RFR(M): 6921087: G1: remove per-GC-thread expansion tables from the fine-grain remembered sets

[John Cuthbertson]

Hi Bengt,

A similar question regarding PRT_COUNT_OCCUPIED was asked by Thomas.

It looks like the code under SAMPLE_FOR_EVICTION describe alternative 
strategies for determining which PerRegionTable to evict from the fine 
grain entries. If SAMPLE_FOR_EVICTION is defined TRUE then the PRT 
selected for eviction is chosen from a small subset of the PRTs; 
otherwise we look at all the PRTs and select the one with most number of 
entries. Using the non SAMPLE_FOR_EVICTION code will most likely lead to 
regressions during RSet updating except when _n_fine_entries is less 
than _fine_eviction_sample_size.

I'm OK with removing the #if-s  and associated dead code - especially 
since the sample code has been getting exercised for quite a while.

What about PRT_COUNT_OCCUPIED - should we remove those and have the code 
unconditional too?

Thanks,

JohnC

On 06/20/12 05:03, Bengt Rutisson wrote:
>
> Hi John and Thomas,
>
> This looks good to me.
>
> One minor thing:
>
> Not strictly related to this change, but why do we have 
> SAMPLE_FOR_EVICTION defined as 1? I guess this means that it is always 
> been on and thus we won't get any performance regressions from 
> removing the #if SAMPLE_FOR_EVICTION guards. So, why don't we just go 
> ahead and do that? It would simplify the code a bit.
>
> Maybe this should be done as a separate change. It just looks kind of 
> strange to me.
>
> Bengt
>
> P.S. Copyright year in heapRegionRemSet.hpp... ;-)
>
>
>
> On 2012-06-19 21:21, John Cuthbertson wrote:
>> Hi Everyone,
>>
>> Can I have a review for the cleanup changes, supplied by Thomas 
>> Schatzl (Johannes Kepler University at Linz), for this CR? The webrev 
>> can be found at: http://cr.openjdk.java.net/~johnc/6921087/webrev.0/
>>
>> Summary:
>> Thomas has removed the per thread expansion tables (PosParPRT) and 
>> associated, unused, expansion and compaction code along with some 
>> additional unused code. This change significantly reduces the code 
>> complexity of the fine grained RSet entries. These changes are a 
>> prerequisite for some other changes that Thomas has been working on 
>> to optimize the freeing of RSets' fine grained entries.
>>
>> I've looked at the changes and they have a thumbs up from me.
>>
>> Testing: OpenDS (performed by Thomas), the GC test suite with heap 
>> verification enabled (me), and jprt (me).
>>
>> Thanks,
>>
>> JohnC
>