RFR(s): 8221539: [metaspace] Improve MetaspaceObj::is_metaspace_obj() and friends

[Thomas Stüfe]

p.s. nightlies at SAP ok, submit tests are ok

Cheers Thomas

On Tue, Apr 2, 2019 at 7:47 AM Thomas Stüfe <thomas.stuefe at gmail.com> wrote:

> Hi Coleen, Andrew,
>
> thank you for reviewing my little change. Unfortunately, I had an error in
> the space list verification method which needed fixing, so here is a second
> version:
>
>
> http://cr.openjdk.java.net/~stuefe/webrevs/8221539--%5bmetaspace%5d-improve-metaspaceobj--is_metaspace_obj()-and-friends/webrev.01/webrev/
>
> Differences:
> - As Coleen requested: in allocation.cpp I replaced the comparison
> this==NULL with a static helper method
> - I had mistype "envelope" as "envolope" in
> "expand_envelope_to_include_node()". Since that sounded funny I changed it.
> - The real bug was in VirtualSpaceList::verify() where I checked that the
> extension of the envelope is as large as the current nodes. But that is
> wrong, since the envelope never is shrunk (by design) and nodes at the
> border of the envelope may have been unmapped. So the real test should be
> to test if no node is outside the envelope.
>
> Thanks, Thomas
>
>
> On Wed, Mar 27, 2019 at 10:01 PM Thomas Stüfe <thomas.stuefe at gmail.com>
> wrote:
>
>> Hi all,
>>
>> May I please have reviews for this small optimization:
>>
>> cr:
>> http://cr.openjdk.java.net/~stuefe/webrevs/8221539--%5bmetaspace%5d-improve-metaspaceobj--is_metaspace_obj()-and-friends/webrev.00/webrev/index.html
>> Issue: https://bugs.openjdk.java.net/browse/JDK-8221539
>>
>> There are several functions which, given an unknown pointer assumed to be
>> a metaspace object, check if the pointer is indeed a metaspace object by
>> walking the VirtualSpaceList and checking ranges.
>>
>> This patch adds checks which weed out the obvious cases to avoid
>> needlessly walking the vs list.
>>
>> Patch also adds verifications for the VirtualSpaceList in debug cases.
>> Those run only when a new node has been added to the list, or when a node
>> has been purged, so very sparingly.
>>
>> When purging nodes, I removed a small unnecessary and inefficient check
>> which checked whether (one of the) purged nodes was still in the list.
>> Since we now as part of the new VirtualSpaceNode::verify() walk this list,
>> the check is unnecessary.
>>
>> Thanks, Thomas
>>
>>
>>