Less obvious is the fact that theThe memory used by thea compression system reduces the availableamount systemof memory andavailable thusto causes[[Process (computing)|processes]] that a correspondingsystem increaseruns, which may result in overallincreased paging activity. As more primary[[main storagememory]] is used to store compressed data that was paged out, less primary storagememory is available to running programs, causing the level of paging activity to increase, and reducing the overall effectiveness of thea virtual memory compression system.
The relationship between the paging activity and available memory is roughly exponential.<ref, name="DENNING"/><refmeaning name="FREEDMAN"/>that reducing Thisthe meansamount thatof formemory aavailable givento reduction,system <math>x</math>,processes inbelow availablea memorycertain therepoint willresults bein an exponential increase inof paging activity.<ref onname="DENNING" the order of <math/>e^x<ref name="FREEDMAN" /math>. 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 significanthigh increase[[page infault]] rate that leads to paging/[[thrashing (computer science)|thrashing]] and degraded system performance. In circumstances where enough memory is available and paging activity is low, compression may not impact performance enough to be noticeable. The middle ground between two extremities{{mdashb}}low- memory/ with high- paging activity, and high-plenty of memory/ with low- paging activity{{mdashb}}is where virtual memory compression may be most useful. In all circumstancesHowever, the more compressible the program data is, the more pronounced are the performance improvement,improvements becauseas less primarymain storagememory is needed to hold the compressed data.
For example, in order to maximize the use of thea primarycompressed storagepages cache of compressed pages, [[Helix Software Company]]’s Hurricane 2.0 provides a user-configurable threshold that allowsfor the rejection level for compression torejection be adjustedlevel. The program wouldBy compresscompressing the first 256 to 512 bytes of a 4 KiB page, andthis ifvirtual thatmemory smallcompression regionsystem achieveddetermines whether the designatedconfigured compression level ofthreshold compressioncan be achieved for a particular page; if achievable, the rest of the page would be compressed and then retained in a primarycompressed storage buffercache, whileand allotherwise othersa page would be sent to auxiliary storage through the normal paging system. The default setting for this threshold wasis an 8:1 compression ratio.<ref name="PCMAG-HURR-2" />
