Re: CMA alignment question

[Weijie Yang]

On Thu, Nov 6, 2014 at 6:01 AM, Michal Nazarewicz <mina86@xxxxxxxxxx> wrote:
>> On Tue, Nov 04 2014, Gregory Fong wrote:
>>> The alignment in cma_alloc() is done w.r.t. the bitmap.  This is a
>>> problem when, for example:
>>>
>>> - a device requires 16M (order 12) alignment
>>> - the CMA region is not 16 M aligned
>
> On Wed, Nov 05 2014, Weijie Yang wrote:
>> I think the device driver should ensure that situation could not occur,
>> by assign suitable alignment parameter in cma_declare_contiguous().
>
> What about default CMA area? Besides, I think principle of least
> surprise applies here and alignment should be physical.

I agree the current code doesn't handle this issue properly.
However, I prefer to add specific usage to CMA interface rather than
modify the cma code, Because the latter hide the issue and could waste
memory.

> --
> Best regards,                                         _     _
> .o. | Liege of Serenely Enlightened Majesty of      o' \,=./ `o
> ..o | Computer Science,  MichaÅ âmina86â Nazarewicz    (o o)
> ooo +--<mpn@xxxxxxxxxx>--<xmpp:mina86@xxxxxxxxxx>--ooO--(_)--Ooo--
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/