On Thu, Nov 13, 2014 at 07:43:33PM -0500, Trond Myklebust wrote: > On Thu, Nov 13, 2014 at 6:54 PM, Dave Chinner <david@xxxxxxxxxxxxx> wrote: > > On Thu, Nov 13, 2014 at 08:02:43AM -0500, Trond Myklebust wrote: > >> On Wed, Nov 12, 2014 at 7:28 PM, Dave Chinner <david@xxxxxxxxxxxxx> wrote: > >> > On Wed, Nov 12, 2014 at 09:26:16AM -0500, Trond Myklebust wrote: > >> >> On Wed, Nov 12, 2014 at 5:24 AM, Christoph Hellwig <hch@xxxxxx> wrote: > >> >> > On Wed, Nov 12, 2014 at 09:27:10AM +1100, Dave Chinner wrote: > >> >> >> To clarify what Christoph wrote, XFS updates i_version is updated > >> >> >> once per transaction that modifies the inode. So if a VFS level > >> >> >> operation results in multiple transactions then each transaction > >> >> >> will but the version. > >> >> >> > >> >> >> It was implemented that way because nobody could tell me what the > >> >> >> actual granularity requirement for change detection was. Hence what > >> >> >> I implemented was "be able to detect any persistent change that is > >> >> >> made" to cover all bases. > > > > FWIW, ext4 takes the same approach. See Ted's post today: > > > > http://www.spinics.net/lists/linux-ext4/msg46194.html > > > > "The inode_inc_iversion() in mark4_ext4_iloc_dirty() is probably not > > necessary, since we already should be incrementing i_version whenever > > ctime and mtime gets updated. The inode_inc_iversion() there is more > > of a "belt and suspenders" safety thing, on the theory that the extra > > bump in i_version won't hurt anything." > > > > It will hurt if it causes all the NFS clients to blow their caches > unnecessarily. Not my problem. We've just implemented what we were asked to implement. > Who asked for this? The only discussion where actual specifications were enumerated was during a thread about using i_version in the integrity measurement code (IMA subsystem). The NFSv4 requirements for the change counter were expressed here: https://lkml.org/lkml/2012/1/5/408 Don't blame us for implementing the vague "changes every time" requirements in a way that results in no chance of a persistent change to either data or metadata being missed by the filesystem. Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
