Linda Walsh <law@sgi.com>:
> David Schwartz wrote:
> > Okay, so suppose you are using only memory you are allowed to use. Later
> > on, the system runs out of memory and swap. Your process touches one of its
> > pages that has been swapped out. The system must page in that page for you
> > in order for your process to continue running. The system, unfortunately,
> > cannot page in for your process since it can't page out because swap is
> > full. Please tell me what the system should do other than kill your process.
> ---
> One would assume the kernel always maintains at least 1 page for its own
> paging purposes. So I touch my swapped out page. The kernel reads my page into
> the 'last page', and immediately pages out some other page, regaining its "last
> page". Repeat as necessary. It's a memory thrashing situation, but not fatal.
Actually, if the system is NOT overcommitted the situation should never arise:
All user pages are already have backing. If the exchange between real memory
and swap is deadlocked, then there is a bug in the system (or it is still
overcommitted - error by sysadmin?). There are several ways to defend against
this particular problem - using an already allocated mbuf for instance.
-------------------------------------------------------------------------
Jesse I Pollard, II
Email: pollard@navo.hpc.mil
Any opinions expressed are solely my own.
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