Review request: 8008549: NPG: SystemDictionary::find(...) unnecessarily keeps class loaders alive

[Stefan Karlsson]

Thanks for the review.

StefanK

On 02/26/2013 02:18 PM, Coleen Phillimore wrote:
>
> This is a really clean fix and thank you for finding one of the causes 
> of the problem.
>
> Coleen
>
> On 2/21/2013 11:57 AM, Stefan Karlsson wrote:
>> http://cr.openjdk.java.net/~stefank/8008549/webrev.00/
>>
>> This change fixes a bug, which showed up as a regression in our Jetty 
>> footprint regression testing. The bug prevents the young GCs from 
>> reclaiming some java.util.zip.Inflaters, which in turn holds on to 7 
>> KB of native memory each.
>>
>> Description from the bug report:
>> Before the PermGen removal a class loader could be garbage collected 
>> by a young GC if it didn't load any classes and all references to it 
>> were dropped.
>>
>> After the PermGen removal, there's an unnecessary call to 
>> register_loader in the SystemDictionary::find(...) function:
>> ClassLoaderData* loader_data = register_loader(class_loader, 
>> CHECK_NULL);
>>
>> which prevents these kind of class loader from being garbage 
>> collected by the young GCs.
>>
>> Fortunately, we don't have to register a ClassLoaderData for the 
>> class loader in the find(...) function. The rational is that if we 
>> haven't already setup a ClassLoaderData for the class loader, then it 
>> won't have an entry in the dictionary, and we can safely return NULL.
>>
>> This bug is one of the reasons for the memory footprint regressions 
>> seen in:
>> JDK-8001590 <https://jbs.oracle.com/bugs/browse/JDK-8001590>: NPG: 
>> Footprint increase when running Jetty
>>
>> thanks,
>> StefanK & Erik Helin
>

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