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

[Stuart Monteith]

Hello Per,
  I notice you've left "UseNewCode" in size_t
ZPhysicalMemoryBacking::commit(size_t offset, size_t length). I
presume this is accidental. The rest looks ok to me.

Thanks,
  Stuart

On Thu, 23 Jan 2020 at 10:02, Per Liden <per.liden at oracle.com> 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