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

[Zhengyu Gu]

Thanks for the quick review, Andrew!

-Zhengyu

On 11/16/2017 04:48 AM, Andrew Dinn wrote:
> On 15/11/17 22:25, Zhengyu Gu wrote:
>> This is Linux only enhancement for now, can be extended for other
>> platforms. (See bug for details)
>>
>> Current implementation, thread stack is tracked when thread is created,
>> its available stack space is tagged as reserved and committed.
>>
>> However, this is not how stack works. Stack pages are committed on
>> demand, so this approach overstates its memory usage.
>>
>> This enhancement gathers thread stack usage at NMT query time, so that
>> it can report more accurate usage.
>>
>> Bug: https://bugs.openjdk.java.net/browse/JDK-8191369
>> Webrev: http://cr.openjdk.java.net/~zgu/8191369/webrev.00/index.html
> 
> The fix looks good to me.
> 
> It was very handy that get_stack_commited_bottom was already present in
> os_linux.cpp for other reasons -- although as David says it really ought
> to be spelled correctly with a double t in committed :-)
> 
> It is a good idea to try to extend this to other Unix-variant OSes that
> support mincore and to Windows (by whatever other means) but I don't
> think that should stop this being added to Linux now. This is too useful
> and important to omit because . . .
> 
> Footprint is a major concern for cloud deployments (where memory use is
> part of costing) and Linux underpins a significant proportion of cloud
> deployments. More accurate measurement of JVM footprint on Linux is
> going to be a great help to Java users when it comes to identifying and
> reducing the cost of cloud deployments.
> 
> regards,
> 
> 
> Andrew Dinn
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