What is Vmalloc Linux?

What is Vmalloc Linux?

Linux provides a mechanism via vmalloc() where non-contiguous physically memory can be used that is contiguous in virtual memory. An area is reserved in the virtual address space between VMALLOC_START and VMALLOC_END.

When should I use Kmalloc?

The kmalloc() function is a simple interface for obtaining kernel memory in byte-sized chunks. If you need whole pages, the previously discussed interfaces might be a better choice. For most kernel allocations, however, kmalloc() is the preferred interface.

Does Kmalloc allocate contiguous physical memory?

Kmalloc is similar to malloc function, we use in our C program to allocate memory in user space. kmalloc allocates memory in kernel space. kmalloc allocates contiguous memory in physical memory as well as virtual memory.

What is Kmalloc and Vmalloc?

void * kmalloc(size_t size , int flags); void * vmalloc(unsigned long size); Kmalloc() is use to allocate memory requested from the kernel. The memory allocated is returned by the API and it is physically as well virtually contiguous. Vmalloc() is used to allocate memory from the kernel.

What are the differences between Vmalloc and Kmalloc which is preferred to use in device drivers?

vmalloc is often slower than kmalloc, because it may have to remap the buffer space into a virtually contiguous range. kmalloc never remaps, though if not called with GFP_ATOMIC kmalloc can block. kmalloc is limited in the size of buffer it can provide: 128 KBytes*).

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

For a 32bit x86 machine, with 1GB RAM or more, vmalloc is limited to 128MB (for all allocations together, not just for one).

What is slab allocator in Linux?

The slab allocator aims to to cache the freed object so that the basic structure is preserved between uses [ Bon94 ]. The slab allocator consists of a variable number of caches that are linked together on a doubly linked circular list called a cache chain.

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.

What is the difference between kmalloc() and vmalloc() functions?

The kmalloc () & vmalloc () functions are a simple interface for obtaining kernel memory in byte-sized chunks. The kmalloc () function guarantees that the pages are physically contiguous (and virtually contiguous).

Should I use kmalloc or not?

I’ve googled around and found most people advocating the use of kmalloc, as you’re guaranteed to get contiguous physical blocks of memory. However, it also seems as though kmalloc can fail if a contiguous physical block that you want can’t be found.

What is the difference between kmalloc and GPF_highmem?

One of other differences is kmalloc will return logical address (else you specify GPF_HIGHMEM). Logical addresses are placed in “low memory” (in the first gigabyte of physical memory) and are mapped directly to physical addresses (use __pa macro to convert it).

Is it possible to pass GFP_atomic to kmalloc?

For a system call you don’t need to pass GFP_ATOMIC to kmalloc (), you can use GFP_KERNEL. You’re not an interrupt handler: the application code enters the kernel context by means of a trap, it is not an interrupt.