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> Run, do not walk, to mmap(2).

running -- slowly.

> P.S. By the way, handles are completely unnecessary in Mac OS X...

I've read that but my feet are heavily weighted by practice of using handles.
Thank you for reminding me.


W.


----------------------
Message: 6
Date: Tue, 29 Mar 2005 21:49:28 -0800
From: Chris Espinosa <email@hidden>
Subject: Re: performance issues
To: "Carbon Dev." <email@hidden>
Message-ID: <email@hidden>
Content-Type: text/plain; charset="us-ascii"


On Mar 29, 2005, at 3:42 PM, Edwards, Waverly wrote:

> Would someone provide me with some tips for getting the most
> performance out of my operating systems / virtual memory.
>
> I have a 378 megabyte file that I
>
> 1. read the entire file into a handle

Stop right there.

Don't do this.

You'll just end up making a copy of the file on disk (in the form of 
your 378Mb being swapped out to VM).

Run, do not walk, to mmap(2).
http://developer.apple.com/documentation/Darwin/Reference/ManPages/
man2/mmap.2.html

Yes, you'll have to learn how to handle POSIX-style system calls in 
your Carbon app, but it isn't that hard.  But what this does is it 
logically joins your file to the virtual memory system, so that each 
block of the file behaves as if it's already in your memory space.

Now given that, if you walk through a 378Mb file and touch every page, 
yes, there will be a lot of disk I/O.  But far less than if you try to 
read the whole file in, fault half of it out, fault back in the first 
half to write to it, fault it out to write it, fault the second half 
back in, etc.

Chris

P.S. By the way, handles are completely unnecessary in Mac OS X, except 
for backwards-compatibility with Carbon functions that take them.  With 
Mac OS X's VM system, you can resize a pointer just as easily as you 
could resize a handle in Mac OS 9.

"Mac OS X implements a highly-tuned, threadsafe allocation library, 
providing standard implementations of the malloc, calloc, realloc, and 
free routines, among others. If you are allocating memory using older 
routines such as NewPtr or NewHandle, you should change your code to 
use malloc instead. The end result is the same since most legacy 
routines are now wrappers for malloc anyway."

http://developer.apple.com/documentation/Performance/Conceptual/
ManagingMemory/Concepts/AboutMemory.html



----------------------------------------------------------------
Waverly Edwards
NA Support Center
Genesys Conferencing - Reston
Email - email@hidden  Phone: 866-343-HELP/4357
Direct:  703-736-7121 


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