Sent: 14 June 2019 14:47

Many architectures (e.g. arm, m68 and sh) have always used exact
allocation in their dma coherent allocator, which avoids a lot of
memory waste especially for larger allocations.  Lift this behavior
into the generic allocator so that dma-direct and the generic IOMMU
code benefit from this behavior as well.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 include/linux/dma-contiguous.h |  8 +++++---
 kernel/dma/contiguous.c        | 17 +++++++++++------
 2 files changed, 16 insertions(+), 9 deletions(-)

diff --git a/include/linux/dma-contiguous.h b/include/linux/dma-contiguous.h
index c05d4e661489..2e542e314acf 100644
--- a/include/linux/dma-contiguous.h
+++ b/include/linux/dma-contiguous.h

@@ -161,15 +161,17 @@ static inline struct page *dma_alloc_contiguous(struct device *dev, size_t size,
 		gfp_t gfp)
 {
 	int node = dev ? dev_to_node(dev) : NUMA_NO_NODE;
-	size_t align = get_order(PAGE_ALIGN(size));
+	void *cpu_addr = alloc_pages_exact_node(node, size, gfp);

-	return alloc_pages_node(node, gfp, align);
+	if (!cpu_addr)
+		return NULL;
+	return virt_to_page(p);
 }