[PATCH 2/4] memcg: set page->mapping NULL before uncharge

[KAMEZAWA Hiroyuki]

This patch tries to make page->mapping to be NULL before
mem_cgroup_uncharge_cache_page() is called.

"page->mapping == NULL" is a good check for "whether the page is still
radix-tree or not".
This patch also adds BUG_ON() to mem_cgroup_uncharge_cache_page();


Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>

 mm/filemap.c    |    2 +-
 mm/memcontrol.c |    1 +
 mm/migrate.c    |    9 +++++++--
 3 files changed, 9 insertions(+), 3 deletions(-)

Index: mmotm-2.6.27-rc7+/mm/filemap.c
===================================================================
--- mmotm-2.6.27-rc7+.orig/mm/filemap.c
+++ mmotm-2.6.27-rc7+/mm/filemap.c
@@ -116,12 +116,12 @@ void __remove_from_page_cache(struct pag
 {
 	struct address_space *mapping = page->mapping;
 
-	mem_cgroup_uncharge_cache_page(page);
 	radix_tree_delete(&mapping->page_tree, page->index);
 	page->mapping = NULL;
 	mapping->nrpages--;
 	__dec_zone_page_state(page, NR_FILE_PAGES);
 	BUG_ON(page_mapped(page));
+	mem_cgroup_uncharge_cache_page(page);
 
 	/*
 	 * Some filesystems seem to re-dirty the page even after
Index: mmotm-2.6.27-rc7+/mm/memcontrol.c
===================================================================
--- mmotm-2.6.27-rc7+.orig/mm/memcontrol.c
+++ mmotm-2.6.27-rc7+/mm/memcontrol.c
@@ -734,6 +734,7 @@ void mem_cgroup_uncharge_page(struct pag
 void mem_cgroup_uncharge_cache_page(struct page *page)
 {
 	VM_BUG_ON(page_mapped(page));
+	VM_BUG_ON(page->mapping);
 	__mem_cgroup_uncharge_common(page, MEM_CGROUP_CHARGE_TYPE_CACHE);
 }
 
Index: mmotm-2.6.27-rc7+/mm/migrate.c
===================================================================
--- mmotm-2.6.27-rc7+.orig/mm/migrate.c
+++ mmotm-2.6.27-rc7+/mm/migrate.c
@@ -330,8 +330,6 @@ static int migrate_page_move_mapping(str
 	__inc_zone_page_state(newpage, NR_FILE_PAGES);
 
 	spin_unlock_irq(&mapping->tree_lock);
-	if (!PageSwapCache(newpage))
-		mem_cgroup_uncharge_cache_page(page);
 
 	return 0;
 }
@@ -341,6 +339,8 @@ static int migrate_page_move_mapping(str
  */
 static void migrate_page_copy(struct page *newpage, struct page *page)
 {
+	int anon;
+
 	copy_highpage(newpage, page);
 
 	if (PageError(page))
@@ -378,8 +378,13 @@ static void migrate_page_copy(struct pag
 #endif
 	ClearPagePrivate(page);
 	set_page_private(page, 0);
+	/* page->mapping contains a flag for PageAnon() */
+	anon = PageAnon(page);
 	page->mapping = NULL;
 
+	if (!anon) /* This page was removed from radix-tree. */
+		mem_cgroup_uncharge_cache_page(page);
+
 	/*
 	 * If any waiters have accumulated on the new page then
 	 * wake them up.

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