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    SubjectRe: [RFC PATCH] Make swap accounting default behavior configurable v2
    On Fri, 12 Nov 2010 09:31:03 +0100
    Michal Hocko <mhocko@suse.cz> wrote:

    > On Fri 12-11-10 09:41:18, Daisuke Nishimura wrote:
    > > On Thu, 11 Nov 2010 10:31:55 +0100
    > > Michal Hocko <mhocko@suse.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@suse.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@suse.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@suse.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.
    >
    (I've add Andrew and Balbir to CC-list.)
    It seems that almost all parameters are listed in alphabetic order in the document,
    so I think it would be better to obey the rule.

    Thanks,
    Daisuke Nishimura.

    > 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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