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From: Daniel Phillips <phillips@bonn-fries.net>
To: Andrew Morton <akpm@zip.com.au>
Subject: Re: [patch] sys_sync livelock fix
Date: Thu, 14 Feb 2002 01:49:03 +0100
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Cc: Bill Davidsen <davidsen@tmr.com>, lkml <linux-kernel@vger.kernel.org>
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On February 14, 2002 01:37 am, Andrew Morton wrote:
> Daniel Phillips wrote:
> > 
> > On February 13, 2002 11:24 pm, Bill Davidsen wrote:
> > > ...
> > > It doesn't matter, if you write the existing dirty buffers the filesystem
> > > type is irrelevant.
> > 
> > Incorrect.  The modern crop of filesystems has the concept of consistency
> > points, and data written after a consistency point is irrelevant except to the
> > next consistency point.  IOW, it's often ok to leave some buffers dirty on a
> > sync.  But for a dumb filesystem you just have to guess at what's needed for
> > a consistency point, and the best guess is 'whatever's dirty at the time of
> > sync'.
> > 
> > For metadata-only journalling the issues get more subtle and we need a ruling
> > from the ext3 guys.
> 
> The current implementation of fsync_dev is about as good as
> it'll get for journal=writeback mode - write the data,
> run a commit, write the data again then wait on it all.

What's the theory behind writing the data both before and after the commit?

> > 
> > Sorry, I don't see the connection to sync.
> 
> I don't understand the whole thread :)

Dangerous advocacy of the broken SuS semantics for sync, has to be stamped
out before it spreads ;-)

-- 
Daniel
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