Re: [PATCH] strict VM overcommit accounting for 2.4.32/2.4.33-pre1

[Al Boldi <a1426z@gawab.com>]

Alan Cox wrote:
> On Gwe, 2005-12-30 at 23:06 +0300, Al Boldi wrote:
> > > +3 - (NEW) paranoid overcommit The total address space commit
> > > +      for the system is not permitted to exceed swap. The machine
> > > +      will never kill a process accessing pages it has mapped
> > > +      except due to a bug (ie report it!)
> >
> > This one isn't in 2.6, which is critical for a stable system.
>
> Actually it is
>
> In the 2.4 case we took  "50% RAM + swap" as the safe sane world 'never
> OOM kill' and to all intents and purposes it works. We also had a 100%
> paranoia mode.
>
> When it was ported to 2.6 (not by me) whoever did it very sensibly made
> the percentage tunable and removed "mode 3" since its mode 2 0% ram and
> can be set that way.

Only, doesn't this imply that you cannot control overcommit unless backed by 
swap?  i.e Without swap the kernel cannot use all of ram, because it would 
overcommit no-matter what, thus invoking OOM-killer.

Which raises an important question:  What's overcommit to do with limiting 
access to physical RAM?

Thanks!

--
Al