Re: [RFC] [patch 0/3] i_version update for ext4

From: Trond Myklebust <trond.myklebust@fys.uio.no>
To: Mingming Cao <cmm@us.ibm.com>
Cc: linux-ext4@vger.kernel.org, nfsv4@linux-nfs.org,
	Cordenner jean noel <jean-noel.cordenner@bull.net>,
	Andreas Dilger <adilger@clusterfs.com>
Subject: Re: [RFC] [patch 0/3] i_version update for ext4
Date: Wed, 24 Jan 2007 10:12:00 -0800	[thread overview]
Message-ID: <1169662320.6280.13.camel@lade.trondhjem.org> (raw)
In-Reply-To: <45B79A12.4060004@us.ibm.com>

On Wed, 2007-01-24 at 09:40 -0800, Mingming Cao wrote:
> Cordenner jean noel wrote:
> > Andreas Dilger a écrit :
> > 
> >> On Jan 23, 2007  18:23 +0100, Cordenner jean noel wrote:
> >>
> >>> I've updated what was previously the change attribute patch for ext4
> >>> initially posted by Alexandre Ratchov. The previous patch was
> >>> introducing a change_attribute field, now it uses the i_version field of
> >>> the inode.
> >>>
> >>> The i_version field is a counter that is set on every inode creation and
> >>> that is incremented every time the inode data is modified (similarly to
> >>> the "ctime" time-stamp).
> >>> The aim is to fulfill NFSv4 requirements for rfc3530.
> >>> For the moent, the counter is only a 32bit value but it is planned to be
> >>> 64bit as required.
> >>>
> >>> The patch is divided into 3 parts, the vfs layer, the ext4 specific code
> >>> and an user part to check i_version changes via stat.
> >>
> >>
> >> Have you had a chance to look at the performance impact of this change
> >> (possible with oprofile)?  Always marking the inodes dirty for ext3
> >> may have some noticable overhead.
> >>
> > 
> > I did some tests using fileop with the previous version of the patch
> > which was very similar. I was surprised that there was no noticable
> > overhead:
> >  http://www.bullopensource.org/ext4/change_attribute/index.html
> > 
> > I will use oprofile to check it again.
> 
> Could we just increment the counter each time the mtime is modifies(not 
> the ctime)? Is that enough to serve NFSv4 need?

No. That would not conform to RFC3530:

5.5.  Mandatory Attributes - Definitions

   Name              #    DataType     Access   Description
   ___________________________________________________________________

.....

   change            3    uint64       READ     A value created by the
                                                server that the client
                                                can use to determine
                                                if file data,
                                                directory contents or
                                                attributes of the
                                                object have been
                                                modified.  The server
                                                may return the
                                                object's time_metadata
                                                attribute for this
                                                attribute's value but
                                                only if the filesystem
                                                object can not be
                                                updated more
                                                frequently than the
                                                resolution of
                                                time_metadata.

so the change attribute needs to change on both data and metadata
updates.

Cheers,
  Trond

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