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Date:	Wed, 01 Feb 2012 00:03:09 +0800
From:	Tao Ma <tm@....ma>
To:	Eric Sandeen <sandeen@...hat.com>
CC:	ext4 development <linux-ext4@...r.kernel.org>,
	Theodore Ts'o <tytso@....edu>
Subject: Re: Bigalloc ENOSPC woes

On 01/31/2012 05:19 AM, Eric Sandeen wrote:
> I got nervous when I tried this on an -O bigalloc -C 65536 fs:
> 
> # echo foo > blah; du -hc blah; sync; du -hc blah
> 4.0K blah
> 4.0K total
> 64K blah
> 64K total
> 
> Seems that du should never report less than the cluster size, should it?
It is a bug and the corresponding fix is sent with the subject "ext4:
let getattr report the right blocks in delalloc+bigalloc."
> 
> And that made me wonder about ENOSPC handling - are we tracing delalloc allocations correctly?
> 
> From running xfstest 204 on a similarly-created fs, it really seems that we are not.
> 
> A manual test of creating 4-byte files until ENOSPC (which was really when I ran out of inodes) and then issuing a sync led to a storm of kernel messages about allocation failures:
> 
> [  482.154538] EXT4-fs (sdb6): delayed block allocation failed for inode 1664 at logical offset 0 with max blocks 1 with error -28
> [  482.154540] EXT4-fs (sdb6): This should not happen!! Data will be lost
> 
> <ad infinitum, or at least 600 or so in my case>
> 
> and an end result of a bunch of 4 byte long files with no extents.  Almost like files full of NULLs.  Careful - that is hard to live down.  :)
yeah, I can reproduce it easily and more investigation is needed here.

Thanks
Tao
> 
> Ted, are you aware of those issues in bigalloc?
> 
> -Eric
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