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Re: Opportunistic GC


From: Stefan Monnier
Subject: Re: Opportunistic GC
Date: Mon, 08 Mar 2021 10:46:25 -0500
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/28.0.50 (gnu/linux)

>> Ah, so not really an easy change after all.
>
> For conses, it's easy. Instead of keeping the mark bits in the cons
> block, we keep a pointer to the mark bits in the cons block, and
> allocate the mark bits separately and (hopefully) on a different page.

What you mean is that it's easy because the markbits are already
separate from the cons objects (same for floats).  We could also just
increase the size of the cons blocks such that their markbits area takes
up a whole page.  That means cons blocks of about (* 16B/cons 8b/B) =>
128 pages => 512KB.

>> And how do you propose to keep the mark bits separately and still
>> maintain coherency between the object and its bits?
> Just as we do for pdumper, which already does this.  In fact, I'm
> pretty sure it was Daniel who said a while ago that he wants to extend
> that to all GCable objects, not just those that live in the pdmp.

Yes, it's a good idea to do that in general.


        Stefan




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