Malloc calls which system call

Star 5. New issue. Jump to bottom. When do malloc and free invoke an OS system-call? Labels Answered. Linked pull requests. Copy link. What system call would it invoke for Linux? Member Author. Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment. You signed in with another tab or window. The malloc implementation will go through the list of free memory physical memory , we will call it free list, and find an appropriate chunk that is greater than or equal to 4 Bytes.

Once it finds such a chunk, it will be deleted from free list and added to a used list. Then that physical memory will be mapped to the process heap vma struct. He didn't seem to be quite satisfied with this answer. How does the buddy system fit into this? Any help would be greatly appreciated. When user space applications call malloc , that call isn't implemented in the kernel. Instead, it's a library call implemented glibc or similar.

This gives glibc a big contiguous regarding virtual memory addresses chunk of memory, which the malloc implementation further slices and dices in smaller chunks and hands out to your application. Here 's a small malloc implementation that'll give you the idea, along with many, many links. There's a mistake in your answer - malloc does not deal with physical memory directly. It deals with paged virtual memory - although I'm not certain if it's true for every architecture out there.

When your program tries to allocate memory and the free list doesn't contain a chunk of equal or larger size than the requested size, an entire new page is allocated. The page size is architecture dependent bytes on x Page allocation is something only the kernel can perform, thus a malloc call may cause a system call.

The new address is then added to the free list, and malloc manipulates the free list according to its implemention check glibc for example. Stack Overflow for Teams — Collaborate and share knowledge with a private group.

Create a free Team What is Teams? Collectives on Stack Overflow. Learn more. Ask Question. Asked 10 years, 6 months ago. Making any use of ptr after the call to free e. Toggle navigation Shichao's Notes. Files and Directories Chapter 5. System Data Files and Information Chapter 7. Process Environment Chapter 8. Process Control Chapter 9. Process Relationships Chapter Signals Chapter Threads Chapter Thread Control Chapter Daemon Processes Chapter Interprocess Communication Chapter Introduction Chapter 2.

Sockets Introduction Chapter 4. Socket Options Chapter 8. The Internet Address Architecture Chapter 3. Link Layer Chapter 4.