Freeing vnodes.

[Stephan Uphoff]

On Tue, 2005-03-15 at 00:39, Jeff Roberson wrote:
> On Mon, 14 Mar 2005, Stephan Uphoff wrote:
> 
> > On Mon, 2005-03-14 at 21:38, Jeff Roberson wrote:
> > > I have a patch at http://www.chesapeake.net/~jroberson/freevnodes.diff
> > > that allows us to start reclaiming vnodes from the free list and release
> > > their memory.  It also changes the semantics of wantfreevnodes, and makes
> > > getnewvnode() much prettier.
> > >
> > > The changes attempt to keep some number of vnodes, currently 2.5% of
> > > desiredvnodes, that are free in memory.  Free vnodes are vnodes which
> > > have no references or pages in memory.  For example, if an application
> > > simply stat's a vnode, it will end up on the free list at the end of the
> > > operation.  The algorithm that is currently in place will immediately
> > > recycle these vnodes once there is enough pressure, which will cause us to
> > > do a full lookup and reread the inode, etc. as soon as it is stat'd again.
> > >
> > > This also removes the recycling from the getnewvnode() path.  Instead, it
> > > is done by a new helper function that is called from vnlru_proc().  This
> > > function just frees vnodes from the head of the list until we reach our
> > > wantfreevnodes target.
> > >
> > > I haven't perf tested this yet, but I have a box that is doing a
> > > buildworld with a fairly constant freevnodes count which shows that vnodes
> > > are actually being uma_zfree'd.
> > >
> > > Comments?  Anyone willing to do some perf tests for me?
> > >
> > > Thanks,
> > > Jeff
> >
> > Just looked at the raw diff and might have missed it -  how are the
> > parent directory "name" cache entries ( vnode fields v_dd, v_ddid)
> > handled?
> 
> Just as they were before, by calling cache_purge.

This purges the fields of the vnode that will be recycled.
 
I am worried about the v_dd,v_ddid fields of a directory B that has the
to be released vnode A as parent. (Obviously in this case there is no
namecache entry with the vnode A as the directory (nc_dvp))
  
Right now A is type stable - but if A is released, access to B->v_dd
may cause a page fault.

Stephan