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SubjectRe: [PATCH 6/6] mm/page_owner: use stackdepot to store stacktrace
On Thu 05-05-16 00:30:35, Joonsoo Kim wrote:
> 2016-05-04 18:21 GMT+09:00 Michal Hocko <mhocko@kernel.org>:
[...]
> > 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
SUSE Labs

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