Re: cgroups and overcommit question

[Balbir Singh <balbir@linux.vnet.ibm.com>]

* nishimura@mxp.nes.nec.co.jp <nishimura@mxp.nes.nec.co.jp> [2011-01-13 10:57:41]:

> Hi.
> 
> On Wed, 12 Jan 2011 18:40:37 +0300
> Evgeniy Ivanov <lolkaantimat@gmail.com> wrote:
> 
> > Hello,
> > 
> > When I forbid memory overcommiting, malloc() returns 0 if can't
> > reserve memory, but in a cgroup it will always succeed, when it can
> > succeed when not in the group.
> > E.g. I've set 2 to overcommit_memory, limit is 10M: I can ask malloc
> > 100M and it will not return any error (kernel is 2.6.32).
> > Is it expected behavior?
> > 
> Yes. Because memory cgroup can be used for limiting the memory(and swap) size
> which is physically used, not the malloc'ed size.
>

I had rlimit based cgroup to limit virtual memory size, but the
patches were never merged due to lack of use cases :( 

See http://lwn.net/Articles/283287/

I did advocate as use case the ability to prevent overcommit. I
suspect another way of solving this problem is to have overcommit
control. The problem today is that OOM is our backup to overcommit,
not a very comfortable feeling.

-- 
	Three Cheers,
	Balbir

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