[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>

1 files changed, 60 insertions, 0 deletions

diff --git a/fs/buffer.c b/fs/buffer.c
index 3dc712f29d2d..8bcbac87a28c 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -3050,6 +3050,66 @@ asmlinkage long sys_bdflush(int func, long data)
 }
 
 /*
+ * Migration function for pages with buffers. This function can only be used
+ * if the underlying filesystem guarantees that no other references to "page"
+ * exist.
+ */
+#ifdef CONFIG_MIGRATION
+int buffer_migrate_page(struct page *newpage, struct page *page)
+{
+        struct address_space *mapping = page->mapping;
+        struct buffer_head *bh, *head;
+
+        if (!mapping)
+                return -EAGAIN;
+
+        if (!page_has_buffers(page))
+                return migrate_page(newpage, page);
+
+        head = page_buffers(page);
+
+        if (migrate_page_remove_references(newpage, page, 3))
+                return -EAGAIN;
+
+        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);
+#endif
+
+/*
  * Buffer-head allocation
  */
 static kmem_cache_t *bh_cachep;