Hello ghc-devs, I wrote about this issue to haskell-cafe, but received no reply as of today, so I'm hoping I could get some answer(s) here. I wrote a small Servant server that communicates with the same other server(s). When compiled without "-with-rtsopts=-T", I see in 'gnome-system-monitor' that memory used by each server constantly growing. I was investigating the issue, and found that it is (probably) not in my code, but in one http call (Servant client call to the same server). When I compile it with "-with-rtsopts=-T", the memory is constant and steady. Tested on Arch Linux with Stack LTS 13.14. If any one wants to test this, here are the steps: (server is standalone and does not require any external services (like DB, Redis, etc) and uses just a few MBs of RAM.) $ hg clone https://bitbucket.org/vlatkoB/poomas && cd poomas && stack build ## open your system monitor ## open two terminals in 'poomas' dir and in one run $ srvb.sh 5 ## and in the other # $ srvb.sh 6 ## (5 and 6 represent port number added to 3000, i.e. 3005 and 3006) ## Notice that memory is steady, around 6 MB on my machine. ## In 'server/package.yaml' comment out the line 139 (#-with-rtsopts=-T) $ stack build --force-dirty ## start those two servers again and see memory usage growing. Can anyone shed some light what could be happening here? Best regards, vlatko