GFP_KERNEL

allocate memory:

1. GFP_KERNEL:

    kmalloc() is allowed to go to sleep and wait for pages to get freed up.

2.GFP_ATOMIC:

   Used by interrupt context code to get hold of memory. In this mode, kmalloc() is not allowed to    sleep-wait for free pages, so the probability of successful allocation with GFP_ATOMIC is lower    than with GFP_KERNEL.