title: How does an OS generally go about managing kernel memory and page handling?
body: <p>I'm working on kernel design, and I've got some questions concerning paging.</p>
  
  <p>The basic idea that I have so far is this: Each program gets its own (or so it thinks) 4G of memory, minus a section somewhere that I reserve for kernel functions that the program can call. So, the OS needs to figure out some way to load the pages in memory that the program needs to use during its operation.</p>
  
  <p>Now, assuming that we had infinite amounts of memory and processor time, I could load/allocate any page the program wrote to or read from as it happened using page faults for pages that didn't exist (or were swapped out) so the OS could quickly allocate them or swap them in. In the real world though, I need to optimize this process, so that we don't have a program constantly consuming all memory that it ever touched.</p>
  
  <p>So I guess my question is, how does an OS generally go about this? My initial thought is to create a function that the program calls to set/free pages, which it can then memory manage on its own, but does a program generally do this, or does the compiler assume it has free reign? Also, how does the compiler handle situations where it needs to allocate a fairly large segment of memory? Do I need to provide a function that tries to give it X pages in order?</p>
  
  <p>This is obviously not a language specific question, but I'm partial to standard C and good with C++, so I'd like any code examples to be in either that or assembly. (Assembly shouldn't be necessary, I fully intend to make it work with as much C code as possible, and optimize as a last step.)</p>
  
  <p>Another thing that should be easier to answer as well: How does one generally handle kernel functions that a program needs to call? Is it OK just to have a set area of memory (I was thinking toward the end of virtual space) that contains most basic functions/process specific memory that the program can call? My thought from there would be to have the kernel functions do something very fancy and swap the pages out (so that programs couldn't see sensitive kernel functions in their own space) when programs needed to do anything major, but I'm not really focusing on security at this point.</p>
  
  <p>So I guess I'm more worried about the general design ideas than the specifics. I'd like to make the kernel completely compatible with GCC (somehow) and I need to make sure that it provides everything that a normal program would need.</p>
  
  <p>Thanks for any advice.</p>