Re: large page patch (fwd) (fwd)

Daniel Phillips
2002-08-09T18:38:30Z

On Friday 09 August 2002 20:32, Hubertus Franke wrote:
> On Friday 09 August 2002 11:20 am, Daniel Phillips wrote:
> > On Sunday 04 August 2002 19:19, Hubertus Franke wrote:
> > > "General Purpose Operating System Support for Multiple Page Sizes"
> > > htpp://www.usenix.org/publications/library/proceedings/usenix98/full_pape
> > >rs/ganapathy/ganapathy.pdf
> >
> > This reference describes roughly what I had in mind for active
> > defragmentation, which depends on reverse mapping. The main additional
> > wrinkle I'd contemplated is introducing a new ZONE_LARGE, and GPF_LARGE,
> > which means the caller promises not to pin the allocation unit for long
> > periods and does not mind if the underlying physical page changes
> > spontaneously. Defragmenting in this zone is straightforward.
>
> I think the objection to that is that in many cases the cost of
> defragmentation is to heavy to be recollectable through TLB miss handling
> alone.

You pay the cost only on transition from a load that doesn't use many large
pages to one that does, it is not an ongoing cost.

> [...]
>
> Defragmenting to me seems a matter of last resort, Copying pages is expensive.

It is the only way to ever have a seamless implementation. Really, I don't
understand this fear of active defragmentation. Oh well, like davem said,
code talks.

--
Daniel