Functions like kmalloc() accetp a "flags" argument:
	p = kmalloc(size, flags);
What do these flags represent?

The second kmalloc() argument, of type gfp_t (get free pages type) is a
bitmask containing multiple flags that specify where kmalloc() is going
to get the memory from, if the allocator can block waiting for I/O or
something else, if the allocator can fail, etc...

Some pre-defined constants provide important and useful flags combinations:
- GFP_ATOMIC: the allocation is important and cannot block in any way
              (generally used in ISRs or BHs)
- GFP_NOWAIT: the allocation cannot start any filesystem access or I/O, but
  can wake up a kernel thread performing by page reclaiming
- GFP_KERNEL: "typical" allocation of memory for the kernel... This memory
              cannot be shared with user-space
- GFP_USER: allocation of memory to be shared between user-space and
            kernel-space

Some more information can be found at https://www.kernel.org/doc/html/latest/core-api/memory-allocation.html