bufbackoff
} while (bufbackoff(&dma_constraint, atop(size)) >= atop(size));
} while ((bufbackoff(where, size) >= size));
extern unsigned long bufbackoff(struct uvm_constraint_range*, long);
if (bufbackoff(NULL, 4) >= 4)
shortage -= bufbackoff(&constraint, size * 2);
if (bufbackoff(NULL, atop(size)) >= atop(size)) {