On 30.03.2016 20:47, Tejun Heo wrote: > Hmmm... cgroup writeback support shouldn't affect fuse at all as the > backing device doesn't enable cgroup support. I probably made some > silly mistake. Is there a simple reproducer I can play with?
Hi Tejun! A simple reproducer is at https://github.com/rfjakob/mmapwrite . What seems to be happening in the kernel is that the estimated device bandwith drops to zero. I'm not even sure how this works for FUSE, but that's what I gathered from some printk debugging. What I also found is that once mmapwrite is hung, you can unblock it for some time by running something like cat /dev/zero > /var/tmp/foo mmapwrite will then steam ahead as long as cat is writing, even though encfs writes to /tmp (tmpfs) and /var is on the ext4 disk. Note that the hang happens regardless of the backing device, on both tmpfs and ext4. Best regards, Jakob
