Re: [PATCH 3/4] OOM, PM: OOM killed task shouldn't escape PM suspend

[Tejun Heo <tj@kernel.org>]

On Wed, Nov 05, 2014 at 05:39:56PM +0100, Michal Hocko wrote:
> On Wed 05-11-14 11:29:29, Tejun Heo wrote:
> > Hello, Michal.
> > 
> > On Wed, Nov 05, 2014 at 05:01:15PM +0100, Michal Hocko wrote:
> > > I am not sure I am following. With the latest patch OOM path is no
> > > longer blocked by the PM (aka oom_killer_disable()). Allocations simply
> > > fail if the read_trylock fails.
> > > oom_killer_disable is moved before tasks are frozen and it will wait for
> > > all on-going OOM killers on the write lock. OOM killer is enabled again
> > > on the resume path.
> > 
> > Sure, but why are we exposing new interfaces?  Can't we just make
> > oom_killer_disable() first set the disable flag and wait for the
> > on-going ones to finish (and make the function fail if it gets chosen
> > as an OOM victim)?
> 
> Still not following. How do you want to detect an on-going OOM without
> any interface around out_of_memory?

I thought you were using oom_killer_allowed_start() outside OOM path.
Ugh.... why is everything weirdly structured?  oom_killer_disabled
implies that oom killer may fail, right?  Why is
__alloc_pages_slowpath() checking it directly?  If whether oom killing
failed or not is relevant to its users, make out_of_memory() return an
error code.  There's no reason for the exclusion detail to leak out of
the oom killer proper.  The only interface should be disable/enable
and whether oom killing failed or not.

Thanks.

-- 
tejun

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