Re: [RFC PATCH] Make swap accounting default behavior configurable

[Michal Hocko]

On Thu 11-11-10 09:46:13, Daisuke Nishimura wrote:
> On Wed, 10 Nov 2010 13:51:54 +0100
> Michal Hocko <mhocko@xxxxxxx> 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).

> 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.

> 
> Thanks,
> Daisuke Nishimura.
> 
> > The patch is based on the current Linus tree.
> > 
> > Any thoughts?
> > ---
> > 
> > From c874f2c1ff1493e49611f19308434e564c2d37c6 Mon Sep 17 00:00:00 2001
> > From: Michal Hocko <mhocko@xxxxxxx>
> > 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@xxxxxxx>
> > ---
> >  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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-- 
Michal Hocko
L3 team 
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9    
Czech Republic
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