On Wed, 2015-11-18 at 10:53 -0500, Jeff Moyer wrote: > Hi, > > When running the nvml library's test suite against an ext4 file system > mounted with -o dax, I ran into an issue where many of the tests would > simply timeout. The problem appears to be that the pmd fault handler > never returns to userspace (the application is doing a memcpy of 512 > bytes into pmem). Here's the 'perf report -g' output: > > - 88.30% 0.01% blk_non_zero.st libc-2.17.so [.] __memmove_ssse3_back > - 88.30% __memmove_ssse3_back > - 66.63% page_fault > - 66.47% do_page_fault > - 66.16% __do_page_fault > - 63.38% handle_mm_fault > - 61.15% ext4_dax_pmd_fault > - 45.04% __dax_pmd_fault > - 37.05% vmf_insert_pfn_pmd > - track_pfn_insert > - 35.58% lookup_memtype > - 33.80% pat_pagerange_is_ram > - 33.40% walk_system_ram_range > - 31.63% find_next_iomem_res > 21.78% strcmp > > And here's 'perf top': > > Samples: 2M of event 'cycles:pp', Event count (approx.): 56080150519 > Overhead Shared Object Symbol > 22.55% [kernel] [k] strcmp > 20.33% [unknown] [k] 0x00007f9f549ef3f3 > 10.01% [kernel] [k] native_irq_return_iret > 9.54% [kernel] [k] find_next_iomem_res > 3.00% [jbd2] [k] start_this_handle > > This is easily reproduced by doing the following: > > git clone https://github.com/pmem/nvml.git > cd nvml > make > make test > cd src/test/blk_non_zero > ./blk_non_zero.static-nondebug 512 /path/to/ext4/dax/fs/testfile1 c 1073741824 w:0 > > I also ran the test suite against xfs, and the problem is not present > there. However, I did not verify that the xfs tests were getting pmd > faults. > > I'm happy to help diagnose the problem further, if necessary. Thanks for the report, I'll take a look. - Ross ��.n��������+%������w��{.n�����{�����ܨ}���Ơz�j:+v�����w����ޙ��&�)ߡ�a����z�ޗ���ݢj��w�f
