[Vm-dev] Re: [squeak-dev] uncompacting classes

[Mariano Martinez Peck]

On Tue, Nov 29, 2011 at 10:27 PM, Eliot Miranda <eliot.miranda at gmail.com>wrote:

>
>
>
> On Tue, Nov 29, 2011 at 11:54 AM, Mariano Martinez Peck <
> marianopeck at gmail.com> wrote:
>
>>
>>
>>
>> On Mon, Nov 28, 2011 at 7:25 PM, Eliot Miranda <eliot.miranda at gmail.com>wrote:
>>
>>>
>>>
>>>
>>> On Sat, Nov 26, 2011 at 3:02 PM, Chris Muller <asqueaker at gmail.com>wrote:
>>>
>>>> Compact classes cannot be made uncompact in a Cog+JIT VM.
>>>>
>>>
>>> Not exactly true.  Certain classes cannot be uncompacted.  These are as
>>> defined by
>>>     StackInterpreter>>#checkAssumedCompactClasses
>>> and the ones that can't be uncompacted are
>>> Array
>>> LargeNegativeInteger
>>>  LargePositiveInteger
>>> Float
>>> MethodContext
>>>
>>> There is a performance advantage to being able to identify instances of
>>> these classes from the compact class index.
>>>
>>> But any other classes should be able to be compacted and uncompacted.
>>>
>>
>>
>> Eliot, should we validate this in image side (#becomeUncompact)  ?
>>
>
> I suppose so.  The "right" way to do this would be to ask the VM (via a
> primitive) for the set of assumed compact classes, but that's too much
> work.
>

I agree. So I will try to add the validation.


>  I hope that a new GC/object representation will become available before I
> would ever think of changing the set of compact classes, so having the
> method document what the current VM requires is ok.
>

Eliot, a simple question: In Pharo:
Smalltalk compactClassesArray asSet size -> 15
Smalltalk compactClassesArray asSet size -> 13

I would like to have one extra free bit in the object header. I can hack my
own VM which uses 4 bits for CompactClasses rather than 5, but do you think
we can do this for the official Cog VM as well? this would allow
"researched" a much nice infrastructure out of the box. How much work can
be such change? is there someone needing 32 compact classes?  if I do a
SpaceTally new printSpaceAnalysis  it looks like if I only need the first
10 classes....

I know in the future you want to change all this thing about compact
classes, but if we can have one free bit tomorrow (instead of "in the
future"), then this is very very good.

Thanks in advance,




>
>
>>
>>
>>>
>>>
>>>> Can compact classes be made uncompact when running the StackInterpreter
>>>> VM?
>>>>
>>>
>>> It is exactly the same story.  The same classes are assumed to be
>>> compact in the StackInterpreter VM as the CoInterpreter VM.
>>>
>>>
>>>> Thanks.
>>>>
>>>>
>>>
>>> HTH
>>> --
>>> best,
>>> Eliot
>>>
>>>
>>>
>>
>>
>> --
>> Mariano
>> http://marianopeck.wordpress.com
>>
>>
>>
>
>
> --
> best,
> Eliot
>
>
>


-- 
Mariano
http://marianopeck.wordpress.com
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