Re: [PATCH] sched/auto_group: fix consume memory even if add'noautogroup' in the cmdline

[Mike Galbraith]

On Mon, 2014-01-06 at 13:17 +0100, Peter Zijlstra wrote: 
> On Fri, Dec 27, 2013 at 06:22:31PM +0800, Wanpeng Li wrote:
> > We have a server which have 200 CPUs and 8G memory, there is auto_group creation 
> 
> I'm hoping that is 8T, otherwise that's a severely under provisioned
> system, that's a mere 40M per cpu, does that even work?
> 
> > which will almost consume 12MB memory even if add 'noautogroup' in the kernel 
> > boot parameter. In addtion, SLUB per cpu partial caches freeing that is local to 
> > a processor which requires the taking of locks at the price of more indeterminism 
> > in the latency of the free. This patch fix it by check noautogroup earlier to avoid 
> > free after unnecessary memory consumption.
> 
> That's just a bad changelog. It fails to explain the actual problem and
> it babbles about unrelated things like SLUB details.
> 
> Also, I'm not entirely sure what the intention was of this code, I've so
> far tried to ignore the entire autogroup fest... 
> 
> It looks like it creates and maintains the entire autogroup hierarchy,
> such that if you at runtime enable the sysclt and move tasks 'back' to
> the root cgroup you get the autogroup behaviour.
> 
> Was this intended? Mike?

Yeah, it was intended that autogroups always exist if you config it in.
We could make is such that noautogroup makes it irreversibly off/dead.  

People with 200 ram starved CPUs can turn it off in their .config too :)

-Mike

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