From 03f3c433648a97ae7c86be789edba67690f6ea60 Mon Sep 17 00:00:00 2001 From: KAMEZAWA Hiroyuki Date: Wed, 7 Jan 2009 18:08:31 -0800 Subject: memcg: fix swap accounting leak Fix swapin charge operation of memcg. Now, memcg has hooks to swap-out operation and checks SwapCache is really unused or not. That check depends on contents of struct page. I.e. If PageAnon(page) && page_mapped(page), the page is recoginized as still-in-use. Now, reuse_swap_page() calles delete_from_swap_cache() before establishment of any rmap. Then, in followinig sequence (Page fault with WRITE) try_charge() (charge += PAGESIZE) commit_charge() (Check page_cgroup is used or not..) reuse_swap_page() -> delete_from_swapcache() -> mem_cgroup_uncharge_swapcache() (charge -= PAGESIZE) ...... New charge is uncharged soon.... To avoid this, move commit_charge() after page_mapcount() goes up to 1. By this, try_charge() (usage += PAGESIZE) reuse_swap_page() (may usage -= PAGESIZE if PCG_USED is set) commit_charge() (If page_cgroup is not marked as PCG_USED, add new charge.) Accounting will be correct. Changelog (v2) -> (v3) - fixed invalid charge to swp_entry==0. - updated documentation. Changelog (v1) -> (v2) - fixed comment. [nishimura@mxp.nes.nec.co.jp: swap accounting leak doc fix] Signed-off-by: KAMEZAWA Hiroyuki Acked-by: Balbir Singh Tested-by: Balbir Singh Cc: Hugh Dickins Cc: Daisuke Nishimura Signed-off-by: Daisuke Nishimura Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- Documentation/controllers/memcg_test.txt | 41 ++++++++++++++++++++++++++++---- 1 file changed, 36 insertions(+), 5 deletions(-) (limited to 'Documentation') diff --git a/Documentation/controllers/memcg_test.txt b/Documentation/controllers/memcg_test.txt index c91f69b0b54..08d4d3ea0d7 100644 --- a/Documentation/controllers/memcg_test.txt +++ b/Documentation/controllers/memcg_test.txt @@ -1,6 +1,6 @@ Memory Resource Controller(Memcg) Implementation Memo. -Last Updated: 2008/12/10 -Base Kernel Version: based on 2.6.28-rc7-mm. +Last Updated: 2008/12/15 +Base Kernel Version: based on 2.6.28-rc8-mm. Because VM is getting complex (one of reasons is memcg...), memcg's behavior is complex. This is a document for memcg's internal behavior. @@ -111,9 +111,40 @@ Under below explanation, we assume CONFIG_MEM_RES_CTRL_SWAP=y. (b) If the SwapCache has been mapped by processes, it has been charged already. - In case (a), we charge it. In case (b), we don't charge it. - (But racy state between (a) and (b) exists. We do check it.) - At charging, a charge recorded in swap_cgroup is moved to page_cgroup. + This swap-in is one of the most complicated work. In do_swap_page(), + following events occur when pte is unchanged. + + (1) the page (SwapCache) is looked up. + (2) lock_page() + (3) try_charge_swapin() + (4) reuse_swap_page() (may call delete_swap_cache()) + (5) commit_charge_swapin() + (6) swap_free(). + + Considering following situation for example. + + (A) The page has not been charged before (2) and reuse_swap_page() + doesn't call delete_from_swap_cache(). + (B) The page has not been charged before (2) and reuse_swap_page() + calls delete_from_swap_cache(). + (C) The page has been charged before (2) and reuse_swap_page() doesn't + call delete_from_swap_cache(). + (D) The page has been charged before (2) and reuse_swap_page() calls + delete_from_swap_cache(). + + memory.usage/memsw.usage changes to this page/swp_entry will be + Case (A) (B) (C) (D) + Event + Before (2) 0/ 1 0/ 1 1/ 1 1/ 1 + =========================================== + (3) +1/+1 +1/+1 +1/+1 +1/+1 + (4) - 0/ 0 - -1/ 0 + (5) 0/-1 0/ 0 -1/-1 0/ 0 + (6) - 0/-1 - 0/-1 + =========================================== + Result 1/ 1 1/ 1 1/ 1 1/ 1 + + In any cases, charges to this page should be 1/ 1. 4.2 Swap-out. At swap-out, typical state transition is below. -- cgit v1.2.3