[Devel] Re: [PATCH 04/10] memcg: Introduce __GFP_NOACCOUNT.

[KAMEZAWA Hiroyuki]

On Wed, 29 Feb 2012 21:24:11 -0300
Glauber Costa <glommer at parallels.com> wrote:

> On 02/29/2012 09:10 PM, KAMEZAWA Hiroyuki wrote:
> > On Wed, 29 Feb 2012 11:09:50 -0800
> > Suleiman Souhlal<suleiman at google.com>  wrote:
> >
> >> On Tue, Feb 28, 2012 at 10:00 PM, KAMEZAWA Hiroyuki
> >> <kamezawa.hiroyu at jp.fujitsu.com>  wrote:
> >>> On Mon, 27 Feb 2012 14:58:47 -0800
> >>> Suleiman Souhlal<ssouhlal at FreeBSD.org>  wrote:
> >>>
> >>>> This is used to indicate that we don't want an allocation to be accounted
> >>>> to the current cgroup.
> >>>>
> >>>> Signed-off-by: Suleiman Souhlal<suleiman at google.com>
> >>>
> >>> I don't like this.
> >>>
> >>> Please add
> >>>
> >>> ___GFP_ACCOUNT  "account this allocation to memcg"
> >>>
> >>> Or make this as slab's flag if this work is for slab allocation.
> >>
> >> We would like to account for all the slab allocations that happen in
> >> process context.
> >>
> >> Manually marking every single allocation or kmem_cache with a GFP flag
> >> really doesn't seem like the right thing to do..
> >>
> >> Can you explain why you don't like this flag?
> >>
> >
> > For example, tcp buffer limiting has another logic for buffer size controling.
> > _AND_, most of kernel pages are not reclaimable at all.
> > I think you should start from reclaimable caches as dcache, icache etc.
> >
> > If you want to use this wider, you can discuss
> >
> > + #define GFP_KERNEL	(.....| ___GFP_ACCOUNT)
> >
> > in future. I'd like to see small start because memory allocation failure
> > is always terrible and make the system unstable. Even if you notify
> > "Ah, kernel memory allocation failed because of memory.limit? and
> >   many unreclaimable memory usage. Please tweak the limitation or kill tasks!!"
> >
> > The user can't do anything because he can't create any new task because of OOM.
> >
> > The system will be being unstable until an admin, who is not under any limit,
> > tweaks something or reboot the system.
> >
> > Please do small start until you provide Eco-System to avoid a case that
> > the admin cannot login and what he can do was only reboot.
> >
> Having the root cgroup to be always unlimited should already take care 
> of the most extreme cases, right?
> 
If an admin can login into root cgroup ;)
Anyway, if someone have a container under cgroup via hosting service,
he can do noting if oom killer cannot recover his container. It can be
caused by kernel memory limit. And I'm not sure he can do shutdown because
he can't login.

Thanks,
-Kame