Depth first object copying for all GC?

Jon Masamitsu jon.masamitsu at oracle.com
Thu May 7 19:25:35 UTC 2015


Ramki,

Did you ever make ParNew depth-first copying?

Jon

On 05/07/2015 11:51 AM, Jon Masamitsu wrote:
>
>
> On 05/06/2015 07:56 PM, Tangwei (Euler Architecture & Design Dept) wrote:
>>
>> Would you help to list the object copying policy for different GC?  
>> Or pointing out where to find such information?
>>
>
> For the most part UseParallelGC and UseG1GC has depth-first copying.  
> UseConcMarkSweepGC
> and UseSerialGC use breadth-first.  I qualify that because I've heard 
> people argue about whether
> that's 100% true.
>
> Jon
>
>> Regards!
>>
>> wei
>>
>> *From:*hotspot-gc-dev 
>> [mailto:hotspot-gc-dev-bounces at openjdk.java.net] *On Behalf Of * Jon 
>> Masamitsu
>> *Sent:* Thursday, May 07, 2015 8:23 AM
>> *To:* hotspot-gc-dev at openjdk.java.net
>> *Subject:* Re: Depth first object copying for all GC?
>>
>> 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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