Guy wrote:
So, the question is: Assume I have enough RAM to never need to swap. Do I need any swap space with Linux?
This has been hashed out at great length on linux-kernel - with a few entrenched positions emerging, if I recall correctly.
There are those that think if they size the machine correctly, they shouldn't need swap, and they're right.
I had 8 Meg of swap space. So 12 meg total available virtual memory. One day I added 16 Meg of RAM. So now I had 20 Meg of RAM. I deleted my swap space. Everyone told me I needed 20-40 Meg of swap space now! Swap space should be 2 time RAM size. How crazy, my memory requirements did not change, just the amount of memory. I used that system for a year or so like that. Go figure!
This story pretty much sums up that position, and I've certainly been in that position myself.
There are others (notably the maintainer of part of that code - Andrea Arcangeli if I recall correctly, though I apologize if that's a misattribution) who believe you should always have swap because it will allow your system to have higher throughput. If you process a large I/O, for instance, the kernel can swap out live processes to devote more RAM to VFS caching. That hurts latency though, and the nightly slocate run is a pathlogical example of this. You wake up in the morning and your machine is crawling while it swaps everything back in.
There's a "swappiness" knob you can twiddle in /proc or /sys to alter this, but the general idea is that you can improve throughput on a machine by having swap even if there is enough ram for all processes
I've got machines with and without swap, but I typically run all servers with swap to handle ram-usage spikes I'm not expecting (you never know) while I run my laptop without swap when possible to avoid latency issues with swappiness.
As with all things, its policy decisions and tradeoffs :-)
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