On Wed, 2005-02-23 at 19:16 +0000, Hugh Dickins wrote:
> On Wed, 23 Feb 2005, Lee Revell wrote:
> > 
> > Did something change recently in the VM that made copy_pte_range and
> > clear_page_range a lot more expensive?  I noticed a reference in the
> > "Page Table Iterators" thread to excessive overhead introduced by
> > aggressive page freeing.  That sure looks like what is going on in
> > trace2.  trace1 and trace3 look like big fork latencies associated with
> > copy_pte_range.
> 
> I'm just about to test this patch below: please give it a try: thanks...
> 
> Ingo's patch to reduce scheduling latencies, by checking for lockbreak
> in copy_page_range, was in the -VP and -mm patchsets some months ago;
> but got preempted by the 4level rework, and not reinstated since.
> Restore it now in copy_pte_range - which mercifully makes it easier.

Aha, that explains why all the latency regressions involve the VM
subsystem. 

Thanks, your patch fixes the copy_pte_range latency.  Now zap_pte_range,
which Ingo also fixed a few months ago, is the worst offender.  Can this
fix be easily ported too?

Lee