Hello, On Tuesday 28 October 2014 09:48:26 Peter Hurley wrote: > [ +cc Andrew Morton ] > > On 10/28/2014 08:38 AM, Michal Nazarewicz wrote: > > On Sun, Oct 26 2014, 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. > > > > 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. [ 94.730000] __test_page_isolated_in_pageblock: failed at pfn 6b845: buddy 0 count 0 migratetype 4 poison 0 [ 94.740000] alloc_contig_range test_pages_isolated(6b845, 6b846) failed (-16) [ 202.140000] __test_page_isolated_in_pageblock: failed at pfn 6b843: buddy 0 count 0 migratetype 4 poison 0 [ 202.150000] alloc_contig_range test_pages_isolated(6b843, 6b844) failed (-16) (4 is MIGRATE_CMA) > 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. The messages got me worried, and if there's nothing to worry about, that's bad :-) -- 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>