Re: Merging scratch/no-purespace to remove unexec and purespace

["Gerd Möllmann" <gerd.moellmann@gmail.com>]

Stefan Monnier <monnier@iro.umontreal.ca> writes:

>> My idea is this: we add an extra mark bit area to the pdumper file for
>> objects which we know to be "tenured": i.e. objects that we'll treat as
>> immortal, but for which we also know that all referenced objects will
>> also be "tenured", or static.
>
> IIUC this sounds like a kind of generational GC, except that promotion
> to the "tenured" set is made somewhat visible instead of being 100% internal.
>
>> If we write to such an object, we clear the bit, and put it on a special
>> set to maintain its tenure (it'd be nicer to simply set another bit, but
>> non-MPS pdumper cannot do so).  This should happen rarely, but it's
>> better than the current CHECK_IMPURE thing.
>
> If my understanding above is correct, then the
> `CHECK_IMPURE/check_writable` is what we usually call "write barrier",
> and the "special set" above is what we usually call the "remembered set".
>

Same understanding here.