RFR: 8245106: ZGC: Fix incorrect setup when using -XX:+UseTransparentHugePages

[Stefan Karlsson]

I talked to Per directly about some nits and additional comments. Other 
than that, this looks good to me.

StefanK

On 2020-05-15 14:04, Per Liden wrote:
> When using -XX:+UseTransparentHugePages, ZGC mistakenly calls 
> madvise(..., MADV_HUGE); too late. The end result is that large pages 
> are never allocated on first page fault, only via THP defrag. This in 
> turn means that the majority of the heap will typically not be backed 
> by large pages, which can have a very noticeable performance impact.
>
> This patch depends on "8245098: Make SafeFetch32/N available earlier", 
> which is currently out for review on hotspot-dev.
>
> Bug: https://bugs.openjdk.java.net/browse/JDK-8245106
> Webrev: http://cr.openjdk.java.net/~pliden/8245106/webrev.0
>
> /Per