[Devel] Re: memrlimit controller merge to mainline

[Hugh Dickins]

On Fri, 25 Jul 2008, Paul Menage wrote:
> On Fri, Jul 25, 2008 at 12:46 PM, Hugh Dickins <hugh at veritas.com> wrote:
> > No, I'm trying to say something stronger than that.  I'm saying,
> > as I've said before, that I cannot imagine why anyone would want
> > to control swap itself - what they want to control is the total
> > of mem+swap.  Swap is a second-class citizen, nobody wants swap
> > if they can have mem, so why control it separately?
> 
> Scheduling jobs on to machines is much more straightforward when they
> request xGB of memory and yGB of swap rather than just (x+y)GB of
> (memory+swap). We want to be able to guarantee to jobs that they will
> be able to use xGB of real memory.

I don't see that I'm denying you a way to guarantee that (though I've
been thinking more of the limits than the guarantees): I'm not saying
that you cannot have a mem controller, I'm saying that you can also
have a mem+swap controller; but that a swap-by-itself controller
makes no sense to me.

> Actually my preferred approach to swap controlling would be something like:
> 
> - allow malloc to support mmaping pages from a temporary file rather
> than mmapping anonymous memory

I think that works until you get to fork: shared files and
private/anonymous/swap behave differently from then on.

Hugh
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