Date:	Fri, 12 Nov 2010 09:31:03 +0100
From:	Michal Hocko <mhocko@...e.cz>
To:	Daisuke Nishimura <nishimura@....nes.nec.co.jp>
Cc:	linux-mm@...ck.org,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH] Make swap accounting default behavior configurable
 v2

On Fri 12-11-10 09:41:18, Daisuke Nishimura wrote:
> On Thu, 11 Nov 2010 10:31:55 +0100
> Michal Hocko <mhocko@...e.cz> wrote:
> 
> > On Thu 11-11-10 09:46:13, Daisuke Nishimura wrote:
> > > On Wed, 10 Nov 2010 13:51:54 +0100
> > > Michal Hocko <mhocko@...e.cz> wrote:
> > > 
> > > > 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.
> > > > 
> > > hmm, I agree that current parameter name(noswapaccount) is not desirable
> > > for yes|no, but IMHO changing the user interface(iow, making what worked before 
> > > unusable) is worse.
> > > 
> > > Although I'm not sure how many people are using this parameter, I vote for
> > > using "noswapaccount[=(yes|no)]".
> > 
> > Isn't a new swapaccount parameter better than that? I know we don't want
> > to have too many parameters but having a something with a clear meaning
> > is better IMO (noswapaccount=no doesn't sound very intuitive to me).
> > 
> Fair enough. It's just an trade-off between compatibility and understandability.
> 
> > > And you should update Documentation/kernel-parameters.txt too.
> > 
> > Yes, I am aware of that and will do that once there is an agreement on
> > the patch itself. At this stage, I just wanted to have a feadback about
> > the change.
> > 
> I'll ack your patch when it's been released with documentation update.

Changes since v1:
* do not remove noswapaccount parameter and add swapaccount parameter
  instead
* Documentation/kernel-parameters.txt updated

--- 
>From c60e3d76702cd9b4b5b13c01be335da31d03bc1c 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). If the option is selected
then the feature is turned on by default.

It also adds a new boot parameter swapaccount which (contrary to
noswapaccount) enables the feature. (I would consider swapaccount=yes|no
semantic with removed noswapaccount parameter much better but this
parameter is kind of API which might be in use and unexpected breakage
is no-go.)

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>
---
 Documentation/kernel-parameters.txt |    2 ++
 init/Kconfig                        |   13 +++++++++++++
 mm/memcontrol.c                     |   15 ++++++++++++++-
 3 files changed, 29 insertions(+), 1 deletions(-)

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index ed45e98..7077148 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -1752,6 +1752,8 @@ and is between 256 and 4096 characters. It is defined in the file
 
 	noswapaccount	[KNL] Disable accounting of swap in memory resource
 			controller. (See Documentation/cgroups/memory.txt)
+	swapaccount	[KNL] Enable accounting of swap in memory resource
+			controller. (See Documentation/cgroups/memory.txt)
 
 	nosync		[HW,M68K] Disables sync negotiation for all devices.
 
diff --git a/init/Kconfig b/init/Kconfig
index 88c1046..c972899 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 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 noswapaccount does the trick).
 
 menuconfig CGROUP_SCHED
 	bool "Group CPU scheduler"
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 9a99cfa..4f479fe 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
@@ -4909,6 +4916,12 @@ struct cgroup_subsys mem_cgroup_subsys = {
 };
 
 #ifdef CONFIG_CGROUP_MEM_RES_CTLR_SWAP
+static int __init enable_swap_account(char *s)
+{
+	really_do_swap_account = 1;
+	return 1;
+}
+__setup("swapaccount", enable_swap_account);
 
 static int __init disable_swap_account(char *s)
 {
-- 
1.7.2.3

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