From: Greg Freemyer <greg.freemyer@gmail.com>
Subject: Re: [PATCH 1/3] e4defrag: output blocks per extent by -c option
Date: Tue, 6 Oct 2009 14:24:50 -0400
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Cc: linux-ext4@vger.kernel.org, Theodore Tso <tytso@mit.edu>
To: Kazuya Mio <k-mio@sx.jp.nec.com>
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2009/10/6 Kazuya Mio <k-mio@sx.jp.nec.com>:
> 2009/10/03 0:28, Greg Freemyer wrote::
>> 2009/10/1 Kazuya Mio <k-mio@sx.jp.nec.com>:
>>> 2009/10/01 3:28, Greg Freemyer wrote::
>>>> 2009/9/30 Kazuya Mio <k-mio@sx.jp.nec.com>:
>>>>> e4defrag with -c option outputs "ratio" that means the levels of
>>>>> fragmentation. However, it's difficult for users to understand, s=
o we will
>>>>> use blocks per extent instead of ratio.
>>>>>
>>>>> Before:
>>>>> # e4defrag -c /mnt/mp1/file
>>>>> <File> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0=
 =A0 =A0 =A0 =A0 =A0 now/best =A0 =A0 =A0 =A0 =A0ratio
>>>>> /mnt/mp1/file =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0=
 =A0 =A0 =A0 =A0 14/1 =A0 =A0 =A0 =A0 =A0 =A0 0.01%
>>>>>
>>>>> =A0Total/best extents =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0=
 =A0 =A0 =A0 14/1
>>>>> =A0Fragmentation ratio =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0=
 =A0 =A0 =A00.01%
>>>>> =A0Fragmentation score =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0=
 =A0 =A0 =A00.10
>>>>> =A0[0-30 no problem: 31-55 a little bit fragmented: 55- needs def=
rag]
>>>>> =A0This file(/mnt/mp1/file) does not need defragmentation.
>>>>> =A0Done.
>>>>>
>>>>> After:
>>>>> # e4defrag -c /mnt/mp1/file
>>>>> <File> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0=
 =A0 =A0 =A0 =A0 =A0 now/best =A0 =A0 =A0 =A0blk/ext
>>>>> /mnt/mp1/file =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0=
 =A0 =A0 =A0 =A0 14/1 =A0 =A0 =A0 =A0 =A0 =A0 =A07142
>>>>>
>>>>> =A0Total/best extents =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0=
 =A0 =A0 =A0 14/1
>>>>> =A0Average blocks per extent =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =
=A0 =A07142
>>>>> =A0Fragmentation score =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0=
 =A0 =A0 =A00
>>>>> =A0[0-30 no problem: 31-55 a little bit fragmented: 55- needs def=
rag]
>>>>> =A0This file(/mnt/mp1/file) does not need defragmentation.
>>>>> =A0Done.
>>>> RFC
>>>>
>>>> If we are going go that far (which I like), how about adding the a=
vg
>>>> extent size in bytes. =A0(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 =A0 =A0 32,768 =A0(128MiB)
>>> Your ideas sound good. How about the following output image?
>>>
>>> # e4defrag -c /mnt/mp1/file
>>> <File> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =
=A0 =A0 =A0 =A0 =A0 now/best =A0 =A0 =A0 =A0 KB/ext
>>> /mnt/mp1/file =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0=
 =A0 =A0 =A0 14/1 =A0 =A0 =A0 =A0 =A0 =A0 =A04000
>>>
>>> =A0Total/best extents =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0=
 =A0 =A0 14/1
>>> =A0Min bytes per extent =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0=
 =A0 =A0 1024 KB
>>> =A0Max bytes per extent =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0=
 =A0 =A0 20489 KB
>>> =A0Average bytes per extent =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0=
 =A0 4000 KB
>>> =A0Fragmentation score =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =
=A0 =A0 =A00
>>> =A0[0-30 no problem: 31-55 a little bit fragmented: 55- needs defra=
g]
>>> =A0This file(/mnt/mp1/file) does not need defragmentation.
>>> =A0Done.
>>>
>>> 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. =A0They could easily be 100's of G=
B 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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