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From "Weldon Washburn" <weldon...@gmail.com>
Subject Re: [DRLVM][MMTk GC] marksweep configuration works in "user mode"
Date Wed, 30 Aug 2006 13:37:24 GMT
The selection of header bits for object hash is controlled by HASH_MASK
located in mon_enter_exit.h.  By happy coincidence, there was an unused bit
in the header.  The old version:

#define HASH_MASK 0x7e

The hacked on version for MMTk:

#define HASH_MASK 0xfc

A question for those who know the thread manager code.  Will the above cause
a problem today?  Will it cause a problem with what the thread manager wants
to do with header bits tomorrow?

Now the semispace collector definitely goes further before it falls down.  I
had a long IM session with Steve Blackburn (MMTk expert) last night to
figure out the next debug steps.  We realized a few important items but, of
course, none of this is recorded in harmony-dev email.  I will start a
second mmtk thread to record the current state of MMTk debugging.


On 8/29/06, Geir Magnusson Jr. <geir@pobox.com> wrote:
>
>
>
> Weldon Washburn wrote:
> > On 8/29/06, Geir Magnusson Jr. <geir@pobox.com> wrote:
> >>
> >>
> >> Weldon Washburn wrote:
> >> > All,
> >> >
> >> > I just committed mods that allow MMTk marksweep configuration to run
> >> > the simple tests in test.java.
> >> >
> >>
> >> That's cool - what do we do with it next? :)
> >
> > The next step is to get MMTk semispace collector running.  I am
> > working on it right now.  It turns out MMTk needs the mark bit and the
> > forwarding bit adjacent to each other in the same byte of the object
> > header.  This may mean shoving around the bits in DRLVM object header
> > to get the required space.
>
> In neither case is it configurable via  a mask or something?
>
> >
> >>
> >> geir
> >
>
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-- 
Weldon Washburn
Intel Middleware Products Division

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