[PATCH] page migration reorg

Centralize the page migration functions in anticipation of additional
tinkering.  Creates a new file mm/migrate.c

1. Extract buffer_migrate_page() from fs/buffer.c

2. Extract central migration code from vmscan.c

3. Extract some components from mempolicy.c

4. Export pageout() and remove_from_swap() from vmscan.c

5. Make it possible to configure NUMA systems without page migration
   and non-NUMA systems with page migration.

I had to so some #ifdeffing in mempolicy.c that may need a cleanup.

Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 2 insertions, 489 deletions

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 548e023c193b..fd572bbdc9f5 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -42,18 +42,6 @@
 
 #include "internal.h"
 
-/* possible outcome of pageout() */
-typedef enum {
-        /* failed to write page out, page is locked */
-        PAGE_KEEP,
-        /* move page to the active list, page is locked */
-        PAGE_ACTIVATE,
-        /* page has been sent to the disk successfully, page is unlocked */
-        PAGE_SUCCESS,
-        /* page is clean and locked */
-        PAGE_CLEAN,
-} pageout_t;
-
 struct scan_control {
         /* Incremented by the number of inactive pages that were scanned */
         unsigned long nr_scanned;
@@ -304,7 +292,7 @@ static void handle_write_error(struct address_space *mapping,
  * pageout is called by shrink_page_list() for each dirty page.
  * Calls ->writepage().
  */
-static pageout_t pageout(struct page *page, struct address_space *mapping)
+pageout_t pageout(struct page *page, struct address_space *mapping)
 {
         /*
          * If the page is dirty, only perform writeback if that write
@@ -372,7 +360,7 @@ static pageout_t pageout(struct page *page, struct address_space *mapping)
         return PAGE_CLEAN;
 }
 
-static int remove_mapping(struct address_space *mapping, struct page *page)
+int remove_mapping(struct address_space *mapping, struct page *page)
 {
         if (!mapping)
                 return 0;               /* truncate got there first */
@@ -570,481 +558,6 @@ keep:
         return nr_reclaimed;
 }
 
-#ifdef CONFIG_MIGRATION
-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.
- */
-unsigned long putback_lru_pages(struct list_head *l)
-{
-        struct page *page;
-        struct page *page2;
-        unsigned long 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;
-}
-EXPORT_SYMBOL(swap_page);
-
-/*
- * 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>
- */
-
-/*
- * 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.
- */
-unsigned long migrate_pages(struct list_head *from, struct list_head *to,
-                  struct list_head *moved, struct list_head *failed)
-{
-        unsigned long retry;
-        unsigned long 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;
-                }
-
-                /*
-                 * 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;
-}
-
-/*
- * Isolate one page from the LRU lists and put it on the
- * indicated list with elevated refcount.
- *
- * Result:
- *  0 = page not on LRU list
- *  1 = page removed from LRU list and added to the specified list.
- */
-int isolate_lru_page(struct page *page)
-{
-        int ret = 0;
-
-        if (PageLRU(page)) {
-                struct zone *zone = page_zone(page);
-                spin_lock_irq(&zone->lru_lock);
-                if (PageLRU(page)) {
-                        ret = 1;
-                        get_page(page);
-                        ClearPageLRU(page);
-                        if (PageActive(page))
-                                del_page_from_active_list(zone, page);
-                        else
-                                del_page_from_inactive_list(zone, page);
-                }
-                spin_unlock_irq(&zone->lru_lock);
-        }
-
-        return ret;
-}
-#endif
-
 /*
  * zone->lru_lock is heavily contended.  Some of the functions that
  * shrink the lists perform better by taking out a batch of pages