The point was that calling the method added the method to the child's namespace so that @ISA needs not be scanned on later calls to that method.

Your questions go way beyond that, but I'll be happy to answer them anyway.

I think (some sort of NULL pointer changes to be a pointer to a CV, which new pointer holds the same address as Base::f's pointer?)

The CV field of the structure is the CODE slot of the glob. (See perldata)

I was showing that *Child::f{CODE} was assigned *Base::f{CODE}. That means Base::f and Child::f are the same function at that point.

do you mean "this CVGEN 'slot' is used for nothing else than method dispatch"?

*Child::f{CODE} is effectively undefined for everything that isn't a method call when CVGEN is true.

No idea what 0x4d is, but within struct gp in gp.h, there is [generational validity of cached gv_cv]

The cached entries need to be expired when there's a change to an @ISA, but keeping track of all the cached entries would require a fair amount of resource.

Instead of clearing all the cached entries (which would require keeping track of them), changing any @ISA simply increments a counter. If the cache's counter (CVGEN) is lower than the change counter, the cache is stale and thus ignored.

Or so goes my understanding.