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

[Thomas Stüfe]

On Thu, Apr 4, 2019 at 2:04 AM <coleen.phillimore at oracle.com> wrote:

>
> This looks good, with the unnecessary null checks removed.  I don't need
> to see another version but do a sanity build before pushing please!
> Thanks!
> Coleen
>

Thanks Coleen.

I run jdk-submit before every push. Which is why I usually delay running it
for after the reviews, to avoid uncessary re-tests.

Thanks, Thomas


>
>
> On 4/3/19 4:57 AM, Thomas Stüfe wrote:
>
> Hi all,
>
> new version:
>
> Delta:
>
> http://cr.openjdk.java.net/~stuefe/webrevs/8221539--%5bmetaspace%5d-improve-metaspaceobj--is_metaspace_obj()-and-friends/delta_to_4/webrev/index.html
>
> Full:
>
> http://cr.openjdk.java.net/~stuefe/webrevs/8221539--%5bmetaspace%5d-improve-metaspaceobj--is_metaspace_obj()-and-friends/webrev.04/webrev/
>
> Changes:
>
> - As Coleen wished, I completely removed the non-static variant of
> MetaspaceObj::is_metaspace_obj() and fixed the callers.
> - I also renamed the static variant of MetaspaceObj::is_metaspace_obj() to
> MetaspaceObj::is_valid() to be in line with similar calls, e.g.
> Symbol::is_valid().
>
> @Coleen: This envelope should only weed out obvious non-null bogus values
> and hopefully stack and C-heap addresses; my hope is that nodes come and go
> but that the total envelope size will be always minuscule compare to the
> 64bit address range and outside C-heap and stacks. Usually mmap regions are
> clustered, as are C-Heap allocations and stacks.
>
> But if that turns out to be inefficient after a while, we may recalculate
> the envelope; just have to make sure no concurrent lock-less walks happen.
>
> Thanks, Thomas
>
>
>
> On Tue, Apr 2, 2019 at 2:21 PM <coleen.phillimore at oracle.com> wrote:
>
>>
>>
>> On 4/2/19 1:47 AM, Thomas Stüfe 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 think you have to change the callers to not pass this as null.  So you
>> can't do metaspaceobj->is_metaspace_object() because you're calling with
>> "this" potentially NULL.
>>
>> So remove this function:
>>
>>  bool MetaspaceObj::is_metaspace_object() const {-  return Metaspace::contains((void*)this);+  return MetaspaceObj::is_metaspace_object(this);
>>  }
>>
>>
>>
>> - 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.
>>
>>
>> So this envelope is an interesting concept and name.  It seems okay.  I
>> guess over time, it won't give you a very good answer.  Maybe you'll have
>> to fix the boundaries someday.
>>
>> Looks good though.  Thank you for making this improvement for performance.
>>
>> Coleen
>>
>>
>> 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
>>>
>>>
>>>
>>
>