How much swap?

John Van Ostrand john-Da48MpWaEp0CzWx7n4ubxQ at public.gmane.org
Wed Oct 25 14:19:36 UTC 2006


On Wed, 2006-10-25 at 09:57 -0400, Giles Orr wrote:
> Can anyone explain the whole swap=2xRAM thing to me?  Thanks.

HP-UX was the place that I heard this and I think it's a Solaris thing
too. The kernel would allocate memory and swap at the same time
essentially pre-reserving swap in case it needed it. The only reason I
could conger up for doing this was so that in the event of a kernel
panic the entire memory could be dumped to swap and the problem could be
debugged.

Linux has crash-dump which can dump memory to another server, assuming
the network interface is up.

When I allocated swap I usually imagine what system performance would be
like if the swap was fully utilized and then make my determination based
on that. On a single user system, or single purpose system I usually go
lower. On multi-user systems I usually go a little higher.
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