On May 14, 9:24am, Jack Scheible wrote:
> Subject: Re: Fragmentation; was Re: memory leak
> Shenkin wrote:
> > If you still disagree, I suggest we take the discussion off-line.
>
> Only if _I_ get the last word _online_. :-)
I see your point. :-) The problem is that you guys drive on the
wrong side of the road, so it's obvious that you define things
backwards, too.
This is devolving into I said / you said, so maybe it's time to
stop. I think we disagree on several points, which I'll try
to do little more than list.
I think the virtual address space is the set of addresses that
the program has allocated to it, whether or not they are tied
to physical resources. Virtual memory is basically another
term for this. You disagree.
You think:
> ... no process can have the
> combined sizes of it's program, data, and stack exceed RAM+swap.
I think it depends on what you mean by "combined sized...".
The virtual address space -- the ranges of addresses allocated to
a process (its virtual memory) -- need not all be backed up by RAM
and/or SWAP, though some OS's do it this way. When the OS does not
do it this way, the strategy is termed "overcommitment of virtual
memory". This strategy is at least available, and is usually the
default, on most modern UNIX operating systems. Certainly, the
part of the virtual memory assigned to physical resources, and
the sum of these for all processes, must fit within RAM + swap.
You think:
> ...we programmers don't have to worry about fragmenting
> memory, until we reach the 4 gig limit. The OS writers have already
> solved the problem.
I think this assertion is mainly incorrect. I do believe that
it's usually not enough of a problem to worry about most of the
time, but I do not believe that it's a non-problem. Fragmentation
of virtual memory can take place, and this does waste physical
resources, even for processes that are nowhere near the maximum
limits of the system.
Regardless of how you define virtual memory (i.e., if you want to use
another term for the address space of a process), the considerations
in my earlier email (which you felt was too tedious to read) explained
why.
You should now feel free to have your last word, because I've had
mine, on-line at least.
-P.
--
*********** How can we have ethnic music without ethnic hatred? ***********
* Peter S. Shenkin; Chemistry, Columbia U.; 3000 Broadway, Mail Code 3153 *
** NY, NY 10027; [log in to unmask]; (212)854-5143; FAX: 678-9039 ***
*MacroModel WWW page: http://www.columbia.edu/cu/chemistry/mmod/mmod.html *
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