You can't really compare these 2 memory usages. PHP 5.x allocates memory on request, while PHP 7.x allocates a large chunk of memory when it starts. This benefits PHP 7.x's performance because it doesn't need to allocate mem every time your program needs it. On the other hand, it increases mom consumption for 'small' scripts. The VIRT column with the 3,7G (if I'm correct) represents the max memory this process can address. (RAM, mapped disk memoryfiles, memory shared with other processes, etc). The SHR column shows how much memory is actually used.