Re: [PATCH v7 10/10] Disable task moving when using kernel memoryaccounting

[Glauber Costa]

On 11/30/2011 12:22 AM, KAMEZAWA Hiroyuki wrote:
> On Tue, 29 Nov 2011 21:57:01 -0200
> Glauber Costa<glommer@xxxxxxxxxxxxx>  wrote:
>
> > Since this code is still experimental, we are leaving the exact
> > details of how to move tasks between cgroups when kernel memory
> > accounting is used as future work.
> >
> > For now, we simply disallow movement if there are any pending
> > accounted memory.
> >
> > Signed-off-by: Glauber Costa<glommer@xxxxxxxxxxxxx>
> > CC: Hiroyouki Kamezawa<kamezawa.hiroyu@xxxxxxxxxxxxxx>
> > ---
> >   mm/memcontrol.c |   23 ++++++++++++++++++++++-
> >   1 files changed, 22 insertions(+), 1 deletions(-)
> >
> > diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> > index a31a278..dd9a6d9 100644
> > --- a/mm/memcontrol.c
> > +++ b/mm/memcontrol.c
> > @@ -5453,10 +5453,19 @@ static int mem_cgroup_can_attach(struct cgroup_subsys *ss,
> >   {
> >   	int ret = 0;
> >   	struct mem_cgroup *memcg = mem_cgroup_from_cont(cgroup);
> > +	struct mem_cgroup *from = mem_cgroup_from_task(p);
> > +
> > +#if defined(CONFIG_CGROUP_MEM_RES_CTLR_KMEM)&&  defined(CONFIG_INET)
> > +	if (from != memcg&&  !mem_cgroup_is_root(from)&&
> > +	    res_counter_read_u64(&from->tcp_mem.tcp_memory_allocated, RES_USAGE)) {
> > +		printk(KERN_WARNING "Can't move tasks between cgroups: "
> > +			"Kernel memory held.\n");
> > +		return 1;
> > +	}
> > +#endif
>
> I wonder....reading all codes again, this is incorrect check.
>
> Hm, let me cralify. IIUC, in old code, "prevent moving" is because you hold
> reference count of cgroup, which can cause trouble at rmdir() as leaking refcnt.
right.

> BTW, because socket is a shared resource between cgroup, changes in mm->owner
> may cause task cgroup moving implicitly. So, if you allow leak of resource
> here, I guess... you can take mem_cgroup_get() refcnt which is memcg-local and
> allow rmdir(). Then, this limitation may disappear.

Sorry, I didn't fully understand. Can you clarify further?
If the task is implicitly moved, it will end up calling can_attach as 
well, right?


> Then, users will be happy but admins will have unseen kernel resource usage in
> not populated(by rmdir) memcg. Hm, big trouble ?
>
> Thanks,
> -Kame

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/