runtime: 1.3 garbage collector not releasing server memory back to system from finished goroutines #8287
Description
by matusis:
What does 'go version' print? go version go1.3 linux/amd64 This program http://play.golang.org/p/vnKYk3sO5d creates 100000 goroutines, with each goroutine allocating some memory and then finishing. The program prints RES memory of the process as seen by "top" and also prints runtime.ReadMemStats every 25 minutes. 1. Build the program from http://play.golang.org/p/vnKYk3sO5d on a server and run it 2. Wait at least for 50 minutes for two printouts What happened? After 50 minutes, the program produces output like this: Creating 100000 goroutines PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND 19155 alecm 20 0 151m 84m 760 S 0 0.5 0:01.46 bugrep1.3 Free #0; HeapAlloc: 10531984, HeapInuse: 10813440, HeapReleased: 0, HeapObjs: 36575 Done creating goroutines, freeing memory (every 25 mins) PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND 19155 alecm 20 0 151m 79m 836 S 2 0.5 0:01.69 bugrep1.3 Free #1; HeapAlloc: 5492784, HeapInuse: 5791744, HeapReleased: 5742592, HeapObjs: 18014 PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND 19155 alecm 20 0 151m 79m 860 S 0 0.5 0:01.88 bugrep1.3 Free #2; HeapAlloc: 5494912, HeapInuse: 5791744, HeapReleased: 5742592, HeapObjs: 18061 The program released only 5MB or RES memory after 50 min. HeapReleased value matches RES drop displayed by "top". What should have happened instead? Since goroutines exit and the slices created in them are not stored, most memory (>80MB) should be returned to the OS. Only 5MB is returned however. PS. We first saw this behavior in a simple TCP server accepting, reading from and closing 10000 connections: please see https://groups.google.com/forum/#!topic/golang-nuts/0WSOKnHGBZE