Re: the new VMt

["Stephen C. Tweedie" <sct@redhat.com>]

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
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