Mac RAM release question

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rabbitmountain
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p.1 #1 · Mac RAM release question

I'm running a 2010 Mac Pro, 2.8GHz Quad Core Xenon with 12GB of RAM. Lately, when using lots of programs simultaneously, closing and opening other programs etc, the system starts being less responsive at some point.

When I check Activity Monitor, there is about 6GB taken by Wired (Red) and Active (Yellow), there is no Free (Green), but there is a huge amount of Inactive (Blue) memory. Isn't the OS supposed to immediately release the Inactive memory and dispense it to my current memory demanding applications?

At first I was thinking I should upgrade the RAM from 12GB to 24GB, but now I'm not so sure anymore.

Ideas? Diagnostics?

Thanks.

Stay good,
Ralph.

Sep 11, 2012 at 07:15 PM

howardm4
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p.1 #2 · Mac RAM release question

no, actually the system caches what was in memory so in case it's needed again, it's already there. But, if you're truly running out of RAM, it should start dumping the cache.

try using the command line command to force it: purge

12G really ought to be enough but w/o knowing what you're running, it's impossible to say

Sep 11, 2012 at 08:37 PM

rabbitmountain
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p.1 #3 · Mac RAM release question

It usually happens when I'm running the following applications simultaneously:
- Mail
- Firefox
- Lightroom4.1
- Photoshop CS5
OR
- Mail
- Firefox
- Lightroom 4.1
- VMware Windows 7

Performance drop happens mostly when I have been running the system for the entire day, or two days without reboot.
I start seeing the ugly Page-Outs, which means the system is writing to the hard drive. But why is it doing that if I have 6GB of Inactive RAM? Why doesn't it just throw away what's inside that Inactive RAM and make it available for new apps?

This is probably something I just don't understand. And I want to understand just enough to be able to decide whether or not I need a RAM upgrade.

Sep 11, 2012 at 09:36 PM

rabbitmountain
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p.1 #4 · Mac RAM release question

OK after reading some more it is my understanding that OSX keeps all memory allocated by currently running applications but not recently used, into "Inactive". But these are running applications, not applications that have been closed again.

So if there is no Free memory left, and all memory is either Wired, Active and Inactive, all memory is in use by my applications and I've filled the 12GB of RAM. Opening more programs causes the system to write chunks of memory from the RAM (inactive section) to the hard drive to free up RAM for my new program. The Page-Outs start to rise.

So far so good. Well not good, but I understand it, at least. That is, if I interpreted it correctly.

Question:
How come my RAM seems to fill up much more than the physical RAM used for my applications? I did a test:
- Rebooted and checked Activity monitor. 600 MB used.
- Launched Firefox and Lightroom 4.1. According to Activity Monitor, LR eats 1.4GB and Firefox 330MB. That's 1,73 together. Still Free RAM fell to 8.27 GB, so 3.73 is in use. How come?600MB + 1.73GB = 2.33 GB, not 3.73.
- I can go on with other programs, the sum of the physical memory is not the amount of used memory.

Anyway, when the page-outs keep appearing, it's time to add memory. Whether the math is right or not (well I suppose the math is always right, but I just don't understand zip of it).

Question
Assuming that 16GB will be enough for my usual workload, one would think that adding 1 4GB module will do the trick. However, the system will be slower because 3 modules (of any given identical size) works fastest in this configuration. So for best performance, I should upgrade to 3x8=24GB RAM.

But that's much more expensive AND I need to order it from the USA because in the Netherlands it costs about 155 € (180$) per 8GB chip, so 560$ for 24GB. OWC has an upgrade kit for 245$.

I'll have to give this some thought......

Sep 11, 2012 at 10:35 PM

Alan321
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p.1 #5 · Mac RAM release question

I think that the 4 vs 3 memory module thing is over-rated because it makes only a small difference in real world applications. What performance you gain by having more actually used RAM installed will far outweigh what you lose by having the wrong number of memory modules.

I suggest that going from 12 to 16GB is just tinkering. If you are actually running low on RAM then double it at least so that the improvement is obvious - so long as you don't break the bank by going to the latest large-capacity memory modules to do it.

Have you checked out Lloyd Chambers' mac performance guide ?

- Alan

Sep 12, 2012 at 12:37 PM

rabbitmountain
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p.1 #6 · Mac RAM release question

Yes checked him out.

1 extra 4GB module: 33 Euros (to upgrade to 16GB total)
3 8GB modules: At local Apple reseller: 465 Euros (to upgrade to 24GB total)
3 8GB modules: From OWC, USA: 245 $

Going to 16 really is the cheapest option. However, I know that at some point I'll need more. I think though that with ever decreasing RAM prices, 33 Euros is a smart investment if I can postpone a big upgrade for a year or so.

Sep 12, 2012 at 12:51 PM

Alan321
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p.1 #7 · Mac RAM release question

Apparently Ps likes to have 3/4 of the RAM but there is no necessity to give it that much once you upgrade to 16GB. Then your other applications will get to share the extra 4GB. Ps can have what it gets now and be no worse off.

Adding a single 8GB module might be better value than a single 4GB module in terms of perceived performance boost and deferring the next upgrade. Not sure how much you'll get hit for the delivery to the Netherlands but it won't be cheap compared with the price of a single RAM module. It's generally better value to combine such purchases with other items on your wish list to get better value from the delivery fees.

Sep 12, 2012 at 04:46 PM

rabbitmountain
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p.1 #8 · Mac RAM release question

^ ^
Just before I read your message I ordered the 4GB module. €1.64 delivery costs. Bugger I should have ordered that new iPad with it, to cut delivery fees

I suppose this is the easiest, cheapest way to get me going again. This is purely a business consideration. If it had been for private stuff, I'd have probably ordered 3 or 4 8GB modules from OWC, along with a good SSD.

I'll have a look at PS and its memory configuration.

Thanks for the help, much appreciated as always.

Sep 12, 2012 at 05:39 PM

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