On 10/26/2014 2:09 PM, Laurent Pinchart wrote:
Hello, I've run into a CMA-related issue while testing a DMA engine driver with dmatest on a Renesas R-Car ARM platform. When allocating contiguous memory through CMA the kernel prints the following messages to the kernel log. [ 99.770000] alloc_contig_range test_pages_isolated(6b843, 6b844) failed [ 124.220000] alloc_contig_range test_pages_isolated(6b843, 6b844) failed [ 127.550000] alloc_contig_range test_pages_isolated(6b845, 6b846) failed [ 132.850000] alloc_contig_range test_pages_isolated(6b845, 6b846) failed [ 151.390000] alloc_contig_range test_pages_isolated(6b843, 6b844) failed [ 166.490000] alloc_contig_range test_pages_isolated(6b843, 6b844) failed [ 181.450000] alloc_contig_range test_pages_isolated(6b845, 6b846) failed I've stripped the dmatest module down as much as possible to remove any hardware dependencies and came up with the following implementation.
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Loading the module will start 4 threads that will allocate and free DMA coherent memory in a tight loop and eventually produce the error. It seems like the probability of occurrence grows with the number of threads, which could indicate a race condition. The tests have been run on 3.18-rc1, but previous tests on 3.16 did exhibit the same behaviour. I'm not that familiar with the CMA internals, help would be appreciated to debug the problem.
Are you actually seeing allocation failures or is it just the messages? The messages themselves may be harmless if the allocation is succeeding. It's an indication that the particular range could not be isolated and therefore another range should be used for the CMA allocation. Joonsoo Kim had a patch series[1] that was designed to correct some problems with isolation and from my testing it helps fix some CMA related errors. You might try picking that up to see if it helps. Thanks, Laura [1] https://lkml.org/lkml/2014/10/23/90 -- Qualcomm Innovation Center, Inc. Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>