From mboxrd@z Thu Jan  1 00:00:00 1970
From: julien.grall@citrix.com (Julien Grall)
Date: Fri, 28 Aug 2015 16:10:24 +0100
Subject: [Xen-devel] [PATCH v3 12/20] xen/balloon: Don't rely on the page
 granularity is the same for Xen and Linux
In-Reply-To: <55D5A51D.2060106@citrix.com>
References: <1438966019-19322-1-git-send-email-julien.grall@citrix.com>
 <1438966019-19322-13-git-send-email-julien.grall@citrix.com>
 <55D5A51D.2060106@citrix.com>
Message-ID: <55E079E0.3000507@citrix.com>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

On 20/08/15 10:59, David Vrabel wrote:
> On 07/08/15 17:46, Julien Grall wrote:
>> For ARM64 guests, Linux is able to support either 64K or 4K page
>> granularity. Although, the hypercall interface is always based on 4K
>> page granularity.
>>
>> With 64K page granularity, a single page will be spread over multiple
>> Xen frame.
>>
>> To avoid splitting the page into 4K frame, take advantage of the
>> extent_order field to directly allocate/free chunk of the Linux page
>> size.
>>
>> Note that PVMMU is only used for PV guest (which is x86) and the page
>> granularity is always 4KB. Some BUILD_BUG_ON has been added to ensure
>> that because the code has not been modified.
> [...]
>>  #ifdef CONFIG_XEN_HAVE_PVMMU
>> +		/* We don't support PV MMU when Linux and Xen is using
>> +		 * different page granularity.
>> +		 */
>> +		BUILD_BUG_ON(XEN_PAGE_SIZE != PAGE_SIZE);
> 
> You don't need this BUILD_BUG_ON() twice.

I put twice the BUILD_BUG_ON so if we ever decide to drop one of the
#ifdef CONFIG_XEN_HAVE_PVMMU, the check will still be present.

So I'd like to keep it.

> Otherwise,
> 
> Reviewed-by: David Vrabel <david.vrabel@citrix.com>

Based on the discussion with Stefano I rework a bit the balloon code to
re-use lru field (see [1]), so I won't retain your reviewed-by on the
next series.

Regards,

[1] http://lists.xen.org/archives/html/xen-devel/2015-08/msg00781.html

-- 
Julien Grall