ClabureDB: Classified Bug-Reports Database

   /*
    * 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)\n", page_mapcount(page));
                         printk (KERN_EMERG "  page pfn = %lx\n", page_to_pfn(page));
                         printk (KERN_EMERG "  page->flags = %lx\n", page->flags);
                         printk (KERN_EMERG "  page->count = %x\n", page_count(page));
                         printk (KERN_EMERG "  page->mapping = %p\n", page->mapping);
                         print_symbol (KERN_EMERG "  vma->vm_ops = %s\n", (unsigned long)vma->vm_ops);
                         if (vma->vm_ops) {
                                 print_symbol (KERN_EMERG "  vma->vm_ops->fault = %s\n", (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\n", (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