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List:       linux-kernel
Subject:    Re: Long `rm` times.
From:       "Stephen C. Tweedie" <sct () redhat ! com>
Date:       1999-05-31 23:18:50
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Hi,

On Fri, 28 May 1999 18:03:03 -0400 (EDT), "Theodore Y. Ts'o"
<tytso@mit.edu> said:

>    Date: 	Wed, 26 May 1999 17:23:06 +0200
>    From: Helge Hafting <helge.hafting@c2i.net>

>    Consider the case of a huge file with lots of fragments.  We want to
>    find block x in the last half of the file.

> This is why any scheme using extents must also be combined with
> appropriate algorithsm to avoid fragmentation.  If you look at a typical
> ext2 filesystem, most files aren't fragmented at all; allocating files
> across multiple block groups and using preallocation really helps avoid
> fragmentation issues.

Also note that if the fragment list is maintained in a btree then
access to the extent information is still relatively fast even when we
get fragmented.  Doing this also helps to keep unix semantics
regarding sparse files, as the ability to insert into the middle of a
btree lets you write to holes in the file.

--Stephen

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