mm: speculative page references

[safe/jmp/linux-2.6] / mm / 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
 */

#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 <linux/memcontrol.h>
#include <linux/syscalls.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;
}

/*
 * 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;

        /*
         * Yes, ignore the return value from a GFP_ATOMIC mem_cgroup_charge.
         * Failure is not an option here: we're now expected to remove every
         * migration pte, and will cause crashes otherwise.  Normally this
         * is not an issue: mem_cgroup_prepare_migration bumped up the old
         * page_cgroup count for safety, that's now attached to the new page,
         * so this charge should just be another incrementation of the count,
         * to keep in balance with rmap.c's mem_cgroup_uncharging.  But if
         * there's been a force_empty, those reference counts may no longer
         * be reliable, and this charge can actually fail: oh well, we don't
         * make the situation any worse by proceeding as if it had succeeded.
         */
        mem_cgroup_charge(new, mm, GFP_ATOMIC);

        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);

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

/*
 * Replace the page in the mapping.
 *
 * The number of remaining references must be:
 * 1 for anonymous pages without a mapping
 * 2 for pages with a mapping
 * 3 for pages with a mapping and PagePrivate set.
 */
static int migrate_page_move_mapping(struct address_space *mapping,
                struct page *newpage, struct page *page)
{
        int expected_count;
        void **pslot;

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

        write_lock_irq(&mapping->tree_lock);

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

        expected_count = 2 + !!PagePrivate(page);
        if (page_count(page) != expected_count ||
                        (struct page *)radix_tree_deref_slot(pslot) != page) {
                write_unlock_irq(&mapping->tree_lock);
                return -EAGAIN;
        }

        if (!page_freeze_refs(page, expected_count)) {
                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);

        page_unfreeze_refs(page, expected_count);
        /*
         * Drop cache reference from old page.
         * We know this isn't the last reference.
         */
        __put_page(page);

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

        write_unlock_irq(&mapping->tree_lock);
        if (!PageSwapCache(newpage)) {
                mem_cgroup_uncharge_cache_page(page);
        }

        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);
                /*
                 * Want to mark the page and the radix tree as dirty, and
                 * redo the accounting that clear_page_dirty_for_io undid,
                 * but we can't use set_page_dirty because that function
                 * is actually a signal that all of the page has become dirty.
                 * Wheras only part of our page may be dirty.
                 */
                __set_page_dirty_nobuffers(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;
        int charge = 0;

        if (!newpage)
                return -ENOMEM;

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

        charge = mem_cgroup_prepare_migration(page, newpage);
        if (charge == -ENOMEM) {
                rc = -ENOMEM;
                goto move_newpage;
        }
        /* prepare cgroup just returns 0 or -ENOMEM */
        BUG_ON(charge);

        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;
        }

        /*
         * Corner case handling:
         * 1. When a new swap-cache page is read into, it is added to the LRU
         * and treated as swapcache but it has no rmap yet.
         * Calling try_to_unmap() against a page->mapping==NULL page will
         * trigger a BUG.  So handle it here.
         * 2. An orphaned page (see truncate_complete_page) might have
         * fs-private metadata. The page can be picked up due to memory
         * offlining.  Everywhere else except page reclaim, the page is
         * invisible to the vm, so the page can not be migrated.  So try to
         * free the metadata, so the page can be freed.
         */
        if (!page->mapping) {
                if (!PageAnon(page) && PagePrivate(page)) {
                        /*
                         * Go direct to try_to_free_buffers() here because
                         * a) that's what try_to_release_page() would do anyway
                         * b) we may be under rcu_read_lock() here, so we can't
                         *    use GFP_KERNEL which is what try_to_release_page()
                         *    needs to be effective.
                         */
                        try_to_free_buffers(page);
                }
                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:
        if (!charge)
                mem_cgroup_end_migration(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 = PTR_ERR(page);
                if (IS_ERR(page))
                        goto set_status;

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

                err = -ENOENT;
                /* Use PageReserved to check for zero page */
                if (!page || PageReserved(page))
                        goto set_status;

                err = page_to_nid(page);
set_status:
                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;
}

/*
 * 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;
}
#endif