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SubjectRe: the new VMt
Hello,

On Tue, Sep 26, 2000 at 01:10:30PM +0100, Mark Hemment wrote:
>
> On Mon, 25 Sep 2000, Stephen C. Tweedie wrote:
> > So you have run out of physical memory --- what do you do about it?
>
> Why let the system get into the state where it is neccessary to kill a
> process?
> Per-user/task resource counters should prevent unprivileged users from
> soaking up too many resources. That is the DoS protection.
>
[snip]
> It is possible to do true, system wide, resource counting of physical
> memory and swap space, and to deny a fork() or mmap() which would cause
> over committing of memoy resources if everyone cashed in their
> requirements.
[snip]

People use overcommitting not because they are fans of the idea.
Overcommitting simply is the _efficient_ way of resource sharing.
It's a waste of resources to reserve memory+swap for the case that every
running process decides to modify libc code (and, thus, should receive its
private copy of the pages). A real waste!
I always agree to take the risk of some applications being killed in such a
case of all processes turning crazy.

The approach I believe in is:
- ensure that accidental or intentional madness of applications of one user
may cause only limited damage to other users; and
- introduce a way to tell the kernel that some applications should be
saved longer than others when troubles begin and ways to set up some
guaranteed amounts for important processes.
Certainly, a lot of processes may consume more than their guarantee until
bad things start to happen. Then the rules of user protection and killing
order apply.
That's how I develop the resource control in the beancounter patch
ftp://ftp.sw.com.sg/pub/Linux/people/saw/kernel/user_beancounter/UserBeancounter.html#s7

Best regards
Andrey
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