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authorKAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>2009-01-07 18:08:31 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2009-01-08 08:31:10 -0800
commit03f3c433648a97ae7c86be789edba67690f6ea60 (patch)
treed92a17f6fe9d90d3a6b46762742ef239bf5ecc44 /Documentation
parent42e9abb628def2c335a4ecf130bb6c88d916d885 (diff)
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 <kamezawa.hiroyu@jp.fujitsu.com> Acked-by: Balbir Singh <balbir@linux.vnet.ibm.com> Tested-by: Balbir Singh <balbir@linux.vnet.ibm.com> Cc: Hugh Dickins <hugh@veritas.com> Cc: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> Signed-off-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'Documentation')
-rw-r--r--Documentation/controllers/memcg_test.txt41
1 files changed, 36 insertions, 5 deletions
diff --git a/Documentation/controllers/memcg_test.txt b/Documentation/controllers/memcg_test.txt
index c91f69b0b549..08d4d3ea0d79 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.