linux-kernel - Re: [PATCH V3] xen: eliminate scalability issues from initial mapping setup

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Message-ID: <54217145.7090206@citrix.com>
Date:	Tue, 23 Sep 2014 14:10:29 +0100
From:	David Vrabel <david.vrabel@...rix.com>
To:	Juergen Gross <jgross@...e.com>, <linux-kernel@...r.kernel.org>,
	<xen-devel@...ts.xensource.com>, <konrad.wilk@...cle.com>,
	<boris.ostrovsky@...cle.com>, <jbeulich@...e.com>
Subject: Re: [PATCH V3] xen: eliminate scalability issues from initial mapping
 setup

On 23/09/14 04:58, Juergen Gross wrote:
> On 09/17/2014 04:59 PM, Juergen Gross wrote:
>> Direct Xen to place the initial P->M table outside of the initial
>> mapping, as otherwise the 1G (implementation) / 2G (theoretical)
>> restriction on the size of the initial mapping limits the amount
>> of memory a domain can be handed initially.
>>
>> As the initial P->M table is copied rather early during boot to
>> domain private memory and it's initial virtual mapping is dropped,
>> the easiest way to avoid virtual address conflicts with other
>> addresses in the kernel is to use a user address area for the
>> virtual address of the initial P->M table. This allows us to just
>> throw away the page tables of the initial mapping after the copy
>> without having to care about address invalidation.
>>
>> It should be noted that this patch won't enable a pv-domain to USE
>> more than 512 GB of RAM. It just enables it to be started with a
>> P->M table covering more memory. This is especially important for
>> being able to boot a Dom0 on a system with more than 512 GB memory.
>>
>> Signed-off-by: Juergen Gross <jgross@...e.com>
>> Signed-off-by: Jan Beulich <jbeulich@...e.com>
> 
> Any Acks/Naks?

Sorry for the delay.  We only have one machine with 1 TB of RAM and it's
very busy.

>> +static void xen_cleanmfnmap_free_pgtbl(void *pgtbl)

This needs to be __init.  But I'll fix this up.  In future, can you make
sure you build with the option that finds these
(CONFIG_DEBUG_SECTION_MISMATCH).

David
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