Message-ID: <544E61DD.8050305@citrix.com>
Date: Mon, 27 Oct 2014 15:16:45 +0000
From: David Vrabel <david.vrabel@citrix.com>
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To: Juergen Gross <jgross@suse.com>, <linux-kernel@vger.kernel.org>,
        <xen-devel@lists.xensource.com>, <konrad.wilk@oracle.com>,
        <boris.ostrovsky@oracle.com>
Subject: Re: [PATCH 0/2] xen: Switch to virtual mapped linear p2m list
References: <1414421551-31555-1-git-send-email-jgross@suse.com>
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On 27/10/14 14:52, Juergen Gross wrote:
> Paravirtualized kernels running on Xen use a three level tree for
> translation of guest specific physical addresses to machine global
> addresses. This p2m tree is used for construction of page table
> entries, so the p2m tree walk is performance critical.
> 
> By using a linear virtual mapped p2m list accesses to p2m elements
> can be sped up while even simplifying code. To achieve this goal
> some p2m related initializations have to be performed later in the
> boot process, as the final p2m list can be set up only after basic
> memory management functions are available.

What impact does this have on 32-bit guests which don't have huge amount
of virtual address space?

I think a 32-bit guest could have up to 64 GiB of PFNs, which would
require a 128 MiB p2m array, which is too large?

David
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