[PATCH] memcg: handle shmem's swap cache (Was 2.6.26-rc8-mm1

KAMEZAWA Hiroyuki
2008-07-04T09:09:13Z

My swapcache accounting under memcg patch failed to catch tmpfs(shmem)'s one.
Can I test this under -mm tree ?
(If -mm is busy, I'm not in hurry.)
This patch works well in my box.
=
SwapCache handling fix.

shmem's swapcache behavior is a little different from anonymous's one and
memcg failed to handle it. This patch tries to fix it.

After this:

Any page marked as SwapCache is not uncharged. (delelte_from_swap_cache()
delete the SwapCache flag.)

To check a shmem-page-cache is alive or not we use
page->mapping && !PageAnon(page) instead of
pc->flags & PAGE_CGROUP_FLAG_CACHE.

Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>

Index: test-2.6.26-rc8-mm1/mm/memcontrol.c
===================================================================
--- test-2.6.26-rc8-mm1.orig/mm/memcontrol.c
+++ test-2.6.26-rc8-mm1/mm/memcontrol.c
@@ -687,11 +687,45 @@ __mem_cgroup_uncharge_common(struct page

VM_BUG_ON(pc->page != page);

- if ((ctype == MEM_CGROUP_CHARGE_TYPE_MAPPED)
- && ((pc->flags & PAGE_CGROUP_FLAG_CACHE)
- || page_mapped(page)
- || PageSwapCache(page)))
+ /*
+ * File Cache
+ * If called with MEM_CGROUP_CHARGE_TYPE_MAPPED, check page->mapping.
+ * add_to_page_cache() .... charged before inserting radix-tree.
+ * remove_from_page_cache() .... uncharged at removing from radix-tree.
+ * page->mapping && !PageAnon(page) catches file cache.
+ *
+ * Anon/Shmem.....We check PageSwapCache(page).
+ * Anon .... charged before mapped.
+ * Shmem .... charged at add_to_page_cache() as usual File Cache.
+ *
+ * This page will be finally uncharged when removed from swap-cache
+ *
+ * we treat 2 cases here.
+ * A. anonymous page B. shmem.
+ * We never uncharge if page is marked as SwapCache.
+ * add_to_swap_cache() have nothing to do with charge/uncharge.
+ * SwapCache flag is deleted before delete_from_swap_cache() calls this
+ *
+ * shmem's behavior is following. (see shmem.c/swap_state.c also)
+ * at swap-out:
+ * 0. add_to_page_cache()//charged at page creation.
+ * 1. add_to_swap_cache() (marked as SwapCache)
+ * 2. remove_from_page_cache(). (calls this.)
+ * (finally) delete_from_swap_cache(). (calls this.)
+ * at swap-in:
+ * 3. add_to_swap_cache() (no charge here.)
+ * 4. add_to_page_cache() (charged here.)
+ * 5. delete_from_swap_cache() (calls this.)
+ * PageSwapCache(page) catches "2".
+ * page->mapping && !PageAnon() catches "5" and avoid uncharging.
+ */
+ if (PageSwapCache(page))
goto unlock;
+ /* called from unmap or delete_from_swap_cache() */
+ if ((ctype == MEM_CGROUP_CHARGE_TYPE_MAPPED)
+ && (page_mapped(page)
+ || (page->mapping && !PageAnon(page))))/* alive cache ? */
+ goto unlock;

mz = page_cgroup_zoneinfo(pc);
spin_lock_irqsave(&mz->lru_lock, flags);