[리눅스-커널] GFP_USER 질문

// gfp_zone
static inline enum zone_type gfp_zone(gfp_t flags)
{
        enum zone_type z;
        int bit = (__force int) (flags & GFP_ZONEMASK);
 
        z = (GFP_ZONE_TABLE >> (bit * ZONES_SHIFT)) &
                                         ((1 << ZONES_SHIFT) - 1);
        VM_BUG_ON((GFP_ZONE_BAD >> bit) & 1);
        return z;
}
 
 
unsigned long nr_free_buffer_pages(void)
{
return nr_free_zone_pages(gfp_zone(GFP_USER));
}
 
#define GFP_USER        (__GFP_WAIT | __GFP_IO | __GFP_FS | __GFP_HARDWALL)
 
#define ___GFP_WAIT             0x10u
#define ___GFP_IO               0x40u
#define ___GFP_FS               0x80u
#define ___GFP_HARDWALL         0x20000u