RFR (S): JDK-6348447 - Specifying -XX:OldSize crashes 64-bit VMs

Jesper Wilhelmsson jesper.wilhelmsson at oracle.com
Mon Jan 14 17:10:38 UTC 2013


Hi,

I would like a couple of reviews of a small fix for JDK-6348447 - Specifying 
-XX:OldSize crashes 64-bit VMs

Webrev:
http://cr.openjdk.java.net/~jwilhelm/6348447/webrev/

Summary:
When starting HotSpot with an OldSize larger than the default heap size one 
will run into a couple of problems. Basically what happens is that the OldSize 
is ignored because it is incompatible with the heap size. A debug build will 
assert since a calculation on the way results in a negative number, but since 
it is a size_t an if(x<0) won't trigger and the assert catches it later on as 
incompatible flags.

Changes:
I have made two changes to fix this.

The first is to change the calculation in 
TwoGenerationCollectorPolicy::adjust_gen0_sizes so that it won't result in a 
negative number in the if statement. This way we will catch the case where the 
OldSize is larger than the heap size and adjust the OldSize instead of the 
young size. There are also some cosmetic changes here. For instance the 
argument min_gen0_size is actually used for the old generation size which was 
a bit confusing initially. I renamed it to min_gen1_size (which it already was 
called in the header file).

The second change is in Arguments::set_heap_size. My reasoning here is that if 
the user sets the OldSize we should probably adjust the heap size to 
accommodate that OldSize instead of complaining that the heap is too small. We 
determine the heap size first and the generation sizes later on while 
initializing the VM. To be able to fit the generations if the user specifies 
sizes on the command line we need to look at the generation size flags a 
little already when setting up the heap size.

Thanks,
/Jesper

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