Subject: Re: Recommended swap (from install notes)
To: Greg Hudson <ghudson@MIT.EDU>
From: Chris G Demetriou <Chris_G_Demetriou@ux2.sp.cs.cmu.edu>
Date: 08/11/1996 21:18:14
> email@example.com wrote:
> > Most of the ports' install notes recommend a swapspace of 2*ram.
> > On a 4mb machine this would give <12Mb of virtual memory, which
> > seems very tight.
> cgd wrote:
> > It's worth noting that I _do_ think that ~12M of virtual memory is
> > not unreasonable for a 4M machine (remember, text pages don't count
> > against that).
> I'd like to point out that, assuming what people have told me is true,
> you don't get 12MB of virtual memory out of that setup. Apart from
> the fact that the kernel and any resident text pages come out of the
> 4MB of physical memory, once a swap page is allocated for a given vm
> object, it's never deallocated until the object goes away. Therefore,
> your safe VM size is only the amount of swap space you have allocated,
> or 8MB. If at any point you have more than 8MB of pages that could
> potentially be swapped out, you can run out of swap space as soon as
> every such page is swapped out once. And we all know how gracefully
> NetBSD deals with running out of swap space.
It's effectively (much) more than 8, because of text pages.
re: the objects not getting collapsed: "that's a bug, and it should be
fixed." Additionally, it's not clear to me how much that matters on
4M machines (sure, it's a problem because of less ram, but people
_really_ shouldn't be putting heavy load on them).