RFR (XS): 8234127: BasicHashtable does not support small table_size

[Ioi Lam]

On 11/14/19 1:47 PM, Man Cao wrote:
> Thanks for the review.
>
>> It's not directly related, I'm wondering why such small hashtable is
>> needed in your use case.
> The test G1AddMetaspaceDependency.java sets -XX:G1UpdateBufferSize=1, which
> would create a size-one hashtable with my pending change for JDK-8087198.
> Real users should probably not set G1UpdateBufferSize so small, unless they
> want to stress G1's code for concurrent refinement.
>
> -Man

If a minimum size of 1 doesn't make sense, maybe in your patch for 
JDK-8087198, you can update the allowable range in globals.hpp, or 
manually override it to a minimum size that makes sense? That can 
prevent incorrect settings that would cause unintended slow down.

   product(size_t, G1UpdateBufferSize, 
256,                                  \
           "Size of an update 
buffer")                                       \
           range(1, NOT_LP64(32*M) 
LP64_ONLY(1*G))                           \
\

Thanks
- Ioi

>
> On Thu, Nov 14, 2019 at 1:20 PM Jiangli Zhou <jianglizhou at google.com> wrote:
>
>> Hi Man,
>>
>> Just took a look. Looks fine to me as well.
>>
>> It's not directly related, I'm wondering why such small hashtable is
>> needed in your use case.
>>
>> Thanks,
>> Jiangli
>>
>> On Thu, Nov 14, 2019 at 11:19 AM Man Cao <manc at google.com> wrote:
>>> Thanks for the review. Yes, I will try using ResourceHashtable in new
>> code.
>>> The BasicHashtable does not work with size 2 and 3, either. In my use
>> case,
>>> the initial size is based on a JVM flag (G1UpdateBufferSize), so it is
>>> dependent on user input.
>>>
>>> -Man
>>>
>>>
>>> On Thu, Nov 14, 2019 at 10:52 AM <coleen.phillimore at oracle.com> wrote:
>>>
>>>> This fix seems fine, but having a hashtable with a starting length 1
>>>> seems silly.   Unless I'm reading this wrong.   As Ioi wrote in his
>>>> comment, there might be a better hashtable for your work.
>>>>
>>>> Thanks,
>>>> Coleen
>>>>
>>>> On 11/13/19 8:00 PM, Man Cao wrote:
>>>>> Hi all,
>>>>>
>>>>> Can I have reviews for this small bug fix?
>>>>> Webrev: https://cr.openjdk.java.net/~manc/8234127/webrev.00/
>>>>> Bug: https://bugs.openjdk.java.net/browse/JDK-8234127
>>>>>
>>>>> I'm trying to make use of KVHashtable in JDK-8087198 and encountered
>> this
>>>>> bug.
>>>>>
>>>>> -Man
>>>>