Re: [PATCH 6/6] mm/page_owner: use stackdepot to store stacktrace

From: Michal Hocko
Date: Wed May 04 2016 - 15:40:27 EST

On Thu 05-05-16 00:30:35, Joonsoo Kim wrote:
> 2016-05-04 18:21 GMT+09:00 Michal Hocko <mhocko@xxxxxxxxxx>:
> > Do we really consume 512B of stack during reclaim. That sounds more than
> > worrying to me.
> Hmm...I checked it by ./script/stackusage and result is as below.
> shrink_zone() 128
> shrink_zone_memcg() 248
> shrink_active_list() 176
> We have a call path that shrink_zone() -> shrink_zone_memcg() ->
> shrink_active_list().
> I'm not sure whether it is the deepest path or not.

This is definitely not the deepest path. Slab shrinkers can take more
but 512B is still a lot. Some call paths are already too deep when
calling into the allocator and some of them already use GFP_NOFS to
prevent from potentially deep callchain slab shrinkers. Anyway worth
exploring for better solutions.

And I believe it would be better to solve this in the stackdepot
directly so other users do not have to invent their own ways around the
same issue. I have just checked the code and set_track uses save_stack
which does the same thing and it seems to be called from the slab
allocator. I have missed this usage before so the problem already does
exist. It would be unfair to request you to fix that in order to add a
new user. It would be great if this got addressed though.
Michal Hocko