Re: [patch -mm 4/9 v2] oom: remove compulsory panic_on_oom mode

[KAMEZAWA Hiroyuki]

On Tue, 16 Feb 2010 16:31:39 -0800 (PST)
David Rientjes <rientjes@xxxxxxxxxx> wrote:

> On Wed, 17 Feb 2010, KAMEZAWA Hiroyuki wrote:
> 
> > Hmm, I have a few reason to add special behavior to memcg rather than panic.
> > 
> >  - freeze_at_oom is enough.
> >    If OOM can be notified, the management daemon can do useful jobs. Shutdown
> >    all other cgroups or migrate them to other host and do kdump.
> > 
> 
> The same could be said for cpusets if users use that for memory isolation.
> 
cpuset's difficulty is that there are some methods which share the limitation.

It's not simple that we have
  - cpuset
  - mempolicy per task
  - mempolicy per vma

Sigh..but they are for their own purpose.


> > But, Hmm...I'd like to go this way.
> > 
> >  1. At first, support panic_on_oom=2 in memcg.
> > 
> 
> This should panic in mem_cgroup_out_of_memory() and the documentation 
> should be added to Documentation/sysctl/vm.txt.
> 
> The memory controller also has some protection in the pagefault oom 
> handler that seems like it could be made more general: instead of checking 
> for mem_cgroup_oom_called(), I'd rather do a tasklist scan to check for 
> already oom killed task (checking for the TIF_MEMDIE bit) and check all 
> zones for ZONE_OOM_LOCKED.  If no oom killed tasks are found and no zones 
> are locked, we can check sysctl_panic_on_oom and invoke the system-wide 
> oom.
> 
plz remove memcg's hook after doing that. Current implemantation is desgined 
not to affect too much to other cgroups by doing unnecessary jobs.


> >  2. Second, I'll add OOM-notifier and freeze_at_oom to memcg.
> >     and don't call memcg_out_of_memory in oom_kill.c in this case. Because
> >     we don't kill anything. Taking coredumps of all procs in memcg is not
> >     very difficult.
> > 
> 
> The oom notifier would be at a higher level than the oom killer, the oom 
> killer's job is simply to kill a task when it is called. 
> So for these particular cases, you would never even call into out_of_memory() to panic 
> the machine in the first place. 

That's my point. 

Thanks,
-Kame


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