Re: [PATCH 4/9] dma-mapping: move the arm64 ncoherent alloc/free support to common code

[Christoph Hellwig]

> > +int __init dma_atomic_pool_init(gfp_t gfp, pgprot_t prot)
> > +{
> > +	unsigned int pool_size_order = get_order(atomic_pool_size);
> > +	unsigned long nr_pages = atomic_pool_size >> PAGE_SHIFT;
> > +	struct page *page;
> > +	void *addr;
> > +	int ret;
> > +
> > +	if (dev_get_cma_area(NULL))
> > +		page = dma_alloc_from_contiguous(NULL, nr_pages,
> > +						 pool_size_order, false);
> > +	else
> > +		page = alloc_pages(gfp, pool_size_order);
> > +	if (!page)
> > +		goto out;
> > +
> > +	memset(page_address(page), 0, atomic_pool_size);
> 
> Note that this won't work if 'page' is a highmem page - should there
> be a check for that, or a check for the gfp flags?
>
> Also, is this memset() actually useful, or a waste of cycles - when we
> allocate from this pool (see dma_alloc_from_pool()), we always memset()
> the buffer.

Currently there is no user that supports highmem, but yes, the memset
should probably simply be removed.