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Message-ID: <1472561404.3179.3.camel@gmail.com>
Subject: Re: BTRFS constantly reports "No space left on device" even with a
 huge unallocated space
From: Ronan Arraes Jardim Chagas <ronisbr@gmail.com>
To: Wang Xiaoguang <wangxg.fnst@cn.fujitsu.com>, linux-btrfs@vger.kernel.org
Date: Tue, 30 Aug 2016 09:50:04 -0300
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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?

Best regards,
Ronan Arraes