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From Jan Lukavsk√Ĺ <jan.lukav...@firma.seznam.cz>
Subject Re: ProcFsBasedProcessTree and clean pages in smaps
Date Fri, 05 Feb 2016 13:15:49 GMT
Hi Chris,

thanks for your reply. As far as I can see right, new linux kernels show 
the locked memory in "Locked" field.

If mmap file a mlock it, I see the following in 'smaps' file:

7efd20aeb000-7efd2172b000 r--p 00000000 103:04 1870                      
/tmp/file.bin
Size:              12544 kB
Rss:               12544 kB
Pss:               12544 kB
Shared_Clean:          0 kB
Shared_Dirty:          0 kB
Private_Clean:     12544 kB
Private_Dirty:         0 kB
Referenced:        12544 kB
Anonymous:             0 kB
AnonHugePages:         0 kB
Swap:                  0 kB
KernelPageSize:        4 kB
MMUPageSize:           4 kB
Locked:            12544 kB

...
# uname -a
Linux XXXXXX 3.2.0-4-amd64 #1 SMP Debian 3.2.68-1+deb7u3 x86_64 GNU/Linux

If I do this on an older kernel (2.6.x), the Locked field is missing.

I can make a patch for the ProcfsBasedProcessTree that will calculate 
the "Locked" pages instead of the "Private_Clean" (based on 
configuration option). The question is - should there be made even more 
changes in the way the memory footprint is calculated? For instance, I 
believe the kernel can write to disk even all dirty pages (if they are 
backed by a file), making them clean and therefore can later free them. 
Should I open a JIRA for this to have some discussion on this topic?

Regards,
  Jan


On 02/04/2016 07:20 PM, Chris Nauroth wrote:
> Hello Jan,
>
> I am moving this thread from user@hadoop.apache.org to
> yarn-dev@hadoop.apache.org, since it's less a question of general usage
> and more a question of internal code implementation details and possible
> enhancements.
>
> I think the issue is that it's not guaranteed in the general case that
> Private_Clean pages are easily evictable from page cache by the kernel.
> For example, if the pages have been pinned into RAM by calling mlock [1],
> then the kernel cannot evict them.  Since YARN can execute any code
> submitted by an application, including possibly code that calls mlock, it
> takes a cautious approach and assumes that these pages must be counted
> towards the process footprint.  Although your Spark use case won't mlock
> the pages (I assume), YARN doesn't have a way to identify this.
>
> Perhaps there is room for improvement here.  If there is a reliable way to
> count only mlock'ed pages, then perhaps that behavior could be added as
> another option in ProcfsBasedProcessTree.  Off the top of my head, I can't
> think of a reliable way to do this, and I can't research it further
> immediately.  Do others on the thread have ideas?
>
> --Chris Nauroth
>
> [1] http://linux.die.net/man/2/mlock
>
>
>
>
> On 2/4/16, 5:11 AM, "Jan Lukavsk√Ĺ" <jan.lukavsky@firma.seznam.cz> wrote:
>
>> Hello,
>>
>> I have a question about the way LinuxResourceCalculatorPlugin calculates
>> memory consumed by process tree (it is calculated via
>> ProcfsBasedProcessTree class). When we enable caching (disk) in apache
>> spark jobs run on YARN cluster, the node manager starts to kill the
>> containers while reading the cached data, because of "Container is
>> running beyond memory limits ...". The reason is that even if we enable
>> parsing of the smaps file
>> (yarn.nodemanager.container-monitor.procfs-tree.smaps-based-rss.enabled)
>> the ProcfsBasedProcessTree calculates mmaped read-only pages as consumed
>> by the process tree, while spark uses FileChannel.map(MapMode.READ_ONLY)
>> to read the cached data. The JVM then consumes *a lot* more memory than
>> the configured heap size (and it cannot be really controlled), but this
>> memory is IMO not really consumed by the process, the kernel can reclaim
>> these pages, if needed. My question is - is there any explicit reason
>> why "Private_Clean" pages are calculated as consumed by process tree? I
>> patched the ProcfsBasedProcessTree not to calculate them, but I don't
>> know if this is the "correct" solution.
>>
>> Thanks for opinions,
>>   cheers,
>>   Jan
>>
>>
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