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From: Hubertus Franke <frankeh@watson.ibm.com>
Reply-To: frankeh@watson.ibm.com
Organization: IBM Research
To: Daniel Phillips <phillips@arcor.de>, 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 15:17:55 -0400
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On Friday 09 August 2002 02:43 pm, Daniel Phillips wrote:
> 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.
>

Correct. Maybe I misunderstood, when are you doing the coalloction of 
adjacent pages (page-clusters, super pages).
Our intend was to do it at page fault time and breakup only during 
memory pressure. 

> > [...]
> >
> > 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.

-- 
-- Hubertus Franke  (frankeh@watson.ibm.com)
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