RFR (M): 8064458 OopMap class could be more compact

[Vladimir Kozlov]

It is better now. I am fine with inner Mapping class.

One thing left. I think only Mapping and fields could be private since only ImmutableOopMapBuilder accesses them:


+ class ImmutableOopMapBuilder {
+ public:
+   class Mapping;
+
+ public:
+   const OopMapSet* _set;

thanks,
Vladimir

On 4/30/15 7:18 AM, Rickard Bäckman wrote:
> On 04/29, Vladimir Kozlov wrote:
>> On 4/29/15 7:52 AM, Rickard Bäckman wrote:
>>> On 04/28, Vladimir Kozlov wrote:
>>>> You need closed SA changes.
>>>
>>> I have them, just forgot to send the mail. Small changes too.
>>>
>>>>
>>>> Style:
>>>>
>>>> Move fields to the beginning of ImmutableOopMapBuilder and classes.
>>>> Add comments describing each field in ALL new classes. Add comments
>>>> to fields in old class. It will help next persone who will look on
>>>> oop maps later.
>>>
>>> All fields are at the beginning? Just following style and keeping
>>> friends above fields as other classes in the same file has.
>>
>>    friends
>>    fields
>>    methods
>>
>> It is better to see fields before methods which access them. I am
>> not sure what codding style you are talking about. All classes in
>> oopMap.hpp has above layout.
>>
>> I am asking to change layout of ImmutableOopMapBuilder and Mapping classes. Also why Mapping is inner class?
>
> Ah, I was looking at oopMap.hpp and didn't see them. Fixed.
> Mapping is an inner class because it is only used by the Builder and I
> didn't want to clutter the namespace with something as general (and bad)
> as Mapping. I can move it out if that is preferred.
>
>>
>>
>>>
>>>>
>>>> Add ResourceMark into ImmutableOopMapSet::build_from() to free memory allocated in ImmutableOopMapBuilder().
>>
>> no ResourceMark in 8064458.2
>
> Added.
>
>>
>>>> Why you need ImmutableOopMapBuilder to be friend of class ImmutableOopMap?
>>>
>>> It makes a call to data_addr() which is private. Only for debug builds
>>> so I wrapped it in DEBUG_ONLY.
>>
>> Put ImmutableOopMapBuilder::verify() under #ifdef ASSERT and its declaration in DEBUG_ONLY.
>>
>
> Done.
>
> Updated webrev: http://cr.openjdk.java.net/~rbackman/8064458.4
>
> Thanks
> /R
>
>> Thanks,
>> Vladimir
>>
>>>
>>>>
>>>> I think a simple loop in ImmutableOopMapBuilder::verify() would be faster than calling memcmp.
>>>
>>> Fixed.
>>>
>>>>
>>>> Field _end is not used.
>>>
>>> Removed.
>>>
>>>>
>>>> ImmutableOopMapBuilder() calls reset() and next called heap_size()
>>>> calls reset() again. May be move reset() to the end of heap_size()
>>>> so that you don't need to call it in fill().
>>>>
>>>
>>> Better yet, the reset() method isn't required anymore.
>>>
>>> Updated webrev: http://cr.openjdk.java.net/~rbackman/8064458.2
>>>
>>> /R
>>>
>>>> Thanks,
>>>> Vladimir
>>>>
>>>> On 4/28/15 3:03 AM, Rickard Bäckman wrote:
>>>>> Hi all,
>>>>>
>>>>> can I please have reviews for this change:
>>>>>
>>>>> RFR: http://cr.openjdk.java.net/~rbackman/8064458.1/
>>>>> RFE: http://bugs.openjdk.java.net/browse/JDK-8064458
>>>>>
>>>>> While looking at OopMaps a while ago I noticed that there were a couple
>>>>> of different fields that were unused after the OopMaps were finalised.
>>>>>
>>>>> I took some time to investigate and rearrange the OopMaps. Since I
>>>>> didn't want to change how the OopMaps are built I introduced new data
>>>>> structures. ImmutableOopMapSet and ImmutableOopMap. The original OopMap
>>>>> structures are used to build up the OopMaps and when finalised they are
>>>>> copied into the Immutable variants.
>>>>>
>>>>> The ImmutableOopMapSet contains a few fields [size, count] and then a
>>>>> list of [pc, offset]. The offset points to the offset after the list
>>>>> where the ImmutableOopMap is placed. By moving pc out from OopMap to be
>>>>> part of the list we can now have multiple pcs with identical OopMaps
>>>>> point to the same data.
>>>>>
>>>>> We only keep 1 empty OopMap, and the other compaction that is done in
>>>>> this change is to check if the OopMap is identical to the previous one
>>>>> and then reuse that one. So no complete uniqueness check.
>>>>>
>>>>> I ran a couple of small benchmarks and printed the size of the old
>>>>> OopMaps vs the new. The new layout uses about 20 - 25% of the space on
>>>>> the benchmarks I've run.
>>>>>
>>>>> Tested by running through JPRT, running BigApps and NSK.quick.testlist
>>>>>
>>>>> Thanks
>>>>> /R
>>>>>