linux-kernel - Re: [Xen-devel] [PATCH 1/2] xen: vnuma support for PV guests running as domU.

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Date:	Thu, 14 Nov 2013 11:21:28 +0000
From:	David Vrabel <david.vrabel@...rix.com>
To:	Dario Faggioli <dario.faggioli@...rix.com>
CC:	Elena Ufimtseva <ufimtseva@...il.com>,
	<xen-devel@...ts.xenproject.org>, <akpm@...ux-foundation.org>,
	<wency@...fujitsu.com>, <x86@...nel.org>,
	<linux-kernel@...r.kernel.org>, <tangchen@...fujitsu.com>,
	<mingo@...hat.com>, <hpa@...or.com>, <boris.ostrovsky@...cle.com>,
	<tglx@...utronix.de>, <stefano.stabellini@...citrix.com>,
	<ian.campbell@...rix.com>
Subject: Re: [Xen-devel] [PATCH 1/2] xen: vnuma support for PV guests running
 as domU.

On 14/11/13 07:26, Dario Faggioli wrote:
> On mer, 2013-11-13 at 22:36 -0500, Elena Ufimtseva wrote:
>> +	/*
>> +	 * Set the "dummy" node and exit without error so Linux
>> +	 * will not try any NUMA init functions which might break
>> +	 * guests in the future. This will discard all previous
>> +	 * settings.
>> +	 */
> IIRC, it's more something that was already happening (the breakage, I
> mean), than a "safety net" for the unforeseeable future. Might be worth
> giving some context about it, perhaps referencing the email thread or
> the git commit hash in the comment.

Yes, a comment like:

/*
 * Set a dummy node and return success.  This prevents calling any
 * hardware-specific initializers which do not work in a PV guest.
 */

is better.  No need to refer to any specific threads.  It's pretty clear
that any hardware-specific init isn't appropriate for a PV guest.

>> +	if (rc != 0) {
>> +		for (i = 0; i < MAX_LOCAL_APIC; i++)
>> +			set_apicid_to_node(i, NUMA_NO_NODE);
>> +		nodes_clear(numa_nodes_parsed);
>> +		nodes_clear(node_possible_map);
>> +		nodes_clear(node_online_map);
>> +		node_set(0, numa_nodes_parsed);
>> +		numa_add_memblk(0, 0, PFN_PHYS(max_pfn));
>> +	}
>> +	return 0;
>>
> Ok, so, we always return 'success', as we were saying during last round.
> However, we do not call dummy_numa_init() directly, and instead we do
> all these stuff, with the last two statements being exactly what
> dummy_numa_init() does. Reason is linking, i.e., the fact that
> dummy_numa_init() is not exported and you can't reach it from here,
> right?

I think this bit is fine as-is.

David
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