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xen-devel
RE: [Xen-devel] [RFC][PATCH]Large Page Support for HAP
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To: |
Ian Pratt <Ian.Pratt@xxxxxxxxxxxxx> |
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Subject: |
RE: [Xen-devel] [RFC][PATCH]Large Page Support for HAP |
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From: |
"Stephen C. Tweedie" <sct@xxxxxxxxxx> |
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Date: |
Tue, 20 Nov 2007 17:19:32 +0000 |
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Cc: |
Tim Deegan <Tim.Deegan@xxxxxxxxxxxxx>, Stephen Tweedie <sct@xxxxxxxxxx>, "Huang2, Wei" <Wei.Huang2@xxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx> |
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Tue, 20 Nov 2007 09:21:12 -0800 |
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<C3686702.106F9%Keir.Fraser@xxxxxxxxxxxx> <1195559786.7102.10.camel@xxxxxxxxxxxxxxxxxxxxx> <DD74FBB8EE28D441903D56487861CD9D23EF9A16@xxxxxxxxxxxxxxxxxxxxxx> |
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Hi,
On Tue, 2007-11-20 at 12:31 +0000, Ian Pratt wrote:
> Unfortunately, a number of guests assume big pages without actually
> checking for the feature bit explicitly. For example x86_64 Linux
> running HVM will assume it has big pages.
Yes, but there's a _big_ difference between the opportunistic uses Linux
makes of PSE (bigpage mappings for large static areas like the kernel
text), and places where it is an explicit part of the ABI made to
applications, as in the case of hugetlbfs.
It's the latter case which concerns me, as hugetlbfs is basically an
explicit contract between the guest OS and an application running on it.
Providing faked PSE at that level is something that would be best
avoided.
I don't have any objection to doing opportunistic PSE for the former
case. But telling the two apart is rather hard.
--Stephen
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