[ZGC] [aarch64] Unable to allocate heap for certain Linux kernel configurations

[Florian Weimer]

* Stefan Karlsson:

>> Note that you can speed this up a little bit on recent-ish kernels if
>> you use MAP_FIXED_NOREPLACE.
>
> I didn't realize that this would make the probing faster. I tested
> this by blocking out the address ranges we probe with:
>
>
>   reserve_contiguous_platform(ZAddress::marked0(0), ZAddressOffsetMax);
>   reserve_contiguous_platform(ZAddress::marked1(0), ZAddressOffsetMax);
>   reserve_contiguous_platform(ZAddress::remapped(0), ZAddressOffsetMax);
>
> and ran with and without MAP_FIXED_NOREPLACE. I could see a decrease
> in in the worst-case times. Is this something you want to provide a
> patch for? If not, I can create a JBS entry and send out a patch for
> review.

No, sorry, it was just a random comment from the sidelines.

Florian