RFR: 8222145: Add -XX:SoftMaxHeapSize flag

[Per Liden]

On 04/10/2019 04:33 PM, Erik Österlund wrote:
> Hi Per,
> 
> 723 manageable(size_t, SoftMaxHeapSize, 0, \
> 724 "Soft limit for maximum heap size (in bytes)") \
> 725 constraint(SoftMaxHeapSizeConstraintFunc,AfterMemoryInit) \
> 726 \ Seems like the indentation is a bit off here. Otherwise, this 
> looks good. Don't need another webrev for the indentation fix. Thanks, 

Thanks for reviewing Erik!

As far as I can tell, this is the dominating indentation style used this 
and the other *globals.hpp files (there are a few random exceptions), so 
I think it's actually "correct".

cheers,
Per

> /Erik
> 
> On 2019-04-10 14:06, Per Liden wrote:
>> Introduce a manageable SoftMaxHeapSize flag. When set, the GC should 
>> strive to not grow heap size beyond the specified size. But as the 
>> flag name suggests, this is a soft limit. In other words, the GC is 
>> allowed to grow the heap size beyond SoftMaxHeapSize if needed.
>>
>> There are a few different use cases where this flag could be useful. 
>> For example, when you want to keep the heap footprint down, while 
>> retaining the capability to deal with a temporary increase in heap 
>> space requirement. Or when you want to play it safe, with lots of 
>> margin, to increase confidence that you will not run into an 
>> allocation stall because of an unforeseen increase in allocation rate.
>>
>> The SoftMaxHeapSize should not be allowed to be set to a value smaller 
>> than min heap size (-Xms) or greater than max heap size (-Xmx). When 
>> not set on the command-line, this flag should default to the max heap 
>> size.
>>
>> Bug: https://bugs.openjdk.java.net/browse/JDK-8222145
>> CSR: https://bugs.openjdk.java.net/browse/JDK-8222181
>> Webrev: http://cr.openjdk.java.net/~pliden/8222145/webrev.1
>>
>> /Per
>