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

[Rickard Bäckman]

Updated again.

http://cr.openjdk.java.net/~rbackman/8064458.5

Thanks

On 04/30, Vladimir Kozlov wrote:
> 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
> >>>>>
/R
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