Mountain Lion seems to have addressed the memory management issues in OS X

It's important to get the terminology correct when discussing VM behavior. Page-outs are not identical to swap-outs. And unfortunately, due to the age and architecture of the Mach kernel, there's no way I'm aware of on OS X to measure the rate of the latter.<p>Page-outs refer to a file-backed page being committed to disk; these are perfectly normal and expected (program writes to a file, kernel eventually commits to disk). Every OS guarantees that file-backed pages be committed within some reasonably short period of time to reduce the risk of lost data in the event of a power outage (the sync interval).<p>A high page-out rate doesn't necessarily imply memory pressure; it may simply mean some program running on the system is writing to files frequently. However, memory pressure may temporarily increase the page-out rate if the sync interval hasn't yet kicked in.<p>Swap-outs, on the other hand, relate to anonymous memory pages (i.e. the heap). Swap-outs, in contrast to page-outs, are generally bad and indicate severe memory pressure.

I still ended up with an 8 GB page file after a few days of regular usage (nothing too hard like VMs or anything - just your typical Xcode dev workflow, including opening up Photoshop once or twice to export graphics).<p>This is on a MBP with 8 GB RAM.<p>I never had any memory-related performance issues in Lion, (maybe because I have an SSD), but I always end up with a big pagefile of stale data.

It seems as though a lot of people are noticing some speed enhancements. I haven't quantified any of it, so my experience is all anecdotal, but I definitely notice the boost as well.<p>The changes in Mountain Lion have been subtle, but I really love the upgrade. I performed a full disk backup which took the longest amount of time. The actual install (2012 MacBook Air) took like 15-20 minutes. If anyone is in doubt, definitely do yourself the favor and upgrade. Typically I am hesitant to do major OS upgrades due to things like python or ruby breaking most of my local websites ... everything works great!<p>I had to modify some apache2 settings (I use the built-in webserver for PHP development) but that was about it. Oh also, apache is still there. A lot of people think that it's gone because the preferences pane is missing, but it's still hiding within the belly of the beast.<p>I feel like I can throw anything at this. I've never multitasked like this before.

One of the things I've noticed is that the new Xcode 4.4 (released the same time as Mountain Lion) seems to be an awful lot snappier to me. My theory is that this is happening because they might have switched Xcode from being garbage collected to ARC (since it used to be GC ever since Snow Leopard came out but GC is now deprecated).

We've been hearing this for a long time:<p>“free memory is wasted memory” vs “inactive memory is never released”<p>“Purge is the worst thing you could do” vs “Purge solves the issue”<p>We have the kernels's source[1] and DTrace. Let's get some real data?<p>[1]<a href="http://opensource.apple.com/source/xnu/xnu-2050.7.9/" rel="nofollow">http://opensource.apple.com/source/xnu/xnu-2050.7.9/</a>

Haven't seen the paging issues Adam was noticing, but I'm still gobsmacked by the amount of memory some applications seem to take. The OS (kernel_task, mds, WindowServer, and friends) regularly eat up .75 of a gig, and Firefox consumes .5 - 1 gig without much effort (other browsers seem to have a similar profile).<p>Quick poll, what are you running, and what's your memory consumption? Here's me:<p>Currently running: Firefox, Spotify, Mail, Calendar, Terminal, Mongo (mongo using 100mb).<p>Memory Used: 3.75 GB

I can concur with OP. My MacBook Pro suffered severe paging issues under Lion, but seems to be (mostly) gone in Mountain Lion. Running Eclipse, Photoshop, Chrome, and Parallels at the same time is possible once again without major slow down on my machine. As always, YMMV.

Odd. I had this problem in 10.6 (Snow Leopard) and it went away when I upgraded to 10.7 (Lion). The most obvious symptom is the machine does not seem to be able to make use of the inactive memory (the blue slice of the pie in Activity Monitor). I did not notice the problem at all when I first started using 10.6. When I hunted around on the help forums a few months ago I found lots of users with the symptoms, but nobody acknowledging the "validity" of the problem. In fact a lot of deniers out there. I wonder if it was quietly fixed or will recur after the system gets used for a while.

I don't suppose anyone can comment on whether Mountain Lion has done anything for the mouse lag issue[1]?<p>I can't upgrade yet because I disabled HFS+ journaling and nothing seems to be able to re-enable it (the installer requires journaling to be enabled).<p>[1] <a href="http://d43.me/blog/1205/the-cause-for-all-your-mac-os-x-mouse-annoyances/" rel="nofollow">http://d43.me/blog/1205/the-cause-for-all-your-mac-os-x-mous...</a>

Since the GM, I also noticed this on my production machine. Previously I had custom settings for the dynamic pager, but it seems that is not longer necessary.<p>Subtle changes and I'm happy with them. Probably the next year, we'll see some subtle improvements on the backend.

This is the reason I installed Mountain Lion. I've only used it a bit in the last few days, but I haven't seen crazy amounts of mds RAM usage since installing either.

Only thing holding me back from upgrading is the complete lack of wanting to hex edit my ATI kext again.. heck it might not even be compatbile with ML.<p>Hackintoshes :/

My battery life seems to last as long as it did on Snow Leopard, too.

Yup, memory management seemed to be fixed as of 10.7.4 even.<p>I've found new bug in ML, whenever I switch users, Mountain Lion seems to think I've a desktop much smaller than what I actually have. And sometimes the "virtual" desktop isn't even positioned at 0,0 on my actual desktop. :-/

OK, that's enough reason to do the upgrade.<p>Parallels gets abysmally slow for me when TimeMachine starts up.

I would not describe this as "the memory management issues in OS X". It should be obvious to anyone how much of an oversimplification that is.

Question: (2009 15" MBP, 8GB 1333MHz RAM, 7200rpm HDD, Mountain Lion)<p>I have zillions of apps open.<p><pre><code> 1GB wired, 3.25GB active, 1GB inactive, 2.55 free 757,197 Page Ins 0 Page Outs </code></pre> It's confusing... If I haven't "swapped out" (page out) anything to disk, then how come I've "swapped in" (page in) 750,000 pages <i>from</i> the disk?

It's much, much worse for me. Things go into Inactive memory, which is fine, but then it doesn't get freed when it's needed, or else it does so very slowly. So I have 20 MB of Free memory and 4 GB of Inactive and everything slows to an unusable crawl and I have to run `purge` to get my computer to start behaving properly again.

Does anyone still have a 4gb MBP? I'm still on SL and wondering if I should switch.

I am running Mountain Lion on a 24 GB ExpressCard (about 3 GB free) with 4 GB of RAM. After upgrading to Mountain Lion I am getting a "Hard disk is nearly full" message much more frequently. Almost never seen that on Lion. Could this memory management change be the culprit?

Anyone did the upgrade from SL? Is a clean install always recommended?

&#62; addressed the memory pun intended?

This guys initial advice was terrible and should never have been paraded around as a solution