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

[vinayak menon]

On Wed, Aug 10, 2016 at 6:56 PM, PINTU KUMAR <pintu.k@xxxxxxxxxxx> wrote:
> Hi,
>
>> -----Original Message-----
>> From: Pavel Machek [mailto:pavel@xxxxxx]
>> Sent: Saturday, August 06, 2016 2:20 AM
>> To: PINTU KUMAR
>> Cc: 'Minchan Kim'; linux-kernel@xxxxxxxxxxxxxxx; linux-mm@xxxxxxxxx;
>> jaejoon.seo@xxxxxxxxxxx; jy0.jeon@xxxxxxxxxxx; vishnu.ps@xxxxxxxxxxx
>> Subject: Re: [linux-mm] Drastic increase in application memory usage with
> Kernel
>> version upgrade
>>
>> 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...
>>
> Thanks for the reply and confirmation.
> Our exact kernel version is: 3.18.14
> And, we already have this patch:
> /*
> mm: do not call do_fault_around for non-linear fault
> Ingo Korb reported that "repeated mapping of the same file on tmpfs
> using remap_file_pages sometimes triggers a BUG at mm/filemap.c:202 when
> the process exits".
> He bisected the bug to d7c1755179b8 ("mm: implement ->map_pages for
> shmem/tmpfs"), although the bug was actually added by commit
> 8c6e50b0290c ("mm: introduce vm_ops->map_pages()").
> */
>
> So, I guess, reverting this patch (8c6e50b0290c), is not required ?
> But, still we have memory usage issue.
>
I had observed the PSS increase with 3.18, and that was because of the
faultaround patch which MInchan mentioned.
Without reverting the patch you can just try reducing
fault_around_bytes (mm/memory.c) to PAGE_SIZE. That should
bring down the PSS.

Thanks,
Vinayak