CODEWITHSUNDEEP
linuxprocessx86kernel
ijuio
ijuio

Reputation: 91

How is user address memory organized?

I always read that, at any given time, the processor can only run one process at a time. So one and only one process is in state running. However, we can have a number of runnable processes. These are all of these processes who are waiting for the scheduler to schedule their execution.

At any given time, do all these runnable processes exist in user address space? Or has the currently running process in user address space, and it is only once they are scheduled that they are brought back to RAM from disk. In which case, does it mean that the kernel keeps the process task descriptor in its list of all runnable processes even if they are in disk? I guess you can tell I am confused.

Upvotes: 0

Views: 56

Answers (1)

Stian Skjelstad
Stian Skjelstad

Reputation: 2335

If CPU supports virtual memory addressing, each process has a unique view of the memory. Two different processes that tries to read from the same memory address, will map to different location in physical memory, unless the memory maps tells otherwize (shared memory, like DLL files are mapped read only like this for instance)

If CPU does not support virtual memory, but only memory protection, the memory from the other processes will be protected away, so that the running process can only access its own memory.

Upvotes: 1

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