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Date: Tue, 16 Dec 2008 13:02:30 +0900
From: Daisuke Nishimura <nishimura@....nes.nec.co.jp>
To: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc: "Hugh Dickins" <hugh@...itas.com>,
"linux-mm@...ck.org" <linux-mm@...ck.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"balbir@...ux.vnet.ibm.com" <balbir@...ux.vnet.ibm.com>,
"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
nishimura@....nes.nec.co.jp
Subject: [PATCH mmotm] memcg: fix for documentation (Re: [BUGFIX][PATCH
mmotm] memcg fix swap accounting leak (v3))
Sorry for late reply.
> @@ -111,9 +111,40 @@ Under below explanation, we assume CONFI
> (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/-1 -1/-1 0/ 0
> + (6) - - - 0/-1
> + ===========================================
> + Result 1/ 1 1/1 1/ 1 1/ 1
> +
> + In any cases, charges to this page should be 1/ 1.
>
I've verified that charges will result in valid values by tracing source code
in all of these cases, but in case of (B) I don't think commit_charge_swapin
does memsw-- because PageSwapCache has been cleared already. swap_free does
memsw-- in this case.
I attached a fix patch.
Thanks,
Daisuke Nishimura.
===
From: Daisuke Nishimura <nishimura@....nes.nec.co.jp>
fix for documentation.
Signed-off-by: Daisuke Nishimura <nishimura@....nes.nec.co.jp>
---
Documentation/controllers/memcg_test.txt | 6 +++---
1 files changed, 3 insertions(+), 3 deletions(-)
diff --git a/Documentation/controllers/memcg_test.txt b/Documentation/controllers/memcg_test.txt
index 3c1458a..08d4d3e 100644
--- a/Documentation/controllers/memcg_test.txt
+++ b/Documentation/controllers/memcg_test.txt
@@ -139,10 +139,10 @@ Under below explanation, we assume CONFIG_MEM_RES_CTRL_SWAP=y.
===========================================
(3) +1/+1 +1/+1 +1/+1 +1/+1
(4) - 0/ 0 - -1/ 0
- (5) 0/ 1 0/-1 -1/-1 0/ 0
- (6) - - - 0/-1
+ (5) 0/-1 0/ 0 -1/-1 0/ 0
+ (6) - 0/-1 - 0/-1
===========================================
- Result 1/ 1 1/1 1/ 1 1/ 1
+ Result 1/ 1 1/ 1 1/ 1 1/ 1
In any cases, charges to this page should be 1/ 1.
--
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