Re: [RFC][PATCH] memcg: page fault oom improvement v2

[David Rientjes]

On Wed, 24 Feb 2010, KAMEZAWA Hiroyuki wrote:

> > > > This allows us to hijack the TIF_MEMDIE bit to detect when there is a 
> > > > parallel pagefault oom killing when the oom killer hasn't necessarily been 
> > > > invoked to kill a system-wide task (it's simply killing current, by 
> > > > default, and giving it access to memory reserves).  Then, we can change 
> > > > out_of_memory(), which also now handles memcg oom conditions, to always 
> > > > scan the tasklist first (including for mempolicy and cpuset constrained 
> > > > ooms), check for any candidates that have TIF_MEMDIE, and return 
> > > > ERR_PTR(-1UL) if so.  That catches the parallel pagefault oom conditions 
> > > > from needlessly killing memcg tasks.  panic_on_oom would only panic after 
> > > > the tasklist scan has completed and returned != ERR_PTR(-1UL), meaning 
> > > > pagefault ooms are exempt from that sysctl.
> > > > 
> > > Sorry, I see your concern but I'd like not to do clean-up and bug-fix at
> > > the same time.  
> > > 
> > > I think clean up after fix is easy in this case.
> > > 
> > 
> > If you develop on top of my oom killer rewrite, pagefault ooms already 
> > attempt to kill current first and then defer back to killing another task 
> > if current is unkillable.  
> 
> After my fix, page_fault_out_of_memory is never called. (because memcg doesn't
> return needless failure.)
> 

Of course it's called, it's called from the pagefault handler whenever we 
return VM_FAULT_OOM.  Whenever that happens, we'd needlessly panic the 
machine for panic_on_oom if we didn't do the tasklist scan and check for 
eligible tasks with TIF_MEMDIE set because it prefers to kill current 
first in pagefault conditions without consideration given to the sysctl.  
pagefault_out_of_memory() has changed radically with my rewrite, so I'd 
encourage you to develop on top of that where I've completely removed 
mem_cgroup_oom_called() and memcg->last_oom_jiffies already because 
they're nonsense.

My patches are available from 
http://www.kernel.org/pub/linux/kernel/people/rientjes/oom-killer-rewrite

Thanks.
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