linux-kernel - Re: [Xen-devel] [PATCHv2 10/10] xen/balloon: pre-allocate p2m entries for ballooned pages

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Date:	Mon, 27 Jul 2015 12:01:02 +0100
From:	Julien Grall <julien.grall@...rix.com>
To:	David Vrabel <david.vrabel@...rix.com>,
	<xen-devel@...ts.xenproject.org>
CC:	<linux-mm@...ck.org>, Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	"Daniel Kiper" <daniel.kiper@...cle.com>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [Xen-devel] [PATCHv2 10/10] xen/balloon: pre-allocate p2m entries
 for ballooned pages

On 27/07/15 10:30, David Vrabel wrote:
> On 25/07/15 00:21, Julien Grall wrote:
>> On 24/07/2015 12:47, David Vrabel wrote:
>>> @@ -550,6 +551,11 @@ int alloc_xenballooned_pages(int nr_pages, struct
>>> page **pages)
>>>           page = balloon_retrieve(true);
>>>           if (page) {
>>>               pages[pgno++] = page;
>>> +#ifdef CONFIG_XEN_HAVE_PVMMU
>>> +            ret = xen_alloc_p2m_entry(page_to_pfn(page));
>>
>> Don't you want to call this function only when the guest is not using
>> auto-translated physmap?
> 
> xen_alloc_p2m_entry() is a nop in auto-xlate guests, so no need for an
> additional check here.

I don't have the impression it's the case or it's not obvious.

For instance xen_p2m_addr, used within with the xen_alloc_p2m_entry (old
name alloc_p2m) is never set for auto-xlate guests. Therefore the value
is 0.

Same for p2m_identity and p2m_missing & co.

Regards,

-- 
Julien Grall
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