GFP_NOIO: "NOIO" is the point rather than "can't sleep"
__GFP_HIGHMEM: allocation can happens at either ZONE_NORMAL or ZONE_HIGHMEM
GFP_ATOMIC: allocation don't have to be in a "process"(e.g. in an interupt handler)
Signed-off-by: qinyu <chinyu0704@outlook.com>