On Thu, Dec 17, 2020 at 06:44:51PM +0100, Donald Buczek wrote: > Dear xfs developer, > > I was doing some testing on a Linux 5.10.1 system with two 100 TB xfs filesystems on md raid6 raids. > > The stress test was essentially `cp -a`ing a Linux source repository with two threads in parallel on each filesystem. > > After about on hour, the processes to one filesystem (md1) blocked, 30 minutes later the process to the other filesystem (md0) did. > > root 7322 2167 0 Dec16 pts/1 00:00:06 cp -a /jbod/M8068/scratch/linux /jbod/M8068/scratch/1/linux.018.TMP > root 7329 2169 0 Dec16 pts/1 00:00:05 cp -a /jbod/M8068/scratch/linux /jbod/M8068/scratch/2/linux.019.TMP > root 13856 2170 0 Dec16 pts/1 00:00:08 cp -a /jbod/M8067/scratch/linux /jbod/M8067/scratch/2/linux.028.TMP > root 13899 2168 0 Dec16 pts/1 00:00:05 cp -a /jbod/M8067/scratch/linux /jbod/M8067/scratch/1/linux.027.TMP > > Some info from the system (all stack traces, slabinfo) is available here: https://owww.molgen.mpg.de/~buczek/2020-12-16.info.txt > > It stands out, that there are many (549 for md0, but only 10 for md1) "xfs-conv" threads all with stacks like this > > [<0>] xfs_log_commit_cil+0x6cc/0x7c0 > [<0>] __xfs_trans_commit+0xab/0x320 > [<0>] xfs_iomap_write_unwritten+0xcb/0x2e0 > [<0>] xfs_end_ioend+0xc6/0x110 > [<0>] xfs_end_io+0xad/0xe0 > [<0>] process_one_work+0x1dd/0x3e0 > [<0>] worker_thread+0x2d/0x3b0 > [<0>] kthread+0x118/0x130 > [<0>] ret_from_fork+0x22/0x30 > > xfs_log_commit_cil+0x6cc is > > xfs_log_commit_cil() > xlog_cil_push_background(log) > xlog_wait(&cil->xc_push_wait, &cil->xc_push_lock); > > Some other threads, including the four "cp" commands are also blocking at xfs_log_commit_cil+0x6cc > > There are also single "flush" process for each md device with this stack signature: > > [<0>] xfs_map_blocks+0xbf/0x400 > [<0>] iomap_do_writepage+0x15e/0x880 > [<0>] write_cache_pages+0x175/0x3f0 > [<0>] iomap_writepages+0x1c/0x40 > [<0>] xfs_vm_writepages+0x59/0x80 > [<0>] do_writepages+0x4b/0xe0 > [<0>] __writeback_single_inode+0x42/0x300 > [<0>] writeback_sb_inodes+0x198/0x3f0 > [<0>] __writeback_inodes_wb+0x5e/0xc0 > [<0>] wb_writeback+0x246/0x2d0 > [<0>] wb_workfn+0x26e/0x490 > [<0>] process_one_work+0x1dd/0x3e0 > [<0>] worker_thread+0x2d/0x3b0 > [<0>] kthread+0x118/0x130 > [<0>] ret_from_fork+0x22/0x30 > > xfs_map_blocks+0xbf is the > > xfs_ilock(ip, XFS_ILOCK_SHARED); > > in xfs_map_blocks(). > > The system is low on free memory > > MemTotal: 197587764 kB > MemFree: 2196496 kB > MemAvailable: 189895408 kB > > but responsive. > > I have an out of tree driver for the HBA ( smartpqi 2.1.6-005 pulled from linux-scsi) , but it is unlikely that this blocking is related to that, because the md block devices itself are responsive (`xxd /dev/md0` ) > > I can keep the system in the state for a while. Is there an idea what was going from or an idea what data I could collect from the running system to help? I have full debug info and could walk lists or retrieve data structures with gdb. > It might be useful to dump the values under /sys/fs/xfs/<dev>/log/* for each fs to get an idea of the state of the logs as well... Brian > Best > Donald >
