Comments on: Mac Virtual Memory – What it is, the Swap Location, and How to Disable Swap in Mac OS X

By: dwasserman

dwasserman — Sat, 23 Mar 2013 22:26:18 +0000

Can I change te location of swap file, for example creating a small partition? If yes, how?

By: Tesselator

Tesselator — Fri, 08 Feb 2013 03:41:05 +0000

I’ve been using my MacPro (32GB RAM) like this for about a week now. I notice SIGNIFICANTLY less drive chatter and many many operations are noticeably faster. Especially OS operations like browsing around in folders with hundreds or thousands of images in each. Icons once displayed are actually instant… I don’t mean fast either. On my system they were fast before. This is instant. Poof! A maximized window populated with any sized icons of RAW (or any kind of) images just appears and scrolling to the bottom of multiple folders each containing 4,000+ images works the same way. Browsing images in LR was sped up by about 10 or 20% too. Good news for those who like LR. Bridge was already very fast (about 6 to 8 times faster than LR) for poking around in image folders but it too became slightly faster. It’s too fast in the first place to measure proper differences but doing the best I could with my stop-watch it’s about double the speed with 1st time page displays (from about 2s to about 1s) and instant every time after that – for hours and hours and hours… and hours…

I don’t recommend doing this with only 8GB or less however. But if you have 24GB or more then I feel comfortable recommending running your machine full-time with the dynamic pager turned off. 16GB would probably be OK too. It works on my older 12GB mac pro system just fine. This is why “with lots of RAM” is in the title. Furthermore you should probably run some kind of memory monitor in the BG. I’ve been using MenuMeters since, like, forever… so I didn’t need to add anything to the installation.

I guess this will help with all versions of OS X from about 10.5 on up – which is when the paging system in OS X became slightly ridiculous.

By: Tesselator

Tesselator — Fri, 08 Feb 2013 03:38:26 +0000

No, it’s:

launchctl load -wF /System/Library/LaunchDaemons/com.apple.dynamic_pager.plist

By: arlet bode

arlet bode — Sun, 13 Jan 2013 01:29:36 +0000

Hey I wouldnt mess with the swap files because I wanted to save some space on my mac and it ended up freezing some days after. I had to restart it but it didn’t turn on. I had to take it to apple and had it reset. Maybe it was for something else, but just in case, dont delete them.

By: bdens

bdens — Fri, 14 Dec 2012 15:32:40 +0000

Thank you so much, this post gave me the info I needed to move my swap off the SSD and on to the secondary HD.
—-
Bdens

Setup:
Mac Mini 2011 2.5, 8g Ram, 2 HD mod, and Arctic silver 5 – thermal paste

P.S. Apple, PLEASE use better thermal paste and Apply it correctly I lost 10c doing this!

By: Sonee

Sonee — Thu, 23 Aug 2012 23:02:18 +0000

do you have do to a reset for this to worK?

By: jtgans

jtgans — Wed, 08 Aug 2012 14:26:55 +0000

three_jeeps is absolutely right, guys — if you disable virtual memory, you’re going to have a bad time.

Seriously, though, unless you’re doing arcane, deep black magic stuff with the kernel or OS research, DO NOT DO THIS! Very bad things can happen, from your system just being slow and unresponsive to DATA LOSS from the system memory management routines forcibly killing off processes when memory has run out for allocation requests.

By: Azziza

Azziza — Fri, 03 Aug 2012 08:10:39 +0000

Thanks for the article. Can anyone tell me if we can delete previous swapfiles? I’m not too clear on that.

I’ve got Swapfile0 to Swapfile5 with 3 files being over 250mb. Would like to delete 0-4 but don’t want to get in over my head… Thoughts?

By: Mickey Sattler

Mickey Sattler — Thu, 31 May 2012 18:16:15 +0000

Disabling VM is a bad idea. A better way of doing things is to force the dynamic pager to do garbage collection with the command

sudo dynamic_pager -L 1073741824

Details at

By: Hank Roberts

Hank Roberts — Sat, 28 Apr 2012 14:54:44 +0000

Has anyone done this?

Tell us how this has been working out — is the warning from ‘Three Jeeps’ above scaring people off?

I’ve got 12GB of RAM on a current Mini, and am puzzling over whether this disabling VM is a good idea.

Or, whether increasing the size of the swap file instead (how?)

By: Simon

Simon — Wed, 22 Feb 2012 20:23:39 +0000

I have a swap file of 209 GB.
How to set a maximum size for it?

By: Mac N Cheese

Mac N Cheese — Tue, 06 Dec 2011 01:53:19 +0000

Mac OS X and virtual memory. While it is true that Mac OS X is built on Unix base, the management of virtual memory by OS X is not akin to raw Unix or Linux vm management since virtual memory allocations occur via the microkernel API (Mach).

The Darwin and osfmk source tree does not directly tie to any PPC hardware or x86 hardware related to paging, so that if you’re expecting to find an operating system structure (exposed and accessible through _asm() or c/c++ lib), you will find none. In fact, if you attempt to access memory that is not “pre-allocated” by Mac OS X, it achieves a “bus error” and fails whereas some Unix OS would allocate another VM page and continue. In cases where the kernel can not create more VM for itself, it enters a hard stop and crashes (why you should leave VM “on”).

The latter is also why porting “other Unix” code to Mac OS X is a chore if the c/c++ source is not well-behaved and cooperating with OS API to allocate VM. These “rules” prevent code allocating beyond (overrun) established code and data boundaries (especially the heap and stack).

Also, to thwart “hacking,” the structures used to govern memory allocation are not exposed in c/c++ API libraries, not even for _setjmp() and _longjmp() functions.

Another layer of protection is that virtual memory init begins during Open Firmware initialization and setup of context which is based as “values” for Mach-O to use.

By: three_jeeps

three_jeeps — Thu, 17 Nov 2011 05:23:30 +0000

I just read this article and the majority of posts and all I can say that it is extremely bad advice to turn off your swap space. To be blunt, this is a very stupid idea. The entire operating system is built around the idea of a backing store for RAM – that is basic Operating System Design 101. Memory allocation and deallocation use some fairly complicated algorithms to provide low-latency response to having multiple applications loaded, run, and then deactivated. Having a very small amount of RAM (e.g. 1 Gig) causes the allocation/deallocation algorithms to be somewhat inefficient, causing bottlenecked or wedged applications. The more apps one runs, the worse the situation becomes. Your system will literally crawl or wedge. Buy as much RAM as you can afford, and increase your swap to something like 10GB or more. Disks are cheap and althought not as fast as RAM, it will not slow your system to a crawl.If you are worried about killing your SSD, you have two choices: max out the RAM and buy a mechanical HD, or, disable swap and watch your system crawl…..To be honest, the likely hood of destroying your SSD is very slim.

By: Nick D

Nick D — Wed, 10 Aug 2011 10:14:47 +0000

DO NOT disable dynamic_pager!

I had it disabled for a few weeks and noticed that my Mac’s wired memory usage would grow out of control. Turns out that dynamic_pager is involved in cleaning up wired memory…

“Wired memory is not immediately released back to the free list when it becomes invalid. Instead it is “garbage collected” when the free-page count falls below the threshold that triggers page out events.”

- http://developer.apple.com/library/mac/#documentation/Performance/Conceptual/ManagingMemory/Articles/AboutMemory.html#//apple_ref/doc/uid/20001880-99714-TPXREF106

By: Mikee

Mikee — Thu, 09 Jun 2011 09:18:49 +0000

Hi,

Very interesting post.
My Mac is becoming sluggish, especially with “heavy” apps like Firefox 4 (which remains a memory eater…), or LibreOffice. As the harddrive gets full, the sluggishness becomes more and more noticeable.

So, as you pointed out, I wonder why Apple didn’t take back Unix/Linux precepts like automatically create a swap partition during first install???

Swap partitions are normally formatted “raw” (without enhanced filesystems) to assure io speed. If I shrink my actual system partition to add a swap partition, I will be force to use HFS on it? Or there is a way to format it for swap?

Next step: how to tell the system that its swap is now longer located on /private/var/vm/ ? Will a symbolic or hard link suffice?

More important: if I move/link the /private/var/vm/ folder, you said that it’s also the place for sleepimage, what should be the size of the partition? Size of physical memory in bytes plus swap files? But how to anticipate the system’s need with swapfiles?

And also: why it seems not possible to adjust (like with mkswap, and swap on/off) the size of the swap? As computers are shipped with more and more memory, it could be useful (especially for SSD) to reduce (shrink) swap space/size/use.

Regards.