Re: [patch -mm] mm, oom: add global access to memory reserves on livelock

[Michal Hocko <mhocko@kernel.org>]

On Mon 24-08-15 14:10:10, David Rientjes wrote:
> On Fri, 21 Aug 2015, Tetsuo Handa wrote:
> 
> > Why can't we think about choosing more OOM victims instead of granting access
> > to memory reserves?
> > 
> 
> We have no indication of which thread is holding a mutex that would need 
> to be killed, so we'd be randomly killing processes waiting for forward 
> progress.  A worst-case scenario would be the thread is OOM_DISABLE and we 
> kill every process on the system needlessly.  This problem obviously 
> occurs often enough that killing all userspace isnt going to be a viable 
> solution.
> 
> > Also, SysRq might not be usable under OOM because workqueues can get stuck.
> > The panic_on_oom_timeout was first proposed using a workqueue but was
> > updated to use a timer because there is no guarantee that workqueues work
> > as expected under OOM.
> > 
> 
> I don't know anything about a panic_on_oom_timeout,

You were CCed on the discussion
http://lkml.kernel.org/r/20150609170310.GA8990%40dhcp22.suse.cz

> but panicking would 
> only be a reasonable action if memory reserves were fully depleted.  That 
> could easily be dealt with in the page allocator so there's no timeout 
> involved.

As noted in other email. Just depletion is not a good indicator. The
system can still make a forward progress even when reserves are
depleted.

-- 
Michal Hocko
SUSE Labs

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