RFR(xxxs): 8245707: Increase Metaspace reserve alignment

[Thomas Stüfe]

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>
wrote:

> Hi Ioi,
>
> On Wed, May 27, 2020 at 7:04 AM Ioi Lam <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
>>
>>