iFreeMem 2.0: when you just don't feel like rebooting

You want to reclaim memory? Open Terminal, type "top", hit return and then look at the used and free memory. Remember those numbers. Press and hold ctrl and hit c. That will end top and return you to the shell. Enter the following (without the quotes): "du -k ~/ >/dev/null" and press return and when the prompt returns, type "top", hit return and observe the current amount of used and free memory. You'll often see a sizable increase in free RAM.

Another free version for leopard is to type 'a' into spotlight and make sure you delete the 'a' just before you start paging. The mds process ends up using lots of memory, and when quit it you end up with lots of free memory :)

I've had my Mac running for months on end without any of these memory problems.

Mark Russinovich's great article from a 5 years back went into great details why these things are genuine snake oil even for the PC, let alone Darwin:

http://www.windowsitpro.com/articles/index.cfm?articleid=41095&cpage=97

free reprint: http://license.icopyright.net/user/viewFreeUse.act?fuid=NzgyNzU0

However, just like homeopathy, placebo is powerful medicine, and if it works to make you feel better, let the placebo rule!

There is definitely something that causes my Macs to slow to a crawl after a few days uptime, and kernel_task's memory allocation to approach infinity. I'm going to test iFreeMem along with the weekly script to see if either has any real effect.

If your system is constantly being bagged everytime you launch another app, then spend your money on RAM not cheezy apps like this.

I'd take a wild guess that this app does something not dissimilar the following:

void
free_up_memory()
{
int c;
char *p, *q;

for(c = 0; c < 2048; c++)
{
if(!(p = malloc(1024 * 1024)))
{

return;
}
for(q = p; q < p + (1024 * 1024); q += 4096)
{
*q = 1;
}

}
}

…in other words, it allocates as much memory as it can and makes sure it gets "dirty", forcing everything else to get swapped out. Then it frees it all up again.

The effect is that all your latent caches for applications you're not actually running any more get thrown away, but also all of the memory used by applications which *are* running get swapped out to disk and needs to be pulled back in again.

Really, Darwin's VM could do with a doing a better job of releasing now-unused blocks of virtual memory and gradually swapping things back in which are still running but have been swapped out to make room for the now-dead stuff—I often find it can take a while before the actual amount of “free” memory I have matches what it really should be, and have chunks of VM swapped out that would be more useful swapped back in. In real terms, though, it's a minor quibble, and unlikely to be one that's worth $19 unless you have some sort of psychosomatic condition triggered by Activity Monitor's pie charts.

Snake oil.

Ah, so the memory "recovery" programs have run out of gullible Windows users to sell their products to and they've moved on to gullible Mac users.

I say this with love. I used to use one of these on Windows as well, before I realized it did nothing, other than sometimes crash my computer.

Radek: That is within-application memory fragmentation. Memory in MacOS (and other modem desktop/server OSs) is allocated in pages (typically of 4KB each). On a machine under fairly heavy use, many of those pages are temporarily stored on disk (swap space, aka. scratch space). When your app has allocated lots of those pages, but only touches a few bytes in each page, the OS may end up writing to/reading from swap much more than necessary. That's what your linked page is about.

However, when the app quits, all pages are returned to the system.

Brett: It is true that in somewhat uncommon circumstances you gain some responsiveness by proactively reclaiming pages. It sounds like you have reliably identified circumstances where it helps you. However, you don't need to buy an app to achieve that. And more often than not, it decreases responsiveness. (Did you also run "sudo periodic weekly" also, or just the "daily" variant?)