[PATCH 16/16] dma-mapping: use exact allocation in dma_alloc_contiguous

Christoph Hellwig
2019-06-14T13:49:48Z

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);
}

static inline void dma_free_contiguous(struct device *dev, struct page *page,
size_t size)
{
- __free_pages(page, get_order(size));
+ free_pages_exact(page_address(page), get_order(size));
}

#endif
diff --git a/kernel/dma/contiguous.c b/kernel/dma/contiguous.c
index bfc0c17f2a3d..84f41eea2741 100644
--- a/kernel/dma/contiguous.c
+++ b/kernel/dma/contiguous.c
@@ -232,9 +232,8 @@ 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 count = PAGE_ALIGN(size) >> PAGE_SHIFT;
- size_t align = get_order(PAGE_ALIGN(size));
- struct page *page = NULL;
struct cma *cma = NULL;
+ void *cpu_addr;

if (dev && dev->cma_area)
cma = dev->cma_area;
@@ -243,14 +242,20 @@ struct page *dma_alloc_contiguous(struct device *dev, size_t size, gfp_t gfp)

/* CMA can be used only in the context which permits sleeping */
if (cma && gfpflags_allow_blocking(gfp)) {
+ size_t align = get_order(PAGE_ALIGN(size));
+ struct page *page;
+
align = min_t(size_t, align, CONFIG_CMA_ALIGNMENT);
page = cma_alloc(cma, count, align, gfp & __GFP_NOWARN);
+ if (page)
+ return page;
}

/* Fallback allocation of normal pages */
- if (!page)
- page = alloc_pages_node(node, gfp, align);
- return page;
+ cpu_addr = alloc_pages_exact_node(node, size, gfp);
+ if (!cpu_addr)
+ return NULL;
+ return virt_to_page(cpu_addr);
}

/**
@@ -267,7 +272,7 @@ struct page *dma_alloc_contiguous(struct device *dev, size_t size, gfp_t gfp)
void dma_free_contiguous(struct device *dev, struct page *page, size_t size)
{
if (!cma_release(dev_get_cma_area(dev), page, size >> PAGE_SHIFT))
- __free_pages(page, get_order(size));
+ free_pages_exact(page_address(page), get_order(size));
}

/*
--
2.20.1