Request for review: 8008079 G1: Add nextObject routine to CMBitMapRO and replace nextWord

Tao Mao tao.mao at oracle.com
Fri Mar 1 17:19:55 PST 2013


integrated the suggestion. A new webrev is updated.
http://cr.openjdk.java.net/~tamao/8008079/webrev.01/

again, passed gc-test-suite for fastdebug build with stressing marking 
cycles
script:
./run.sh /home/tamao/jdk1.8.0 --bits 64 --args -tamao -XX:+UseG1GC 
-XX:InitiatingHeapOccupancyPercent=5 -XX:+UnlockDiagnosticVMOptions 
-XX:+VerifyDuringGC

On 2/25/13 3:06 PM, John Cuthbertson wrote:
> Hi Tao,
>
> Looks fine except for the following nits....
>
> concurrentMark.hpp:100
> Can you remove the line:
>
> // XXX Fix these so that offsets are size_t's...
>
> concurrentMark.hpp:111
> It might be safer to return:
>
> return offsetToHeapWord(heapWordToOffset(addr + obj->size()));
>
> or assert something like:
>
> HeapWord* res = addr + obj->size();
> assert(offsetToHeapWord(heapWordToOffset(res)) == res, "sanity");
> return res;
>
> JohnC
> On 2/21/2013 6:16 PM, Tao Mao wrote:
>> 8008079 G1: Add nextObject routine to CMBitMapRO and replace nextWord
>> https://jbs.oracle.com/bugs/browse/JDK-8008079
>>
>> webrev:
>> http://cr.openjdk.java.net/~tamao/8008079/webrev.00/
>>
>> changeset:
>> When concurrent marking scans an object, the task local finger is 
>> updated to point to the start of the object. If the marking task is 
>> asked to abort, the local finger is updated to the next word where 
>> another could possibly start. When the marking task is restarted, we 
>> restart scanning the marking bitmap from the updated local finger.
>>
>> This is a safe implementation but has not been fully exploited for 
>> efficiency because the contents of the marking bitmap should be all 
>> 0's until the offset associated with the actual start of the next 
>> object. When the marking task is restarted, we will scan these 0's 
>> looking for the first set bit.
>>
>> We can avoid this redundant scanning by updating the finger to and 
>> re-starting the scan at the actual offset where the next object starts.
>>
>> testing:
>> passed gc-test-suite with stressing marking cycles
>> script:
>> ./run.sh /home/tamao/jdk1.8.0 --bits 64 --args -tamao -XX:+UseG1GC 
>> -XX:InitiatingHeapOccupancyPercent=10 -XX:+UnlockDiagnosticVMOptions 
>> -XX:+VerifyDuringGC
>
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