Re: options NO_SWAPPING, still wants swap

On Saturday 12 April 2003 03:42 pm, Lucky Green wrote:
> On Fri, 11 Apr 2003, Bruce Evans wrote:
> > On Thu, 10 Apr 2003, Lucky Green wrote:
> > > I compiled a kernel with "options NO_SWAPPING", yet CURRENT still
> > > attempts to allocate swap space:
> >
> > NO_SWAPPING has nothing to do with not allocating swap space.  It
> > prevents swapping of upages and stack pages only.
> >
> > Unfortunately, NOTES' description of NO_SWAPPING says that it disables
> > swapping without explaining what swapping is (it is just swapping of
> > upages and stack, and has nothing to do with generic VM paging).
> > NO_SWAPPING is documented mainlly in the commitlog for the change that
> > added it:
>
> Perhaps a kind comitter could modify NOTES to help make users aware that
> NO_SWAPPING does not disable swapping of memory to disk and to look to man

but it does disable swapping.  The confusing part is that the terms swapping 
and paging mean different things and both use swap space.  Paging is just the 
normal movement of pages between main memory and swap space.  Pages get paged 
out to most effectively use memory for other processes.  Swapping is the more 
serious case of when there is a shortage of memory that the pagedaemon cannot 
provide for .  The swapper completely removes a process from main memory.

> rc.conf for information about the latter?

I am fully in support of the difference being documented in NOTES
As a side note the value of having swap space even if you have enough main 
memory is being able to get crash dumps.

Information taken from McKusik et al, Design and Implementation...

Tim