What is vmalloc

Return value:- On successful allocation of memory kmalloc return the virtual address of first page allocated. Kfree Kfree function is used to freeing the memory allocated by kmalloc. Return value:- Upon successful allocation of memory it return address of first byte of allocated memory block. Difference between kmalloc vs vmalloc. Next post Linux kernel booting 18 August, MMAP 16 August, Module parameters 16 August, Leave A Reply Cancel reply Connect with:.

The major advantage of vmalloc is that if enough physical contiguous memory is not available then it will allocate memory virtually in chunks and will link that memory so it appears to be virtually contiguous. Your email address will not be published. Search for:. Difference between Kmalloc and Vmalloc In order to allocate memory from kernel various types of API application programming interfaces are used.

For the most part, only hardware devices require physically contiguous memory allocations. On many architectures, hardware devices live on the other side of the memory management unit and, thus, do not understand virtual addresses. Consequently, any regions of memory that hardware devices work with must exist as a physically contiguous block and not merely a virtually contiguous one.

Blocks of memory used only by softwarefor example, process-related buffersare fine using memory that is only virtually contiguous. In your programming, you will never know the difference. All memory appears to the kernel as logically contiguous. The function vfree is responsible for freeing a virtual area. It walks the page tables freeing up the page table entries and associated pages for the region. Non-contiguous memory allocation remains essentially the same in 2.

The main difference is a slightly different internal API which affects when the pages are allocated. When called, it behaves the same as previously as it searches the entire vmalloc virtual address space for a free area. This is only used by the ARM architecture when loading modules. The last significant change is the introduction of a new interface vmap for the insertion of an array of pages in the vmalloc address space and is only used by the sound subsystem core.