On 5 Jun, 05:40, "Mike Richards" <[email protected]> wrote:
Here's something that's been bugging me for a while now...
I have several Linux servers that have been given enough RAM that they
rarely ever use any swap space. For example, here's the typical output
of uptime and free:
root@veronica$ uptime; free
03:55:33 up 225 days, 17:34, 0 users, load average: 0.09, 0.13, 0.19
total used free shared buffers cached
Mem: 2076136 1931288 144848 0 150220 964108
-/+ buffers/cache: 816960 1259176
Swap: 524280 156 524124
As you can see, it's been up for the better part of a year and is only
using 156k of swap. The swappiness is set to the default of 60, so
there's no reason why the server *shouldn't* be using swap -- it just
never does.
On some of my older servers with a little less RAM and the 2.4 kernel
I'll occasionally see the swap go up into the double digits, but even
this is relatively infrequent. On all the machines with a 2.6 kernel
and 2GB+ RAM, I've almost never seen more than 1-2MB swap used.
[snip]
The consensus these days seems to be that since hard drives are so big
now, go with a gig or more of swap even if you have plenty of RAM.
However, the way I'm seeing it is this: What's the point of having a
gig of swap if it only gets used during the worst possible time?
Provided you won't be running an application which will require all
the memory, I've found 256MB swap on small (1GB mem) and larger (8GB)
servers to be adequate, but this clearly depends on what you're
running.
The idea would be to allow linux to swap out cold pages which are
(almost) never accessed while runaway processes get selected by the
OOM killer sooner. You may find 512MB to be more useful on large
untuned servers with lots of processes perhaps.
Daniel
--
Daniel J Blueman
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