What is the maximum memory that can be allocated using Kmalloc?

The maximum size allocatable by kmalloc() is 1024 pages, or 4MB on x86. Generally for requests larger than 64kB, one should use __get_free_page() functions to ensure inter-platform compatibility.

How kmalloc works?

On IA-32, DMA memory must be at an address that is addressable with 16 bits. This is how kmalloc() works. When kmalloc() is called, all it does is search through the general caches until it finds a suitably sized cache, and then calls __kmem_cache_alloc() to grab an object from that cache and returns it to the caller.

Does malloc use Kmalloc?

What is different functions: malloc() and kmalloc()? They differ only in that: the malloc() can be called in user-space and kernel-space, and it allocates a physically fragmented memory area. but kmalloc() can be called only in kernel-space, and it allocates physically contiguous memory chunk.

Does Kmalloc return physical address?

1 Answer. You’re right, kmalloc is returning a virtual address, not a physical one. The memory map you linked to is describing the virtual memory map, not the physical memory map. A virtual address typically is translated to a physical address by the MMU when you access data at the address.

How does Kmalloc differ from normal malloc or why can’t we use malloc in kernel code?

They differ only in that: the malloc() can be called in user-space and kernel-space, and it allocates a physically fragmented memory area. but kmalloc() can be called only in kernel-space, and it allocates physically contiguous memory chunk.

Does Kmalloc return contiguous memory?

The kmalloc() function returns physically and therefore virtually contiguous memory.

Does Kmalloc allocate contiguous memory?

How memory is allocated in Linux?

When Linux uses system RAM, it creates a virtual memory layer to then assigns processes to virtual memory. Virtual memory is actually a combination of both RAM and swap space; swap space is a section of your hard drive designated as available for use in case usable RAM runs out.

How do you free memory allocated by Kmalloc?

When the allocated memory is no longer needed it must be freed. You can use kvfree() for the memory allocated with kmalloc , vmalloc and kvmalloc . The slab caches should be freed with kmem_cache_free() . And don’t forget to destroy the cache with kmem_cache_destroy().