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From "Daniel Feinberg" <csdr...@gmail.com>
Subject Fwd: [DRLVM] proposal to port MMTK to drlvm
Date Wed, 24 May 2006 20:13:50 GMT
---------- Forwarded message ----------
From: Daniel Feinberg <csdread@gmail.com>
Date: May 24, 2006 2:13 PM
Subject: Re: [DRLVM] proposal to port MMTK to drlvm
To: Weldon Washburn <weldonwjw@gmail.com>


Something like a reference counter does not really need a write
barrier. They are mostly used when you are partitioning the heap into
specific regions for objects that fit cirtian specifications. And
again only if you are going to be collecting a region that has
pointers that flow into the collected section of the heap. There might
be other uses of write barriers. Another kind of collector that might
be of interest that i dont believe is included in MMTK though it
should be is the Older First collector which you can get the paper at
the DaCapo website.


Daniel

On 5/24/06, Weldon Washburn <weldonwjw@gmail.com> wrote:
> On 5/24/06, Daniel Feinberg <csdread@gmail.com> wrote:
> > > >My understanding of write barriers is as an optimization.
> > > That fits with my understanding of write barriers also.   I do not
> > > know for certain but suspect that MMTK can somehow be configured such
> > > that write barriers are not required for correctness.  Maybe Dan
> > > Feinberg can tell the mailing list.
> >
> > So MMTK is a toolkit for building GCs. When doing generational
> > collection the write barrier is used to keep track of pointers that go
> > from older generations to yonger generations. You must have a way to
> > track these objects because when you do a partial heap collection (aka
> > just the nursery or nursery and old1) you need to build a root set of
> > all things that point into that space. Then you trace this root set to
> > find all live objects that need to be moved to an older generation. In
> > other methods of collecting the write barrier is not as important.
>
> Thanks. This fits my expectations.  One follow-up question.  By "not
> as important", do you mean functionally correct but bad performance or
> something else?
>
>
> > Here unless you can find all of these pointers that point into a space
> > from an older space you must use a write barrier.
>
> >
> >
> > Daniel
> >
> > ---------------------------------------------------------------------
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> >
> >
>
>
> --
> Weldon Washburn
> Intel Middleware Products Division
>


--
Daniel Feinberg
http://www.cs.unm.edu/~danielf


-- 
Daniel Feinberg
http://www.cs.unm.edu/~danielf

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