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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20160510085706.GG23576@dhcp22.suse.cz>
Date:	Tue, 10 May 2016 10:57:06 +0200
From:	Michal Hocko <mhocko@...nel.org>
To:	Joonsoo Kim <js1304@...il.com>
Cc:	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Vlastimil Babka <vbabka@...e.cz>,
	Mel Gorman <mgorman@...hsingularity.net>,
	Minchan Kim <minchan@...nel.org>,
	Alexander Potapenko <glider@...gle.com>,
	Linux Memory Management List <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 6/6] mm/page_owner: use stackdepot to store stacktrace

On Tue 10-05-16 16:07:14, Joonsoo Kim wrote:
> 2016-05-05 4:40 GMT+09:00 Michal Hocko <mhocko@...nel.org>:
> > On Thu 05-05-16 00:30:35, Joonsoo Kim wrote:
> >> 2016-05-04 18:21 GMT+09:00 Michal Hocko <mhocko@...nel.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.
> 
> Yes, fixing it in stackdepot looks more reasonable.
> Then, I will just change PAGE_OWNER_STACK_DEPTH from 64 to 16 and
> leave the code as is for now. With this change, we will just consume 128B stack
> and would not cause stack problem. If anyone has an objection,
> please let me know.

128B is still quite a lot but considering there is a plan to make it
more robust I can live with it as a temporary workaround.

-- 
Michal Hocko
SUSE Labs