If I run the same program twice under linux

[LarryChen]

what section would be shared in the memory? Thanks.

[OReubens]

I'm not entirely sure about Linux.
But eligible sections would be:

- code
Typically in a copy on write scenario. Assuming it's located at it's prefered load address, which would usually be the case for executables and "maybe" for dynamic libraries, and assuming there is no such thing active as load address randomization.
- const data
again in a copy on write scenario (see above)
- embedded resources
assuming they don't have literal pointers but use offsets, otherwise, again, copy-on-write see above
- import and export tables
- address fixup table



If you cannot guarantee prefered load address...

It is possible to write code that does not have pointers and instead uses offsets only (this doesn't mean you can't use C++ pointers). There are compilers that help you do this, without compiler support, this is "difficult" and will require a considerable amount of effort on your part.
There is no benefit to doing this if you can guarantee prefered load address.

It is possible to organize your const data in such a way to avoid copy-on-write effects. For 'flat' C/C++ data this is fairly easy.
It is somewhat problematic for literal strings, you will need to convert them all to a single unit and access all string access indirectly by offset/index. The same is true for any other structures accessed by address.
While this takes effort on your part, it actually results in a better/cleaner approach to const data, and depending on needs, may actually have significant performance boosts as well.

[monarch_dodra]

Pretty sure that "If I run the same program twice under linux", then nothing will be shared in memory.

[OReubens]

One strike up for windows and one strike down for Linux if that's the case.

In a system where you could be running the same executable image multiple times (system dll's are obvious examples), but also consider things like terminal services where dozens of users may be running the same executables at the same time.
ALlowing the system to share sections of the images means a huge boost to overal memoryusage.