linux-ext4 - Re: [PATCH] ext4: turn on i_version updates by default

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Date:	Mon, 14 May 2012 13:58:22 -0400
From:	Ted Ts'o <tytso@....edu>
To:	Andreas Dilger <adilger@...ger.ca>
Cc:	"J. Bruce Fields" <bfields@...ldses.org>,
	"linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>,
	"linux-nfs@...r.kernel.org" <linux-nfs@...r.kernel.org>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>
Subject: Re: [PATCH] ext4: turn on i_version updates by default

On Mon, May 14, 2012 at 11:27:42AM -0600, Andreas Dilger wrote:
> > And if it at all possible I'd rather have it be something that Just
> > Works rather than something that requires extra configuration.
> 
> Sure, but this is only useful for NFSv4, but costs everyone using
> ext4 continuous overhead, so it isn't a clear-cut case to enable
> the version just on the thought that NFS might one day be used on
> any particular filesystem.

It's not a matter of "NFSv4 might one day be used"; if we don't turn
on i_version updates until the file system is actually exported via
NFSv4, there would be no deleterious effects.

I always thought that was going to be the plan; that there would be
some flag that would be set in struct super_block when the file system
was exported that would enable i_version updates.

That way we satisfy the "no extra configuration" needed requirement,
which I agree is ideal, but we also don't waste any CPU overhead if
the file system is not exported via NFSv4.  I tried to implement
anything along these lines because I don't care enough, and I don't
use NFSv4 personally....

							- Ted
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