linux-kernel - Re: 2.6.29 -mm merge plans

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Date:	Thu, 8 Jan 2009 14:22:49 +0100
From:	Pavel Machek <pavel@...e.cz>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, Nick Piggin <npiggin@...e.de>,
	jack@...e.cz
Subject: Re: 2.6.29 -mm merge plans

Hi!

> > > I'm not sure this is a good idea.  Concurrent syncs are a bad idea
> > > to start with and we should just synchronyze do_sync completely.
> > > sync_filesystems as one of the main components of do_sync already
> > > is synchronized in that way, and taking that to a higher level would
> > > get rid of all the worries about concurrent syncs.
> > 
> > Yes, single-threading sys_sync() would fix the problem which that patch
> > addresses.
> > 
> > However there are a lot of performance and correctness issues around
> > sys_sync()-versus-fsync(), etc for which such a simple fix won't be
> > acceptable.
> 
> fsync should really not much interac with sync at that level.  While
> they both end up at same primitives at the lowest level those aren't
> the ones we're trying to protect against.  I'm currently in the process
> of a major rework of sys_sync/do_sync to make it work properly for
> modern filesystems and the global synchronization was one of the first
> things I did..
> 
> So if you have any workloads where that causes a problem please send
> them my way.  Not that I can really thing of them, given the global
> nature of sys_sync I can't see any benefit of doing multiple of these
> in parallel.

I did play with fsync() a bit, and realized it mostly does not
work. (Yes, I did physically unplug the media). I have some scripts,
and am currently converting them to nbd so that I will not have to
physically pull anything.

Jack has some ext2 fix provoked by those tests...
								Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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