linux-ext4 - Re: [PATCH 1/3] e4defrag: output blocks per extent by -c option

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Message-ID: <87f94c370910061124h745c4cap5035b99a35d81eb@mail.gmail.com>
Date:	Tue, 6 Oct 2009 14:24:50 -0400
From:	Greg Freemyer <greg.freemyer@...il.com>
To:	Kazuya Mio <k-mio@...jp.nec.com>
Cc:	linux-ext4@...r.kernel.org, Theodore Tso <tytso@....edu>
Subject: Re: [PATCH 1/3] e4defrag: output blocks per extent by -c option

2009/10/6 Kazuya Mio <k-mio@...jp.nec.com>:
> 2009/10/03 0:28, Greg Freemyer wrote::
>> 2009/10/1 Kazuya Mio <k-mio@...jp.nec.com>:
>>> 2009/10/01 3:28, Greg Freemyer wrote::
>>>> 2009/9/30 Kazuya Mio <k-mio@...jp.nec.com>:
>>>>> e4defrag with -c option outputs "ratio" that means the levels of
>>>>> fragmentation. However, it's difficult for users to understand, so we will
>>>>> use blocks per extent instead of ratio.
>>>>>
>>>>> Before:
>>>>> # e4defrag -c /mnt/mp1/file
>>>>> <File>                                         now/best          ratio
>>>>> /mnt/mp1/file                                   14/1             0.01%
>>>>>
>>>>>  Total/best extents                             14/1
>>>>>  Fragmentation ratio                            0.01%
>>>>>  Fragmentation score                            0.10
>>>>>  [0-30 no problem: 31-55 a little bit fragmented: 55- needs defrag]
>>>>>  This file(/mnt/mp1/file) does not need defragmentation.
>>>>>  Done.
>>>>>
>>>>> After:
>>>>> # e4defrag -c /mnt/mp1/file
>>>>> <File>                                         now/best        blk/ext
>>>>> /mnt/mp1/file                                   14/1              7142
>>>>>
>>>>>  Total/best extents                             14/1
>>>>>  Average blocks per extent                      7142
>>>>>  Fragmentation score                            0
>>>>>  [0-30 no problem: 31-55 a little bit fragmented: 55- needs defrag]
>>>>>  This file(/mnt/mp1/file) does not need defragmentation.
>>>>>  Done.
>>>> RFC
>>>>
>>>> If we are going go that far (which I like), how about adding the avg
>>>> extent size in bytes.  (ie. 7142 * blocksize I assume).
>>>>
>>>> Also a note about the max blocks / extent might be good.
>>>>
>>>> ie. Add a more or less hard coded line
>>>> Ext4 max blocks per extent     32,768  (128MiB)
>>> Your ideas sound good. How about the following output image?
>>>
>>> # e4defrag -c /mnt/mp1/file
>>> <File>                                         now/best         KB/ext
>>> /mnt/mp1/file                                   14/1              4000
>>>
>>>  Total/best extents                             14/1
>>>  Min bytes per extent                           1024 KB
>>>  Max bytes per extent                           20489 KB
>>>  Average bytes per extent                       4000 KB
>>>  Fragmentation score                            0
>>>  [0-30 no problem: 31-55 a little bit fragmented: 55- needs defrag]
>>>  This file(/mnt/mp1/file) does not need defragmentation.
>>>  Done.
>>>
>>> Regards,
>>>
>>> Kazuya Mio
>>
>> I was thinking more of the theoretical max bytes per extent, not the
>> largest extent found in the actual file.
>>
>> I say this because most users of e4defrag won't know what perfection
>> is, so they won't know if and when they have come close if they don't
>> know what the ultimate goal is.
>>
>> Specifically, think of a admin hosting a few virtual machines where
>> the virtual disks are ext4 files.  They could easily be 100's of GB so
>> they may think even 128MB / extent can be improved on, even though
>> they have already achieved the theoretical max.
>>
>> Greg
>
> I see. But I think e4defrag doesn't always need to print logical max
> bytes per extent. So, I will add it to e4defrag man page instead of
> standard output. What do you think?
>
> Regards,
>
> Kazuya Mio

I had not thought about the man page for some reason, but it would
satisfy my concern.

Greg



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