linux-kernel - Re: Linux 2.6.29

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Message-ID: <f73f7ab80903252003j248b416ewe52b613c5b53066c@mail.gmail.com>
Date:	Wed, 25 Mar 2009 23:03:03 -0400
From:	Kyle Moffett <kyle@...fetthome.net>
To:	Jeff Garzik <jeff@...zik.org>
Cc:	Matthew Garrett <mjg59@...f.ucam.org>,
	Theodore Tso <tytso@....edu>,
	Christoph Hellwig <hch@...radead.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Jan Kara <jack@...e.cz>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Arjan van de Ven <arjan@...radead.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Nick Piggin <npiggin@...e.de>,
	Jens Axboe <jens.axboe@...cle.com>,
	David Rees <drees76@...il.com>, Jesper Krogh <jesper@...gh.cc>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Linux 2.6.29

On Wed, Mar 25, 2009 at 10:51 PM, Jeff Garzik <jeff@...zik.org> wrote:
> Then you have just reinvented the transactional userspace API that people
> often want to replace POSIX API with.  Maybe one day they will succeed.
>
> But "POSIX API replacement" is an area never short of proposals... :)

Well, I think the goal is not to *replace* the POSIX API or even
provide "transactional" guarantees.  The performance penalty for
atomic transactions is pretty high, and most programs (like GIT) don't
really give a damn, as they provide that on a higher level.

It's like the difference between a modern SMP system that supports
memory barriers and write snooping and one of the theoretical
"transactional memory" designs that have never caught on.

To be honest I think we could provide much better data consistency
guarantees and remove a lot of fsync() calls with just a basic
per-filesystem barrier() call.

Cheers,
Kyle Moffett
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