[josephlord]

Server memory usage may be stable but there are likely to be some cold spots that rarely (maybe never) actually get accessed so having a some swap space should have very little negative performance impact and give you a little more headroom before you hit the limit and processes start dying on you.

If you hit the point when it thrashes because the working set isn't fitting in memory then that is obviously a bad place but there is a fair chance you can stay a host size smaller and save money by running some swap.

As for what the cold spots might be I can easily imagine libraries being included/required in an interpreted language and only small fractions of their functionality used. Unlike native libraries they won't just be memory mapped in without using real memory.