RFR: 8237649: ZGC: Improved NUMA support when using small pages

[Per Liden]

Thanks Erik!

/Per

On 1/24/20 3:58 PM, erik.osterlund at oracle.com wrote:
> Hi Per,
> 
> Looks good.
> 
> Thanks,
> /Erik
> 
> On 1/23/20 11:02 AM, Per Liden wrote:
>> The NUMA allocation support in ZGC works as expected only when using 
>> -XX:+UseLargePages. The reason is that, on Linux, small pages are 
>> allocated at commit/fallocate time and is controlled by the NUMA 
>> policy of the current thread, while large pages are allocated at page 
>> fault time and is controlled by the NUMA policy of the memory range. 
>> ZGC currently only sets up the NUMA policy for the memory range, which 
>> has no effect on small pages (since they are allocated by tmpfs rather 
>> than being anonymous mappings).
>>
>> We should fix this, so that the NUMA allocation support works equally 
>> well for small pages.
>>
>> Bug: https://bugs.openjdk.java.net/browse/JDK-8237649
>> Webrev: http://cr.openjdk.java.net/~pliden/8237649/webrev.0
>>
>> /Per
>