[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, 655 insertions, 0 deletions

diff --git a/mm/migrate.c b/mm/migrate.c
new file mode 100644
index 000000000000..09f6e4aa87fc
--- /dev/null
+++ b/mm/migrate.c
@@ -0,0 +1,655 @@
+/*
+ * 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>  /* for try_to_release_page(),
+                                        buffer_heads_over_limit */
+#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"
+
+#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;
+}
+EXPORT_SYMBOL(swap_page);
+
+/*
+ * 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 1;
+        }
+
+        /*
+         * 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;
+                }
+
+                /*
+                 * 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;
+}