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

[Stefan Karlsson]

Thanks, Karen!

StefanK

On 26 feb 2013, at 18:21, Karen Kinnear <karen.kinnear at oracle.com> wrote:

> Stefan,
> 
> The fix looks good.
> 
> Thank you for catching that!
> 
> thanks,
> Karen
> 
> On Feb 26, 2013, at 8:46 AM, Stefan Karlsson wrote:
> 
>> 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: NPG: Footprint increase when running Jetty
>>>> 
>>>> thanks,
>>>> StefanK & Erik Helin
> 
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