Hi Laura, On Monday 27 October 2014 13:38:19 Laura Abbott wrote: > 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. > > ... > > > 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? It's just the messages, I haven't noticed allocation failures. > 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 I've tested the patches but they don't seem to have any influence on the isolation test failures. -- Regards, Laurent Pinchart -- 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>