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To: linux-kernel@vger.kernel.org
From: torvalds@transmeta.com (Linus Torvalds)
Subject: Re: [BK][PATCH] Reiser4, will double Linux FS performance, pleaseapply
Date: Fri, 1 Nov 2002 04:36:12 +0000 (UTC)
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In article <3DC1D9D0.684326AC@digeo.com>,
Andrew Morton  <akpm@digeo.com> wrote:
>
>But it should be done based on "feature equivalency".  By default,
>ext3 uses ordered data writes.  Data is written to disk before
>the metadata to which that data refers is committed to journal.

Andrew, that's not necessarily a _good_ feature. 

Journaling is _not_ a great idea.  There are other approaches to
handling atomicity than journaling, like phase trees, that give
equivalent atomicity guarantees without having to write out extra stuff,
or even impose a very strict ordering between data and meta-data.

I didn't read the reiser papers yet, but from Hans' description it
sounds like reiser4 gives all the guarantees ext3 does with ordered
writes, _and_ they get good performance. 

(In fact, from the description it sounds like it gives _more_ guarantees
than even ext3 with ordered writes, in that it gives transactional
behaviour for arbitrary writes. Maybe I should read the paper).

		Linus
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