[PATCH] page migration cleanup: extract try_to_unmap from migration functions
Extract try_to_unmap and rename remove_references -> move_mapping
try_to_unmap() may significantly change the page state by for example setting
the dirty bit. It is therefore best to unmap in migrate_pages() before
calling any migration functions.
migrate_page_remove_references() will then only move the new page in place of
the old page in the mapping. Rename the function to
migrate_page_move_mapping().
This allows us to get rid of the special unmapping for the fallback path.
Signed-off-by: Christoph Lameter <clameter@sgi.com>
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 2803a66..8095c60 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -166,15 +166,14 @@
}
/*
- * Remove references for a page and establish the new page with the correct
- * basic settings to be able to stop accesses to the page.
+ * Replace the page in the mapping.
*
* 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,
+static int migrate_page_move_mapping(struct page *newpage,
struct page *page)
{
struct address_space *mapping = page_mapping(page);
@@ -183,35 +182,6 @@
if (!mapping)
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(
@@ -310,7 +280,7 @@
BUG_ON(PageWriteback(page)); /* Writeback must be complete */
- rc = migrate_page_remove_references(newpage, page);
+ rc = migrate_page_move_mapping(newpage, page);
if (rc)
return rc;
@@ -349,7 +319,7 @@
head = page_buffers(page);
- rc = migrate_page_remove_references(newpage, page);
+ rc = migrate_page_move_mapping(newpage, page);
if (rc)
return rc;
@@ -482,6 +452,33 @@
lock_page(newpage);
/*
+ * 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.
+ */
+ rc = -EPERM;
+ if (try_to_unmap(page, 1) == SWAP_FAIL)
+ /* A vma has VM_LOCKED set -> permanent failure */
+ goto unlock_both;
+
+ rc = -EAGAIN;
+ if (page_mapped(page))
+ goto unlock_both;
+ /*
* Pages are properly locked and writeback is complete.
* Try to migrate the page.
*/
@@ -501,17 +498,6 @@
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