On May 8, 2013, at 1:05 AM, Christian Kujau <lists@xxxxxxxxxxxxxxx> wrote: > On Mon, 6 May 2013 at 17:16, David Shaw wrote: >> What I'm doing is creating a snapshot using DM directly (not through >> LVM), mounting the snapshot, and then writing to both sides (the mounted >> snapshot as well as the original filesystem). > [...] >> I managed to get this down to a simple reproduction case. All this >> is starting with a LVM VG named "tests", which contains two LVs named > > I'm confused: are your using LVM or not? In effect, yes, I am. The only difference is that I'm calling the dmsetup commands manually rather than creating the snapshot via lvcreate. My apologies - I think in an effort to be complete, I used way too much verbiage and confused the issue. To restate this in a simpler way: I create a LVM snapshot of a large (~6TB) ext4 filesystem, then mount it. On occasion (so this is not 100% reproducible) overwriting a file on the snapshot blocks for a long time (~60 seconds) before completing. I can write to the origin volume without any problem, and I can write new files to the snapshot without any problem. It's only when overwriting a file on the snapshot (i.e. a file that exists on the origin, but I'm overwriting it on the snapshot) does the block happen. Once the initial blockage has passed, things generally proceed without any further blockage. I got a backtrace via "echo t > /proc/sysrq-trigger" of /bin/cp stuck in this state, which is pasted below. A week or two ago, there was a post here about "(LONG) Delay when writing to ext4 LVM after boot". Reading that post over again, it sounds somewhat similar, at least in symptoms. My case isn't a new boot, but the snapshot is certainly a newly-mounted filesystem. FWIW, flex_bg is set on my filesystem. The flex block group size is 16. A possibly useful tidbit is that both the snap and origin are mounted nodelalloc. > $ uname -rv > 3.8-trunk-amd64 #1 SMP Debian 3.8-1~experimental.1 I'm running 2.6.35.14-97.fc14.x86_64 (i.e. Fedora 14) The backtrace: 2013-05-06 15:53:41 foobar kernel: [1057700.540986] cp D 0000000000000000 0 18683 18670 0x00000000 2013-05-06 15:53:41 foobar kernel: [1057700.540989] ffff880018f5d438 0000000000000082 ffff880000000000 ffff88005ec245c0 2013-05-06 15:53:41 foobar kernel: [1057700.540991] 0000000000015540 0000000000015540 ffff880018f5dfd8 0000000000015540 2013-05-06 15:53:41 foobar kernel: [1057700.540994] 0000000000015540 0000000000015540 0000000000015540 ffff880018f5dfd8 2013-05-06 15:53:41 foobar kernel: [1057700.540996] Call Trace: 2013-05-06 15:53:41 foobar kernel: [1057700.540999] [<ffffffff81138b9b>] ? sync_buffer+0x0/0x2e 2013-05-06 15:53:41 foobar kernel: [1057700.541001] [<ffffffff81138b9b>] ? sync_buffer+0x0/0x2e 2013-05-06 15:53:41 foobar kernel: [1057700.541003] [<ffffffff81468b35>] io_schedule+0x48/0x63 2013-05-06 15:53:41 foobar kernel: [1057700.541005] [<ffffffff81138bc5>] sync_buffer+0x2a/0x2e 2013-05-06 15:53:41 foobar kernel: [1057700.541007] [<ffffffff814690dd>] __wait_on_bit+0x48/0x7b 2013-05-06 15:53:41 foobar kernel: [1057700.541010] [<ffffffff8146917e>] out_of_line_wait_on_bit+0x6e/0x79 2013-05-06 15:53:41 foobar kernel: [1057700.541012] [<ffffffff81138b9b>] ? sync_buffer+0x0/0x2e 2013-05-06 15:53:41 foobar kernel: [1057700.541014] [<ffffffff81066a44>] ? wake_bit_function+0x0/0x31 2013-05-06 15:53:41 foobar kernel: [1057700.541017] [<ffffffff81138b58>] __wait_on_buffer+0x24/0x26 2013-05-06 15:53:41 foobar kernel: [1057700.541019] [<ffffffff811abb14>] ext4_mb_init_cache+0x26b/0x55b 2013-05-06 15:53:41 foobar kernel: [1057700.541022] [<ffffffff811ac863>] ext4_mb_init_group+0xa3/0x20e 2013-05-06 15:53:41 foobar kernel: [1057700.541025] [<ffffffff811adc57>] ext4_mb_good_group+0x53/0xd6 2013-05-06 15:53:41 foobar kernel: [1057700.541028] [<ffffffff811ade0d>] ext4_mb_regular_allocator+0x133/0x281 2013-05-06 15:53:41 foobar kernel: [1057700.541031] [<ffffffff811aeb67>] ext4_mb_new_blocks+0x189/0x38c 2013-05-06 15:53:41 foobar kernel: [1057700.541033] [<ffffffff811a4bd6>] ? ext4_ext_find_extent+0x51/0x2b2 2013-05-06 15:53:41 foobar kernel: [1057700.541036] [<ffffffff811a7af9>] ext4_ext_map_blocks+0x15d1/0x186f 2013-05-06 15:53:41 foobar kernel: [1057700.541039] [<ffffffff812479a0>] ? alloc_iova+0x1cb/0x1dd 2013-05-06 15:53:41 foobar kernel: [1057700.541042] [<ffffffff810e7951>] ? zone_statistics+0x65/0x6a 2013-05-06 15:53:41 foobar kernel: [1057700.541044] [<ffffffff810da22f>] ? get_page_from_freelist+0x3fd/0x674 2013-05-06 15:53:41 foobar kernel: [1057700.541047] [<ffffffff8103c165>] ? need_resched+0x23/0x2d 2013-05-06 15:53:41 foobar kernel: [1057700.541050] [<ffffffff8118e2b4>] ext4_map_blocks+0x13b/0x21d 2013-05-06 15:53:41 foobar kernel: [1057700.541053] [<ffffffff8118e434>] _ext4_get_block+0x9e/0x126 2013-05-06 15:53:41 foobar kernel: [1057700.541055] [<ffffffff81137f3b>] ? attach_page_buffers+0x27/0x35 2013-05-06 15:53:41 foobar kernel: [1057700.541058] [<ffffffff8118e50c>] ext4_get_block+0x16/0x18 2013-05-06 15:53:41 foobar kernel: [1057700.541061] [<ffffffff8113a0fa>] __block_prepare_write+0x12e/0x28d 2013-05-06 15:53:41 foobar kernel: [1057700.541063] [<ffffffff8118e4f6>] ? ext4_get_block+0x0/0x18 2013-05-06 15:53:41 foobar kernel: [1057700.541066] [<ffffffff8113a319>] block_write_begin_newtrunc+0x80/0xc1 2013-05-06 15:53:41 foobar kernel: [1057700.541069] [<ffffffff8113a63f>] block_write_begin+0x38/0x71 2013-05-06 15:53:41 foobar kernel: [1057700.541071] [<ffffffff8118e4f6>] ? ext4_get_block+0x0/0x18 2013-05-06 15:53:41 foobar kernel: [1057700.541074] [<ffffffff8118f4f0>] ext4_write_begin+0x14d/0x22e 2013-05-06 15:53:41 foobar kernel: [1057700.541076] [<ffffffff8118e4f6>] ? ext4_get_block+0x0/0x18 2013-05-06 15:53:41 foobar kernel: [1057700.541079] [<ffffffff810d371f>] generic_file_buffered_write+0xfa/0x23d 2013-05-06 15:53:41 foobar kernel: [1057700.541081] [<ffffffff81190c8f>] ? ext4_dirty_inode+0x45/0x4a 2013-05-06 15:53:41 foobar kernel: [1057700.541084] [<ffffffff810d5184>] __generic_file_aio_write+0x24f/0x27f 2013-05-06 15:53:41 foobar kernel: [1057700.541086] [<ffffffff810d3e51>] ? find_get_page+0x49/0x6e 2013-05-06 15:53:41 foobar kernel: [1057700.541089] [<ffffffff8103c165>] ? need_resched+0x23/0x2d 2013-05-06 15:53:41 foobar kernel: [1057700.541091] [<ffffffff8103c165>] ? need_resched+0x23/0x2d 2013-05-06 15:53:41 foobar kernel: [1057700.541094] [<ffffffff810d520f>] generic_file_aio_write+0x5b/0xab 2013-05-06 15:53:41 foobar kernel: [1057700.541096] [<ffffffff81187b43>] ext4_file_write+0xa0/0xad 2013-05-06 15:53:41 foobar kernel: [1057700.541099] [<ffffffff8111752e>] do_sync_write+0xcb/0x108 2013-05-06 15:53:41 foobar kernel: [1057700.541102] [<ffffffff811dd241>] ? security_file_permission+0x16/0x18 2013-05-06 15:53:41 foobar kernel: [1057700.541105] [<ffffffff81117c08>] vfs_write+0xac/0x100 2013-05-06 15:53:41 foobar kernel: [1057700.541108] [<ffffffff81117e11>] sys_write+0x4a/0x6e 2013-05-06 15:53:41 foobar kernel: [1057700.541110] [<ffffffff81009cb2>] system_call_fastpath+0x16/0x1b David -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
