Re: the new VMt

Stephen C. Tweedie
2000-09-26T10:07:36Z

Hi,

On Mon, Sep 25, 2000 at 03:12:50PM -0600, yodaiken@fsmlabs.com wrote:
> > >
> > > I'm not too sure of what you have in mind, but if it is
> > > "process creates vast virtual space to generate many page table
> > > entries -- using mmap"
> > > the answer is, virtual address space quotas and mmap should kill
> > > the process on low mem for page tables.
> >
> > No. Page tables are not freed after munmap (and for good reason). The
> > counting of page table "beans" is critical.
>
> I've seen the assertion before, reasons would be interesting.

Reason 1: under DoS attack, you want to target not the process using
the most resources, but the *user* using the most resources (else a
fork-bomb style attack can work around your OOM-killer algorithms).

Reason 2: if you've got tasks stuck in low-level page allocation
routines, then you can't immediately kill -9 them, so reactive OOM
killing always has vulnerabilities --- to be robust in preventing
resource exhaustion you want limits on the use of those resources
before they are exhausted --- the necessary accounting being part of
what we refer to as "beancounter".

--Stephen