Man page 9 : __alloc_skb

__alloc_skb - allocate a network buffer

struct sk_buff * __alloc_skb(unsigned int  size , gfp_t  gfp_mask , int  flags , int  node );

size
    size to allocate

gfp_mask
    allocation mask

flags
    If SKB_ALLOC_FCLONE is set, allocate from fclone cache instead of head cache and allocate a cloned (child) skb. If SKB_ALLOC_RX is set, __GFP_MEMALLOC will be used for allocations in case the data is required for writeback

node
    numa node to allocate memory on

Allocate a new sk_buff. The returned buffer has no headroom and a tail room of at least size bytes. The object has a reference count of one. The return is the buffer. On a failure the return is NULL.

Buffers may only be allocated from interrupts using a gfp_mask of GFP_ATOMIC.