Message-ID: <20101110125154.GC5867@tiehlicka.suse.cz>
Date:	Wed, 10 Nov 2010 13:51:54 +0100
From:	Michal Hocko <mhocko@...e.cz>
To:	linux-mm@...ck.org
Cc:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	linux-kernel@...r.kernel.org
Subject: [RFC PATCH] Make swap accounting default behavior configurable

Hi,
could you consider the patch bellow? It basically changes the default
swap accounting behavior (when it is turned on in configuration) to be
configurable as well. 

The rationale is described in the patch but in short it makes it much
more easier to enable this feature in distribution kernels as the
functionality can be provided in the general purpose kernel (with the
option disabled) without any drawbacks and interested users can enable
it. This is not possible currently.

I am aware that boot command line parameter name change is not ideal but
the original semantic wasn't good enough and I don't like
noswapaccount=yes|no very much. 

If we really have to stick to it I can rework the patch to keep the name
and just add the yes|no logic, though. Or we can keep the original one
and add swapaccount paramete which would mean the oposite as the other
one.

The patch is based on the current Linus tree.

Any thoughts?
---

>From c874f2c1ff1493e49611f19308434e564c2d37c6 Mon Sep 17 00:00:00 2001
From: Michal Hocko <mhocko@...e.cz>
Date: Wed, 10 Nov 2010 13:30:04 +0100
Subject: [PATCH] Make swap accounting default behavior configurable

Swap accounting can be configured by CONFIG_CGROUP_MEM_RES_CTLR_SWAP
configuration option and then it is turned on by default. There is
a boot option (noswapaccount) which can disable this feature.

This makes it hard for distributors to enable the configuration option
as this feature leads to a bigger memory consumption and this is a no-go
for general purpose distribution kernel. On the other hand swap
accounting may be very usuful for some workloads.

This patch adds a new configuration option which controls the default
behavior (CGROUP_MEM_RES_CTLR_SWAP_ENABLED) and changes the original
noswapaccount parameter to swapaccount=true|false which provides
a more fine grained way to control this feature.

The default behavior is unchanged (if CONFIG_CGROUP_MEM_RES_CTLR_SWAP is
enabled then CONFIG_CGROUP_MEM_RES_CTLR_SWAP_ENABLED is enabled as well)

Signed-off-by: Michal Hocko <mhocko@...e.cz>
---
 init/Kconfig    |   13 +++++++++++++
 mm/memcontrol.c |   19 ++++++++++++++-----
 2 files changed, 27 insertions(+), 5 deletions(-)

diff --git a/init/Kconfig b/init/Kconfig
index 88c1046..61d55a7 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -613,6 +613,19 @@ config CGROUP_MEM_RES_CTLR_SWAP
 	  if boot option "noswapaccount" is set, swap will not be accounted.
 	  Now, memory usage of swap_cgroup is 2 bytes per entry. If swap page
 	  size is 4096bytes, 512k per 1Gbytes of swap.
+config CGROUP_MEM_RES_CTLR_SWAP_ENABLED
+	bool "Memory Resource Controller Swap Extension enabled by default"
+	depends on CGROUP_MEM_RES_CTLR_SWAP
+	default y
+	help
+	  Memory Resource Controller Swap Extension comes with its price in
+	  a bigger memory consumption. General purpose distribution kernels
+	  which want to enable the feautre but keep it disabled by default
+	  and let the user enable it by swapaccount=true boot command line
+	  parameter should have this option unselected.
+	  For those who want to have the feature enabled by default should
+	  select this option (if, for some reason, they need to disable it
+	  then swapaccount=false does the trick).
 
 menuconfig CGROUP_SCHED
 	bool "Group CPU scheduler"
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 9a99cfa..7c699b3 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -61,7 +61,14 @@ struct mem_cgroup *root_mem_cgroup __read_mostly;
 #ifdef CONFIG_CGROUP_MEM_RES_CTLR_SWAP
 /* Turned on only when memory cgroup is enabled && really_do_swap_account = 1 */
 int do_swap_account __read_mostly;
-static int really_do_swap_account __initdata = 1; /* for remember boot option*/
+
+/* for remember boot option*/
+#ifdef CONFIG_CGROUP_MEM_RES_CTLR_SWAP_ENABLED
+static int really_do_swap_account __initdata = 1;
+#else
+static int really_do_swap_account __initdata = 0;
+#endif
+
 #else
 #define do_swap_account		(0)
 #endif
@@ -4909,11 +4916,13 @@ struct cgroup_subsys mem_cgroup_subsys = {
 };
 
 #ifdef CONFIG_CGROUP_MEM_RES_CTLR_SWAP
-
-static int __init disable_swap_account(char *s)
+static int __init enable_swap_account(char *s)
 {
-	really_do_swap_account = 0;
+	if (!s || !strcmp(s, "true"))
+		really_do_swap_account = 1;
+	else if (!strcmp(s, "false"))
+		really_do_swap_account = 0;
 	return 1;
 }
-__setup("noswapaccount", disable_swap_account);
+__setup("swapaccount", enable_swap_account);
 #endif
-- 
1.7.2.3


-- 
Michal Hocko
L3 team 
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9    
Czech Republic
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