Actually, purge is completely unrelated to swap. Purge forces disk cache to be flushed to disk, and can be used to approximate a cold disk buffer cache scenario

Actually, purge is completely unrelated to swap. Purge forces disk cache to be flushed to disk, and can be used to approximate a cold disk buffer cache scenario for performance analysis. Some small amount of swap usage (compared to total RAM) is perfectly normal, by the way. More cache, for instance, is a better use of RAM than avoiding swap usage by keeping never-accessed pages present.