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SubjectRe: [RFC][PATCH] memcg: page fault oom improvement v2
On Tue, 23 Feb 2010 18:26:17 -0800 (PST)
David Rientjes <rientjes@google.com> wrote:

> 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
>

I do by myself.

Bye.
-Kame

> Thanks.
>



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