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migrate.c

/*
 * 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 <clameter@sgi.com>
 */

#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/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 "internal.h"

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

/*
 * Isolate one page from the LRU lists. If successful put it onto
 * the indicated list with elevated page count.
 *
 * Result:
 *  -EBUSY: page not on LRU list
 *  0: page removed from LRU list and added to the specified list.
 */
int isolate_lru_page(struct page *page, struct list_head *pagelist)
{
      int ret = -EBUSY;

      if (PageLRU(page)) {
            struct zone *zone = page_zone(page);

            spin_lock_irq(&zone->lru_lock);
            if (PageLRU(page) && get_page_unless_zero(page)) {
                  ret = 0;
                  ClearPageLRU(page);
                  if (PageActive(page))
                        del_page_from_active_list(zone, page);
                  else
                        del_page_from_inactive_list(zone, page);
                  list_add_tail(&page->lru, pagelist);
            }
            spin_unlock_irq(&zone->lru_lock);
      }
      return ret;
}

/*
 * migrate_prep() needs to be called before we start compiling a list of pages
 * to be migrated using isolate_lru_page().
 */
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;
}

static inline void move_to_lru(struct page *page)
{
      if (PageActive(page)) {
            /*
             * lru_cache_add_active checks that
             * the PG_active bit is off.
             */
            ClearPageActive(page);
            lru_cache_add_active(page);
      } else {
            lru_cache_add(page);
      }
      put_page(page);
}

/*
 * Add isolated pages on the list back to the LRU.
 *
 * returns the number of pages put back.
 */
int putback_lru_pages(struct list_head *l)
{
      struct page *page;
      struct page *page2;
      int count = 0;

      list_for_each_entry_safe(page, page2, l, lru) {
            list_del(&page->lru);
            move_to_lru(page);
            count++;
      }
      return count;
}

static inline int is_swap_pte(pte_t pte)
{
      return !pte_none(pte) && !pte_present(pte) && !pte_file(pte);
}

/*
 * Restore a potential migration pte to a working pte entry
 */
static void remove_migration_pte(struct vm_area_struct *vma,
            struct page *old, struct page *new)
{
      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;
      unsigned long addr = page_address_in_vma(new, vma);

      if (addr == -EFAULT)
            return;

      pgd = pgd_offset(mm, addr);
      if (!pgd_present(*pgd))
                return;

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

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

      ptep = pte_offset_map(pmd, addr);

      if (!is_swap_pte(*ptep)) {
            pte_unmap(ptep);
            return;
      }

      ptl = pte_lockptr(mm, pmd);
      spin_lock(ptl);
      pte = *ptep;
      if (!is_swap_pte(pte))
            goto out;

      entry = pte_to_swp_entry(pte);

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

      get_page(new);
      pte = pte_mkold(mk_pte(new, vma->vm_page_prot));
      if (is_write_migration_entry(entry))
            pte = pte_mkwrite(pte);
      flush_cache_page(vma, addr, pte_pfn(pte));
      set_pte_at(mm, addr, ptep, pte);

      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, pte);

out:
      pte_unmap_unlock(ptep, ptl);
}

/*
 * Note that remove_file_migration_ptes will only work on regular mappings,
 * Nonlinear mappings do not use migration entries.
 */
static void remove_file_migration_ptes(struct page *old, struct page *new)
{
      struct vm_area_struct *vma;
      struct address_space *mapping = page_mapping(new);
      struct prio_tree_iter iter;
      pgoff_t pgoff = new->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);

      if (!mapping)
            return;

      spin_lock(&mapping->i_mmap_lock);

      vma_prio_tree_foreach(vma, &iter, &mapping->i_mmap, pgoff, pgoff)
            remove_migration_pte(vma, old, new);

      spin_unlock(&mapping->i_mmap_lock);
}

/*
 * Must hold mmap_sem lock on at least one of the vmas containing
 * the page so that the anon_vma cannot vanish.
 */
static void remove_anon_migration_ptes(struct page *old, struct page *new)
{
      struct anon_vma *anon_vma;
      struct vm_area_struct *vma;
      unsigned long mapping;

      mapping = (unsigned long)new->mapping;

      if (!mapping || (mapping & PAGE_MAPPING_ANON) == 0)
            return;

      /*
       * We hold the mmap_sem lock. So no need to call page_lock_anon_vma.
       */
      anon_vma = (struct anon_vma *) (mapping - PAGE_MAPPING_ANON);
      spin_lock(&anon_vma->lock);

      list_for_each_entry(vma, &anon_vma->head, anon_vma_node)
            remove_migration_pte(vma, old, new);

      spin_unlock(&anon_vma->lock);
}

/*
 * 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)
{
      if (PageAnon(new))
            remove_anon_migration_ptes(old, new);
      else
            remove_file_migration_ptes(old, new);
}

/*
 * 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);

      get_page(page);
      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 set.
 */
static int migrate_page_move_mapping(struct address_space *mapping,
            struct page *newpage, struct page *page)
{
      void **pslot;

      if (!mapping) {
            /* Anonymous page without mapping */
            if (page_count(page) != 1)
                  return -EAGAIN;
            return 0;
      }

      write_lock_irq(&mapping->tree_lock);

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

      if (page_count(page) != 2 + !!PagePrivate(page) ||
                  (struct page *)radix_tree_deref_slot(pslot) != page) {
            write_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 */
#ifdef CONFIG_SWAP
      if (PageSwapCache(page)) {
            SetPageSwapCache(newpage);
            set_page_private(newpage, page_private(page));
      }
#endif

      radix_tree_replace_slot(pslot, newpage);

      /*
       * 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);

      write_unlock_irq(&mapping->tree_lock);

      return 0;
}

/*
 * Copy the page to its new location
 */
static void migrate_page_copy(struct page *newpage, struct page *page)
{
      copy_highpage(newpage, page);

      if (PageError(page))
            SetPageError(newpage);
      if (PageReferenced(page))
            SetPageReferenced(newpage);
      if (PageUptodate(page))
            SetPageUptodate(newpage);
      if (PageActive(page))
            SetPageActive(newpage);
      if (PageChecked(page))
            SetPageChecked(newpage);
      if (PageMappedToDisk(page))
            SetPageMappedToDisk(newpage);

      if (PageDirty(page)) {
            clear_page_dirty_for_io(page);
            set_page_dirty(newpage);
      }

#ifdef CONFIG_SWAP
      ClearPageSwapCache(page);
#endif
      ClearPageActive(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.
 *
 * 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,
            .nonblocking = 1,
            .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 < 0)
            /* I/O Error writing */
            return -EIO;

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

      return -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 (PagePrivate(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.
 */
static int move_to_new_page(struct page *newpage, struct page *page)
{
      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 (TestSetPageLocked(newpage))
            BUG();

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

      mapping = page_mapping(page);
      if (!mapping)
            rc = migrate_page(mapping, newpage, page);
      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)
            remove_migration_ptes(page, newpage);
      else
            newpage->mapping = NULL;

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

      if (!newpage)
            return -ENOMEM;

      if (page_count(page) == 1)
            /* page was freed from under us. So we are done. */
            goto move_newpage;

      rc = -EAGAIN;
      if (TestSetPageLocked(page)) {
            if (!force)
                  goto move_newpage;
            lock_page(page);
      }

      if (PageWriteback(page)) {
            if (!force)
                  goto unlock;
            wait_on_page_writeback(page);
      }
      /*
       * By try_to_unmap(), page->mapcount goes down to 0 here. In this case,
       * we cannot notice that anon_vma is freed while we migrates a page.
       * This rcu_read_lock() 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)) {
            rcu_read_lock();
            rcu_locked = 1;
      }
      /*
       * This is a corner case handling.
       * When a new swap-cache is read into, it is linked to LRU
       * and treated as swapcache but has no rmap yet.
       * Calling try_to_unmap() against a page->mapping==NULL page is
       * BUG. So handle it here.
       */
      if (!page->mapping)
            goto rcu_unlock;
      /* Establish migration ptes or remove ptes */
      try_to_unmap(page, 1);

      if (!page_mapped(page))
            rc = move_to_new_page(newpage, page);

      if (rc)
            remove_migration_ptes(page, page);
rcu_unlock:
      if (rcu_locked)
            rcu_read_unlock();

unlock:

      unlock_page(page);

      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);
            move_to_lru(page);
      }

move_newpage:
      /*
       * Move the new page to the LRU. If migration was not successful
       * then this will free the page.
       */
      move_to_lru(newpage);
      if (result) {
            if (rc)
                  *result = rc;
            else
                  *result = page_to_nid(newpage);
      }
      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. All pages will be
 * returned to the LRU or freed.
 *
 * 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)
{
      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);

                  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;

      putback_lru_pages(from);

      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_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.
 */
static int do_move_pages(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
       */
      migrate_prep();
      for (pp = pm; pp->node != MAX_NUMNODES; pp++) {
            struct vm_area_struct *vma;
            struct page *page;

            /*
             * A valid page pointer that will not match any of the
             * pages that will be moved.
             */
            pp->page = ZERO_PAGE(0);

            err = -EFAULT;
            vma = find_vma(mm, pp->addr);
            if (!vma || !vma_migratable(vma))
                  goto set_status;

            page = follow_page(vma, pp->addr, FOLL_GET);
            err = -ENOENT;
            if (!page)
                  goto set_status;

            if (PageReserved(page))       /* Check for zero 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, &pagelist);
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;
      }

      if (!list_empty(&pagelist))
            err = migrate_pages(&pagelist, new_page_node,
                        (unsigned long)pm);
      else
            err = -ENOENT;

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

/*
 * Determine the nodes of a list of pages. The addr in the pm array
 * must have been set to the virtual address of which we want to determine
 * the node number.
 */
static int do_pages_stat(struct mm_struct *mm, struct page_to_node *pm)
{
      down_read(&mm->mmap_sem);

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

            err = -EFAULT;
            vma = find_vma(mm, pm->addr);
            if (!vma)
                  goto set_status;

            page = follow_page(vma, pm->addr, 0);
            err = -ENOENT;
            /* Use PageReserved to check for zero page */
            if (!page || PageReserved(page))
                  goto set_status;

            err = page_to_nid(page);
set_status:
            pm->status = err;
      }

      up_read(&mm->mmap_sem);
      return 0;
}

/*
 * Move a list of pages in the address space of the currently executing
 * process.
 */
asmlinkage long sys_move_pages(pid_t pid, unsigned long nr_pages,
                  const void __user * __user *pages,
                  const int __user *nodes,
                  int __user *status, int flags)
{
      int err = 0;
      int i;
      struct task_struct *task;
      nodemask_t task_nodes;
      struct mm_struct *mm;
      struct page_to_node *pm = NULL;

      /* 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 */
      read_lock(&tasklist_lock);
      task = pid ? find_task_by_vpid(pid) : current;
      if (!task) {
            read_unlock(&tasklist_lock);
            return -ESRCH;
      }
      mm = get_task_mm(task);
      read_unlock(&tasklist_lock);

      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.
       */
      if ((current->euid != task->suid) && (current->euid != task->uid) &&
          (current->uid != task->suid) && (current->uid != task->uid) &&
          !capable(CAP_SYS_NICE)) {
            err = -EPERM;
            goto out2;
      }

      err = security_task_movememory(task);
      if (err)
            goto out2;


      task_nodes = cpuset_mems_allowed(task);

      /* Limit nr_pages so that the multiplication may not overflow */
      if (nr_pages >= ULONG_MAX / sizeof(struct page_to_node) - 1) {
            err = -E2BIG;
            goto out2;
      }

      pm = vmalloc((nr_pages + 1) * sizeof(struct page_to_node));
      if (!pm) {
            err = -ENOMEM;
            goto out2;
      }

      /*
       * Get parameters from user space and initialize the pm
       * array. Return various errors if the user did something wrong.
       */
      for (i = 0; i < nr_pages; i++) {
            const void __user *p;

            err = -EFAULT;
            if (get_user(p, pages + i))
                  goto out;

            pm[i].addr = (unsigned long)p;
            if (nodes) {
                  int node;

                  if (get_user(node, nodes + i))
                        goto out;

                  err = -ENODEV;
                  if (!node_state(node, N_HIGH_MEMORY))
                        goto out;

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

                  pm[i].node = node;
            } else
                  pm[i].node = 0;   /* anything to not match MAX_NUMNODES */
      }
      /* End marker */
      pm[nr_pages].node = MAX_NUMNODES;

      if (nodes)
            err = do_move_pages(mm, pm, flags & MPOL_MF_MOVE_ALL);
      else
            err = do_pages_stat(mm, pm);

      if (err >= 0)
            /* Return status information */
            for (i = 0; i < nr_pages; i++)
                  if (put_user(pm[i].status, status + i))
                        err = -EFAULT;

out:
      vfree(pm);
out2:
      mmput(mm);
      return err;
}
#endif

/*
 * 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->vm_next && !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;
}

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