[PATCH] page migration cleanup: drop nr_refs in remove_references()

Drop nr_refs parameter from migrate_page_remove_references()

The nr_refs parameter is not really useful since the number of remaining
references is always

1 for anonymous pages without a mapping
2 for pages with a mapping
3 for pages with a mapping and PagePrivate set.

Remove the early check for the number of references since we are checking
page_mapcount() earlier.  Ultimately only the refcount matters after the
tree_lock has been obtained.

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

diff --git a/mm/migrate.c b/mm/migrate.c
index be3f141e53a42a4aad9d4b5678f06a3f343154d2..2803a6698dd690e1ef87e2879d313cfddbb0f535 100644 (file)
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -168,19 +168,19 @@ retry:
 /*
  * Remove references for a page and establish the new page with the correct
  * basic settings to be able to stop accesses to the page.
+ *
+ * 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_remove_references(struct page *newpage,
-                               struct page *page, int nr_refs)
+                               struct page *page)
 {
        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))
+       if (!mapping)
                return -EAGAIN;
 
        /*
@@ -218,7 +218,8 @@ static int migrate_page_remove_references(struct page *newpage,
                                                &mapping->page_tree,
                                                page_index(page));
 
-       if (!page_mapping(page) || page_count(page) != nr_refs ||
+       if (!page_mapping(page) ||
+                       page_count(page) != 2 + !!PagePrivate(page) ||
                        *radix_pointer != page) {
                write_unlock_irq(&mapping->tree_lock);
                return -EAGAIN;
@@ -309,7 +310,7 @@ int migrate_page(struct page *newpage, struct page *page)
 
        BUG_ON(PageWriteback(page));    /* Writeback must be complete */
 
-       rc = migrate_page_remove_references(newpage, page, 2);
+       rc = migrate_page_remove_references(newpage, page);
 
        if (rc)
                return rc;
@@ -348,7 +349,7 @@ int buffer_migrate_page(struct page *newpage, struct page *page)
 
        head = page_buffers(page);
 
-       rc = migrate_page_remove_references(newpage, page, 3);
+       rc = migrate_page_remove_references(newpage, page);
 
        if (rc)
                return rc;