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SubjectRe: [PATCH 2/4] memcg: set page->mapping NULL before uncharge
On Mon, 29 Sep 2008 19:22:40 +0900, KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote:
> 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@jp.fujitsu.com>
>
Looks good to me.

Reviewed-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>

> 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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