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

[Minchan Kim]

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()].