linux-ext4 - Re: [PATCH 2/3] ext4: Fix and simplify s

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Message-ID: <20090501134506.GB7681@mit.edu>
Date:	Fri, 1 May 2009 09:45:06 -0400
From:	Theodore Tso <tytso@....edu>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	Ext4 Developers List <linux-ext4@...r.kernel.org>
Subject: Re: [PATCH 2/3] ext4: Fix and simplify s_dirt handling

On Fri, May 01, 2009 at 03:02:55AM -0400, Christoph Hellwig wrote:
> On Fri, May 01, 2009 at 12:37:16AM -0400, Theodore Ts'o wrote:
> > The s_dirt flag wasn't completely handled correctly, but it didn't
> > really matter when journalling was enabled.  It turns out that when
> > ext4 runs without a journal, we don't clear s_dirt in places where we
> > should have, with the result that the high-level write_super()
> > function was writing the superblock when it wasn't necessary.
> > 
> > So we fix this by making ext4_commit_super() clear the s_dirt flag,
> > and removing many of the other places where s_dirt is manipulated.
> > When journalling is enabled, the s_dirt flag might be left set more
> > often, but s_dirt really doesn't matter when journalling is enabled.
> 
> Btw, you might want to move all s_dirt setting into a wrapper, so that
> it never gets set for journal mode.  That way we can avoid superflous
> calls into the filesystem in that default mode.

I thought about doing this, but currently the VFS core checks for the
presence for the write_super method function before it checks for
s_dirt, so it didn't seem to matter much whether or not s_dirt was set
if the filesystem doesn't have a NULL write_super function.

       		  	       	      - Ted
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