为什么golang中的内存不减少？

Question

When the server started , the memory it took was about 83MB, which I checked by top. And When some connections were accepted and did something , the memory it took was about 500MB, Then, I closed all the connections and server cleard all the structs, after sometime, the memory decreased a little , about 30MB.The memory didn't return to the level when the server started.

when server started , I looked up heap info

# runtime.MemStats
# Alloc = 7251528
# TotalAlloc = 52713992
# Sys = 15010040
# Lookups = 49
# Mallocs = 2072338
# Frees = 2038576
# HeapAlloc = 7251528
# HeapSys = 12025856
# HeapIdle = 2121728
# HeapInuse = 9904128
# HeapReleased = 0
# HeapObjects = 33762
# Stack = 425984 / 425984
# MSpan = 75504 / 81920
# MCache = 4800 / 16384
# BuckHashSys = 1457768
# NextGC = 11496656

And when all connections closed, after sometime and gc, I looked up again

# runtime.MemStats
# Alloc = 5845912
# TotalAlloc = 13053679584
# Sys = 73128248
# Lookups = 794
# Mallocs = 22728491
# Frees = 22699056
# HeapAlloc = 5845912
# HeapSys = 60112896
# HeapIdle = 52166656
# HeapInuse = 7946240
# HeapReleased = 0
# HeapObjects = 29435
# Stack = 3719168 / 3719168
# MSpan = 88608 / 180224
# MCache = 4800 / 16384
# BuckHashSys = 1597264
# NextGC = 9428528

And I didn't know why it decrease so little. Because I have already clear the variables saved in server. Would anyone give some advice on how I find the problom?

PS. It is not concerned about goroutine, I checked it, and the numbers of goroutine didn't increase. And I already use pprof and open gcdebug.

Answer 1

Because it's not entirely up to Go to shrink it's own memory. The Go garbage collector occasionally makes requests to the OS to release unused memory. The OS may decide to not release the memory because the system has plenty to spare, other some other reason.

If you are really concerned about you app taking too much memory or leaking memory then pay attention to the HeapAlloc value over time. Make sure that this value stays in your expected range.

Also, don't expect debug.FreeOSMemory() or runtime.GC() to do what you expect.