[ +cc Andrew Morton ] On 10/28/2014 08:38 AM, Michal Nazarewicz wrote: > On Sun, Oct 26 2014, Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx> 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. > > Like Laura wrote, the message is not (should not be) a problem in > itself: [...] > So as you can see cma_alloc will try another part of the cma region if > test_pages_isolated fails. > > Obviously, if CMA region is fragmented or there's enough space for only > one allocation of required size isolation failures will cause allocation > failures, so it's best to avoid them, but they are not always avoidable. > > To debug you would probably want to add more debug information about the > page (i.e. data from struct page) that failed isolation after the > pr_warn in alloc_contig_range. If the message does not indicate an actual problem, then its printk level is too high. These messages have been reported when using 3.16+ distro kernels. Regards, Peter Hurley -- 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>