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

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Date:	Tue, 15 May 2012 00:13:13 +0000
From:	"Myklebust, Trond" <Trond.Myklebust@...app.com>
To:	Andreas Dilger <adilger@...ger.ca>
CC:	"J. Bruce Fields" <bfields@...ldses.org>,
	"Theodore Ts'o" <tytso@....edu>,
	"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, 2012-05-14 at 17:33 -0600, Andreas Dilger wrote:
> Even better than just blindly bumping the i_version on every change,
> it would be better to have users of i_version (i.e. knfsd) flag the
> inode with "needs i_version update" then read the version.  When the
> filesystem/VFS bumps i_version the next time it can clear this flag
> and not update i_version again until after the next time i_version
> is actually used.

That doubly penalises actual users of i_version: not only does the
filesystem have to bump it on a file change, but it now has to set and
write this flag on the next read of i_version.

If those reads of i_version were really few and far between, then I
agree that it might be a solution, but most NFS clients will ask for the
updated i_version after every change that they make to the file because
they need to track that value for cache consistency management purposes.

-- 
Trond Myklebust
Linux NFS client maintainer

NetApp
Trond.Myklebust@...app.com
www.netapp.com