[PATCH] page migration cleanup: move fallback handling into special function

Move the fallback code into a new fallback function and make the function
behave like any other migration function.  This requires retaking the lock if
pageout() drops it.

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, 39 insertions, 51 deletions

diff --git a/mm/migrate.c b/mm/migrate.c
index f65e69d94527..5a340f4ca212 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -349,6 +349,42 @@ int buffer_migrate_page(struct address_space *mapping,
 }
 EXPORT_SYMBOL(buffer_migrate_page);
 
+static int fallback_migrate_page(struct address_space *mapping,
+        struct page *newpage, struct page *page)
+{
+        /*
+         * 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:
+                        return -EAGAIN;
+
+                case PAGE_SUCCESS:
+                        /* Relock since we lost the lock */
+                        lock_page(page);
+                        /* Must retry since page state may have changed */
+                        return -EAGAIN;
+
+                case PAGE_CLEAN:
+                        ; /* try to migrate the page below */
+                }
+        }
+
+        /*
+         * Buffers may be 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))
+                return -EAGAIN;
+
+        return migrate_page(mapping, newpage, page);
+}
+
 /*
  * migrate_pages
  *
@@ -478,7 +514,7 @@ redo:
                 if (!mapping)
                         goto unlock_both;
 
-                if (mapping->a_ops->migratepage) {
+                if (mapping->a_ops->migratepage)
                         /*
                          * Most pages have a mapping and most filesystems
                          * should provide a migration function. Anonymous
@@ -488,56 +524,8 @@ redo:
                          */
                         rc = mapping->a_ops->migratepage(mapping,
                                                         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(mapping, 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;
-                }
+                else
+                        rc = fallback_migrate_page(mapping, newpage, page);
 
 unlock_both:
                 unlock_page(newpage);