Re: [RFC][PATCH] memcg: page fault oom improvement

[KAMEZAWA Hiroyuki]

On Tue, 23 Feb 2010 11:40:20 +0530
Balbir Singh <balbir@xxxxxxxxxxxxxxxxxx> wrote:

> * KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> [2010-02-23 12:03:15]:
> 
> > Nishimura-san, could you review and test your extreme test case with this ?
> > 
> > ==
> > From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
> > 
> > Now, because of page_fault_oom_kill, returning VM_FAULT_OOM means
> > random oom-killer should be called. Considering memcg, it handles
> > OOM-kill in its own logic, there was a problem as "oom-killer called
> > twice" problem.
> > 
> > By commit a636b327f731143ccc544b966cfd8de6cb6d72c6, I added a check
> > in pagefault_oom_killer shouldn't kill some (random) task if
> > memcg's oom-killer already killed anyone.
> > That was done by comapring current jiffies and last oom jiffies of memcg.
> > 
> > I thought that easy fix was enough, but Nishimura could write a test case
> > where checking jiffies is not enough. So, my fix was not enough.
> > This is a fix of above commit.
> > 
> > This new one does this.
> >  * memcg's try_charge() never returns -ENOMEM if oom-killer is allowed.
> >  * If someone is calling oom-killer, wait for it in try_charge().
> >  * If TIF_MEMDIE is set as a result of try_charge(), return 0 and
> >    allow process to make progress (and die.) 
> >  * removed hook in pagefault_out_of_memory.
> > 
> > By this, pagefult_out_of_memory will be never called if memcg's oom-killer
> > is called and scattered codes are now in memcg's charge logic again.
> > 
> > TODO:
> >  If __GFP_WAIT is not specified in gfp_mask flag, VM_FAULT_OOM will return
> >  anyway. We need to investigate it whether there is a case.
> > 
> > Cc: David Rientjes <rientjes@xxxxxxxxxx>
> > Cc: Balbir Singh <balbir@xxxxxxxxxx>
> > Cc: Daisuke Nishimura <nishimura@xxxxxxxxxxxxxxxxx>
> > Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
> 
> I've not reviewed David's latest OOM killer changes. Are these changes based on top of
> what is going to come in with David's proposal?

About this change. no. This is an independent patch.
But through these a few month work, I(we) noticed page_fault_out_of_memory() is
dangerous and VM_FALUT_OOM should not be returned as much as possible.
About memcg, it's not necessary to return VM_FAULT_OOM when we know oom-killer
is called.

This fix itself is straightforward. But difficult thing here is test case, I think.

Thanks,
-Kame


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