Re: [patch][v2] swap: virtual swap readahead

[Rik van Riel]

Johannes Weiner wrote:
> On Wed, Jun 03, 2009 at 01:34:57AM +0200, Andi Kleen wrote:
> > On Wed, Jun 03, 2009 at 12:37:39AM +0200, Johannes Weiner wrote:

> > > +		pgd = pgd_offset(vma->vm_mm, pos);
> > > +		if (!pgd_present(*pgd))
> > > +			continue;
> > > +		pud = pud_offset(pgd, pos);
> > > +		if (!pud_present(*pud))
> > > +			continue;
> > > +		pmd = pmd_offset(pud, pos);
> > > +		if (!pmd_present(*pmd))
> > > +			continue;
> > > +		pte = pte_offset_map_lock(vma->vm_mm, pmd, pos, &ptl);
> > You could be more efficient here by using the standard mm/* nested loop
> > pattern that avoids relookup of everything in each iteration. I suppose
> > it would mainly make a difference with 32bit highpte where mapping a pte
> > can be somewhat costly. And you would take less locks this way.
>
> I ran into weird problems here.  The above version is actually faster
> in the benchmarks than writing a nested level walker or using
> walk_page_range().  Still digging but it can take some time.  Busy
> week :(

I'm not too worried about not walking the page tables,
because swap is an extreme slow path anyway.

--
All rights reversed.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/