The prototype of kmalloc is:
void *kmalloc(size_t size,int flags);
The first argument to the kmalloc is the size of the block to be allocated.The second argument is allocation flag.
The most commonly used allocation flag is GFP_KERNEL means that allocation is performed on behalf of a process running in the kernel space.This means that the calling function is executing a system call on behalf of a process.Using GFP_KERNEL means that kmalloc can put the current process to sleep waiting for a page when called in low-memory situations.
A function that allocates memory using GFP_KERNEL must, therefore, be reentrant and cannot be running in atomic context. While the current process sleeps, the kernel takes proper action to locate some free memory, either by flushing buffers to disk or by swapping out memory from a user process.
