Provided are a computer program product, system, and method for processing cache miss rates to determine memory space to add to an active cache to reduce a cache miss rate for the active cache. During caching operations to the active cache, information is gathered on an active cache miss rate based on a rate of access to tracks that are not indicated in the active cache list and a cache demote rate. A determination is made as to whether adding additional memory space to the active cache would result in the active cache miss rate being less than the cache demote rate when the active cache miss rate exceeds the cache demote rate. A message is generated indicating to add the additional memory space when adding the additional memory space would result in the active cache miss rate being less than the cache demote rate.
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