RFR: 8184765: Dynamically resize SystemDictionary

[coleen.phillimore at oracle.com]

Hi Gerard,

This looks great.  One small question:

*+ // straight forward brute force*
*+ inline static int _next_prime(int n) {*
*+ int p = n;*
*+ for (int i = n; i < (n * n); i++) {*
*+ if ((i % 2) != 0) {*
*+ p = i;*
*+ break;*
*+ }*
*+ }*
*+ return p;*
*+ }*


Is this how you calculate next prime?  Wouldn't you check if it can mod 
by 3 and 5 as well?

Thanks,
Coleen


On 10/27/17 2:25 PM, Gerard Ziemski wrote:
> hi Coleen,
>
> Thank you for the review.
>
> Updated webrev: http://cr.openjdk.java.net/~gziemski/8184765_rev2
>
>> On Oct 11, 2017, at 9:10 AM, coleen.phillimore at oracle.com wrote:
>>
>>
>> Gerard, some preliminary comments.
>>
>> http://cr.openjdk.java.net/~gziemski/8184765_rev1/src/hotspot/share/classfile/systemDictionary.cpp.udiff.html
>>
>> *+{*
>> *!_MutexLocker mu(SystemDictionary_lock, THREAD_);*
>> *!_Klass* probe = dictionary->find(_d_hash, name, protection_domain);*
>> *if (probe != NULL) return probe;*
>> **
>> *+ }*
>>
>> I don't think you need this because dictionary->find() should have the NoSafepointVerifier, so the index will not change.
> Done, good catch.
>
>
>> http://cr.openjdk.java.net/~gziemski/8184765_rev1/src/hotspot/share/classfile/classLoaderData.cpp.udiff.html
>>
>> I think we want a global _some_dictionary_needs_resizing to avoid walking through the CLDG.
>>
>> And have Dictionary have a field _resizing_needed to avoid the calculation during the safepoint, which is set when adding an entry.
>>
>> _resizing_needed = *(number_of_entries() > (_resize_load_trigger*table_size());
>> *CLDG::_any_resizing_needed |= _resizing_needed;   // or something like that.
>>
>> I can write more about the rationale of this change in the bug report, if needed.
> Done.
>
>
>> Thank you for doing this change.
>> Coleen
>>
>>
>> On 10/10/17 4:40 PM, Gerard Ziemski wrote:
>>> hi all,
>>>
>>> Please review this change that adds dynamic resizing of system dictionaries.
>>>
>>> The biggest change is refactoring of the code that protects calculating of the table entry’s index using SystemDictionary_lock
>>>
>>> A few notes:
>>>
>>> - dynamic resizing is off when either dumping or using shared spaces
>>> - we remove the experimental runtime option “PredictedLoadedClassCount” and add “DynamicallyResizeSystemDictionaries” to turn the resizing off (it’s on by default)
>>> - the jtreg test uses stream of bytes to dynamically load numbered classes from memory instead of disk (thank you Ioi)
>>>
>>> bug:    https://bugs.openjdk.java.net/browse/JDK-8184765
>>> webrev: http://cr.openjdk.java.net/~gziemski/8184765_rev1
>>>
>>>
>>> cheers
>>>