Re: [opensuse] nfs_update_inode: inode X mode changed, Y to Z

[Timothy Shimmin <tes@xxxxxxx>]

Hi Neil,

NeilBrown wrote:
> On Wed, March 26, 2008 8:24 am, Josef 'Jeff' Sipek wrote:
>
> > Unless you specify the "ikeep" mount option, XFS will remove unused inode
> > clusters.  The newly freed blocks can be then used to store data or
> > possibly
> > a new inode cluster.  If the blocks get reused for inodes, you'll end up
> > with inodes whose generation numbers regressed. (inode number = f(block
> > number))
> >
> > Using the "ikeep" mount option causes to _never_ free empty inode
> > clusters.
> > This means that if you create many files and then unlink them, you'll end
> > up
> > with many unused inodes that are still allocated (and taking up disk
> > space)
> > but free to be used by the next creat(2)/mkdir(2)/etc..
> >
> > This "problem" is inherent to any file system which dynamically allocates
> > inodes.
>
> Yes, I understand all that.
>
> However you still need to do something about the generation number.  It
> must be set to something.
>
> When you allocate an inode that doesn't currently exist on the device,
> you obviously cannot increment the old value and use that.
> However you can do a lot better than always using 0.
Yes, this is a known problem.
We came across it in about August last year I believe in the context of
DMF as it wants to keep persistent file handles with gen#s in them:
  SGI bug:
  969192: Default mount option "noikeep" makes the inode generation number 
non-persistent
I vaguely remember at the time that a number of different schemes were
tossed around but in the end we just turned off the ikeep
for DMAPI mounted filesystems.
I thought we had a bug open to do a real fix but can't see
it at the moment. Will look into it and discuss with our group.

Cheers,
--Tim