How ZGC allocates memory for the Java heap (opens in new tab)

In the beginning of the 32 bit revolution, when the future was here but unevenly distributed, there was a lot of talk about how 32 bit pointers would fundamentally change how people wrote code. Among other things it got rid of a bunch of odd bookkeeping, and if you don’t have to do the bookkeeping you don’t have to write the code in a way that supports it, so you can do other things.

Not too long after someone asked what sort of interesting changes 64 bit will bring. And I’ve been keeping that question in the back of my mind ever since.

Aliasing memory multiple times in order to do read or write barriers and make GC much cheaper is a pretty good one. But another one I know of is that one of the secrets of the L4 microkernel is that its IPC speed comes substantially from reducing the amount of TLB work that needs to be done to switch to another process running in a different address space. They use the same address space and only swap out the access rights which cuts the call overhead in half. It’s pretty easy to put a bunch of processes into a 64 bit address space and just throw each one a randomly located 4GB slice of RAM.

When your comment and the article refer to “physical” addresses, those are physical in the context of the JVM, right? To the OS they’re virtual addresses in the JVM process space?