RFR: 8252221: Use multiple workers for Parallel GC pre-touching

[Amit Pawar]

On Mon, 28 Sep 2020 04:11:16 GMT, Amit Pawar <github.com+71302734+amitdpawar at openjdk.org> wrote:

>> Hi Thomas,
>> 
>> Thanks for replying again and will do as per your suggestion.
>> 
>> Regarding using multiple threads to pre-touch old gen post resize.
>> Initial debugging showed that GC threads do reach here to initialize old gen memory post resizing. This limits to
>> single threaded only as GC thread is already executing a task and needs special handling. Please see generated log
>> messages below that included thread name.  2.116s][debug][gc   ] GC(9) Expanding ParOldGen thread name VM Thread from
>> 5632K by 3584K to 9216K 2.249s][debug][gc   ] GC(12) Expanding ParOldGen thread name VM Thread from 9216K by 6144K to
>> 15360K 5.768s][debug][gc   ] GC(33) Expanding ParOldGen thread name GC Thread#139 from 15360K by 512K to 15872K
>> 5.769s][debug][gc   ] GC(33) Expanding ParOldGen thread name GC Thread#92 from 15872K by 512K to 16384K
>> 5.769s][debug][gc   ] GC(33) Expanding ParOldGen thread name GC Thread#13 from 16384K by 512K to 16896K
>> 
>> I would like to fix this in two separate patches.
>> 
>> 1st Patch: Current PR fixes JVM startup time only. Pre-touching post resize do it multi-threaded with VM thread and
>> single threaded with non VM threads. This will be a partial fix but not complete. Complete fix can be done in second
>> patch.  2nd Patch: Please check log messages from 33th GC. Old gen size was changed three times in the same GC by three
>> different GC threads. This makes separate Pre-touching needs to be done post every resize. In the second patch this can
>> be done once by combining after all the resizes. I am interested in fixing this but need more time.  Please suggest.
>> 
>> Thanks,
>> Amit
>
> Thanks for agreeing and will update the PR with suggested changes for final review.
> 
> Thanks,
> Amit

Hi Thomas,

PR is updated with suggested changes. Please review.

Thanks,
Amit

-------------

PR: https://git.openjdk.java.net/jdk/pull/180