RFR(S): 8134889: Kitchensink stress test crashes with out of memory error

[Derek White]

Hi Mikael,

On 4/21/16 10:36 AM, Derek White wrote:
> Hi Mikael,
>
> On 4/21/16 4:02 AM, Mikael Gerdin wrote:
>> Hi Derek,
>>
>> On 2016-04-20 23:48, Derek White wrote:
>>> Still looking for reviews for a small fix for a P2 bug...
>>>
>>> Thanks!
>>>
>>> On 4/7/16 6:07 PM, Derek White wrote:
>>>> Summary:
>>>> The remaining part of this bug deals with running out of address space
>>>> on 32-bit JVMs running on Win64. This fix is simply to have a hard
>>>> limit on GC threads (still larger than necessary) on 32-bit JVMs. The
>>>> new limit is 16 (2 * switch_pt).
>>>>
>>>> Note that this overlaps somewhat with several "# of GC thread" bugs
>>>> including:
>>>>  - 8131932 <https://bugs.openjdk.java.net/browse/JDK-8131932> :
>>>> Ergonomics oversize number of GC threads for small JVMs on large 
>>>> systems
>>>>  - 8153225 <https://bugs.openjdk.java.net/browse/JDK-8153225>: G1
>>>> creates too many concurrent refinement threads by default
>>>>  - 7189147 <https://bugs.openjdk.java.net/browse/JDK-7189147>: GC
>>>> threads should be created as needed not all at once
>>>>
>>>> Doing the correct thing in general will require a lot more performance
>>>> analysis. The fix here is simple, only affects 32-bit JVMs running on
>>>> >= 24 core machines, and will reduce OOM crashes in nightly testing.
>>>>
>>>> BUG: 8134889 <https://bugs.openjdk.java.net/browse/JDK-8134889>
>>>> WEBREV: http://cr.openjdk.java.net/~drwhite/8134889/webrev.01/
>>
>> Fix looks good.
>> I wonder about the cast to unsigned int, though.
>> It seems weird that it's needed since all the other operands are 
>> unsigned ints in the calculation.
>
> Yes, that does look weird. I can't recall why I added it either.
>
>      unsigned int switch_pt = bar;
>      unsigned int threads = foo;
>      threads = MIN2(threads, 2*switch_pt)
>
> Wait a minute, according to the interweb, the type of the literal '2' 
> is "int" (eg. signed). I think one compiler complained on a jprt run. 
> Doing a jprt run without the cast...
So jprt is happy with or with the cast. I had the type promotion rules 
wrong in my head.
signed * unsigned = unsigned.

I'll remove the cast and update the webrev.

Thanks,

   - Derek
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