RFR 8252500: ZGC on aarch64: Unable to allocate heap for certain Linux kernel configurations

[Christoph Göttschkes]

Hi Thomas,

On 2020-09-03 17:27, Thomas Stüfe wrote:
> Not a full review, just some small remarks.
> 
> Instead of using msync, how about using os::is_readable_pointer()? You 
> should be far enough in initialization to have initialized safefetch 
> stubs. That would tell you if the address is mapped. If that returns 
> false, I'd use mmap with MAP_FIXED_NOREPLACE.

I would like to avoid MAP_FIXED_NOREPLACE. According to the man page, it 
has been added in Linux 4.17. There are still plenty of stable kernel 
versions around which will not have that feature, which means we need to 
implement a workaround for it. Some of my test devices also have a 
kernel version lower than that.

-- Christoph