mbuf leak with SMP and debug.mpsafenet=1

[Andrew Gallatin]

Robert Watson writes:
 > 
 > Yeah -- I've been trying to avoid committing this patch since atomic
 > operations hurt the P4 quite a bit more than one would hope.  We already
 > do MPSAFE stats in UMA, so an interesting question might be whether these
 > stats are redundant to stats already gathered and we can use them instead. 
 > One of the theoretical advantages of mbuma is that mbufs become just
 > another case of existing slab allocated memory resources, so I would think
 > most of the interesting stats should be there. 

Getting the stats from uma seems like the right thing to do in the
long run, but the atomic stats is a low-risk way to avoid bogus
mbuf leak reports from 5.3-RELEASE users.

 > > I think there may have been a real leak in the past; at least I ran a
 > > box out of mbufs a week ago.  It only came back when I ifconfig'ed down
 > > my driver, freeing a bunch of mbufs.  But this was before green's recent
 > > mbuf leak fix, and in the middle of driver development.  So who knows.. 
 > 
 > If it was with if_em, the queueing bugs that were fixed recently may also
 > have helped.

It was actually with my driver from a week ago.  At that point in the
development,  I would not be surprised by a leak...

Drew