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Turning off the VM to enhancing performance?
Authored by: romulis on Aug 19, '04 08:52:24AM
OK - security issues asside, I'd like to know a little about VM performance. (what ARE you people hiding? You do have backups, right?).

My setup: a dual 2GHz G5, 4.5GB RAM, 128MB swap (in 2 files). I'm running an oracle server (for development). I do a lot of data munging and, at the moment, image manipulation (the job I've got running now will probably finish in 12 hours or so).

I'm using MenuMeters (beta, version 1.1.1 can't handle 4GB :-) and the activity monitor to get a handle on system performance.

I've noticed that when heavily loaded, even this machine swaps like crazy. I often see 1,000+ pagein/outs per second (ie: swapping 4+MB data/sec).

Now I've turned off the VM and.... (almost) no change!

Activity Monitor thinks that the VM is 12GB large (with the dynamic pager turned off. huh?) It's not paging out any more, but it is still paging in endlessly. (With the VM turned on page-outs were in the same order of magnitude as page-ins). Could it be that these stats are counting normal data reads (initiated by applications) as well as vm reads (ie: reads initiated by the VM system)?

The memory usage stats are even more confusing: 300MB wired (system code?), 300MB active (programs & data) and the rest is inactive (does this include 'freed' memory? Is it OS-X's file cache? If the OS needs more space, does it just throw this away?)

Anyway, after this little experiment I'm going to turn the VM back on again, for no other reason than complying with the standard setup.

Does anyone have any other ideas to prevent OS-X from swapping?

Thanks for the original tip, and thanks for any other suggestions!


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