

And how does cache space figure in to this? I have a server with 64GB of RAM, of which 46GB is being used by system cache, but I only have 450MB of free memory and 140MB of free swap. The only ‘volatile’ service I have running is slapd which can run in bursts of activity, otherwise the only thing of consequence running is webmin and some VMs which collectively can use up to 24GB (though they actually use about half that) but there’s no reason those should hit swap space. I just don’t get why the swap space is being run dry here.
But why doesn’t it ever empty the swap space? I’ve been using vm.swappiness=10 and I’ve tried vm.vfs_cache_pressure at 100 and 50. Checking ps I’m not seeing any services that would be idling in the background, so I’m not sure why the system thought it needed to put anything in swap. (And FWIW, I run two servers with identical services that I load balance to, but the other machine has barely used any swap space – which adds to my confusion about the differences).
Why would I want to reduce the amount of memory in the server? Isn’t all that cache memory being used to help things run smoother and reduce drive I/O?