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

[PINTU KUMAR]

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.

Thank You!

Regards,
Pintu