When should I use Kmalloc?

kmalloc is the preferred way, as long as you don’t need very big areas. The trouble is, if you want to do DMA from/to some hardware device, you’ll need to use kmalloc, and you’ll probably need bigger chunk. The solution is to allocate memory as soon as possible, before memory gets fragmented.

Does Kmalloc allocate contiguous memory?

kmalloc allocates contiguous memory in physical memory as well as virtual memory. 1)size:- it specify the size of memory to be allocated.

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.

What is Linux Kmalloc?

kmalloc is the normal method of allocating memory for objects smaller than page size in the kernel. The flags argument may be one of: GFP_USER – Allocate memory on behalf of user.

Can I call Kmalloc Gfp_kernel while holding a spinlock?

You cannot, however, do anything that will sleep while holding a spinlock. For example, never call any function that touches user memory, kmalloc() with the GFP_KERNEL flag, any semaphore functions or any of the schedule functions while holding a spinlock.

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.

What is Container_of?

container_of takes the offset of age at the beginning of the struct into account to get the correct pointer location. If you subtract the offset of the field age from the pointer age_ptr, you will get the correct location. This is what the macro’s last line does: (type *)( (char *)__mptr – offsetof(type,member) );

Why can’t we use malloc in kernel code?

None whatsoever. This means that ANY function you’re calling in the kernel needs to be defined in the kernel. Linux does not define a malloc, hence you can’t use it. There is a memory allocator and a family of memory allocation functions.

How do you declare a malloc function?

Syntax: ptr = (cast-type*) malloc(byte-size) For Example: ptr = (int*) malloc(100 * sizeof(int)); Since the size of int is 4 bytes, this statement will allocate 400 bytes of memory.

What are different memory zone in Linux?

The Linux kernel divides memory into memory zones. On a mainframe, three zones are used: DMA , Normal , and Movable . Memory in the Movable zone cannot be used for arbitrary kernel allocations, but only for memory buffers that can easily be moved by the kernel, such as user memory allocations and page cache memory.

Can mutex be interrupted?

With an OS one can just create a mutex for each critical part and carry on and the scheduler will switch between tasks for example. If a mutex is used in an interrupt it will just lock forever so obviously this cannot work.

What is spin lock in Linux?

The basic form of locking in the Linux kernel is the spinlock. Spinlocks take their name from the fact that they continuously loop, or spin, waiting to acquire a lock. This section of code sets the spin_lock to “unlocked,” or 0, on line 66 and initializes the other variables in the structure.

What’s the difference between kmalloc and vmalloc?

If memory required in driver needs to be contiguous in physical memory then we have to use kmalloc for allocation of memory. vmalloc is the other call to allocate memory in kernel space as like kmalloc. vmalloc allocates contiguous memory in virtual memory but it doesn’t guarantee that memory allocated in physical memory will be contiguous.

How does vmalloc allocate memory in kernel space?

vmalloc is the other call to allocate memory in kernel space as like kmalloc. vmalloc allocates contiguous memory in virtual memory but it doesn’t guarantee that memory allocated in physical memory will be contiguous. Vmalloc is declared in . usage of vmalloc call is similar to malloc call.

How are kmalloc and get _ free _ pages virtual addresses?

It’s worth stressing that memory addresses returned by kmalloc and get_free_pages are also virtual addresses. Their actual value is still massaged by the MMU (memory management unit, usually part of the CPU) before it is used to address physical memory.

What’s the difference between vmalloc and ioremap?

Like vmalloc, ioremap builds new page tables; unlike vmalloc, however, it doesn’t actually allocate any memory. The return value of ioremap is a special virtual address that can be used to access the specified physical address range; the virtual address obtained is eventually released by calling iounmap.