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

[Pavel Machek <pavel@ucw.cz>]

On Fri 2016-08-05 20:17:36, PINTU KUMAR wrote:
> Hi,

> > 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 ?

I guess you should try it...

You may want to try the same kernel version, once in 32-bit and once
in 64-bit version. And you may consider moving to recent kernel.

Yes, 64-bit kernel will increase memory usage _of kernel_, but...

									Pavel
-- 
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