System call invoked when writing into a heap memory

Question

I know for malloc sbrk is the system call invoked ,Similarly What is the system cal invoked when i write to a malloed memory(heap memory)

int main

{

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Answer 1

Accessing memory does not require a system call. On the contrary, accessing memory is what most of your code does most of the time! On a modern OS, you have a flat view of a contiguous range of virtual memory, and you typically only need a system call to mark a particular region (a "page") of that memory as valid; other times, contiguously growing memory ranges such as the call stack don't even require any action on your program's part. It's solely the job of your operating system's memory manager to intercept accesses to memory that isn't mapped to physical memory (via a page fault), do some kernel magic to bring the desired memory into physical space and return control to your program.

The only reason malloc occasionally needs to perform a system call is because it asks the operating system for a random piece of virtual memory somewhere in the middle. If your program were to only function with global and local variables (but no dynamic allocation), you wouldn't need any system calls for memory management.