Re: BASE_PURESIZE

[Stephen J. Turnbull]

Dan Nicolaescu writes:

 >   > 1.  XEmacs abandoned pure space years ago on the assumption that (bugs
 >   >     aside) copy-on-write means that dumped text will be shared anyway.
 >   >     Is that incorrect?
 > 
 > Do you have generational GC? If not, all the data in the dumped image
 > dumped image will be GCed every time, and that means lots of pages will
 > get written to, so won't be shareable.

I don't think that's necessarily true.  I'm not sure what the
mechanism for avoiding writes to dumped objects is in XEmacs; it might
be something like setting a "permanently marked object" bit and
putting them all in the set of GC roots at dumptime.  (It's been a
while and I wasn't involved in that work at all.)  And doesn't Emacs
keep its mark bits separately, being able to do that because objects
are allocated in arrays of same-sized blocks?