RFR(xxxs): 8245707: Increase Metaspace reserve alignment

[Ioi Lam]

Hi Thomas,

If (UseLargePages && UseLargePagesInMetaspace) is true, then 
_reserve_alignment will be 4*os::large_page_size(). Is this what you want?

Or, do you want to do the *4 only when large page is not used?

Why did you choose *4? Would *2 also accomplish what you want?

Thanks
- Ioi

On 5/25/20 10:57 PM, Thomas Stüfe wrote:
> Hi all,
>
> may I have reviews for this tiny change:
>
> JBS: https://bugs.openjdk.java.net/browse/JDK-8245707
> webrev:
> http://cr.openjdk.java.net/~stuefe/webrevs/8245707-increase-metaspace-reserve-alignment/webrev.00/webrev/
>
> One of the motivations behind JDK-8243392 was to decouple CDS reservation
> alignment from metaspace alignment and prevent misuse of metaspace reserve
> alignment outside metaspace. This is needed since with the upcoming new
> metaspace (JDK-8221173) its reserve alignment requirement will be much
> higher than CDS alignment.
>
> For the time being, until JDK-8221173 finds its way into jdk mainline, we
> should increase metaspace reserve alignment in jdk mainline to trigger any
> remaining illegal uses of metaspace reserve alignments and to prevent new
> ones from creeping in.
>
> All CI tests at SAP went through successfully, so at the moment we seem to
> be clean.
>
> Thanks, Thomas