Re: page fault scalability patch final : i386 tested, x86_64

Andrew Morton
2004-08-28T05:39:54Z

Christoph Lameter <clameter@sgi.com> wrote:
>
> On Fri, 27 Aug 2004, Andrew Morton wrote:
>
> > Christoph Lameter <clameter@sgi.com> wrote:
> > >
> > > So I think the move to atomic for rss acceptable?
> >
> > Short-term, yes. Longer term (within 12 months), no - 50-bit addresses on
> > power5 will cause it to overflow.
>
> I would expect the page size to rise as well. On IA64 we already have
> 16KB-64KB pages corresponding to 256TB - 1PB. Having to manage a couple of
> billion pages could be a significant performance impact. Better increase
> the page size.

I don't know if that's an option on the power architecture.

And we need larger atomic types _anyway_ for page->_count. An unprivileged
app can mmap the same page 4G times and can then munmap it once. Do it on
purpose and it's a security hole. Due it by accident and it's a crash.

> I still would also like to see atomic64_t. I think there was a patch
> posted to linux-ia64 a couple of months back introducing atomic64_t but it
> was rejected since it would not be supportable on other arches.

atomic64_t already appears to be implemented on alpha, ia64, mips, s390 and
sparc64.

As I said - for both these applications we need a new type which is
atomic64_t on 64-bit and atomic_t on 32-bit.