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From: David Mosberger <davidm@napali.hpl.hp.com>
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Date: Mon, 5 Aug 2002 22:01:16 -0700
To: "Seth, Rohit" <rohit.seth@intel.com>
Cc: "'frankeh@watson.ibm.com'" <frankeh@watson.ibm.com>,
       Linus Torvalds <torvalds@transmeta.com>,
       "David S. Miller" <davem@redhat.com>, davidm@hpl.hp.com, gh@us.ibm.com,
       Martin.Bligh@us.ibm.com, wli@holomorphy.com,
       linux-kernel@vger.kernel.org
Subject: RE: large page patch (fwd) (fwd)
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>>>>> On Mon, 5 Aug 2002 16:30:54 -0700 , "Seth, Rohit" <rohit.seth@intel.com> said:

  Rohit> I'm afraid you may be wasting a lot of extra memory by
  Rohit> replicaitng these PTEs(Take an example of one 4G large TLB
  Rohit> size entry and assume there are few hunderd processes using
  Rohit> that same physical page.)

In my opinion, this is perhaps the strongest argument *for* a separate
"giant page" syscall interface.  It will be very hard (perhaps
impossible) to optimize superpages to work efficiently when the ratio
of superpage/basepage grows huge (as, by definition, the kernel would
manage them as a set of basepages).  For example, even if we used a
base page-size of 64KB, a 4GB giant page (as supported by Itanium 2)
would correspond to 65536 base pages.  A superpage of this size would
almost certainly still do a lot better than 65536 base pages, but
compared to a single giant page, it probably stands no chance
performance-wise.

	--david
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