[PATCH] Direct Migration V9: Avoid writeback / page_migrate() method

Migrate a page with buffers without requiring writeback

This introduces a new address space operation migratepage() that may be used
by a filesystem to implement its own version of page migration.

A version is provided that migrates buffers attached to pages.  Some
filesystems (ext2, ext3, xfs) are modified to utilize this feature.

The swapper address space operation are modified so that a regular
migrate_page() will occur for anonymous pages without writeback (migrate_pages
forces every anonymous page to have a swap entry).

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

3 files changed, 21 insertions, 1 deletions

diff --git a/mm/rmap.c b/mm/rmap.c
index f4b91d7aa5cf..df2c41c2a9a2 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -233,6 +233,7 @@ void remove_from_swap(struct page *page)
 
         delete_from_swap_cache(page);
 }
+EXPORT_SYMBOL(remove_from_swap);
 #endif
 
 /*
diff --git a/mm/swap_state.c b/mm/swap_state.c
index 7b09ac503fec..db8a3d3e1636 100644
--- a/mm/swap_state.c
+++ b/mm/swap_state.c
@@ -27,6 +27,7 @@ static struct address_space_operations swap_aops = {
         .writepage      = swap_writepage,
         .sync_page      = block_sync_page,
         .set_page_dirty = __set_page_dirty_nobuffers,
+        .migratepage    = migrate_page,
 };
 
 static struct backing_dev_info swap_backing_dev_info = {
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 5e98b86feb74..5a610804cd06 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -615,6 +615,15 @@ int putback_lru_pages(struct list_head *l)
 }
 
 /*
+ * 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
  */
@@ -659,6 +668,7 @@ unlock_retry:
 retry:
         return -EAGAIN;
 }
+EXPORT_SYMBOL(swap_page);
 
 /*
  * Page migration was first developed in the context of the memory hotplug
@@ -674,7 +684,7 @@ 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.
  */
-static int migrate_page_remove_references(struct page *newpage,
+int migrate_page_remove_references(struct page *newpage,
                                 struct page *page, int nr_refs)
 {
         struct address_space *mapping = page_mapping(page);
@@ -749,6 +759,7 @@ static int migrate_page_remove_references(struct page *newpage,
 
         return 0;
 }
+EXPORT_SYMBOL(migrate_page_remove_references);
 
 /*
  * Copy the page to its new location
@@ -788,6 +799,7 @@ void migrate_page_copy(struct page *newpage, struct page *page)
         if (PageWriteback(newpage))
                 end_page_writeback(newpage);
 }
+EXPORT_SYMBOL(migrate_page_copy);
 
 /*
  * Common logic to directly migrate a single page suitable for
@@ -815,6 +827,7 @@ int migrate_page(struct page *newpage, struct page *page)
         remove_from_swap(newpage);
         return 0;
 }
+EXPORT_SYMBOL(migrate_page);
 
 /*
  * migrate_pages
@@ -914,6 +927,11 @@ redo:
                 if (!mapping)
                         goto unlock_both;
 
+                if (mapping->a_ops->migratepage) {
+                        rc = mapping->a_ops->migratepage(newpage, page);
+                        goto unlock_both;
+                }
+
                 /*
                  * Trigger writeout if page is dirty
                  */