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===Increased thrashing===
The [[main memory]] used by a compression system reduces the amount of memory available to [[Process (computing)|processes]] that a system runs, which may result in increased paging activity and reduced overall effectiveness of a virtual memory compression system. This relationship between the paging activity and available memory is roughly exponential, meaning that reducing the amount of main memory available to system processes below a certain point results in an exponential increase of paging activity.<ref name="DENNING" /><ref name="FREEDMAN" />
In circumstances where the amount of free memory is low and paging is fairly prevalent, any gains in available virtual memory may be offset by a high [[page fault]] rate that leads to [[thrashing (computer science)|thrashing]] and degraded system performance. In an opposite state, where enough main memory is available and paging activity is low, compression may not impact performance enough to be noticeable. The middle ground between these two circumstances{{mdashb}}low memory with high paging activity, and plenty of memory with low paging activity{{mdashb}}is where virtual memory compression may be most useful. However, the more compressible the program data is, the more pronounced are the performance improvements as less main memory is needed to hold the compressed data.
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