[Info-vax] VMS Alpha, JVM & P0 space issue

[abrsvc]

On Saturday, June 12, 2021 at 5:26:36 PM UTC-4, Arne Vajhøj wrote:
> I have a program running on JVM (Jython not Java but that 
> should not matter). 
> 
> And I noticed a weird problem. 
> 
> do A 
> do B 
> 
> fails 
> 
> do B 
> do A 
> 
> works 
> 
> A use JNI aka load a shareable image 
> 
> B use a lot of memory 
> 
> So my hypothesis is: 
> * JVM allocate some heap in P0 
> * A load the shareable image into P0 
> * B needs more memory so JVM tries to extend heap 
> * extend fail because heap cannot be extended contiguous 
> because of the shareable image 
> 
> Questions: 
> 
> 1) Does the hypothesis sound right? 
> 2) Is it possible to link the shareable image so that it get loaded 
> higher like at 1 GB mark leaving empty P0 space between heap 
> and it? 
> 3) Will the JVM be able to use that empty P0 space to extend heap? 
> 
> Arne
If you can pause the program prior to the second step, then ANAL/SYS is your friend here.  Look at the process memory and see where things are placed.