RFR(XS) 8191369: NMT: Enhance thread stack tracking

[David Holmes]

Hi Andrew,

On 17/11/2017 1:46 AM, Andrew Haley wrote:
> On 16/11/17 06:58, David Holmes wrote:
> 
>> I can't review this in detail as I'm not familiar with NMT workings, but
>> have a couple of comments.
>>
>> On 16/11/2017 8:25 AM, Zhengyu Gu wrote:
>>> This is Linux only enhancement for now, can be extended for other
>>> platforms. (See bug for details)
>>
>> I'm concerned about unnecessary platform skew. I added some comments to
>> the bug. I think the mincore trick can be used on Solaris and AIX as
>> well - but not on OS X / BSD. It may be that VirtualQuery can be used on
>> Windows to get the same information - but I'm unclear if the memory
>> states support what you're looking for. It would be good to extend this
>> to other platforms that will support it.
> 
> Sure, but as OpenJDK becomes more open and hopefully more diverse, it
> becomes less and less practical to keep everything in step.  I favour
> the classic free software approach, which is to encourage people to
> create new features and everyone else can fill in the gaps, depending
> on how much time and effort is available.  It's this approach that
> allows GCC to support a vast range of targets (and hosts) while not
> holding back development.  I have consistently argued for this in the
> Governing Board.

For OpenJDK I hope there are sufficient safety-nets in place to ensure 
such an approach does not lead to a product where you never know what 
will and won't work on each platform. Whenever we have such a case we 
should at least file sub-tasks for supplying the functionality on the 
missing platforms. We can then determine whether any such missing 
functionality is critical to fix before a release.

David
-----

> So, let's get this done.  It's very important for container memory
> monitoring, which right now usually means Linux.
>