round_down
start = round_down(start, 128);
GEM_BUG_ON(round_up(start, align) > round_down(end - len, align));
range = round_down(end - len, align) - round_up(start, align);
if (unlikely(round_up(start, alignment) > round_down(end - size, alignment)))
count = round_down(count, 4);
u32 base_aligned = round_down(plane_config->base, PAGE_SIZE);
#define cacheline(a) round_down(a, CACHELINE_BYTES)