From mboxrd@z Thu Jan  1 00:00:00 1970
From: David Vrabel <david.vrabel@citrix.com>
Subject: Re: [RFC PATCH] page_alloc: use first half of higher
 order chunks when halving
Date: Wed, 26 Mar 2014 10:44:18 +0000
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To: Matt Wilson <msw@linux.com>
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On 26/03/14 10:17, Matt Wilson wrote:
> 
> Konrad, what's the possibility of fixing this in Linux Xen PV setup
> code? I think it'd be a matter batching up pages and doing larger
> order allocations in linux/arch/x86/xen/setup.c:xen_do_chunk(),
> falling back to smaller pages if allocations fail due to
> fragmentation, etc.

We plan to fix problems caused by non-machine-contiguous memory by
setting up the IOMMU to have 1:1 bus to pseudo-physical mappings.  This
would avoid using the swiotlb always[1], regardless of the machine
layout of dom0 or the driver domain.

I think I would prefer this approach rather than making xen/setup.c even
more horribly complicated.

Malcolm has a working prototype of this already.

David

[1] Unless you have a non-64 bit DMA capable device, but we don't care
about performance with these.