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From "Daniel Feinberg" <csdr...@gmail.com>
Subject Re: [DRLVM] proposal to port MMTK to drlvm
Date Wed, 24 May 2006 19:44:00 GMT
> >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.
Here unless you can find all of these pointers that point into a space
from an older space you must use a write barrier.


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