Review request: 8026391: The Metachunk header wastes memory - 8026392: Metachunks and Metablocks are using a too large alignment

[Stefan Karlsson]

On 2013-10-14 22:40, Jon Masamitsu wrote:
> Comments only on the first patch.
>
> Looks good.  Couple of questions.
>
> Why the change from _is_free to _is_marked_free?
>
> From
>
>   58   bool _is_free;
>
> to
>
>  105   DEBUG_ONLY(bool _is_marked_free;)
>
>
> Is it to specifically distinguish it from the FreeChunk is_free()?
Yes.

>
> The "marked" in the name feels a little like GC when it
> isn't GC related.  Would "_is_tagged_free" make sense?

Sounds good. I'll change it.

>
>
> Did you consider changing the file names from Metachunk.* to
> Metamem.*?  The file contains the classes Metamem, Metablock,
> and Metachunk.  It sees more natural to me to have the file named
> after the more general Metamem class.  Then all the classes in
> the file are Metamem (or derived from), yes?

Coleen, has the opposite opinion. See answers to the other mails.

thanks,
StefanK
>
> Jon
>
> On 10/14/13 4:58 AM, Stefan Karlsson wrote:
>> Please, review these two patches to remove some of the wastages 
>> introduced in the metaspace.
>>
>>
>> 8026391: The Metachunk header wastes memory
>>  http://cr.openjdk.java.net/~stefank/8026391/webrev.00/
>>  https://bugs.openjdk.java.net/browse/JDK-8026391
>>
>> There are a couple of fields in Metachunk that store already known 
>> information, like the beginning and the end of the Metachunk. I 
>> replaced those fields with code instead.
>>
>> To make this easier, I extracted some duplicated code in Metablock 
>> and Metachunk into a super class named Metamem. The extracted code is 
>> purely needed to allow these objects to be placed on the FreeList and 
>> in the BinaryTreeDictionary.
>>
>>
>> 8026392: Metachunks and Metablocks are using a too large alignment
>>  http://cr.openjdk.java.net/~stefank/8026392/webrev.00/
>>  https://bugs.openjdk.java.net/browse/JDK-8026392
>>
>> The metaspace code was using ARENA_ALIGN to align the Metablocks and 
>> Metachunk header. This forced all allocations of metadata to be 16 
>> bytes aligned. This patch patch changes the restriction to be 8 bytes 
>> instead, since that's the restriction needed for 64 bit types like 
>> long, double, pointers and klass pointers,
>>
>>
>> Testing: Added unit test for Metachunk. JPRT (before splitting of the 
>> patches)
>>
>> thanks,
>> StefanK
>