> I've been going over the _old_ documentation to the Kernel's memory
> management and the related sources, as well as the exception handlers.
> And still it isn't clear to me what the actual reason is why Kernel pages
> are taboo w.r.t. paging?
> Theoretically of course anything but the paging-code&page-fault handler
> can be paged out (and since Kernel code is usually clean, it doesn't even
> need to be swapped out as such, just reloaded). Is it just an issue of
> speed? If so, I'd think that a cunningly efficient method could be devised
> to offer just that extra little bit of physical memory at the minimum
> possible swapping speed cost.
>From a practical point of view, I don't see any reason why
kernel code should be swapped, given the complexity and risks
involved. The kernel size is essentially constant, only growing
slightly with time with each release. The kernel is also just
one piece of software, and the size of the kernel is not
substantial compared to the typical amount of RAM in a machine
today. In the old days it would have made sense to swap parts of
the kernel too, today it could make sense to do that on very
low-end hardware. Otherwise it is just putting off memory
starvation just a little bit. I'd say install an extra megabyte
of memory and be happy.
Johan Myreen
jem@iki.fi