Date: Fri, 11 Jan 2008 16:04:31 -0800
From: Andrew Morton <akpm@linux-foundation.org>
To: Daniel Phillips <phillips@phunq.net>
Cc: abhishekrai@google.com, tytso@mit.edu, adilger@sun.com,
       linux-kernel@vger.kernel.org, kenchen@google.com, mikew@google.com,
       rohitseth@google.com
Subject: Re: [PATCH] Clustering indirect blocks in Ext3
Message-Id: <20080111160431.905a853f.akpm@linux-foundation.org>
In-Reply-To: <200801110905.18464.phillips@phunq.net>
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	<200801110905.18464.phillips@phunq.net>
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On Fri, 11 Jan 2008 09:05:17 -0800
Daniel Phillips <phillips@phunq.net> wrote:

> On Thursday 10 January 2008 13:17, Abhishek Rai wrote:
> > Benchmark 5: fsck
> > Description: Prepare a newly formated 400GB disk as follows: create
> > 200 files of 0.5GB each, 100 files of 1GB each, 40 files of 2.5GB
> > ech, and 10 files of 10GB each. fsck command line: fsck -f -n
> > 1. vanilla:
> >  Total: 11m25.3s
> >  User: 13.4s
> >  System: 13.2s
> > 2. mc:
> >  Total: 3m11.0s
> >  User: 13.1s
> >  System: 12.9s
> >
> > Note: I'll report results from kernbench and compilebench shortly.
> >
> > Observations:
> > Sequential write performance is much better with metaclustering than
> > with vanilla. To better understand it, I ran the same benchmark with
> > the new code but with the metaclustering option turned off and I got
> > the same performance as vanilla which makes me believe that there is
> > something about metaclustering that helps write performance though I
> > don't have a very good handle of what that thing might be.
> 
> Your results are very impressive.   In my opinion, the sooner this goes 
> in, the better, since everybody hates waiting for fsck.  The only issue 
> that jumps out at me is, the patch is big and changes a significant 
> amount of Ext3 code outside of the metacluster path, which is not a bad 
> thing except that these changes are going to need to be tested fairly 
> heavily.

It needs to be reviewed.  In exhaustive detail.  Few people can do that and
fewer are inclined to do so.

> The way to do that is, put a big [CALL FOR TESTING] in your subject line 
> the next time you post, and use an attention-getting subject line 
> like "Make Ext3 fsck way faster".   Diff the patch against the latest 
> stable kernel to make things as easy as possible for the people who are 
> hopefully going to download your patch, try it, and report their 
> results.
> 
> The other way is just to ask Andrew to put it in -mm when you feel 
> ready, but your chances are much better if you already have people 
> sending in mails saying how great your patch is.

I went to merge it so it could get some testing while we await review but
the patch has all its tabs replaced with spaces, is seriously wordwrapped
and has random newlines added to it.  Please fix email client and resend
(offlist is OK if it is unaltered).


We should have a think about which workloads are most likely to be
adversely affected by this change.

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