" Freezes when using huge virtual memory
My Mac freezes when it uses too much virtual memory: more than 64GB ... which is far away from the Apple advertised several Exabytes ;). Have you heard from others of a similar experience?

I use an 8-core MacPro, OS 10.5.4, with 10GB Ram and a very fast Raid-0 array which is also used for the swap files of the virtual memory (so using VM hurts not too much). (using a tweak/hack to redirect VM) But the same behavior occurs if I start from the original hard disk, so the effect is not disk or Raid related. (drives check OK I assume?-Mike)

I noticed the following problem: when the VM is around 74 GB, 58GB swapped out, (according to the activity monitor) then the Mac freezes. I can move the mouse, but get no other reaction from the Mac. I have to restart via pressing long the power button.
As long as the VM stays below that I can work normally with the Mac. It makes no difference if one or several processes consume the VM. There is enough free space on the hard disk to swap (so the "no space" in the console below can not refer to that).

I wrote a little C program to test the VM performance which I used to reproduce the freeze. I thing it is not a problem of the program, as if I choose the parameters such that the memory consummation stays below 64GB it runs fine. And If I increase the parameters or launch two instances of the fine running version I get my freeze.

The last entries in the console were:
26.08.08 09:53:02 Xcode152 Xcode(152,0xb0103000) malloc: free_garbage: garbage ptr = 0x2eae980, has non-zero refcount = 1
26.08.08 09:54:33 kernel (default pager): KERNEL: no space in available paging segments
26.08.08 10:10:40 mds30 (Error) FMW: WE ARE DROPPING FMW EVENTS!
26.08.08 10:10:40 mds30 (Warning) FMW: unknown event:999 ac:0 am:0
26.08.08 10:10:42 kernel (default pager): KERNEL: no space in available paging segments
....(more of the last line)
Best wishes, Yves"

Update: Shortly after posting this I recd 2 replies from readers that are not seeing this problem:

" Saw the post this morning about a Mac Pro VM problem. I can't replicate this. On my 2008 Mac Pro using 10.5.4, I'm constantly over 64GB of VM (due to keeping Fusion running all the time for my Windows environments). I only have 6GB of (official Apple) RAM and no RAID array, although I did swap out the original drive for a WD 500GB.
I'm at 77GB of VM as I write this, and all is well. However my swapped memory is only at 1GB, so how is he getting 58GB swapped? What apps is he running?
Maybe he can publish his Xcode program somewhere to see if I get the same issue.
Still extremely happy with this machine after upgrading from the Beige G3. :)
-Joey K"

And another reply on no issues with large VM:

"Hi Mike, I have an 8Core (3Ghz) MacPro with 10GB Ram and 10.5.4 and do not experience these freezes using a Samsung F1 750GB as the startup drive.
At the moment of writing this mail the VM is at 95GB, I have more than 20 apps open, the CPUs are maxed out with Boinc and Logic is playing back a session without any problems.
If I had the program he wrote I could make some tests here.
Best regards, Matthias"

An earlier reply:

" My only comment, why not increase physical RAM to 32GB, and reduce the swap files by 22GB or more. (of course that's an option but eight 4GB FBDIMMs (w/mac pro heatsinks) aren't cheap - I was looking for confirmation that there was a VM size issue/limit - from the later replies above there isn't.-Mike)
Swap files always go to the boot drive, unless you 'hack' the OS to direct it elsewhere, which some have tried but never heard it helped. (A tweak for this was first mentioned here back in 2001 (for OS X 10.0.x) several times (very old pages so off-site links are likely no longer valid) - i.e. OS X Swapfile Sizes and Reference Links (July 2001), "SwapCop" utility (from 2001), Notes/Warnings/Tips on Dedicated OS X Swap File Partition and /etc/fstab (June 2001).-Mike)

Note: Unlike most UNIX-based operating systems, Mac OS X does not use a preallocated swap partition for virtual memory. Instead, it uses all of the available space on the machine*s boot partition.
Ref: developer.apple.com doc About Memory
Viewing Virtual Memory Usage:
developer.apple.com doc on VMPages
-Greg"

"Version 4.0.1: This update addresses compatibility issues with AVCHD camcorders, improves stability when using third-party FxPlug plug-ins, and addresses a number of other minor issues.

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