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From "Geir Magnusson Jr." <g...@pobox.com>
Subject Re: [DRLVM][JIT/GC] Questions on JIRA-1682, incorrect gc enumeration
Date Mon, 16 Oct 2006 11:33:35 GMT


Weldon Washburn wrote:
> On 10/15/06, Geir Magnusson Jr. <geir@pobox.com> wrote:
>>
>>
>>
>> Mikhail Fursov wrote:
>> >
>> > 6)
>> >> Does GCV4 work with jit_gc.diff?
>> >
>> >
>> > Yes. The rootset reported by JIT is the same. The only change is that
>> > instead of the method 'enumerate(mptr, base)' JIT uses the method
>> > 'enumerate(mptr, offset)' that was used before only for mptrs with
>> static
>> > offsets (offsets known during compilation of a method)
>>
>> Why do we care abouve GCv4?
> 
> 
> Well, if I remember correctly, we decided to have GCV4 and GCV4.1 both 
> build
> and run smoke tests.  Perhaps this has changed and I simply did not know.

I guess we could, but the point I thought was keeping v4 around as we 
figured out what v4.1 was about.  Now that we have v5, and v4.1 seems 
reasonable, I'm happy to look forward.

> 
>>
>> > 7)
>> >> Instead of applying jit_gc.diff what about applying
>> >> retrieve_root_set.diff?
>> >> If it is now too hard to rollback SVN, how about reopening JIRA1862 
>> and
>> >> also
>> >> applying retrieve_root_set.diff also?  The rationale is that there has
>> >> not
>> >> been adequate discussion on modifying the semantics of JIT/GC
>> interface.
>> >
>> >
>> > I vote not to rollback JIT patch. JIT is more flexible with this patch
>> > without any additional cost. The  code is slightly increased (4-6 
>> lines)
>> > but
>> > it makes debugging simpler :)
> 
> 
> This is good.  I had no way of knowing this without asking.  Its good this
> is on record.
> 
>>
>> > 8)
>> >> Note that retrieve_root_set.diff does not impact JIT/VM/GC
>> >> interfaces.  It
>> >> is only local to gcv4.1.  Also note retrieve_root_set.diff patch line
>> >> count
>> >> is 13 and jit_gc.diff line count is 179.
>> >
>> >
>> > In the JIT patch I cleaned unused enumeration methods from JIT
>> interface,
>> > added comments and replaced the one large loop with two of smaller
>> > size(precaching, reporting). The real number of new lines is less than
>> 10.
>> >
>> > So IMO the correct fix for this problem is in the trunk. GC has 
>> cmd-line
>> > option to disable object moving during the enumeration and it's enough.
>>
>> Weldon, clearly this modification is a problem for you.  Why?
> 
> 
> Because the above questions had not been asked or answered.  I thought it
> was the job of a committer to ask questions about what they are going to
> commit.

Yes, sure, but it seems like you're dancing around a question.  I'm 
happy to roll this back if there's something wrong with it.

> 
> I have zero problem with the commit as long as it does not imply a 
> change to
> the interface between JIT/GC/VM.  I suspect Xiao Feng will find no problems
> with the commit.  Xiao Feng, please comment.

If there is a change, what is it and why is it bad?

geir

> 
> geir
>>
>>
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>>
> 
> 

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