(I added this line before the exec (our alternate one on line 76) to help with troubleshooting:

echo about to exec $PAGER -F “${ALT_PATH}”/swapfile -S $SIZE -H $HWT -L $LWT at `/bin/date` >> “${ALT_PATH}”/dynamic_pager_wrapper_isUsingThisDirectory.OSis`/usr/bin/uname -r`
)

over the course of surfing around on this, both the inactive number and the swap-in-use number have been growing. WTF?

Minor nit on “the fastest part of the disk”.

Assume you are using the whole disk (not short stroking). In random I/O situations the fastest part of the disk is neither the inside nor the outside, it’s the middle.

Right in the middle means your average seek time to that region is as low as is possible. Access time (seek + rotational latency) is much more important to your random i/o speed than the raw transfer rate of whatever portion of the disk you are looking at. You can’t control rotational latency but you can control the seek time.

In this situation this is largely academic, you probably don’t want to split your mac into three partitions to accomplish this. However, if you had multiple partitions anyway (or an OS with a logical volume manager), putting swap in the middle would be best.

Thanks for this, my MacBook has 4G and has been running like an absolute pig after a few hours. Mind you, I run to Eve Online clients and Netbeans IDE, as well as Safari, Mail.app and various other guff.

But previously switching between apps would SBOD regularly and generally just kill the system for what seemed like hours. But of course it was only seconds.

But now, switching between apps is instant – even though there’s still stuff swapped out I think the lack of having to clean up lots of swap files is really helping.

And as for closing apps…. It’s like night and day. I can close an app and not have to go make a coffee!

Thanks – I owe you a beer or two!

Steve.

P.S. This is on Lion, so it works on Lion too

For example, you should know that
“vi com.apple.dynamic_pager.plist”
really means that you should open the file in a text editor of your choice and make changes similar to those described at http://is.gd/9qZIX , so it’ll run this script instead of running dynamic_pager directly.

And you should know to chmod +x the script appropriately.

OTOH, even if you generally know when & how to do such things, it still helps to have a list of ‘em, so I’ve just emailed such suggestions to Alec.

For anybody who’s fairly technical but not into spending the cash for an SSD quite yet:

A couple weeks ago I followed the advice in dropsafe : Addressing The Outmoded Swapping And Paging Strategy in OSX? to adjust some paging parameters and move paging to a separate (non-journaled) partitioned volume. The results have been extremely satisfying. In no way am I getting SSD-level results, but beachballs are now rare*, and things like quitting Firefox after a long session no longer take acres of forever while swap space is reclaimed.

In other words I can now use my (non-unibody, maxed-out-at-4GB RAM) MacBook Pro all day (in my usual mode of lots of apps running and lots of tabs open) without wanting to punch something. Rage-free (and free) is nice, even if it’s not SSD-nice.

A few caveats:

1. This is a bit of work (and depending on your skillz, maybe a little risk) so it’s not worth doing unless you need it or love tinkering. My wife has an 8GB unibody MBP and it runs so smoothly it’s really not worth doing this on hers.

2. Really should not be attempted unless you are unixy enough to understand the entire article and infer the (very slight) missing pieces, or have ready access to someone who is.

3. Although Disk Utility seems to offer live repartitioning, it did not actually work the first time I tried it — it crashed my Mac (hard, but completely harmlessly) when I was trying to shrink the main partition. In my case the path of least resistance was to boot off my nightly SuperDuper clone and do the partitioning from there while I got some work done, so I didn’t pursue the live-partitioning thing further. (If live repartitioning doesn’t work for you and you don’t have a bootable external, you can always boot off your OS installation or upgrade DVD and go to the utilities from there — assuming you still have that DVD.)

4. After you make your scratch volume, remember to exclude it from Time Machine and Spotlight explicitly so you don’t get pointless extra activity on it. OS X doesn’t automatically know to do this for you.

Also, a tip: I made my scratch partition a little bigger than I expected to need, so that I could move some additional application-specific caches onto it. That was a good call. A few days later I moved the caches for Firefox and one of my video games onto the scratch drive, making an incremental but welcome difference in the general smoothness and non-spasticness of both apps.

If I haven’t made you afraid/reluctant/bored by now, then it’s a good tweak that you might want to try.

*Well, rare except when I do anything in Safari, which just seems ridiculously prone to them, but even in Safari they’re not nearly as long or plentiful as before.

Seriously, if you’re having problems following the instructions – for instance the script does not take any file suffix – then this may not be the right method for you.

I already moved the swap file to a dedicated partition and copied the “dynamic_pager_wrapper.sh.txt” to the /sbin directory.

I’m doing something wrong here huh?

Yes, I m still seeing this, and occasionally I try to investigate what is going on; I too am not seeing reclamation, and I _was_ seeing near-instant creation of two swapfiles although that’s less rapid after I fixed a bug in the script. I do not know what is going on with reclamation, but on the other hand I am seeing considerable benefit to performance from having the swapfiles set out clearly and in the large, so I’m not investigating all that often or much.

Are you tight for disk space?

(place the script in /sbin)

cd /System/Library/LaunchDaemons

cp -p com.apple.dynamic_pager.plist{,_bak}

plutil -convert xml1 com.apple.dynamic_pager.plist

vi com.apple.dynamic_pager.plist

plutil -convert binary1 com.apple.dynamic_pager.plist

(make target swapfile directory)

(check script permissions)

touch /USE_ALTERNATE_SWAP