Re: [PATCH v2 RFC/RFT 1/5] ARM: dma-mapping: Add fallback normal page allocations

From: Christoph Hellwig
Date: Wed Apr 24 2019 - 11:06:57 EST

On Tue, Mar 26, 2019 at 04:01:27PM -0700, Nicolin Chen wrote:
> page = dma_alloc_from_contiguous(dev, count, order, gfp & __GFP_NOWARN);
> + if (!page)
> + page = alloc_pages(gfp, order);

We have this fallback in most callers already. And with me adding
it to the dma-iommu code in one series, and you to arm here I think
we really need to take a step back and think of a better way
to handle this, and the general mess that dma_alloc_from_contiguous.

So what about:

(1) change the dma_alloc_from_contiguous prototype to be:

struct page *dma_alloc_contiguous(struct device *dev, size_t size, gfp_t gfp);

that is: calculate order and count internally, pass the full gfp_t
and mask it internally, and drop the pointless from in the name.
I'd also use the oppurtunity to forbid a NULL dev argument and
opencode those uses.

(2) handle the alloc_pages fallback internally. Note that we should
use alloc_pages_node as we do in dma-direct.

> + if (!dma_release_from_contiguous(dev, page, count))
> + __free_pages(page, get_order(size));

Same for dma_release_from_contiguous - drop the _from, pass the
actual size, and handle the free_pages fallback.