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Date:	Thu, 01 Nov 2007 10:20:18 -0500
From:	Eric Sandeen <sandeen@...hat.com>
To:	Alex Tomas <bzzz.tomas@...il.com>
CC:	Andreas Dilger <adilger@....COM>,
	ext4 development <linux-ext4@...r.kernel.org>
Subject: Re: delalloc fragmenting files?

Alex Tomas wrote:
> please, try the patch attached.

Looks quite a bit better:

http://people.redhat.com/esandeen/seekwatcher/ext4-alex.png
http://people.redhat.com/esandeen/seekwatcher/ext4-alex-ext4-dd-write.png
http://people.redhat.com/esandeen/seekwatcher/ext4-alex-ext4-xfs-dd-write.png

It is much less fragmented, although still not exactly the nice linear
allocation I'd expect from a single threaded large write on a fresh fs...

-Eric

> thanks, Alex
> 
> Eric Sandeen wrote:
>> One thing that seems to be happening is that thanks to delalloc, a nice
>> big request is coming in (only 1036 blocks of the 4096, not quite sure
>> why), but then it gets into ext4_mb_normalize_request(), which finds the
>> most blocks it can "preallocate" is 256, and chops down the request to
>> 256 blocks.  Shouldn't this preallocation be over & above what was asked
>> for, vs. reducing the request?
>>
>> Ok, so, we get allocations in 256-block chunks...  Why they don't all
>> come out contiguous, I don't know yet...
>>
>> -Eric
> 

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