Re: [PATCH v4 0/2] make ballooned out pages have a valid mapping at all times

From: David Vrabel <david.vrabel@citrix.com>
To: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Cc: dcrisan@flexiant.com, xen-devel@lists.xensource.com,
	Ian Campbell <Ian.Campbell@citrix.com>,
	alex@alex.org.uk
Subject: Re: [PATCH v4 0/2] make ballooned out pages have a valid mapping at all times
Date: Mon, 5 Aug 2013 15:53:09 +0100	[thread overview]
Message-ID: <51FFBC55.2090908@citrix.com> (raw)
In-Reply-To: <alpine.DEB.2.02.1308041531220.4893@kaball.uk.xensource.com>

On 04/08/13 15:38, Stefano Stabellini wrote:
> Hi all,
> this patch series limits problems caused by tcp retransmits on NFS when
> the original block pages were mapped from a foreign domain and now the
> mapping is gone.
> 
> It accomplishes the goal by:
> 
> 1) mapping all ballooned out pages to a per-cpu "balloon_scratch_page";
> 2) making sure that once a grant is unmapped, the original mapping to
> the per-cpu balloon_scratch_page is restored atomically.
> 
> The first patch accomplishes (1), the second patch uses
> GNTTABOP_unmap_and_replace to atomically unmap a grant and restore the
> original mapping.
> 
> 
> 
> Changes in this version:
> - add an early_initcall to clear all the possible per_cpu
>   balloon_scratch_page.

I know Konrad asked for this but I don't think it is necessary.  Many
other users of DEFINE_PER_CPU() assume the space is initialized to zero.

e.g., cpufreq_show_table in drivers/cpufreq/freq_table.c

If this is the only change in v4 I would suggest taking the v3 patches
instead.

David