Messages in this thread | | | Date | Fri, 24 May 2019 09:16:19 -0700 | From | Ira Weiny <> | Subject | Re: [PATCH v3 2/2] dma-contiguous: Use fallback alloc_pages for single pages |
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On Thu, May 23, 2019 at 09:06:33PM -0700, Nicolin Chen wrote: > 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.
How does a device know, after this call, if a CMA area was used? From the patches I figured a device should not care.
> > 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(-) > > diff --git a/kernel/dma/contiguous.c b/kernel/dma/contiguous.c > index 21f39a6cb04f..6914b92d5c88 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;
Doesn't dev_get_dma_area() already do this?
Ira
> > /* CMA can be used only in the context which permits sleeping */ > if (cma && gfpflags_allow_blocking(gfp)) { > -- > 2.17.1 >
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