Does Kmalloc allocate contiguous memory?
Does Kmalloc allocate contiguous memory?
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. GFP_ATOMIC means get free pages from kernel in atomic fashion means the allocation will never sleep in between and the priority is also highest.
What is the maximum memory that can be allocated using Kmalloc?
kmalloc() will return a memory chunk with size of power of 2 that matches or exceeds len and will return NULL upon failure. 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.
What is Kzalloc in Linux?
kzalloc — allocate memory. The memory is set to zero. kzalloc_node — allocate zeroed memory from a particular memory node.
How do I allocate more memory to Linux?
Linux provides a variety of APIs for memory allocation. You can allocate small chunks using kmalloc or kmem_cache_alloc families, large virtually contiguous areas using vmalloc and its derivatives, or you can directly request pages from the page allocator with alloc_pages .
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 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.
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 get free Kzalloc?
The memory allocated with kzalloc() should be freed with kfree() . The memory allocated with devm_kzalloc() is freed automatically. It can be freed with devm_kfree() , but it’s usually a sign that the managed memory allocation is not a good fit for the task.
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) );
Can mutex be interrupted?
Mutexes are a perfectly reasonable synchronization primitive to use in interrupts. Of course, you do need to ensure that a thread that holds the mutex can’t be interrupted and run a handler that tries to acquire that same mutex!
Which is slower, a vmalloc or a kmalloc?
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*).
Do you need contiguous memory in Linux kernel?
Linux Kernel Development by Robert Love (Chapter 12, page 244 in 3rd edition) answers this very clearly. Yes, physically contiguous memory is not required in many of the cases.
Do you 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.