> It might be useful to have a call (or a flag to mlock) that says
> "make sure that I have vm resources sufficiently allocated to ensure
> that I won't be killed due to vm shortages, on the condition that I
> don't request any further pages of memory".

I think that flag is already permanently set, since I don't think
processes are ever killed for VM shortages.

The resource that is in short supply in the circumstance in question is
*physical* pages: the kill happens when a process takes a page fault on
a perfectly good virtual page that doesn't have a physical page at the
moment, and the fault handler gets failure when trying to allocate a
physical page for it.

This does imply a VM crunch, because this can't happen until swap is
full - otherwise something is paged out to make room.  (Well, or unless
too much stuff is locked in core; there are limits to prevent that from
happening, but they presumably could in principle be set
inappropriately.)

> Obviously any request for further resources will have to be treated
> with the same way as we treat other requests for resources: it might
> be refused.

And if that `request' takes the form of a page fault?  There is no
overt way to refuse a page fault; that's where we came in.

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