@@ -186,14 +186,23 @@ int __init dma_contiguous_reserve_area(phys_addr_t size, phys_addr_t base,
* This function allocates contiguous memory buffer for specified device. It
* first tries to use device specific contiguous memory area if available or
* the default global one, then tries a fallback allocation of normal pages.
+ *
+ * Note that it byapss one-page size of allocations from the global area as
+ * the addresses within one page are always contiguous, so there is no need
+ * to waste CMA pages for that kind; it also helps reduce fragmentations.
*/
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 cma *cma = dev_get_cma_area(dev);
struct page *page = NULL;
+ struct cma *cma = NULL;
+
+ if (dev && dev->cma_area)
+ cma = dev->cma_area;
+ else if (count > 1)
+ cma = dma_contiguous_default_area;
/* CMA can be used only in the context which permits sleeping */
if (cma && gfpflags_allow_blocking(gfp)) {
The addresses within a single page are always contiguous, so it's not so necessary to always allocate one single page from CMA area. Since the CMA area has a limited predefined size of space, it may run out of space in heavy use cases, where there might be quite a lot CMA pages being allocated for single pages. However, there is also a concern that a device might care where a page comes from -- it might expect the page from CMA area and act differently if the page doesn't. This patch tries to use the fallback alloc_pages path, instead of one-page size allocations from the global CMA area in case that a device does not have its own CMA area. This'd save resources from the CMA global area for more CMA allocations, and also reduce CMA fragmentations resulted from trivial allocations. Signed-off-by: Nicolin Chen <nicoleotsuka@gmail.com> --- kernel/dma/contiguous.c | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-)