linux-ext4 - Re: delalloc fragmenting files?

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Date:	Fri, 26 Oct 2007 21:54:55 -0500
From:	Eric Sandeen <sandeen@...hat.com>
To:	Andreas Dilger <adilger@....com>
CC:	ext4 development <linux-ext4@...r.kernel.org>,
	Alex Tomas <alex.tomas@....com>
Subject: Re: delalloc fragmenting files?

Andreas Dilger wrote:
> On Oct 26, 2007  16:24 -0500, Eric Sandeen wrote:
>> The resulting file had over 4k extents.
>> [root@...r-05 ~]# filefrag -v /mnt/test/foobar  | grep -i extents
>> File is stored in extents format
>> /mnt/test/foobar: 4075 extents found
> 
> On a related note - we're just putting the finishing touches on the
> FIEMAP patches for ext4 + e2fsprogs, so that we can get decent looking
> output from filefrag, and much more efficiently than FIBMAP.

sounds good.

> One of the issues is that w/o delalloc the mballoc code only gets 
> single-block allocations, so there might be a problem with the interface
> to mballoc.  That might be caused by the fact the patches were changed
> at one point from delalloc-atop-mballoc to mballoc-atop-delalloc, and
> something was missed in that conversion.
> 
> Have you tried O_DIRECT?  That is another way to access mballoc w/o
> using delalloc.

I've tried osync:
http://people.redhat.com/esandeen/seekwatcher/ext4-dd-osync-write.png

but not yet O_DIRECT, will do.

-Eric
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