RFR: 8190283 - Default heap sizing options select a MaxHeapSize larger than available physical memory in some case

[Bob Vandette]

> On Nov 3, 2017, at 12:42 PM, Bob Vandette <bob.vandette at oracle.com> wrote:
> 
> I realized that I didn’t post the webrev on our external server.  There was only 1 file changed.
> Here’s the diff:
> 
> *** old/src/hotspot/share/runtime/arguments.cpp	Fri Nov  3 11:50:07 2017
> --- new/src/hotspot/share/runtime/arguments.cpp	Fri Nov  3 11:50:07 2017
> 
> *** 2086,2098 ****
> --- 2086,2099 ----
>    // If the maximum heap size has not been set with -Xmx,
>    // then set it as fraction of the size of physical memory,
>    // respecting the maximum and minimum sizes of the heap.
>    if (FLAG_IS_DEFAULT(MaxHeapSize)) {
>      julong reasonable_max = (julong)((phys_mem * MaxRAMPercentage) / 100);
>      if (phys_mem <= (julong)((MaxHeapSize * MinRAMPercentage) / 100)) {
> +     const julong reasonable_min = (julong)((phys_mem * MinRAMPercentage) / 100);
> +     if (reasonable_min < MaxHeapSize) {
>        // Small physical memory, so use a minimum fraction of it for the heap
> !       reasonable_max = (julong)((phys_mem * MinRAMPercentage) / 100);
> !       reasonable_max = reasonable_min;
>      } else {
>        // Not-small physical memory, so require a heap at least
>        // as large as MaxHeapSize
>        reasonable_max = MAX2(reasonable_max, (julong)MaxHeapSize);
>      }
> Bob
> 
>> On Nov 3, 2017, at 11:58 AM, Bob Vandette <bob.vandette at oracle.com> wrote:
>> 
>> Please review this simple change that alters the algorithm for selecting the
>> default heap size on low (~100MB) memory environments.
>> 
>> This issue is blocking the integration of the container improvements (https://bugs.openjdk.java.net/browse/JDK-8146115 <https://bugs.openjdk.java.net/browse/JDK-8146115>).
>> 
>> 
>> BUG:
>> https://bugs.openjdk.java.net/browse/JDK-8190283 <https://bugs.openjdk.java.net/browse/JDK-8190283>
>> 
>> WEBREV:
>> http://bussund0417.us.oracle.com/export/users/bobv/jdk10hs-base/open/webrev/ <http://bussund0417.us.oracle.com/export/users/bobv/jdk10hs-base/open/webrev/>
>> 
>> Bob.
>> 
>