Patch to protect process from pageout killing

[David Schultz]

Thus spake Poul-Henning Kamp <phk at phk.freebsd.dk>:
> In message <200303280910.32307.wes at softweyr.com>, Wes Peters writes:
> 
> >I've reworked my patch to use the madvise(2) syscall, like the original 
> >4.x patch did.  I've even documented it, in a man page of all places.  
> >Please see attached patch.  If nobody objects, I'll commit sometime this 
> >weekend.
> 
> I'm still not certain about the inheritance of this, do we want/is it
> inherited ?
> 
> Also, thinking about it, on at least a handful of machines I would
> have more use for MADV_KILLMEFIRST having the exact opposite
> behaviour.

KILLMEFIRST is more of an advisory mechanism.  See relevant
discussions of SIGDANGER, priority systems, etc.  These are all
good ideas, but I think they belong in a domain of cooperation and
altruism, whereas MADV_PROTECT is the memory equivalent of rtprio.
At some level, there is generally a set of processes that should
never, ever be killed, e.g. postgres, sshd, apache.  So you're
right that KILLMEFIRST would be useful, but MADV_PROTECT is a very
nice first step.