Re: [PATCH v4 2/3] common: DMA-mapping: add DMA_ATTR_NOHUGEPAGE attribute

[Christoph Hellwig]

On Thu, Jan 07, 2016 at 04:36:44PM -0800, Douglas Anderson wrote:
> This patch adds the DMA_ATTR_NOHUGEPAGE attribute to the DMA-mapping
> subsystem.
> 
> This attribute can be used as a hint to the DMA-mapping subsystem that
> it's likely not worth it to try to allocation large pages behind the
> scenes.  Large pages are likely to make an IOMMU TLB work more
> efficiently but may not be worth it.  See the Documentation contained in
> this patch for more details about this attribute and when to use it.
> 
> Note that the name of the hint (DMA_ATTR_NOHUGEPAGE) is based on the
> name MADV_NOHUGEPAGE, which has the same meaning.  If we have expected
> users, we could also add MADV_HUGEPAGE which has the opposite meaning of
> this hint.

A user of this features seems to be missing in the series.  Please don't
add any clutter with unclear usage to the kernel unless there is a real
need which can be deonstrated in form of patches and numbers.