Re: [RFC 0/4] mm, oom: get rid of TIF_MEMDIE

[Johannes Weiner]

Hi Michal,

On Thu, Sep 01, 2016 at 11:51:00AM +0200, Michal Hocko wrote:
> Hi,
> this is an early RFC to see whether the approach I've taken is acceptable.
> The series is on top of the current mmotm tree (2016-08-31-16-06). I didn't
> get to test it so it might be completely broken.
> 
> The primary point of this series is to get rid of TIF_MEMDIE finally.
> Recent changes in the oom proper allows for that finally, I believe. Now
> that all the oom victims are reapable we are no longer depending on
> ALLOC_NO_WATERMARKS because the memory held by the victim is reclaimed
> asynchronously. A partial access to memory reserves should be sufficient
> just to guarantee that the oom victim is not starved due to other
> memory consumers. This also means that we do not have to pretend to be
> conservative and give access to memory reserves only to one thread from
> the process at the time. This is patch 1.
>
> Patch 2 is a simple cleanup which turns TIF_MEMDIE users to tsk_is_oom_victim
> which is process rather than thread centric. None of those callers really
> requires to be thread aware AFAICS.
> 
> The tricky part then is exit_oom_victim vs. oom_killer_disable because
> TIF_MEMDIE acted as a token there so we had a way to count threads from
> the process. It didn't work 100% reliably and had it own issues but we
> have to replace it with something which doesn't rely on counting threads
> but rather find a moment when all threads have reached steady state in
> do_exit. This is what patch 3 does and I would really appreciate if Oleg
> could double check my thinking there. I am also CCing Al on that one
> because I am moving exit_io_context up in do_exit right before exit_notify.

You're explaining the mechanical thing you are doing, but I'm having
trouble understanding why you want to get rid of TIF_MEMDIE. For one,
it's more code. And apparently, it's also more complicated than what
we have right now.

Can you please explain in the cover letter what's broken/undesirable?

Thanks