RFR: 8184765: Dynamically resize SystemDictionary

[coleen.phillimore at oracle.com]

On 10/30/17 11:24 AM, Gerard Ziemski wrote:
> hi Coleen,
>
>
>> On Oct 30, 2017, at 10:12 AM, coleen.phillimore at oracle.com wrote:
>>
>>
>> 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?
> As long as it’s not even i.e. mod 2 (and strictly speaking larger than 1). 3 and 5 are prime, so no need to check them.

If you passed in 214 (2*107), 215 would look prime but it's not.   I 
think the prime table would be better and limit resizing occurrences.

Coleen
>
> Thank you for the review!
>
>
> cheers
>
>
>> 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
>>>>>
>>>>>