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

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Message-ID: <20160504194146.GF21490@dhcp22.suse.cz>
Date:	Wed, 4 May 2016 21:41:46 +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 Thu 05-05-16 00:45:45, Joonsoo Kim wrote:
> 2016-05-05 0:30 GMT+09:00 Joonsoo Kim <js1304@...il.com>:
> > 2016-05-04 18:21 GMT+09:00 Michal Hocko <mhocko@...nel.org>:
> >> On Wed 04-05-16 11:14:50, Joonsoo Kim wrote:
> >>> On Tue, May 03, 2016 at 10:53:56AM +0200, Michal Hocko wrote:
> >>> > On Tue 03-05-16 14:23:04, Joonsoo Kim wrote:
> >> [...]
> >>> > > Memory saving looks as following. (Boot 4GB memory system with page_owner)
> >>> > >
> >>> > > 92274688 bytes -> 25165824 bytes
> >>> >
> >>> > It is not clear to me whether this is after a fresh boot or some workload
> >>> > which would grow the stack depot as well. What is a usual cap for the
> >>> > memory consumption.
> >>>
> >>> It is static allocation size after a fresh boot. I didn't add size of
> >>> dynamic allocation memory so it could be larger a little. See below line.
> >>> >
> >>> > > 72% reduction in static allocation size. Even if we should add up size of
> >>> > > dynamic allocation memory, it would not that big because stacktrace is
> >>> > > mostly duplicated.
> >>
> >> This would be true only if most of the allocation stacks are basically
> >> same after the boot which I am not really convinced is true. But you are
> >> right that the number of sublicates will grow only a little. I was
> >> interested about how much is that little ;)
> >
> > After a fresh boot, it just uses 14 order-2 pages.
> 
> I missed to add other information. Even after building the kernel,
> it takes 20 order-2 pages. 20 * 4 * 4KB = 320 KB.

Something like that would be useful to mention in the changelog because
measuring right after the fresh boot without any reasonable workload
sounds suspicious.
-- 
Michal Hocko
SUSE Labs