Linux running slow with 0 swap left

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http://unix.stackexchange.com – Our Linux server is responding very slow. Top command doesn’t show any excessive CPU usage. But I observe that even though there’s about 5GB free memory, system is using all of swap with no free swap left. Could this be reason for system running slow as in there being too many processes. Any solutions you may advise other than reducing the number of processes? Secondly, even though there is free memory available, why is Linux switching on to swap already? I thought swap is used only when there’s not actual memory left. free -m total used free shared buff (HowTos)