Re: Maybe a VM bug in 2.4.18-18 from RH 8.0?

[Andrew Morton <akpm@digeo.com>]

Andrea Arcangeli wrote:
> 
> > One way to address this could be to find a way of making the
> > pages present, but still cause a fault on first access.  Then
> > have a special-case fastpath in the fault handler to really wipe
> > the page just before it is used.  I don't know how though - maybe
> > _PAGE_USER?
> 
> I think taking the page fault itself is the biggest overhead that would
> be nice to avoid on every second virtually consecutive page, if we've to
> take the page fault on every page we could as well do the rest of the
> work that should not that big compared to the overhead of
> entering/exiting kernel and preparing to handle the fault.

Yes, 8k at a time would probably be OK.  Say, L1-size/2.

I expect that anything bigger would cause 2x or worse slowdowns of a
range of apps.