Improve code readability: 8 Mb, restart operation

Summary:
This change improves clarity of code:

• An unit was expressed in bytes, requiring to know 1024 multiples to figure it.
• Explain the sv restart phd line at the end.

Test Plan:

$ sh
$ echo $((8*1024*1024))
8388608

Reviewers: dereckson

Subscribers: Nasqueron Docker deployment squad

Tags: Docker images

Differential Revision: https://devcentral.nasqueron.org/D602