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| author |   Nicolin Chen <nicoleotsuka@gmail.com> | 2019-05-23 21:06:33 -0700 |
|---|---|---|
| committer |   Christoph Hellwig <hch@lst.de> | 2019-06-03 16:00:07 +0200 |
| commit | bd2e75633c8012fc8a7431c82fda66237133bf7e (patch) | |
| tree | 7f7b8c21585a18f68acff279c6aa4ca8f582e6eb /kernel/dma | |
| parent | dma-contiguous: add dma_{alloc,free}_contiguous() helpers (diff) | |
| download | linux-dev-bd2e75633c8012fc8a7431c82fda66237133bf7e.tar.xz linux-dev-bd2e75633c8012fc8a7431c82fda66237133bf7e.zip | |
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>
Diffstat (limited to 'kernel/dma')
| -rw-r--r-- | kernel/dma/contiguous.c | 11 |
1 files changed, 10 insertions, 1 deletions
diff --git a/kernel/dma/contiguous.c b/kernel/dma/contiguous.c index 637b120d647b..bfc0c17f2a3d 100644 --- a/kernel/dma/contiguous.c +++ b/kernel/dma/contiguous.c @@ -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)) { |