RFR(xxxs): 8245707: Increase Metaspace reserve alignment

[Ioi Lam]

The new version looks fine to me.

Thanks
- Ioi

On 5/26/20 10:57 PM, Thomas Stüfe wrote:
> New version:
>
> http://cr.openjdk.java.net/~stuefe/webrevs/8245707-increase-metaspace-reserve-alignment/webrev.01/webrev/
>
> Thanks, Thomas
>
> On Wed, May 27, 2020 at 7:42 AM Thomas Stüfe <thomas.stuefe at gmail.com 
> <mailto:thomas.stuefe at gmail.com>> wrote:
>
>     Hi Ioi,
>
>     On Wed, May 27, 2020 at 7:04 AM Ioi Lam <ioi.lam at oracle.com
>     <mailto:ioi.lam at oracle.com>> wrote:
>
>         Hi Thomas,
>
>         If (UseLargePages && UseLargePagesInMetaspace) is true, then
>         _reserve_alignment will be 4*os::large_page_size(). Is this
>         what you want?
>
>
>     No :) That is why I limited this to cases where the page size is 4K.
>
>     However I see that on Windows this would still land us at
>     4*allocation granularity instead, so 256K. I'll change that.
>
>         Or, do you want to do the *4 only when large page is not used?
>
>
>     Only if page size is 4K. The reason is that I want to trip over
>     anyone asserting and calculating alignment (eg. CDS) but not
>     trigger any tests which do test things like memory counters - on
>     some of our platforms we have 64K and I don't want to adjust a
>     bunch of tests.
>
>         Why did you choose *4? Would *2 also accomplish what you want?
>
>
>     *2 would also be acceptable. I'll post an update.
>
>     Thanks! ..Thomas
>
>         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
>