Date:   Fri, 10 Nov 2017 09:43:47 -0500
From:   "Mattthew L. Martin" <linux@...arskydata.com>
To:     mfe555 <mfe555@....de>, linux-ext4@...r.kernel.org
Subject: Re: Significant difference in 'file size' and 'disk usage' for single
 files

Lukas,

Yes, please add any information you have to that bug report. We may be 
developing more information here which I will add to the report once I 
have proven it to the the issue. If it is, I will have a reproducer. 
That may help things along.

Matthew


On 11/7/17 02:30, mfe555 wrote:
> Dear Matthew,
>
> sorry about the misunderstanding. If you agree I will reply to your 
> bug report at bugzilla.kernel.org, providing the details I have posted 
> here initially. Is there anything else you would recommend me to do, 
> or any other information you can share?
>
> Thanks a lot
> Lukas
>
>
> Am 06.11.2017 um 19:56 schrieb Mattthew L. Martin:
>> Lukas,
>>
>> I think you might have misunderstood me. We are pretty much in the 
>> same situation that you find yourself. We currently un-mount and 
>> remount the file systems that have this behavior to ameliorate the 
>> issue. We can provide information, but we don't have the manpower or 
>> skill set to effect a fix.
>>
>> Matthew
>>
>>
>> On 11/6/17 12:35, mfe555 wrote:
>>> Dear Mathew,
>>>
>>> thank you very much for your message and for your offer of helping me.
>>>
>>> In my case, the file system has a cluster size of 262144. bigalloc 
>>> is enabled, please see below for details (tune2fs). I have been able 
>>> to confirm that unmounting and re-mounting the file system helps.
>>>
>>> Please let me know what else I can do for giving you more clues. For 
>>> example, as our linux system is built for over 100 different settop 
>>> boxes, I might be able to get help from other people, performing 
>>> tests on specific linux kernels.
>>>
>>> Kind regards
>>> Lukas
>>>
>>> =================================
>>> # tune2fs -l /dev/sdb1
>>> tune2fs 1.43.4 (31-Jan-2017)
>>> Filesystem volume name:   <none>
>>> Last mounted on:          /media/hdd
>>> Filesystem UUID:          1dbc401d-3ff4-4a46-acc7-8ec7b841bdb0
>>> Filesystem magic number:  0xEF53
>>> Filesystem revision #:    1 (dynamic)
>>> Filesystem features:      has_journal ext_attr resize_inode 
>>> dir_index filetype needs_recovery extent flex_bg sparse_super 
>>> large_file huge_file uninit_bg dir_nlink extra_isize bigalloc
>>> Filesystem flags:         signed_directory_hash
>>> Default mount options:    user_xattr acl
>>> Filesystem state:         clean
>>> Errors behavior:          Continue
>>> Filesystem OS type:       Linux
>>> Inode count:              264688
>>> Block count:              488378368
>>> Reserved block count:     0
>>> Free blocks:              146410368
>>> Free inodes:              260432
>>> First block:              0
>>> Block size:               4096
>>> Cluster size:             262144
>>> Reserved GDT blocks:      14
>>> Blocks per group:         2097152
>>> Clusters per group:       32768
>>> Inodes per group:         1136
>>> Inode blocks per group:   71
>>> Flex block group size:    16
>>> Filesystem created:       Sun Mar 13 16:31:29 2016
>>> Last mount time:          Thu Jan  1 01:00:04 1970
>>> Last write time:          Thu Jan  1 01:00:04 1970
>>> Mount count:              884
>>> Maximum mount count:      -1
>>> Last checked:             Sun Mar 13 16:31:29 2016
>>> Check interval:           0 (<none>)
>>> Lifetime writes:          6971 GB
>>> Reserved blocks uid:      0 (user root)
>>> Reserved blocks gid:      0 (group root)
>>> First inode:              11
>>> Inode size:               256
>>> Required extra isize:     28
>>> Desired extra isize:      28
>>> Journal inode:            8
>>> Default directory hash:   half_md4
>>> Directory Hash Seed:      c69a1039-0065-4c1b-8732-ff1b52b57313
>>> Journal backup:           inode blocks
>>>
>>>
>>>
>>>
>>> Am 06.11.2017 um 16:35 schrieb Mattthew L. Martin:
>>>> I filed a bug for this a while ago:
>>>>
>>>> https://bugzilla.kernel.org/show_bug.cgi?id=151491
>>>>
>>>> We would be happy to help track this down as it is a pain to manage 
>>>> this on running servers.
>>>>
>>>> Matthew
>>>>
>>>>
>>>> On 11/5/17 06:16, mfe555 wrote:
>>>>> Some follow-up:
>>>>>
>>>>> The issue only occurs with "bigalloc" enabled.
>>>>>
>>>>>     echo 3 > /proc/sys/vm/drop_caches
>>>>>
>>>>> seems to detach the blocked disk space from the files (so that 'du 
>>>>> file' no longer includes the offset), but it does not free the 
>>>>> space, 'df' still shows all file overheads as used disk space.
>>>>>
>>>>>
>>>>>
>>>>> Am 02.11.2017 um 20:17 schrieb mfe555:
>>>>>> Hi, I'm using ext4 on a Linux based Enigma2 set-top box, kernel 
>>>>>> 4.8.3.
>>>>>>
>>>>>> When creating a fresh file, there is a significant difference in 
>>>>>> file size (ls -la) and disk usage (du). When making two copies of 
>>>>>> the file ..
>>>>>>
>>>>>> gbquad:/hdd/test# cp file file.copy1
>>>>>> gbquad:/hdd/test# cp file file.copy2
>>>>>> gbquad:/hdd/test# ls -la
>>>>>> -rw-------    1 root     root     581821460 Nov  1 18:52 file
>>>>>> -rw-------    1 root     root     581821460 Nov  1 18:56 file.copy1
>>>>>> -rw-------    1 root     root     581821460 Nov  1 18:57 file.copy2
>>>>>> gbquad:/hdd/test# du *
>>>>>> 607232  file
>>>>>> 658176  file.copy1
>>>>>> 644864  file.copy2
>>>>>>
>>>>>> ... all three files show an overhead in the ~10% range, and the 
>>>>>> overhead is different for these files although their md5sums are 
>>>>>> equal.
>>>>>>
>>>>>> When deleting a file (rm), the overhead remains occupied on the 
>>>>>> disk. For example, after deleting "file", "df" reports approx. 
>>>>>> 581821460 more bytes free, not 607232 kbytes more free space. The 
>>>>>> overhead (607232 kB - 581821460 B =pprox. 39 MB) remains blocked.
>>>>>>
>>>>>> When re-booting, the blocked space becomes free again, and in 
>>>>>> addition the overhead of those files that were not deleted also 
>>>>>> disappears, so that after a reboot the'file size' and 'disk 
>>>>>> usage' match for all files (except for rounding up to some block 
>>>>>> size).
>>>>>>
>>>>>> A colleague and I have observed this on two different "kernel 
>>>>>> 4.8.3" boxes and three ext4 disks, but not on a "kernel 3.14" box 
>>>>>> also using ext4.
>>>>>>
>>>>>> Can anyone help me with this ?
>>>>>>
>>>>>> Thanks a lot
>>>>>> Lukas
>>>>>>
>>>>>
>>>>
>>>
>>
>

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