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dma-contiguous: use fallback alloc_pages for single pages 

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>
Tested-by: dann frazier <dann.frazier@canonical.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
This commit is contained in:
Nicolin Chen 2019-05-23 21:06:33 -07:00 committed by Christoph Hellwig
parent b1d2dc009d
commit bd2e75633c
1 changed files with 10 additions and 1 deletions
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11
kernel/dma/contiguous.c
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@ -223,14 +223,23 @@ bool dma_release_from_contiguous(struct device *dev, struct page *pages,
* 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)) {