BITMAP_SIZE
#define BITMAP_MASK (BITMAP_SIZE - 1)
ph->ph_bitmap + (idx / BITMAP_SIZE);
pool_item_bitmap_t *bitmap = ph->ph_bitmap + (idx / BITMAP_SIZE);
KASSERT((i * BITMAP_SIZE) < pp->pr_itemsperpage);
idx = (i * BITMAP_SIZE) + bit;
const int n = howmany(pp->pr_itemsperpage, BITMAP_SIZE);
ph_bitmap[howmany(nelem, BITMAP_SIZE)]);
(((idx) == 0) ? BITMAP_MIN_SIZE : BITMAP_SIZE * (1 << (idx)))