Welcome to the Lounge

Mike Hankey wrote:

Suitable for when I run into coding problems.

raddevus wrote:

gets an address space which is 4GB in size when the process starts

raddevus wrote:

OS modules take up certain portion of that address space (1GB?)

raddevus wrote:

The rest (3GB) is used for the stack & heap of the running process

const char *howdy (void) {
    return "Howdy";
}

int main()
{
    printf("%s\n", howdy());
    return 0;
}

raddevus wrote:

As the app instantiates new objects (allocates memory for objects) on the heap, the amount of memory the process uses grows -- but it can never grow beyond the 3GB (4GB total) anyways, right?

raddevus wrote:

5 ## This is a biggie ## A process can never eat up more memory than its address space allows 3GB (4GB total) so a process can never really impact another process anyways because each one is limited to 4GB anyways, right?

raddevus wrote:

6. Extreme Example - If there is 128GB RAM in the hardware and we say OS (associated services) take up 28GB (to make things easy) and there are two services running (2 X 4GB = 8GB) then this machine could never run out of memory, since it would have 92GB just sitting idle

raddevus wrote:

Driving A Point Home - So when a developer notices that the app he wrote running on the Server keeps crashing with "out of memory" error, then looks around and says, "Hey, wait a second, I think your service (which has been running on the Server long before aforementioned dev's app) is eating up memory and making mine die", then that developer is an idiot who doesn't understand process address space, right? Right? Right!

raddevus wrote:

You cannot solve memory problems of a service or app that crashes due to low memory (since it is simply eating it's own memory) by installing more memory (even if hardware is furhter expandable).

raddevus wrote:

My point is that a single process cannot just consume all memory on a box, right?

raddevus wrote:

It's limited to some address space size, I'm guessing.

raddevus wrote:

But, maybe I'm wrong, maybe a process can consume all 128GB of ram??

raddevus wrote:

I think it cannot becuase it would be quite easy for a malicious process to crash other processes and the OS if this were true.

raddevus wrote:

When a process gets memory from heap (for newing up objects) it gets it from its own address space. When that memory is gone then you get "out of memory" but doesn't mean you ate all the memory on the box.