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

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Date:	Fri, 2 Oct 2009 11:28:56 -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

2009/10/1 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
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