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From: Daniel Phillips <phillips@arcor.de>
To: frankeh@watson.ibm.com, davidm@hpl.hp.com,
       David Mosberger <davidm@napali.hpl.hp.com>,
       "David S. Miller" <davem@redhat.com>
Subject: Re: large page patch (fwd) (fwd)
Date: Fri, 9 Aug 2002 20:43:42 +0200
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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
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