On Wed, 20 May 2020 10:26:50 +0530, Pintu Agarwal said:
> I know it is weird to manually arrive a MemTotal from the values of meminfo.
> But I am actually looking for general formula.

You missed the point - the "general formula" has probably changed over the years.

> With this I could arrive to some result, but I have some doubts:
> * Is Mapped already included in Active/Inactive (file) ? Because
> mapped is coming from NR_FILE_MAPPED.

And that's the sort of question that can have different answers for 3.18 and 5.7.