Re: large page patch (fwd) (fwd)

[Daniel Phillips <phillips@arcor.de>]

On Saturday 10 August 2002 20:20, Eric W. Biederman wrote:
> Andrew Morton <akpm@zip.com.au> writes:
> > The other worry is the ZONE_NORMAL space consumption of pte_chains.
> > We've halved that, but it will still make high sharing levels
> > unfeasible on the big ia32 machines.  We are dependant upon large
> > pages to solve that problem.  (Resurrection of pte_highmem is in
> > progress, but it doesn't work yet).
> 
> There is a second method to address this.  Pages can be swapped out
> of the page tables and still remain in the page cache, the virtual
> scan does this all of the time.  This should allow for arbitrary
> amounts of sharing.  There is some overhead, in faulting the pages
> back in but it is much better than cases that do not work.  A simple
> implementation would have a maximum pte_chain length.

Oh gosh, nice point.  We could put together a lovely cooked benchmark where 
copy_page_range just fails to copy all the mmap pages, which are most of them 
in the bash test.

-- 
Daniel