bug#17535: 24.3.91; Problems with profiling memory

[Eli Zaretskii]

> From: Stefan Monnier <monnier@iro.umontreal.ca>
> Cc: 17535@debbugs.gnu.org
> Date: Tue, 20 May 2014 15:01:34 -0400
> 
> > 2. How to interpret the "memory profile"?  What does a line such as
> >    this in the profile mean:
> >   - execute-extended-command                                  973,272  20%
> >    How were the 973,272 bytes counted, and what are they 20% of?  The
> >    ELisp manual, where this facility is described, does not explain
> >    how to interpret the profiles, and neither can I find anything
> >    about that in the doc strings.
> 
> It's the number of bytes "allocated from the system" during execution of
> this function.

But these numbers are huge.  I have hard time believing that all those
bytes were allocated in just few minutes of an almost-idle Emacs.

> This "allocation" is poorly defined: we don't track allocation of
> individual objects but of things like cons_blocks.

Do we only track allocations of Lisp objects, or just any calls to
xmalloc?

> >   etc.: I see no percentage numbers except 1%, 0%, and -1%.
> 
> This is just most likely a wrap-around due to too-large integers.

Definitely.  I thought these were already fixed, but it looks they
aren't.  I will try to take a better look.  Are there any reasons not
to do this calculation in floating-point?