[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>

fs/buffer.c

@@ -3049,6 +3049,66 @@ asmlinkage long sys_bdflush(int func, long data)
 	return 0;
 }
 
+/*
+ * 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
  */

fs/ext2/inode.c

@@ -706,6 +706,7 @@ struct address_space_operations ext2_aops = {
 	.bmap			= ext2_bmap,
 	.direct_IO		= ext2_direct_IO,
 	.writepages		= ext2_writepages,
+	.migratepage		= buffer_migrate_page,
 };
 
 struct address_space_operations ext2_aops_xip = {
@@ -723,6 +724,7 @@ struct address_space_operations ext2_nobh_aops = {
 	.bmap			= ext2_bmap,
 	.direct_IO		= ext2_direct_IO,
 	.writepages		= ext2_writepages,
+	.migratepage		= buffer_migrate_page,
 };
 
 /*

fs/ext3/inode.c

@@ -1559,6 +1559,7 @@ static struct address_space_operations ext3_ordered_aops = {
 	.invalidatepage	= ext3_invalidatepage,
 	.releasepage	= ext3_releasepage,
 	.direct_IO	= ext3_direct_IO,
+	.migratepage	= buffer_migrate_page,
 };
 
 static struct address_space_operations ext3_writeback_aops = {
@@ -1572,6 +1573,7 @@ static struct address_space_operations ext3_writeback_aops = {
 	.invalidatepage	= ext3_invalidatepage,
 	.releasepage	= ext3_releasepage,
 	.direct_IO	= ext3_direct_IO,
+	.migratepage	= buffer_migrate_page,
 };
 
 static struct address_space_operations ext3_journalled_aops = {

fs/xfs/linux-2.6/xfs_aops.c

@@ -1462,4 +1462,5 @@ struct address_space_operations linvfs_aops = {
 	.commit_write		= generic_commit_write,
 	.bmap			= linvfs_bmap,
 	.direct_IO		= linvfs_direct_IO,
+	.migratepage		= buffer_migrate_page,
 };

fs/xfs/linux-2.6/xfs_buf.c

@@ -1521,6 +1521,7 @@ xfs_mapping_buftarg(
 	struct address_space	*mapping;
 	static struct address_space_operations mapping_aops = {
 		.sync_page = block_sync_page,
+		.migratepage = fail_migrate_page,
 	};
 
 	inode = new_inode(bdev->bd_inode->i_sb);

include/linux/fs.h

@@ -363,6 +363,8 @@ struct address_space_operations {
 			loff_t offset, unsigned long nr_segs);
 	struct page* (*get_xip_page)(struct address_space *, sector_t,
 			int);
+	/* migrate the contents of a page to the specified target */
+	int (*migratepage) (struct page *, struct page *);
 };
 
 struct backing_dev_info;
@@ -1719,6 +1721,12 @@ extern void simple_release_fs(struct vfsmount **mount, int *count);
 
 extern ssize_t simple_read_from_buffer(void __user *, size_t, loff_t *, const void *, size_t);
 
+#ifdef CONFIG_MIGRATION
+extern int buffer_migrate_page(struct page *, struct page *);
+#else
+#define buffer_migrate_page NULL
+#endif
+
 extern int inode_change_ok(struct inode *, struct iattr *);
 extern int __must_check inode_setattr(struct inode *, struct iattr *);
 

include/linux/swap.h

@@ -193,13 +193,18 @@ extern int isolate_lru_page(struct page *p);
 extern int putback_lru_pages(struct list_head *l);
 extern int migrate_page(struct page *, struct page *);
 extern void migrate_page_copy(struct page *, struct page *);
+extern int migrate_page_remove_references(struct page *, struct page *, int);
 extern int migrate_pages(struct list_head *l, struct list_head *t,
 		struct list_head *moved, struct list_head *failed);
+extern int fail_migrate_page(struct page *, struct page *);
 #else
 static inline int isolate_lru_page(struct page *p) { return -ENOSYS; }
 static inline int putback_lru_pages(struct list_head *l) { return 0; }
 static inline int migrate_pages(struct list_head *l, struct list_head *t,
 	struct list_head *moved, struct list_head *failed) { return -ENOSYS; }
+/* Possible settings for the migrate_page() method in address_operations */
+#define migrate_page NULL
+#define fail_migrate_page NULL
 #endif
 
 #ifdef CONFIG_MMU

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
 
 /*

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 = {

mm/vmscan.c

@@ -614,6 +614,15 @@ int putback_lru_pages(struct list_head *l)
 	return count;
 }
 
+/*
+ * 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
 		 */