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Re: [Xen-devel] [RFC][PATCH]Large Page Support for HAP

To: "Stephen C. Tweedie" <sct@xxxxxxxxxx>, Ian Pratt <Ian.Pratt@xxxxxxxxxxxxx>
Subject: Re: [Xen-devel] [RFC][PATCH]Large Page Support for HAP
From: Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>
Date: Tue, 20 Nov 2007 17:22:42 +0000
Cc: Tim Deegan <Tim.Deegan@xxxxxxxxxxxxx>, "Huang2, Wei" <Wei.Huang2@xxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>
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On 20/11/07 17:19, "Stephen C. Tweedie" <sct@xxxxxxxxxx> wrote:

> 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.

Support for PV guests would be explicit. Hugetlbfs would know whether it had
superpages or not, and can fail in the latter case.

 -- Keir



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