xfs: combine grant heads into a single 64 bit integer

Prepare for switching the grant heads to atomic variables by
combining the two 32 bit values that make up the grant head into a
single 64 bit variable.  Provide wrapper functions to combine and
split the grant heads appropriately for calculations and use them as
necessary.
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>

fs/xfs/linux-2.6/xfs_trace.h

@@ -786,10 +786,12 @@ DECLARE_EVENT_CLASS(xfs_loggrant_class,
 		__entry->flags = tic->t_flags;
 		__entry->reserveq = list_empty(&log->l_reserveq);
 		__entry->writeq = list_empty(&log->l_writeq);
-		__entry->grant_reserve_cycle = log->l_grant_reserve_cycle;
-		__entry->grant_reserve_bytes = log->l_grant_reserve_bytes;
-		__entry->grant_write_cycle = log->l_grant_write_cycle;
-		__entry->grant_write_bytes = log->l_grant_write_bytes;
+		xlog_crack_grant_head(&log->l_grant_reserve_head,
+				&__entry->grant_reserve_cycle,
+				&__entry->grant_reserve_bytes);
+		xlog_crack_grant_head(&log->l_grant_write_head,
+				&__entry->grant_write_cycle,
+				&__entry->grant_write_bytes);
 		__entry->curr_cycle = log->l_curr_cycle;
 		__entry->curr_block = log->l_curr_block;
 		__entry->tail_lsn = log->l_tail_lsn;

fs/xfs/xfs_log_priv.h

@@ -518,10 +518,8 @@ typedef struct log {
 	spinlock_t		l_grant_lock ____cacheline_aligned_in_smp;
 	struct list_head	l_reserveq;
 	struct list_head	l_writeq;
-	int			l_grant_reserve_cycle;
-	int			l_grant_reserve_bytes;
-	int			l_grant_write_cycle;
-	int			l_grant_write_bytes;
+	int64_t			l_grant_reserve_head;
+	int64_t			l_grant_write_head;
 
 	/* The following field are used for debugging; need to hold icloglock */
 #ifdef DEBUG
@@ -560,6 +558,26 @@ int	xlog_write(struct log *log, struct xfs_log_vec *log_vector,
 				struct xlog_ticket *tic, xfs_lsn_t *start_lsn,
 				xlog_in_core_t **commit_iclog, uint flags);
 
+/*
+ * When we crack the grrant head, we sample it first so that the value will not
+ * change while we are cracking it into the component values. This means we
+ * will always get consistent component values to work from.
+ */
+static inline void
+xlog_crack_grant_head(int64_t *head, int *cycle, int *space)
+{
+	int64_t	val = *head;
+
+	*cycle = val >> 32;
+	*space = val & 0xffffffff;
+}
+
+static inline void
+xlog_assign_grant_head(int64_t *head, int cycle, int space)
+{
+	*head = ((int64_t)cycle << 32) | space;
+}
+
 /*
  * Committed Item List interfaces
  */

fs/xfs/xfs_log_recover.c

@@ -938,10 +938,10 @@ xlog_find_tail(
 		log->l_curr_cycle++;
 	log->l_tail_lsn = be64_to_cpu(rhead->h_tail_lsn);
 	log->l_last_sync_lsn = be64_to_cpu(rhead->h_lsn);
-	log->l_grant_reserve_cycle = log->l_curr_cycle;
-	log->l_grant_reserve_bytes = BBTOB(log->l_curr_block);
-	log->l_grant_write_cycle = log->l_curr_cycle;
-	log->l_grant_write_bytes = BBTOB(log->l_curr_block);
+	xlog_assign_grant_head(&log->l_grant_reserve_head, log->l_curr_cycle,
+					BBTOB(log->l_curr_block));
+	xlog_assign_grant_head(&log->l_grant_write_head, log->l_curr_cycle,
+					BBTOB(log->l_curr_block));
 
 	/*
 	 * Look for unmount record.  If we find it, then we know there