Re: Increasing GNAT's heap

[Eryndlia Mavourneen <eryndlia@gmail.com>]

On Wednesday, November 13, 2013 9:39:23 AM UTC-6, Oliver Kleinke wrote:
> > I don't believe it has anything to do with GCC. It looks clearly like
> > GNAT issue which, BTW, also leads to extremely sluggish compilation.
> > After all, if you allocate 2+ GB of memory you have to fill it with
> > some junk and that takes time, much time.
> 
> I suppose this has to do with swapping/paging, so the sluggishness might
> not be GNAT's fault.

I was thinking along these lines.  It is important to remember that the program being run dictates much of what occurs with paging.  Data references aside, the locality of execution has a great deal to do with the amount of paging and swapping that occurs.  A program that constantly jumps around to widely disparate parts of the address space will experience considerably more paging than a program which is as sequential as possible.  I would think that it is possible to have the linker combine frequently used subprograms together with the main code in a single program section or sections that are loaded together to minimize the paging.

Alternatively, there are tools which help to identify which parts of the code are being heavily executed.  It then is possible to lock as many of these pages into memory as circumstances allow.  This will provide a huge increase in speed with relatively little work.

Not having had to worry too much about these issues in a while, I am not up on the latest tools for these things, but I am certain that others in this group are.

-- Eryndlia Mavourneen (KK1T)