On Thu, Mar 16, 2000 at 11:04:23AM +0000, James Sutherland wrote:
> On 15 Mar 2000, Rask Ingemann Lambertsen wrote:
> > Not at all. COW is a performance optimisation which does not depend on
> > overcommitment of memory in any way. Why would you want to turn it off?
>
> Because it *IS* overcommitment of memory. You can have two processes, each
> with their 200Mb of data, in a machine with 256Mb RAM+swap, quite happily
> - until they start writing to it, at which point you discover you have
> overcommitted your memory, and things go wrong.
He means avoiding overcommit by counting vm requirements but without
actually copying COW pages (denying a COW allocation if it could not
be faulted in at a later time). Resulting in vast areas of unused
RAM.
--
Andreas E. Bombe <andreas.bombe@munich.netsurf.de>
http://home.pages.de/~andreas.bombe/ DSA key 0x04880A44
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