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To: Rik van Riel <riel@conectiva.com.br>
Cc: Andrew Morton <akpm@zip.com.au>, Linus Torvalds <torvalds@transmeta.com>,
       Daniel Phillips <phillips@arcor.de>, <frankeh@watson.ibm.com>,
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       <Martin.Bligh@us.ibm.com>, William Lee Irwin III <wli@holomorphy.com>,
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Subject: Re: large page patch (fwd) (fwd)
References: <Pine.LNX.4.44L.0208101654270.23404-100000@imladris.surriel.com>
From: ebiederm@xmission.com (Eric W. Biederman)
Date: 10 Aug 2002 13:54:47 -0600
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Rik van Riel <riel@conectiva.com.br> writes:

> On 10 Aug 2002, Eric W. Biederman wrote:
> > Andrew Morton <akpm@zip.com.au> writes:
> > >
> > > The other worry is the ZONE_NORMAL space consumption of pte_chains.
> > > We've halved that, but it will still make high sharing levels
> > > unfeasible on the big ia32 machines.
> 
> > There is a second method to address this.  Pages can be swapped out
> > of the page tables and still remain in the page cache, the virtual
> > scan does this all of the time.  This should allow for arbitrary
> > amounts of sharing.  There is some overhead, in faulting the pages
> > back in but it is much better than cases that do not work.  A simple
> > implementation would have a maximum pte_chain length.
> 
> Indeed.  We need this same thing for page tables too, otherwise
> a high sharing situation can easily "require" more page table
> memory than the total amount of physical memory in the system ;)

It's exactly the same situation.  To remove a pte from the chain you must
remove it from the page table as well.  Then we just need to free
pages with no interesting pte entries.
Eric
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