Memory growth issue about crypto module.

Version: v6.9.4 & v8.1.2
Platform: Linux 3.10.0-514.21.2.el7.x86_64 deps: update openssl to 1.0.1j #1 SMP Tue Jun 20 12:24:47 UTC 2017 x86_64 x86_64 x86_64 GNU/Linux

If I run cipher related function many times, I can see memory growth even though execute gc manually.
To be more specific, if I use cipher.final(), it causes memory growth.

Below is test code.

    var crypto = require('crypto');

    function testCipher() {
        var cipher = crypto.createCipheriv('aes-128-gcm', Buffer.from('1234567890123456'), Buffer.from('a1'));
        cipher.setAutoPadding(false);

        return Buffer.concat([cipher.update(Buffer.from('datas')), cipher.final()]);
    }

    for (var i = 0; i < 100000000; i++) {
        testCipher();

        if (i % 200000 === 0) {
            gc(true);
        }
    }