On Tue, Aug 30, 2016 at 6:50 AM, Ronan Arraes Jardim Chagas <roni...@gmail.com> wrote: > Hi! > > Em Ter, 2016-08-30 às 10:12 +0800, Wang Xiaoguang escreveu: >> For metadata, "bytes_may_use" is about 80GB, it's very big, >> I think this value is very abnormal. >> >> So this explains why you have huge unallocated space, you still >> get ENOSPC error. In kernel btrfs, there is a function >> should_alloc_chunk() >> to determine whether to allocate new chunks(new device space) >> num_bytes = total_bytes - bytes_readonly; it's 2147483648 >> num_allocated = bytes_used + bytes_reserved; it's 977354752 >> >> if num_allocated < num_bytes * 0.8, it will not allocate new device >> space :) even you >> have huge unallocated space. >> >> I think the root reason is that bytes_may_use has some computation >> error and >> is not be converted to bytes_used or bytes_reserved. >> >> I just explain why you get ENOSPC error even with huge unallocated >> space >> from >> codes :) >> > > Thanks! At least we known why ENOSPC is happening. > >> Can you work out a reproducer for this ENOSPC error, then I can >> dig into codes to figure out the true reason. > > Unfortunately I failed in every attempt to trigger the problem. It > happens randomly and I could not figure out yet what was triggering it. > First, I though it was related to a build process inside a chroot jail, > but then I see the problem happening after the computer being idle for > a long time (+- 1h). So, no clues yet :( > > Is there any workaround I can do?
It sounds related to read-only snapshots to me. I wonder if this system has something busy that's writing to a file, database, even maybe something just spamming journald, and then there's a read-only snapshot during the write, which then triggers the enospc. Ronan, if you're given a work around, then it's even less likely the bug gets fixed. But if you can disable snapper snapshots entirely and the problem doesn't happen; or if you can increase the frequency of snapper snapshots and the problem happens more often, that might help narrow it down to a point where it's more easily reproduced. If it's not related, that's still useful to know. -- Chris Murphy -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
