Depth first object copying for all GC?

Jon Masamitsu jon.masamitsu at oracle.com
Thu May 7 00:23:19 UTC 2015



On 5/6/2015 4:34 AM, Tangwei (Euler Architecture & Design Dept) wrote:
>
> Hi All,
>
>   As a newbie in GC, I found some discussion on object copying order 
> in following slides: breadth vs. depth.
>
> It mentioned that /“Any static policy will hurt some applications and 
> help others”. /After searching, there is a BZ shows
>
> the object copying order has been switched from breadth to depth for 
> ParallelGC in OpenJDK, please correct if I am wrong.
>
> Anyone can help to confirm if all GC in OpenJDK use depth first 
> copying now?
>

No, not all the GC's use depth first copying.

> Is there any performance consideration to choose depth first instead 
> of controlling by option?
>

Yes, there is a performance cost to optionally using depth-first or 
breadth-first.
ParallelGC used to have such an option.  It made the code harder to 
maintain and,
as far as I can recall, there was very little use of the option.  We 
removed the
it.  I recall maybe 1 complaint about it.

Jon

> http://www.oracle.com/technetwork/server-storage/ts-6434-159339.pdf
>
> https://bugs.openjdk.java.net/browse/JDK-6450584: Improve object 
> copying order in parallel scavenge
>
> Regards!
>
> wei
>

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