[www@server1 tmp]$ ruby test_gc.rb 
ruby 2.5.3p105 (2018-10-18 revision 65156) [x86_64-linux]
2018-12-11 03:14:57 +0000
Memory: Process RSS/System Total Memory/System Free Memory
0m0s 21894	Memory:9.57 MB/3.85 GB/2.74 GB, objspace_mem:4.08 MB
0m3s 21894	Memory:9.57 MB/3.85 GB/2.52 GB, objspace_mem:3.39 MB
0m6s 21894	Memory:9.57 MB/3.85 GB/2.27 GB, objspace_mem:3.39 MB
0m9s 21894	Memory:9.57 MB/3.85 GB/2.14 GB, objspace_mem:3.39 MB
read content from file 214189538[204.27 MB]
0m12s 21894	Memory:213.91 MB/3.85 GB/1.73 GB, objspace_mem:207.65 MB
0m15s 21894	Memory:213.91 MB/3.85 GB/1.72 GB, objspace_mem:207.65 MB
0m18s 21894	Memory:213.91 MB/3.85 GB/1.72 GB, objspace_mem:207.65 MB
0m21s 21894	Memory:213.91 MB/3.85 GB/1.71 GB, objspace_mem:207.65 MB
0m24s 21894	Memory:213.91 MB/3.85 GB/1.71 GB, objspace_mem:207.65 MB
0m27s 21894	Memory:213.91 MB/3.85 GB/1.71 GB, objspace_mem:207.65 MB
0m30s 21894	Memory:213.91 MB/3.85 GB/1.71 GB, objspace_mem:207.65 MB
0m33s 21894	Memory:213.91 MB/3.85 GB/1.71 GB, objspace_mem:207.65 MB
0m36s 21894	Memory:213.91 MB/3.85 GB/1.71 GB, objspace_mem:207.65 MB
0m39s 21894	Memory:213.91 MB/3.85 GB/1.71 GB, objspace_mem:207.65 MB
parse json string to object
0m58s 21894	Memory:1.36 GB/3.85 GB/578.56 MB, objspace_mem:1.23 GB
1m3s 21894	Memory:1.36 GB/3.85 GB/683.79 MB, objspace_mem:1.23 GB
1m7s 21894	Memory:1.36 GB/3.85 GB/784.67 MB, objspace_mem:1.23 GB
1m12s 21894	Memory:1.36 GB/3.85 GB/784.38 MB, objspace_mem:1.23 GB
1m17s 21894	Memory:1.36 GB/3.85 GB/784.25 MB, objspace_mem:1.23 GB
1m21s 21894	Memory:1.36 GB/3.85 GB/784.4 MB, objspace_mem:1.23 GB
1m26s 21894	Memory:1.36 GB/3.85 GB/381.18 MB, objspace_mem:1.23 GB
set string&object to nil, and sleep 30 min to check the memory usage.
1m30s 21894	Memory:1.14 GB/3.85 GB/331.18 MB, objspace_mem:3.39 MB
1m33s 21894	Memory:1.14 GB/3.85 GB/111.63 MB, objspace_mem:3.39 MB
1m36s 21894	Memory:1.14 GB/3.85 GB/36.16 MB, objspace_mem:3.39 MB
1m39s 21894	Memory:1.14 GB/3.85 GB/36.05 MB, objspace_mem:3.39 MB
1m42s 21894	Memory:1.14 GB/3.85 GB/34.88 MB, objspace_mem:3.39 MB
1m45s 21894	Memory:1.04 GB/3.85 GB/143.84 MB, objspace_mem:3.39 MB
1m48s 21894	Memory:964.86 MB/3.85 GB/245.09 MB, objspace_mem:3.39 MB
1m51s 21894	Memory:964.86 MB/3.85 GB/245.2 MB, objspace_mem:3.39 MB
1m54s 21894	Memory:964.75 MB/3.85 GB/35.95 MB, objspace_mem:3.39 MB
1m57s 21894	Memory:964.75 MB/3.85 GB/35.7 MB, objspace_mem:3.39 MB
2m0s 21894	Memory:964.75 MB/3.85 GB/35.41 MB, objspace_mem:3.39 MB
2m3s 21894	Memory:964.75 MB/3.85 GB/35.59 MB, objspace_mem:3.39 MB
2m6s 21894	Memory:964.75 MB/3.85 GB/33.08 MB, objspace_mem:3.39 MB
2m10s 21894	Memory:960.22 MB/3.85 GB/34.18 MB, objspace_mem:3.39 MB
2m13s 21894	Memory:961.45 MB/3.85 GB/370.79 MB, objspace_mem:3.39 MB
2m16s 21894	Memory:961.45 MB/3.85 GB/368.16 MB, objspace_mem:3.39 MB
2m19s 21894	Memory:961.45 MB/3.85 GB/363.53 MB, objspace_mem:3.39 MB
2m22s 21894	Memory:961.45 MB/3.85 GB/365.3 MB, objspace_mem:3.39 MB
2m25s 21894	Memory:961.45 MB/3.85 GB/133.39 MB, objspace_mem:3.39 MB
2m28s 21894	Memory:961.45 MB/3.85 GB/34.87 MB, objspace_mem:3.39 MB
2m31s 21894	Memory:962.37 MB/3.85 GB/64.34 MB, objspace_mem:3.39 MB
2m34s 21894	Memory:957.14 MB/3.85 GB/732.61 MB, objspace_mem:3.39 MB
2m37s 21894	Memory:960.04 MB/3.85 GB/587.55 MB, objspace_mem:3.39 MB
2m40s 21894	Memory:960.04 MB/3.85 GB/376.61 MB, objspace_mem:3.39 MB
2m43s 21894	Memory:960.04 MB/3.85 GB/358.23 MB, objspace_mem:3.39 MB
2m46s 21894	Memory:960.04 MB/3.85 GB/358.07 MB, objspace_mem:3.39 MB
2m49s 21894	Memory:960.04 MB/3.85 GB/358.24 MB, objspace_mem:3.39 MB
2m52s 21894	Memory:960.04 MB/3.85 GB/356.16 MB, objspace_mem:3.39 MB
2m55s 21894	Memory:960.04 MB/3.85 GB/341.06 MB, objspace_mem:3.39 MB
2m58s 21894	Memory:960.04 MB/3.85 GB/341.71 MB, objspace_mem:3.39 MB
3m1s 21894	Memory:960.04 MB/3.85 GB/341.68 MB, objspace_mem:3.39 MB
3m4s 21894	Memory:960.04 MB/3.85 GB/341.34 MB, objspace_mem:3.39 MB
3m7s 21894	Memory:960.04 MB/3.85 GB/340.85 MB, objspace_mem:3.39 MB
3m10s 21894	Memory:960.04 MB/3.85 GB/340.6 MB, objspace_mem:3.39 MB
^CTraceback (most recent call last):
	1: from test_gc.rb:83:in `<main>'
test_gc.rb:83:in `sleep': Interrupt

[www@server1 tmp]$