1. A method of managing a high speed memory, the method comprising: determining, n response to receipt of a demotion request, margin performance losses corresponding to respective non-free indexes, wherein corresponding non-free indexes are set for different types of low speed memory, wherein each non-free index comprises index entries indicating a storage unit in a high speed memory assigned to a corresponding low speed memory, wherein a storage unit in the high speed memory is recovered by demoting an index entry from a given non-free index, wherein a given margin performance loss represents a change in a processor read operation time caused by performing a demotion operation in a corresponding non-free index; comparing the margin performance losses of the respective non-free indexes and selecting as a demotion index a non-free index whose margin performance loss satisfies a demotion condition; and selecting an index entry from the demotion index to perform the demotion operation.