scan further - to the end of the pte page, perhaps.

   *
   * Mlocked pages:  check VM_LOCKED under mmap_sem held for read, if we can
   * acquire it without blocking.  If vma locked, mlock the pages in the cluster,
   * rather than unmapping them.  If we encounter the "check_page" that vmscan is
   * trying to unmap, return SWAP_MLOCK, else default SWAP_AGAIN.

   */
  #define CLUSTER_SIZE	min(32*PAGE_SIZE, PMD_SIZE)
  #define CLUSTER_MASK	(~(CLUSTER_SIZE - 1))

  static int try_to_unmap_cluster(unsigned long cursor, unsigned int *mapcount,
  		struct vm_area_struct *vma, struct page *check_page)

  {
  	struct mm_struct *mm = vma->vm_mm;
  	pgd_t *pgd;
  	pud_t *pud;
  	pmd_t *pmd;

  	pte_t *pte;

  	pte_t pteval;

  	spinlock_t *ptl;

  	struct page *page;
  	unsigned long address;
  	unsigned long end;

  	int ret = SWAP_AGAIN;
  	int locked_vma = 0;

  	address = (vma->vm_start + cursor) & CLUSTER_MASK;
  	end = address + CLUSTER_SIZE;
  	if (address < vma->vm_start)
  		address = vma->vm_start;
  	if (end > vma->vm_end)
  		end = vma->vm_end;
  
  	pgd = pgd_offset(mm, address);
  	if (!pgd_present(*pgd))

  		return ret;

  
  	pud = pud_offset(pgd, address);
  	if (!pud_present(*pud))

  		return ret;

  
  	pmd = pmd_offset(pud, address);
  	if (!pmd_present(*pmd))

  		return ret;
  
  	/*
  	 * MLOCK_PAGES => feature is configured.
  	 * if we can acquire the mmap_sem for read, and vma is VM_LOCKED,
  	 * keep the sem while scanning the cluster for mlocking pages.
  	 */
  	if (MLOCK_PAGES && down_read_trylock(&vma->vm_mm->mmap_sem)) {
  		locked_vma = (vma->vm_flags & VM_LOCKED);
  		if (!locked_vma)
  			up_read(&vma->vm_mm->mmap_sem); /* don't need it */
  	}

  
  	pte = pte_offset_map_lock(mm, pmd, address, &ptl);

  	/* Update high watermark before we lower rss */
  	update_hiwater_rss(mm);

  	for (; address < end; pte++, address += PAGE_SIZE) {

  		if (!pte_present(*pte))
  			continue;

  		page = vm_normal_page(vma, address, *pte);
  		BUG_ON(!page || PageAnon(page));

  		if (locked_vma) {
  			mlock_vma_page(page);   /* no-op if already mlocked */
  			if (page == check_page)
  				ret = SWAP_MLOCK;
  			continue;	/* don't unmap */
  		}

  		if (ptep_clear_flush_young_notify(vma, address, pte))

  			continue;
  
  		/* Nuke the page table entry. */

  		flush_cache_page(vma, address, pte_pfn(*pte));

  		pteval = ptep_clear_flush_notify(vma, address, pte);

  
  		/* If nonlinear, store the file page offset in the pte. */
  		if (page->index != linear_page_index(vma, address))
  			set_pte_at(mm, address, pte, pgoff_to_pte(page->index));
  
  		/* Move the dirty bit to the physical page now the pte is gone. */
  		if (pte_dirty(pteval))
  			set_page_dirty(page);

  		page_remove_rmap(page, vma);

  		page_cache_release(page);

  		dec_mm_counter(mm, file_rss);

  		(*mapcount)--;
  	}

  	pte_unmap_unlock(pte - 1, ptl);

  	if (locked_vma)
  		up_read(&vma->vm_mm->mmap_sem);
  	return ret;

  }

  /*
   * common handling for pages mapped in VM_LOCKED vmas
   */
  static int try_to_mlock_page(struct page *page, struct vm_area_struct *vma)
  {
  	int mlocked = 0;
  
  	if (down_read_trylock(&vma->vm_mm->mmap_sem)) {
  		if (vma->vm_flags & VM_LOCKED) {
  			mlock_vma_page(page);
  			mlocked++;	/* really mlocked the page */
  		}
  		up_read(&vma->vm_mm->mmap_sem);
  	}
  	return mlocked;
  }
  
  /**
   * try_to_unmap_anon - unmap or unlock anonymous page using the object-based
   * rmap method
   * @page: the page to unmap/unlock
   * @unlock:  request for unlock rather than unmap [unlikely]
   * @migration:  unmapping for migration - ignored if @unlock
   *
   * Find all the mappings of a page using the mapping pointer and the vma chains
   * contained in the anon_vma struct it points to.
   *
   * This function is only called from try_to_unmap/try_to_munlock for
   * anonymous pages.
   * When called from try_to_munlock(), the mmap_sem of the mm containing the vma
   * where the page was found will be held for write.  So, we won't recheck
   * vm_flags for that VMA.  That should be OK, because that vma shouldn't be
   * 'LOCKED.
   */
  static int try_to_unmap_anon(struct page *page, int unlock, int migration)

  {
  	struct anon_vma *anon_vma;
  	struct vm_area_struct *vma;

  	unsigned int mlocked = 0;

  	int ret = SWAP_AGAIN;

  	if (MLOCK_PAGES && unlikely(unlock))
  		ret = SWAP_SUCCESS;	/* default for try_to_munlock() */

  	anon_vma = page_lock_anon_vma(page);
  	if (!anon_vma)
  		return ret;
  
  	list_for_each_entry(vma, &anon_vma->head, anon_vma_node) {

  		if (MLOCK_PAGES && unlikely(unlock)) {
  			if (!((vma->vm_flags & VM_LOCKED) &&
  			      page_mapped_in_vma(page, vma)))
  				continue;  /* must visit all unlocked vmas */
  			ret = SWAP_MLOCK;  /* saw at least one mlocked vma */
  		} else {
  			ret = try_to_unmap_one(page, vma, migration);
  			if (ret == SWAP_FAIL || !page_mapped(page))
  				break;
  		}
  		if (ret == SWAP_MLOCK) {
  			mlocked = try_to_mlock_page(page, vma);
  			if (mlocked)
  				break;	/* stop if actually mlocked page */
  		}

  	}

  
  	page_unlock_anon_vma(anon_vma);

  
  	if (mlocked)
  		ret = SWAP_MLOCK;	/* actually mlocked the page */
  	else if (ret == SWAP_MLOCK)
  		ret = SWAP_AGAIN;	/* saw VM_LOCKED vma */

  	return ret;
  }
  
  /**

   * try_to_unmap_file - unmap/unlock file page using the object-based rmap method
   * @page: the page to unmap/unlock
   * @unlock:  request for unlock rather than unmap [unlikely]
   * @migration:  unmapping for migration - ignored if @unlock

   *
   * Find all the mappings of a page using the mapping pointer and the vma chains
   * contained in the address_space struct it points to.
   *

   * This function is only called from try_to_unmap/try_to_munlock for
   * object-based pages.
   * When called from try_to_munlock(), the mmap_sem of the mm containing the vma
   * where the page was found will be held for write.  So, we won't recheck
   * vm_flags for that VMA.  That should be OK, because that vma shouldn't be
   * 'LOCKED.

   */

  static int try_to_unmap_file(struct page *page, int unlock, int migration)

  {
  	struct address_space *mapping = page->mapping;
  	pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
  	struct vm_area_struct *vma;
  	struct prio_tree_iter iter;
  	int ret = SWAP_AGAIN;
  	unsigned long cursor;
  	unsigned long max_nl_cursor = 0;
  	unsigned long max_nl_size = 0;
  	unsigned int mapcount;

  	unsigned int mlocked = 0;
  
  	if (MLOCK_PAGES && unlikely(unlock))
  		ret = SWAP_SUCCESS;	/* default for try_to_munlock() */

  
  	spin_lock(&mapping->i_mmap_lock);
  	vma_prio_tree_foreach(vma, &iter, &mapping->i_mmap, pgoff, pgoff) {

  		if (MLOCK_PAGES && unlikely(unlock)) {
  			if (!(vma->vm_flags & VM_LOCKED))
  				continue;	/* must visit all vmas */
  			ret = SWAP_MLOCK;
  		} else {
  			ret = try_to_unmap_one(page, vma, migration);
  			if (ret == SWAP_FAIL || !page_mapped(page))
  				goto out;
  		}
  		if (ret == SWAP_MLOCK) {
  			mlocked = try_to_mlock_page(page, vma);
  			if (mlocked)
  				break;  /* stop if actually mlocked page */
  		}

  	}

  	if (mlocked)
  		goto out;

  	if (list_empty(&mapping->i_mmap_nonlinear))
  		goto out;
  
  	list_for_each_entry(vma, &mapping->i_mmap_nonlinear,
  						shared.vm_set.list) {

  		if (MLOCK_PAGES && unlikely(unlock)) {
  			if (!(vma->vm_flags & VM_LOCKED))
  				continue;	/* must visit all vmas */
  			ret = SWAP_MLOCK;	/* leave mlocked == 0 */
  			goto out;		/* no need to look further */
  		}
  		if (!MLOCK_PAGES && !migration && (vma->vm_flags & VM_LOCKED))

  			continue;
  		cursor = (unsigned long) vma->vm_private_data;
  		if (cursor > max_nl_cursor)
  			max_nl_cursor = cursor;
  		cursor = vma->vm_end - vma->vm_start;
  		if (cursor > max_nl_size)
  			max_nl_size = cursor;
  	}

  	if (max_nl_size == 0) {	/* all nonlinears locked or reserved ? */

  		ret = SWAP_FAIL;
  		goto out;
  	}
  
  	/*
  	 * We don't try to search for this page in the nonlinear vmas,
  	 * and page_referenced wouldn't have found it anyway.  Instead
  	 * just walk the nonlinear vmas trying to age and unmap some.
  	 * The mapcount of the page we came in with is irrelevant,
  	 * but even so use it as a guide to how hard we should try?
  	 */
  	mapcount = page_mapcount(page);
  	if (!mapcount)
  		goto out;
  	cond_resched_lock(&mapping->i_mmap_lock);
  
  	max_nl_size = (max_nl_size + CLUSTER_SIZE - 1) & CLUSTER_MASK;
  	if (max_nl_cursor == 0)
  		max_nl_cursor = CLUSTER_SIZE;
  
  	do {
  		list_for_each_entry(vma, &mapping->i_mmap_nonlinear,
  						shared.vm_set.list) {

  			if (!MLOCK_PAGES && !migration &&
  			    (vma->vm_flags & VM_LOCKED))

  				continue;
  			cursor = (unsigned long) vma->vm_private_data;

  			while ( cursor < max_nl_cursor &&

  				cursor < vma->vm_end - vma->vm_start) {

  				ret = try_to_unmap_cluster(cursor, &mapcount,
  								vma, page);
  				if (ret == SWAP_MLOCK)
  					mlocked = 2;	/* to return below */

  				cursor += CLUSTER_SIZE;
  				vma->vm_private_data = (void *) cursor;
  				if ((int)mapcount <= 0)
  					goto out;
  			}
  			vma->vm_private_data = (void *) max_nl_cursor;
  		}
  		cond_resched_lock(&mapping->i_mmap_lock);
  		max_nl_cursor += CLUSTER_SIZE;
  	} while (max_nl_cursor <= max_nl_size);
  
  	/*
  	 * Don't loop forever (perhaps all the remaining pages are
  	 * in locked vmas).  Reset cursor on all unreserved nonlinear
  	 * vmas, now forgetting on which ones it had fallen behind.
  	 */

  	list_for_each_entry(vma, &mapping->i_mmap_nonlinear, shared.vm_set.list)
  		vma->vm_private_data = NULL;

  out:
  	spin_unlock(&mapping->i_mmap_lock);

  	if (mlocked)
  		ret = SWAP_MLOCK;	/* actually mlocked the page */
  	else if (ret == SWAP_MLOCK)
  		ret = SWAP_AGAIN;	/* saw VM_LOCKED vma */

  	return ret;
  }
  
  /**
   * try_to_unmap - try to remove all page table mappings to a page
   * @page: the page to get unmapped

   * @migration: migration flag

   *
   * Tries to remove all the page table entries which are mapping this
   * page, used in the pageout path.  Caller must hold the page lock.
   * Return values are:
   *
   * SWAP_SUCCESS	- we succeeded in removing all mappings
   * SWAP_AGAIN	- we missed a mapping, try again later
   * SWAP_FAIL	- the page is unswappable

   * SWAP_MLOCK	- page is mlocked.

   */

  int try_to_unmap(struct page *page, int migration)

  {
  	int ret;

  	BUG_ON(!PageLocked(page));
  
  	if (PageAnon(page))

  		ret = try_to_unmap_anon(page, 0, migration);

  	else

  		ret = try_to_unmap_file(page, 0, migration);
  	if (ret != SWAP_MLOCK && !page_mapped(page))

  		ret = SWAP_SUCCESS;
  	return ret;
  }

  #ifdef CONFIG_UNEVICTABLE_LRU
  /**
   * try_to_munlock - try to munlock a page
   * @page: the page to be munlocked
   *
   * Called from munlock code.  Checks all of the VMAs mapping the page
   * to make sure nobody else has this page mlocked. The page will be
   * returned with PG_mlocked cleared if no other vmas have it mlocked.
   *
   * Return values are:
   *
   * SWAP_SUCCESS	- no vma's holding page mlocked.
   * SWAP_AGAIN	- page mapped in mlocked vma -- couldn't acquire mmap sem
   * SWAP_MLOCK	- page is now mlocked.
   */
  int try_to_munlock(struct page *page)
  {
  	VM_BUG_ON(!PageLocked(page) || PageLRU(page));
  
  	if (PageAnon(page))
  		return try_to_unmap_anon(page, 1, 0);
  	else
  		return try_to_unmap_file(page, 1, 0);
  }
  #endif