Re: WAPBL patch for testing

[Thor Lancelot Simon <tls%rek.tjls.com@localhost>]

On Fri, Oct 31, 2008 at 08:03:32PM +0100, Juergen Hannken-Illjes wrote:
> On Fri, Oct 31, 2008 at 07:03:59PM +0100, Joerg Sonnenberger wrote:
> > Hi all,
> > the attached patch is supposed to fix both hangs (wchan tstile) and
> > performance issues with WAPBL. Please test it and report any issues.
> > I'd like to see some review for this too. I can't find a reason why the
> > WAPBL lock should be hold in that places nor can I find a code path from
> > UFS itself to getpages with lock already being hold, but I could be
> > wrong.
> > 
> > Joerg
> 
> The reason for these wapbl locks is ffs snapshots.  VOP_PUTPAGES() may
> need to copy-on-write which needs to run inside a wapbl transaction
> as we allocate blocks here.

Would this problem be any easier to solve if the snapshot and wapbl
code used the same notion of a "transaction"?  I was very surprised
to see that wapbl brought in an a whole new idea of a "fs transaction"
when the snapshot code already seemed to have one.

Thor