On Mon 06-02-17 09:35:33, Brian Foster wrote: > On Mon, Feb 06, 2017 at 03:29:24PM +0900, Tetsuo Handa wrote: > > Brian Foster wrote: > > > On Fri, Feb 03, 2017 at 03:50:09PM +0100, Michal Hocko wrote: > > > > [Let's CC more xfs people] > > > > > > > > On Fri 03-02-17 19:57:39, Tetsuo Handa wrote: > > > > [...] > > > > > (1) I got an assertion failure. > > > > > > > > I suspect this is a result of > > > > http://lkml.kernel.org/r/20170201092706.9966-2-mhocko@xxxxxxxxxx > > > > I have no idea what the assert means though. > > > > > > > > > > > > > > [ 969.626518] Killed process 6262 (oom-write) total-vm:2166856kB, anon-rss:1128732kB, file-rss:4kB, shmem-rss:0kB > > > > > [ 969.958307] oom_reaper: reaped process 6262 (oom-write), now anon-rss:0kB, file-rss:0kB, shmem-rss:0kB > > > > > [ 972.114644] XFS: Assertion failed: oldlen > newlen, file: fs/xfs/libxfs/xfs_bmap.c, line: 2867 > > > > > > Indirect block reservation underrun on delayed allocation extent merge. > > > These are extra blocks are used for the inode bmap btree when a delalloc > > > extent is converted to physical blocks. We're in a case where we expect > > > to only ever free excess blocks due to a merge of extents with > > > independent reservations, but a situation occurs where we actually need > > > blocks and hence the assert fails. This can occur if an extent is merged > > > with one that has a reservation less than the expected worst case > > > reservation for its size (due to previous extent splits due to hole > > > punches, for example). Therefore, I think the core expectation that > > > xfs_bmap_add_extent_hole_delay() will always have enough blocks > > > pre-reserved is invalid. > > > > > > Can you describe the workload that reproduces this? FWIW, I think the > > > way xfs_bmap_add_extent_hole_delay() currently works is likely broken > > > and have a couple patches to fix up indlen reservation that I haven't > > > posted yet. The diff that deals with this particular bit is appended. > > > Care to give that a try? > > > > The workload is to write to a single file on XFS from 10 processes demonstrated at > > http://lkml.kernel.org/r/201512052133.IAE00551.LSOQFtMFFVOHOJ@xxxxxxxxxxxxxxxxxxx > > using "while :; do ./oom-write; done" loop on a VM with 4CPUs / 2048MB RAM. > > With this XFS_FILBLKS_MIN() change applied, I no longer hit assertion failures. > > > > Thanks for testing. Well, that's an interesting workload. I couldn't > reproduce on a few quick tries in a similarly configured vm. > > Normally I'd expect to see this kind of thing on a hole punching > workload or dealing with large, sparse files that make use of > speculative preallocation (post-eof blocks allocated in anticipation of > file extending writes). I'm wondering if what is happening here is that > the appending writes and file closes due to oom kills are generating > speculative preallocs and prealloc truncates, respectively, and that > causes prealloc extents at the eof boundary to be split up and then > re-merged by surviving appending writers. Can those preallocs be affected by http://lkml.kernel.org/r/20170201092706.9966-2-mhocko@xxxxxxxxxx ? -- Michal Hocko SUSE Labs -- 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>
