Kick write-back I/O against dirty pages before memory migration
if the pages have PG_private and don't have migrate_page method.
It doesn't await completion of the write-back I/O's.
The purpose is just for performance of memory migration.

Signed-off-by: Hirokazu Takahashi <taka@valinux.co.jp>
Signed-off-by: Dave Hansen <haveblue@us.ibm.com>
---

 memhotplug-dave/mm/mmigrate.c |   48 +++++++++++++++++++++++++++++++++++++++---
 1 files changed, 45 insertions(+), 3 deletions(-)

diff -puN mm/mmigrate.c~AA-PM-12.1-mmigrate-pre_writeback mm/mmigrate.c
--- memhotplug/mm/mmigrate.c~AA-PM-12.1-mmigrate-pre_writeback	2005-07-28 13:50:42.000000000 -0700
+++ memhotplug-dave/mm/mmigrate.c	2005-07-28 13:50:42.000000000 -0700
@@ -396,12 +396,55 @@ migrate_onepage(struct page *page)
 int try_to_migrate_pages(struct list_head *page_list)
 {
 	struct page *page, *page2, *newpage;
-	LIST_HEAD(rest_list);
+	struct address_space* mapping;
+	LIST_HEAD(pass1_list);
+	LIST_HEAD(pass2_list);
 	int nr_busy = 0;
 	int nr_noswap = 0;
 
 	current->flags |= PF_KSWAPD;    /*  It's fake */
 	list_for_each_entry_safe(page, page2, page_list, lru) {
+		/*
+		 * Start writeback I/O if it's a dirty page with buffers
+		 */
+		if (PageDirty(page) && PagePrivate(page)) {
+			if (!TestSetPageLocked(page)) {
+				mapping = page_mapping(page);
+				if (!mapping ||
+				    !PageDirty(page) || !PagePrivate(page) ||
+				    PageWriteback(page) ||
+				    pageout(page, mapping) != PAGE_SUCCESS) {
+					unlock_page(page);
+				}
+			}
+		}
+		list_del(&page->lru);
+		list_add(&page->lru, &pass1_list);
+	}
+
+	/*
+	 * Try to migrate easily movable pages first.
+	 */
+	list_for_each_entry_safe(page, page2, &pass1_list, lru) {
+		list_del(&page->lru);
+		if (PageLocked(page) || PageWriteback(page) ||
+		    IS_ERR(newpage = migrate_onepage(page))) {
+			if (page_count(page) == 1) {
+				/* the page is already unused */
+				putback_page_to_lru(page_zone(page), page);
+				page_cache_release(page);
+			} else {
+				list_add(&page->lru, &pass2_list);
+			}
+		} else {
+			putback_page_to_lru(page_zone(newpage), newpage);
+			page_cache_release(newpage);
+		}
+	}
+	/*
+	 * Try to migrate the rest of them.
+	 */
+	list_for_each_entry_safe(page, page2, &pass2_list, lru) {
 		list_del(&page->lru);
 		if (IS_ERR(newpage = migrate_onepage(page))) {
 			if (page_count(page) == 1) {
@@ -413,14 +456,13 @@ int try_to_migrate_pages(struct list_hea
 				nr_busy++;
 				if (PTR_ERR(newpage) == -ENOSPC)
 					nr_noswap++;
-				list_add(&page->lru, &rest_list);
+				list_add(&page->lru, page_list);
 			}
 		} else {
 			putback_page_to_lru(page_zone(newpage), newpage);
 			page_cache_release(newpage);
 		}
 	}
-	list_splice(&rest_list, page_list);
 	current->flags &= ~PF_KSWAPD;
 	if (nr_noswap) {
 		if (printk_ratelimit())
_