On 13.09.2018 18:30, Chris Murphy wrote: > This is the 2nd or 3rd thread containing hanging btrfs send, with > kernel 4.18.x. The subject of one is "btrfs send hung in pipe_wait" > and the other I can't find at the moment. In that case though the hang > is reproducible in 4.14.x and weirdly it only happens when a snapshot > contains (perhaps many) reflinks. Scrub and check lowmem find nothing > wrong. > > I have snapshots with a few reflinks (cp --reflink and also > deduplication), and I see maybe 15-30 second hangs where nothing is > apparently happening (in top or iotop), but I'm also not seeing any > blocked tasks or high CPU usage. Perhaps in my case it's just > recovering quickly. > > Are there any kernel config options in "# Debug Lockups and Hangs" > that might hint at what's going on? Some of these are enabled in > Fedora debug kernels, which are built practically daily, e.g. right > now the latest in the build system is 4.19.0-0.rc3.git2.1 - which > translates to git 54eda9df17f3. If it's a lock-related problem then you need Lock Debugging => Lock debugging: prove locking correctness > > > Chris Murphy >
