Array memory allocation - paging

Question

Not sure if the answer would be the same for Java, C# and C++, so I categorized all of them. Answer for all languages would be nice.

All days I\'ve been thinking, th

Answer 1

With Java and C# certainly. We can show this by running byte[] array = new byte[4097]; on a Windows machine where the memory page size is 4096bytes. It hence must be in more than one page.

Of course paging impacts performance, but this can be one of the cases where GC using frameworks like .NET or Java can have an advantage, because the GC was written by people who know paging happens. There are still advantages in structures that make it more likely to have related elements on the same page (favouring array-backed collections over pointer-chasing collections). This also has an advantage in terms of CPU caches. (Large arrays are still one of the best ways to cause heap fragmentation that the GC has to struggle with, still since the GC is pretty good at doing so, it's still going to be a win over many other ways of dealing with the same issue).

With C++ almost certainly, because we normally code at the level of the memory-management of the operating system - arrays are in contiguous virtual space (whether on the heap or the stack), not contiguous physical space. It's possible in C or C++ to code at a level below that, but that's normally only done by people actually writing the memory-management code itself.