[Linaro-mm-sig] how to avoid allocating or freeze MOVABLE memory in userspace

[Haojian Zhuang]

On Sat, Apr 14, 2012 at 2:27 AM, Christoph Lameter <cl at linux.com> wrote:
> On Fri, 13 Apr 2012, Haojian Zhuang wrote:
>
>> I have one question on memory migration. As we know, malloc() from
>> user app will allocate MIGRATE_MOVABLE pages. But if we want to use
>> this memory as DMA usage, we can't accept MIGRATE_MOVABLE type. Could
>> we change its behavior before DMA working?
>
> MIGRATE_MOVABLE works fine for DMA. If you keep a reference from a device
> driver to user pages then you will have to increase the page refcount
> which will in turn pin the page and make it non movable for as long as you
> keep the refcount.

Hi Christoph,

Thanks for your illustration. But it's a little abstract. Could you
give me a simple example
or show me the code?

Best Regards
Haojian