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

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Date:	Thu, 5 May 2016 00:45:45 +0900
From:	Joonsoo Kim <js1304@...il.com>
To:	Michal Hocko <mhocko@...nel.org>
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

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.

Thanks.