Question about GC

 
Hi. I have been trying to understand a little how the Squeak GC works, and there is something very basic I don't understand. GC is supposed to start from the rootTable and mark all the objects that are reachable. This objects, includes those which are in the "old space".  I mean, the old objects too.

The problem is that I don't find where in the code is that. If i look to ObjectMemory >> markAndTrace: oop    I see:

(self oop: oop isGreaterThanOrEqualTo: youngStart)
        ifTrue: [ header := header bitOr: MarkBit ].  "mark only if young"



So...it is only marked if young.

Then, in ObjectMemory >> startObj   I see

    (self oop: oop isLessThan: youngStartLocal)
        ifTrue: ["old object; skip it"
            field := oop.
            ^ Upward].


So....where are the old objects being marked ?

Thanks in advance.

Mariano

 
Ok....now I found something very hacky :)

Reading a Squeak blue book, it says "Squeak simply forces de system to believe that the old/new boundary is at the bottom of the old region. Thus, the entire image is now considered to be new objects, and all objects will be fully traced."

Cheers

Mariano