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Re: GUILE GC -- Write barrier for vectors

From: Han-Wen
Subject: Re: GUILE GC -- Write barrier for vectors
Date: Wed, 17 Jul 2002 23:53:54 +0200

address@hidden writes:
> > I'm reading the patent (gosh, what verbosity) -- but interestingly,
> > the claim is only made for not copying entire pages (cards in Scheme
> > terms), that are marked conservatively. If you one uses a second set
> > of mark bits, you could leave alone exactly those objects that are
> > marked conservatively (iso. the whole page). The price is that you
> > have another mark-bit vector (1.5 % memory overhead), that the free
> > space in the conservatively marked pages is fragmented, and that there
> > is more overhead (checking the marked-conservatively-bit) during the
> > copy phase.
> Interesting.  But:  isn't the conservatively marked page fragmented
> anyway?  At some time a few objects in a conservatively marked page will
> be collected.  That is, wouldn't we need to keep track of conservatively
> marked cells (in contrast to pages) anyway?

Yes, but the point is that you can not move marked cells in a
conservatively marked page.  Somewhere along the line (if you do
copying GC),  you have to say

        if (conservatively_marked (cell))
           copy_cell_to_new_location ()

for bartlett conservatively_marked() equals "this page contains a
conservatively_marked object". 


Han-Wen Nienhuys   |   address@hidden   | 

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