linux-kernel - RE: [linux-mm] Drastic increase in application memory usage with Kernel version upgrade

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Date:	Fri, 05 Aug 2016 20:17:36 +0530
From:	PINTU KUMAR <pintu.k@...sung.com>
To:	'Minchan Kim' <minchan@...nel.org>
Cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	jaejoon.seo@...sung.com, jy0.jeon@...sung.com,
	vishnu.ps@...sung.com
Subject: RE: [linux-mm] Drastic increase in application memory usage with
 Kernel version upgrade

Hi,
> -----Original Message-----
> From: Minchan Kim [mailto:minchan@...nel.org]
> Sent: Friday, August 05, 2016 1:50 PM
> To: PINTU KUMAR
> Cc: linux-kernel@...r.kernel.org; linux-mm@...ck.org;
> jaejoon.seo@...sung.com; jy0.jeon@...sung.com; vishnu.ps@...sung.com
> Subject: Re: [linux-mm] Drastic increase in application memory usage with
Kernel
> version upgrade
> 
> On Fri, Aug 05, 2016 at 10:26:37AM +0530, PINTU KUMAR wrote:
> > Hi All,
> >
> > For one of our ARM embedded product, we recently updated the Kernel
> > version from
> > 3.4 to 3.18 and we noticed that the same application memory usage (PSS
> > value) gone up by ~10% and for some cases it even crossed ~50%.
> > There is no change in platform part. All platform component was built
> > with ARM 32-bit toolchain.
> > However, the Kernel is changed from 32-bit to 64-bit.
> >
> > Is upgrading Kernel version and moving from 32-bit to 64-bit is such a risk
?
> > After the upgrade, what can we do further to reduce the application
> > memory usage ?
> > Is there any other factor that will help us to improve without major
> > modifications in platform ?
> >
> > As a proof, we did a small experiment on our Ubuntu-32 bit machine.
> > We upgraded Ubuntu Kernel version from 3.13 to 4.01 and we observed
> > the
> > following:
> > ----------------------------------------------------------------------
> > ----------
> > -------------
> > |UBUNTU-32 bit		|Kernel 3.13	|Kernel 4.03	|DIFF	|
> > |CALCULATOR PSS	|6057 KB	|6466 KB	|409 KB	|
> > ----------------------------------------------------------------------
> > ----------
> > -------------
> > So, just by upgrading the Kernel version: PSS value for calculator is
> > increased by 409KB.
> >
> > If anybody knows any in-sight about it please point out more details
> > about the root cause.
> 
> One of culprit is [8c6e50b0290c, mm: introduce vm_ops->map_pages()].
Ok. Thank you for your reply.
So, if I revert this patch, will the memory usage be decreased for the processes
with Kernel 3.18 ?