Re: [Xen-devel] [PATCH v3 12/20] xen/balloon: Don't rely on the page granularity is the same for Xen and Linux

From: Julien Grall
Date: Fri Aug 28 2015 - 11:12:32 EST

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.
> [...]
>> + /* We don't support PV MMU when Linux and Xen is using
>> + * different page granularity.
>> + */
> 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@xxxxxxxxxx>

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.



Julien Grall
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