[Cluster-devel] [PATCH] gfs2: skip dlm_unlock calls in unmount

[David Teigland <teigland@redhat.com>]

On Fri, Nov 09, 2012 at 09:45:17AM +0000, Steven Whitehouse wrote:
> > +	if (test_bit(SDF_SKIP_DLM_UNLOCK, &sdp->sd_flags) &&
> > +	    (!gl->gl_lvb[0] || gl->gl_state != LM_ST_EXCLUSIVE)) {
> I'm still not happy with using !gl->gl_lvb[0] to determine whether the
> LVB is in use or not. I think we need a better test, or alternatively
> just test the lock state, since most locks will be NL anyway before they
> get to this point in time,

Yeah, a glock flag indicating the lvb is used would be best, I'll just
test the lock state.

This actually brings up another improvement you could make.  Right now
gfs2 enables the lvb on all locks, even though it only uses it on a small
minority.  Limiting the lvb to locks that need it would:

- save 64 bytes of memory for every local lock
  (32 in gfs2_glock, 32 in dlm_rsb)

- save 96 bytes of memory for every remote lock
  (32 in gfs2_glock, 32 in local dlm_rsb, 32 in remote dlm_lkb)

- save 32 bytes of network message size in many dlm messages

- save a lot of memcpying of zeros

- save some recovery time