[saturnero@freesbie.org: Weird behaviour of mount_unionfs with executables]

[Stephan Uphoff]

On Sun, 2005-07-03 at 20:21, Scott Long wrote:
> Stephan Uphoff wrote:
> > On Sun, 2005-07-03 at 20:02, Scott Long wrote:
> > 
> >>Stephan Uphoff wrote:
> >>
> >>>I suspect the changes in revision 1.272 of kern_exec.c trigger the
> >>>copy operation.
> >>>
> >>>Looks like you need a noatime option for union_fs.
> >>>
> >>>Stephan
> >>
> >>Does this mean that every vnode that gets executed gets dirtied and all
> >>its pages resynced to the backing store, or just the inode block?
> > 
> > 
> > The kernel calls VOP_SETATTR to set the access time of the file.
> > union_fs detects that it does not have an upper layer copy of the file
> > to modify the attributes on and decides to copy it.
> > The vm layer does not (directly) come into play on this. 
> > 
> > Stephan
> > 
> 
> Ok, so this is just a limitation of unionfs, not the vnode pager.  You
> had me scared that we'd be doing a whole lot of needless disk i/o.

YES - and it looks like just specifying noatime for the union mount
should fix the copy problem for FreeSBIE.

Stephan