Subject: Re: [PATCH] reiserfs v3 fixes and features
From: Chris Mason <mason@suse.com>
To: Marc-Christian Petersen <m.c.p@wolk-project.de>
Cc: linux-kernel@vger.kernel.org, akpm@osdl.org
In-Reply-To: <200404062214.40259@WOLK>
References: <1081274618.30828.30.camel@watt.suse.com>
	 <200404062214.40259@WOLK>
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Date: Tue, 06 Apr 2004 17:06:27 -0400
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On Tue, 2004-04-06 at 16:14, Marc-Christian Petersen wrote:
> On Tuesday 06 April 2004 20:03, Chris Mason wrote:
> 
> Hi Chris,
> 
> > If anyone is interested in experimenting with the block allocator stuff,
> > please let me know.
> 
> I am :)

There are a few different sides to the block allocator work. 

1) don't ruin what the current allocator is good at (desktop esp).  A
sequential tree read of freshly copied data is really fast right now. 
It could be a little better with some metadata readahead, I'm still
trying to safely revive that code.

The patch tries to keep performance for a full tree read by with the -o
packing_groups option.  The basic idea is to reuse bitmap groups for new
subdirectories until the bitmap group is full.  This is done by checking
to see how full a given part of the btree is.
 
2) Improve the fragmentation under multiple writers.   With 20 writers,
the default allocator breaks down, fragmenting badly (20% or so).  The
patch with -o alloc=skip_busy:dirid_groups on makes things sane (3%).

So, to help test, you need some way of measuring fragmentation and a
whole bunch of benchmarks.  I like fibmap:
(http://www.informatik.uni-frankfurt.de/~loizides/reiserfs/fibmap.html)

But Andrew has a fragmentation tool in the ext2 cvs I think.

-chris


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