Techniques convert a first bitmap into a second bitmap. Such techniques involve determining a first plurality of bits in the first bitmap corresponding to a particular bit in the second bitmap; determining whether the first plurality of bits include a dirty bit as a unit of a processor line width; in response to determining that the first plurality of bits include a dirty bit, setting the particular bit as a dirty bit; and in response to determining that the first plurality of bits do not include a dirty bit, setting the particular bit as a non-dirty bit.