How much RAM? How much SWAP?

[augustin]

Hello,

I am building a new Linux box which will be running Kubuntu 9.10.

I am not playing games. The most memory / cpu intensive things I'll do are: Blender 3D, compiz, file encryption with the archive tool dar, some simple video editing...

I am currently using an old box with a 1.5Ghz sempron and 750Mb RAM only. My new system will be based on AM3 PHENOM II x4 945 and plenty of RAM, so I'll be multiplying my main box computing power by at least 6 to 8!!!

My questions are how much RAM is reasonably enough? No need to waste money by purchasing more RAM for only marginal improvements. I am planning on getting 4Gb DDR3 1600 RAM. Is there any reason for me to get more? Beyond 4Gb, would more make a difference?


Also, it's been a long time I have partitioned a disk. Back in the time when 1GB RAM was considered a lot, it was said that the SWAP had to be twice as big as the amount of RAM. Is it still true today?
How much SWAP is recommended, nowadays?
Note: I'm planning to get a 32GB SSD for the root partition, for the OS. Maybe it's a good idea to put the SWAP on the SSD, too.

In case anybody is interested, are are links to other hardware for Linux posts:

ATI or nVidia graphic card for new Linux box?
http://masquilier.org/node/135
-> plenty of links and relevant quotes.

Graphic card recommendations to use for Blender / compiz:
http://blenderartists.org/forum/showthread.php?t=169177

Thanks.

Blessings,

Augustin.

[wizard10000]

Hi, augustin -

The right answer depends on what you do with the machine - if you intend to hibernate the machine you have to be able to hold the entire contents of RAM in your swap partition.

The old "twice the size of RAM" is exactly that - old.  My shiny new Core i7 has 6GB of RAM but rarely uses more than 800MB - the only reason I have 6GB of memory is so that if I stand up a virtual machine I can give it 4GB of RAM.

Other than the hibernation thing the trick is to keep applications in RAM as it's about a billion times faster than disk so what you do is look at how much memory you use now (both physical RAM and swap space).

So - create a worst case scenario.  Open up everything you'd run at once and see how much RAM + swap space you're using now - I'm willing to bet it's a fair bit less than 4GB.

I wouldn't recommend putting a swap partition on an SSD just yet - your money would be better spent getting enough RAM so the thing *doesn't* swap  

Hope this helps -

[Teunis]

I'm mainly browsing and doing photo editing on this laptop with 2 GB RAM, a 1680x1050 screen and NVidia Quatro 130.
I've never seen the use of swap beyond a token 1-2% but due to the nature of Linux the cache will fill up memory.

As you say, in 'the old days' the recommendation was for up to 1GB of RAM swap = double RAM and above RAM+ 1GB.
Still sounds good to me except I'd say swap never needs more than about 2GB.

But...

Some things like Hibernation copy the memory into swap, in such a case you need swap to be at least equal to RAM.

Regarding putting swap on the SSD, some sources claim you might run into wear issues with the SSD.

As a frequent visitor of this and other groups I can say there are more problems with ATI than with NVidea drivers but ATI has promised better...

[augustin]

Thanks Wizard and Teunis for your replies.

Yes, I have decided to stick with nVidia for a while longer.

I had never considered Hibernation; I never did that. Good point.

Also good advice on wear issue with SSD drives. Thanks for that. I guess I'll keep the SSD for the OS only. I'm glad I asked.

My problem is that I can't estimate how much I would need. SWAP + RAM, I currently have 1.7GB. I multitask madly, with several users logged in at once. Sometimes, I max out on the amount of memory I use and my computer freezes. So the best I can say is: I need more than I have now


For the benefit of those reading this thread, here are a few links I found interesting.

Linux: Is Swap Necessary?
http://kerneltrap.org/node/3202
This article is a bit old, but still very relevant on a theoretical point of view. A good read!

Tools and command lines to check how much RAM/SWAP you're currently using:
http://www.cyberciti.biz/tips/how-much-ram-does-my-linux-system.html
Useful.

Linux: Should You Use Twice the Amount of Ram as Swap Space?
http://www.cyberciti.biz/tips/linux-swap-space.html
Several new formulas are offered here.


Thanks for your replies.

[dibl]

I built my rig 3 years ago, and installed 4GB of RAM just to be safe.  The most intensive task I've ever done was doing audio file digital processing, using GWC, and I was able to run two instances of it (one per CPU core), so that would run the RAM utilization up toward 2GB.  But that's as high as I've ever seen it.  Also, suspend to RAM (s2RAM) is a good reason to just pop in the 4 GB so you don't need to think about it.  RAM is fairly cheap.

On swap -- disk space is so cheap today (less than 10 cents per GB), it makes no sense to skimp on the swap space, and "hibernate" (or suspend-to-disk) is a good reason to just go with the "swap = RAM" theory.

My bottom line:  life brings many things to worry about -- why add RAM space and swap space to the list, when it's cheap and easy to over-spec it and then forget about it for good?   

[augustin]

Thanks dibl, good points.

I have the answer I wanted and I will you the way you all suggest. I'll start at 4GB RAM, and have plenty of SWAP to cover future RAM upgrades.

Thanks all.