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>

1 files changed, 22 insertions, 4 deletions

diff --git a/fs/xfs/xfs_log_priv.h b/fs/xfs/xfs_log_priv.h
index a5b3c021a406..2f74c80a7a40 100644
--- a/fs/xfs/xfs_log_priv.h
+++ b/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
@@ -561,6 +559,26 @@ int	xlog_write(struct log *log, struct xfs_log_vec *log_vector,
                                 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
  */
 int     xlog_cil_init(struct log *log);