Linux 2.6.17-rc6

[linux-2.6/next.git] / 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 <clameter@sgi.com>
 */

#include <linux/migrate.h>
#include <linux/module.h>
#include <linux/swap.h>
#include <linux/pagemap.h>
#include <linux/buffer_head.h>
#include <linux/mm_inline.h>
#include <linux/pagevec.h>
#include <linux/rmap.h>
#include <linux/topology.h>
#include <linux/cpu.h>
#include <linux/cpuset.h>
#include <linux/swapops.h>

#include "internal.h"

/* The maximum number of pages to take off the LRU for migration */
#define MIGRATE_CHUNK_SIZE 256

#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)) {
                        ret = 0;
                        get_page(page);
                        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 after we have compiled the list of pages
 * to be migrated using isolate_lru_page() but before we begin a series of calls
 * to migrate_pages().
 */
int migrate_prep(void)
{
        /* Must have swap device for migration */
        if (nr_swap_pages <= 0)
                return -ENODEV;

        /*
         * 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)
{
        list_del(&page->lru);
        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) {
                move_to_lru(page);
                count++;
        }
        return count;
}

/*
 * Non migratable page
 */
int fail_migrate_page(struct page *newpage, struct page *page)
{
        return -EIO;
}
EXPORT_SYMBOL(fail_migrate_page);

/*
 * swapout a single page
 * page is locked upon entry, unlocked on exit
 */
static int swap_page(struct page *page)
{
        struct address_space *mapping = page_mapping(page);

        if (page_mapped(page) && mapping)
                if (try_to_unmap(page, 1) != SWAP_SUCCESS)
                        goto unlock_retry;

        if (PageDirty(page)) {
                /* Page is dirty, try to write it out here */
                switch(pageout(page, mapping)) {
                case PAGE_KEEP:
                case PAGE_ACTIVATE:
                        goto unlock_retry;

                case PAGE_SUCCESS:
                        goto retry;

                case PAGE_CLEAN:
                        ; /* try to free the page below */
                }
        }

        if (PagePrivate(page)) {
                if (!try_to_release_page(page, GFP_KERNEL) ||
                    (!mapping && page_count(page) == 1))
                        goto unlock_retry;
        }

        if (remove_mapping(mapping, page)) {
                /* Success */
                unlock_page(page);
                return 0;
        }

unlock_retry:
        unlock_page(page);

retry:
        return -EAGAIN;
}

/*
 * Remove references for a page and establish the new page with the correct
 * basic settings to be able to stop accesses to the page.
 */
int migrate_page_remove_references(struct page *newpage,
                                struct page *page, int nr_refs)
{
        struct address_space *mapping = page_mapping(page);
        struct page **radix_pointer;

        /*
         * Avoid doing any of the following work if the page count
         * indicates that the page is in use or truncate has removed
         * the page.
         */
        if (!mapping || page_mapcount(page) + nr_refs != page_count(page))
                return -EAGAIN;

        /*
         * Establish swap ptes for anonymous pages or destroy pte
         * maps for files.
         *
         * In order to reestablish file backed mappings the fault handlers
         * will take the radix tree_lock which may then be used to stop
         * processses from accessing this page until the new page is ready.
         *
         * A process accessing via a swap pte (an anonymous page) will take a
         * page_lock on the old page which will block the process until the
         * migration attempt is complete. At that time the PageSwapCache bit
         * will be examined. If the page was migrated then the PageSwapCache
         * bit will be clear and the operation to retrieve the page will be
         * retried which will find the new page in the radix tree. Then a new
         * direct mapping may be generated based on the radix tree contents.
         *
         * If the page was not migrated then the PageSwapCache bit
         * is still set and the operation may continue.
         */
        if (try_to_unmap(page, 1) == SWAP_FAIL)
                /* A vma has VM_LOCKED set -> permanent failure */
                return -EPERM;

        /*
         * Give up if we were unable to remove all mappings.
         */
        if (page_mapcount(page))
                return -EAGAIN;

        write_lock_irq(&mapping->tree_lock);

        radix_pointer = (struct page **)radix_tree_lookup_slot(
                                                &mapping->page_tree,
                                                page_index(page));

        if (!page_mapping(page) || page_count(page) != nr_refs ||
                        *radix_pointer != page) {
                write_unlock_irq(&mapping->tree_lock);
                return -EAGAIN;
        }

        /*
         * Now we know that no one else is looking at the page.
         *
         * Certain minimal information about a page must be available
         * in order for other subsystems to properly handle the page if they
         * find it through the radix tree update before we are finished
         * copying the page.
         */
        get_page(newpage);
        newpage->index = page->index;
        newpage->mapping = page->mapping;
        if (PageSwapCache(page)) {
                SetPageSwapCache(newpage);
                set_page_private(newpage, page_private(page));
        }

        *radix_pointer = newpage;
        __put_page(page);
        write_unlock_irq(&mapping->tree_lock);

        return 0;
}
EXPORT_SYMBOL(migrate_page_remove_references);

/*
 * Copy the page to its new location
 */
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);
        }

        ClearPageSwapCache(page);
        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);
}
EXPORT_SYMBOL(migrate_page_copy);

/*
 * 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 page *newpage, struct page *page)
{
        int rc;

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

        rc = migrate_page_remove_references(newpage, page, 2);

        if (rc)
                return rc;

        migrate_page_copy(newpage, page);

        /*
         * Remove auxiliary swap entries and replace
         * them with real ptes.
         *
         * Note that a real pte entry will allow processes that are not
         * waiting on the page lock to use the new page via the page tables
         * before the new page is unlocked.
         */
        remove_from_swap(newpage);
        return 0;
}
EXPORT_SYMBOL(migrate_page);

/*
 * migrate_pages
 *
 * Two lists are passed to this function. The first list
 * contains the pages isolated from the LRU to be migrated.
 * The second list contains new pages that the pages isolated
 * can be moved to. If the second list is NULL then all
 * pages are swapped out.
 *
 * The function returns after 10 attempts or if no pages
 * are movable anymore because to has become empty
 * or no retryable pages exist anymore.
 *
 * Return: Number of pages not migrated when "to" ran empty.
 */
int migrate_pages(struct list_head *from, struct list_head *to,
                  struct list_head *moved, struct list_head *failed)
{
        int retry;
        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;

redo:
        retry = 0;

        list_for_each_entry_safe(page, page2, from, lru) {
                struct page *newpage = NULL;
                struct address_space *mapping;

                cond_resched();

                rc = 0;
                if (page_count(page) == 1)
                        /* page was freed from under us. So we are done. */
                        goto next;

                if (to && list_empty(to))
                        break;

                /*
                 * Skip locked pages during the first two passes to give the
                 * functions holding the lock time to release the page. Later we
                 * use lock_page() to have a higher chance of acquiring the
                 * lock.
                 */
                rc = -EAGAIN;
                if (pass > 2)
                        lock_page(page);
                else
                        if (TestSetPageLocked(page))
                                goto next;

                /*
                 * Only wait on writeback if we have already done a pass where
                 * we we may have triggered writeouts for lots of pages.
                 */
                if (pass > 0) {
                        wait_on_page_writeback(page);
                } else {
                        if (PageWriteback(page))
                                goto unlock_page;
                }

                /*
                 * Anonymous pages must have swap cache references otherwise
                 * the information contained in the page maps cannot be
                 * preserved.
                 */
                if (PageAnon(page) && !PageSwapCache(page)) {
                        if (!add_to_swap(page, GFP_KERNEL)) {
                                rc = -ENOMEM;
                                goto unlock_page;
                        }
                }

                if (!to) {
                        rc = swap_page(page);
                        goto next;
                }

                newpage = lru_to_page(to);
                lock_page(newpage);

                /*
                 * Pages are properly locked and writeback is complete.
                 * Try to migrate the page.
                 */
                mapping = page_mapping(page);
                if (!mapping)
                        goto unlock_both;

                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(newpage, page);
                        goto unlock_both;
                }

                /* Make sure the dirty bit is up to date */
                if (try_to_unmap(page, 1) == SWAP_FAIL) {
                        rc = -EPERM;
                        goto unlock_both;
                }

                if (page_mapcount(page)) {
                        rc = -EAGAIN;
                        goto unlock_both;
                }

                /*
                 * Default handling if a filesystem does not provide
                 * a migration function. We can only migrate clean
                 * pages so try to write out any dirty pages first.
                 */
                if (PageDirty(page)) {
                        switch (pageout(page, mapping)) {
                        case PAGE_KEEP:
                        case PAGE_ACTIVATE:
                                goto unlock_both;

                        case PAGE_SUCCESS:
                                unlock_page(newpage);
                                goto next;

                        case PAGE_CLEAN:
                                ; /* try to migrate the page below */
                        }
                }

                /*
                 * Buffers are managed in a filesystem specific way.
                 * We must have no buffers or drop them.
                 */
                if (!page_has_buffers(page) ||
                    try_to_release_page(page, GFP_KERNEL)) {
                        rc = migrate_page(newpage, page);
                        goto unlock_both;
                }

                /*
                 * On early passes with mapped pages simply
                 * retry. There may be a lock held for some
                 * buffers that may go away. Later
                 * swap them out.
                 */
                if (pass > 4) {
                        /*
                         * Persistently unable to drop buffers..... As a
                         * measure of last resort we fall back to
                         * swap_page().
                         */
                        unlock_page(newpage);
                        newpage = NULL;
                        rc = swap_page(page);
                        goto next;
                }

unlock_both:
                unlock_page(newpage);

unlock_page:
                unlock_page(page);

next:
                if (rc == -EAGAIN) {
                        retry++;
                } else if (rc) {
                        /* Permanent failure */
                        list_move(&page->lru, failed);
                        nr_failed++;
                } else {
                        if (newpage) {
                                /* Successful migration. Return page to LRU */
                                move_to_lru(newpage);
                        }
                        list_move(&page->lru, moved);
                }
        }
        if (retry && pass++ < 10)
                goto redo;

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

        return nr_failed + retry;
}

/*
 * 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 page *newpage, struct page *page)
{
        struct address_space *mapping = page->mapping;
        struct buffer_head *bh, *head;
        int rc;

        if (!mapping)
                return -EAGAIN;

        if (!page_has_buffers(page))
                return migrate_page(newpage, page);

        head = page_buffers(page);

        rc = migrate_page_remove_references(newpage, page, 3);

        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);

/*
 * Migrate the list 'pagelist' of pages to a certain destination.
 *
 * Specify destination with either non-NULL vma or dest_node >= 0
 * Return the number of pages not migrated or error code
 */
int migrate_pages_to(struct list_head *pagelist,
                        struct vm_area_struct *vma, int dest)
{
        LIST_HEAD(newlist);
        LIST_HEAD(moved);
        LIST_HEAD(failed);
        int err = 0;
        unsigned long offset = 0;
        int nr_pages;
        struct page *page;
        struct list_head *p;

redo:
        nr_pages = 0;
        list_for_each(p, pagelist) {
                if (vma) {
                        /*
                         * The address passed to alloc_page_vma is used to
                         * generate the proper interleave behavior. We fake
                         * the address here by an increasing offset in order
                         * to get the proper distribution of pages.
                         *
                         * No decision has been made as to which page
                         * a certain old page is moved to so we cannot
                         * specify the correct address.
                         */
                        page = alloc_page_vma(GFP_HIGHUSER, vma,
                                        offset + vma->vm_start);
                        offset += PAGE_SIZE;
                }
                else
                        page = alloc_pages_node(dest, GFP_HIGHUSER, 0);

                if (!page) {
                        err = -ENOMEM;
                        goto out;
                }
                list_add_tail(&page->lru, &newlist);
                nr_pages++;
                if (nr_pages > MIGRATE_CHUNK_SIZE)
                        break;
        }
        err = migrate_pages(pagelist, &newlist, &moved, &failed);

        putback_lru_pages(&moved);      /* Call release pages instead ?? */

        if (err >= 0 && list_empty(&newlist) && !list_empty(pagelist))
                goto redo;
out:
        /* Return leftover allocated pages */
        while (!list_empty(&newlist)) {
                page = list_entry(newlist.next, struct page, lru);
                list_del(&page->lru);
                __free_page(page);
        }
        list_splice(&failed, pagelist);
        if (err < 0)
                return err;

        /* Calculate number of leftover pages */
        nr_pages = 0;
        list_for_each(p, pagelist)
                nr_pages++;
        return nr_pages;
}