[Cluster-devel] GFS2: Merge glock state fields into a bitfield

[Steven Whitehouse]

We can only merge the fields into a bitfield if the locking
rules for them are the same. In this case gl_spin covers all
of the fields (write side) but a couple of them are used
with GLF_LOCK as the read side lock, which should be ok
since we know that the field in question won't be changing
at the time.

The gl_req setting has to be done earlier (in glock.c) in order
to place it under gl_spin. The gl_reply setting also has to be
brought under gl_spin in order to comply with the new rules.

This saves 4*sizeof(unsigned int) per glock.

Signed-off-by: Steven Whitehouse <swhiteho at redhat.com>

diff --git a/fs/gfs2/glock.c b/fs/gfs2/glock.c
index 2dd1d72..08a8beb 100644
--- a/fs/gfs2/glock.c
+++ b/fs/gfs2/glock.c
@@ -567,6 +567,7 @@ __acquires(&gl->gl_spin)
 		set_bit(GLF_INVALIDATE_IN_PROGRESS, &gl->gl_flags);
 		do_error(gl, 0); /* Fail queued try locks */
 	}
+	gl->gl_req = target;
 	spin_unlock(&gl->gl_spin);
 	if (glops->go_xmote_th)
 		glops->go_xmote_th(gl);
@@ -1353,24 +1354,28 @@ static int gfs2_should_freeze(const struct gfs2_glock *gl)
  * @gl: Pointer to the glock
  * @ret: The return value from the dlm
  *
+ * The gl_reply field is under the gl_spin lock so that it is ok
+ * to use a bitfield shared with other glock state fields.
  */
 
 void gfs2_glock_complete(struct gfs2_glock *gl, int ret)
 {
 	struct lm_lockstruct *ls = &gl->gl_sbd->sd_lockstruct;
 
+	spin_lock(&gl->gl_spin);
 	gl->gl_reply = ret;
 
 	if (unlikely(test_bit(DFL_BLOCK_LOCKS, &ls->ls_flags))) {
-		spin_lock(&gl->gl_spin);
 		if (gfs2_should_freeze(gl)) {
 			set_bit(GLF_FROZEN, &gl->gl_flags);
 			spin_unlock(&gl->gl_spin);
 			return;
 		}
-		spin_unlock(&gl->gl_spin);
 	}
+
+	spin_unlock(&gl->gl_spin);
 	set_bit(GLF_REPLY_PENDING, &gl->gl_flags);
+	smp_wmb();
 	gfs2_glock_hold(gl);
 	if (queue_delayed_work(glock_workqueue, &gl->gl_work, 0) == 0)
 		gfs2_glock_put(gl);
diff --git a/fs/gfs2/incore.h b/fs/gfs2/incore.h
index 764fbb4..8d3d2b4 100644
--- a/fs/gfs2/incore.h
+++ b/fs/gfs2/incore.h
@@ -207,12 +207,14 @@ struct gfs2_glock {
 
 	spinlock_t gl_spin;
 
-	unsigned int gl_state;
-	unsigned int gl_target;
-	unsigned int gl_reply;
+	/* State fields protected by gl_spin */
+	unsigned int gl_state:2,	/* Current state */
+		     gl_target:2,	/* Target state */
+		     gl_demote_state:2,	/* State requested by remote node */
+		     gl_req:2,		/* State in last dlm request */
+		     gl_reply:8;	/* Last reply from the dlm */
+
 	unsigned int gl_hash;
-	unsigned int gl_req;
-	unsigned int gl_demote_state; /* state requested by remote node */
 	unsigned long gl_demote_time; /* time of first demote request */
 	struct list_head gl_holders;
 
diff --git a/fs/gfs2/lock_dlm.c b/fs/gfs2/lock_dlm.c
index f40ce34..6e493ae 100644
--- a/fs/gfs2/lock_dlm.c
+++ b/fs/gfs2/lock_dlm.c
@@ -153,7 +153,6 @@ static int gdlm_lock(struct gfs2_glock *gl, unsigned int req_state,
 	int req;
 	u32 lkf;
 
-	gl->gl_req = req_state;
 	req = make_mode(req_state);
 	lkf = make_flags(gl->gl_lksb.sb_lkid, flags, req);