If we have infinite memory, then do we still be needing paging?

Question

Paging creates illusion that each process has infinite RAM by moving pages to and from disk. So if we have infinite memory(in some hypothetical situation), do we still need Paging? If yes, then why? I faced this question in an interview.

Microprint

IMO we will still require paging for swapping purpose. And by saying infinite memory are you including RAM also ? – Earful

Answer 1

Assuming that "infinite memory" means infinite randomly accessable memory, or RAM, we will still need paging. Although paging is often associated with the ability to swap pages in and out of RAM to a hard disk to conserve memory, this is merely one aspect of paging. Here are some other reasons to have paging:

• Security. Paging is a method to enforce operating system security and memory protection by ensuring that a processes cannot access the memory of another process and that it cannot modify the resident kernel.
• Multitasking. Paging aids in multitasking by virtualizing the memory space, that is, address 0xFOO in Process A can be something completely different than 0xFOO in Process B
• Memory Allocation. Paging aids in memory allocation by reducing fragmentation and ensuring RAM is only allocated when accessed. What this means is that although a process needs, suppose, 100MB of continuous RAM space, this need not be continuous physically. Additionally, when a program requests 100MB of space, the operating system will tell the program it's safe to use that 100MB of space, yet it will not be actually allocated until the program uses that space to its fullest.

Admittedly, the latter would not be entirely necessary if one had infinite RAM, nonetheless; it is always good practice to be eifficient even when we are not resource constrained. It also demonstrates a use for paging that is sometimes not considered.

Rosellaroselle

Answer 2

This is a philosophical question, so here's a philosophical answer :)

The trick in this question is that you make assumptions about the infinite memory. It's ok to say "no, no need to use paging, BUT". And follow by:

The infinite memory has to be accessible within the acceptable time limit for memory access. If it's not (because infinity takes a lot of space, and the memory sits farther away from the processing unit), there's no difference between it and the disk, both are not satisfying the readily available memory requirement, which is what caching via pages tries to solve.

Take for example Amazon's S3, which for all practical purposes is infinite. If you can rely on S3 to satisfy all your memory requirements in the sense that when you need something fetched within time x you can fetch it from S3, there's no need to page anything or even hold it in "local" memory. Just get it from S3 whenever you need it, as many times as you need it. (Obviously this would have other repercussions like cost and network, but let's ignore that for now).

Of course you can always say that optimally you want memory access to be as fast as possible, and "fast enough" is probably slower than "fastest", so local memory access would give you better performance etc.

And last, if I had to envision a memory which is infinite and has the same access time no matter how "far" the memory unit is from the fetching unit, I would have to envision a sphere where the processing unit is in the middle, so that you can't argue that one memory unit is slower than the other because of the distance. Otherwise you could say that paging would be done internally within the memory so that access is faster to the memory units that are most used (or whatever algorithm you choose to use).

Juliannjulianna