typesizes and memory usage on 64bit vs. 32bit

[Stephan Bergmann]

On 04/11/2012 11:10 AM, Enrico Weigelt wrote:
> does anybody has some knowledge about LO's memory usage increase
> comparing 32 to 64 bit ? (heap data, not code).
>
> I've seen a massive memory consumption increase on Chromium since
> moved from 32bit to 64bit userland. Seems they quite frequently
> used plain int types which of course gets doubled in size then.

"plain int" stays 32 bits in the LP64 model (where only long int and 
pointers go 64 bits), so the main increase in memory consumption is 
typically due to the larger pointers.

In general, the main motivation to switch an application from 32 to 64 
bit on a platform that would support executing either (which is true at 
least for all the x86/x86_64 based Linux, Mac OS X, Windows) should be a 
demand for a large number of threads per process (as the need to 
allocate stack space for them easily conflicts with a small address 
space; but LO is not in need here, I'd say) or removal of legacy 32 bit 
versions of libraries from the system (as apparently happens on Mac, 
e.g. with in-process JVM).  Or, esp. on x86/x86_64 architectures, 
improved application performance due to the larger register set (which 
needs to be judged against the larger pointer size, as there is no 
process model for x86_64 with 32 bit addresses).

Anyway, the trend apparently is to go 64 bit regardless.

Stephan