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>

4 files changed, 119 insertions, 91 deletions

diff --git a/fs/xfs/linux-2.6/xfs_trace.h b/fs/xfs/linux-2.6/xfs_trace.h
index 69b9e1f1baa..3ff6b35f920 100644
--- a/fs/xfs/linux-2.6/xfs_trace.h
+++ b/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;
diff --git a/fs/xfs/xfs_log.c b/fs/xfs/xfs_log.c
index 9a4b9edad84..6bba8b4b859 100644
--- a/fs/xfs/xfs_log.c
+++ b/fs/xfs/xfs_log.c
@@ -47,7 +47,7 @@ STATIC xlog_t *  xlog_alloc_log(xfs_mount_t	*mp,
                                 xfs_buftarg_t   *log_target,
                                 xfs_daddr_t     blk_offset,
                                 int             num_bblks);
-STATIC int       xlog_space_left(xlog_t *log, int cycle, int bytes);
+STATIC int       xlog_space_left(struct log *log, int64_t *head);
 STATIC int       xlog_sync(xlog_t *log, xlog_in_core_t *iclog);
 STATIC void      xlog_dealloc_log(xlog_t *log);
 
@@ -100,32 +100,44 @@ STATIC int	xlog_iclogs_empty(xlog_t *log);
 static void
 xlog_grant_sub_space(
         struct log      *log,
-        int             *cycle,
-        int             *space,
+        int64_t         *head,
         int             bytes)
 {
-        *space -= bytes;
-        if (*space < 0) {
-                *space += log->l_logsize;
-                (*cycle)--;
+        int             cycle, space;
+
+        xlog_crack_grant_head(head, &cycle, &space);
+
+        space -= bytes;
+        if (space < 0) {
+                space += log->l_logsize;
+                cycle--;
         }
+
+        xlog_assign_grant_head(head, cycle, space);
 }
 
 static void
 xlog_grant_add_space(
         struct log      *log,
-        int             *cycle,
-        int             *space,
+        int64_t         *head,
         int             bytes)
 {
-        int tmp = log->l_logsize - *space;
+        int             tmp;
+        int             cycle, space;
+
+        xlog_crack_grant_head(head, &cycle, &space);
+
+        tmp = log->l_logsize - space;
         if (tmp > bytes)
-                *space += bytes;
+                space += bytes;
         else {
-                *space = bytes - tmp;
-                (*cycle)++;
+                space = bytes - tmp;
+                cycle++;
         }
+
+        xlog_assign_grant_head(head, cycle, space);
 }
+
 static void
 xlog_tic_reset_res(xlog_ticket_t *tic)
 {
@@ -654,7 +666,7 @@ xfs_log_move_tail(xfs_mount_t	*mp,
 {
         xlog_ticket_t   *tic;
         xlog_t          *log = mp->m_log;
-        int             need_bytes, free_bytes, cycle, bytes;
+        int             need_bytes, free_bytes;
 
         if (XLOG_FORCED_SHUTDOWN(log))
                 return;
@@ -680,9 +692,7 @@ xfs_log_move_tail(xfs_mount_t	*mp,
                 if (log->l_flags & XLOG_ACTIVE_RECOVERY)
                         panic("Recovery problem");
 #endif
-                cycle = log->l_grant_write_cycle;
-                bytes = log->l_grant_write_bytes;
-                free_bytes = xlog_space_left(log, cycle, bytes);
+                free_bytes = xlog_space_left(log, &log->l_grant_write_head);
                 list_for_each_entry(tic, &log->l_writeq, t_queue) {
                         ASSERT(tic->t_flags & XLOG_TIC_PERM_RESERV);
 
@@ -699,9 +709,7 @@ xfs_log_move_tail(xfs_mount_t	*mp,
                 if (log->l_flags & XLOG_ACTIVE_RECOVERY)
                         panic("Recovery problem");
 #endif
-                cycle = log->l_grant_reserve_cycle;
-                bytes = log->l_grant_reserve_bytes;
-                free_bytes = xlog_space_left(log, cycle, bytes);
+                free_bytes = xlog_space_left(log, &log->l_grant_reserve_head);
                 list_for_each_entry(tic, &log->l_reserveq, t_queue) {
                         if (tic->t_flags & XLOG_TIC_PERM_RESERV)
                                 need_bytes = tic->t_unit_res*tic->t_cnt;
@@ -814,21 +822,26 @@ xlog_assign_tail_lsn(xfs_mount_t *mp)
  * result is that we return the size of the log as the amount of space left.
  */
 STATIC int
-xlog_space_left(xlog_t *log, int cycle, int bytes)
+xlog_space_left(
+        struct log      *log,
+        int64_t         *head)
 {
-        int free_bytes;
-        int tail_bytes;
-        int tail_cycle;
+        int             free_bytes;
+        int             tail_bytes;
+        int             tail_cycle;
+        int             head_cycle;
+        int             head_bytes;
 
+        xlog_crack_grant_head(head, &head_cycle, &head_bytes);
         tail_bytes = BBTOB(BLOCK_LSN(log->l_tail_lsn));
         tail_cycle = CYCLE_LSN(log->l_tail_lsn);
-        if ((tail_cycle == cycle) && (bytes >= tail_bytes)) {
-                free_bytes = log->l_logsize - (bytes - tail_bytes);
-        } else if ((tail_cycle + 1) < cycle) {
+        if (tail_cycle == head_cycle && head_bytes >= tail_bytes)
+                free_bytes = log->l_logsize - (head_bytes - tail_bytes);
+        else if (tail_cycle + 1 < head_cycle)
                 return 0;
-        } else if (tail_cycle < cycle) {
-                ASSERT(tail_cycle == (cycle - 1));
-                free_bytes = tail_bytes - bytes;
+        else if (tail_cycle < head_cycle) {
+                ASSERT(tail_cycle == (head_cycle - 1));
+                free_bytes = tail_bytes - head_bytes;
         } else {
                 /*
                  * The reservation head is behind the tail.
@@ -839,12 +852,12 @@ xlog_space_left(xlog_t *log, int cycle, int bytes)
                         "xlog_space_left: head behind tail\n"
                         "  tail_cycle = %d, tail_bytes = %d\n"
                         "  GH   cycle = %d, GH   bytes = %d",
-                        tail_cycle, tail_bytes, cycle, bytes);
+                        tail_cycle, tail_bytes, head_cycle, head_bytes);
                 ASSERT(0);
                 free_bytes = log->l_logsize;
         }
         return free_bytes;
-}       /* xlog_space_left */
+}
 
 
 /*
@@ -1001,8 +1014,8 @@ xlog_alloc_log(xfs_mount_t	*mp,
         /* log->l_tail_lsn = 0x100000000LL; cycle = 1; current block = 0 */
         log->l_last_sync_lsn = log->l_tail_lsn;
         log->l_curr_cycle  = 1;     /* 0 is bad since this is initial value */
-        log->l_grant_reserve_cycle = 1;
-        log->l_grant_write_cycle = 1;
+        xlog_assign_grant_head(&log->l_grant_reserve_head, 1, 0);
+        xlog_assign_grant_head(&log->l_grant_write_head, 1, 0);
         INIT_LIST_HEAD(&log->l_reserveq);
         INIT_LIST_HEAD(&log->l_writeq);
 
@@ -1190,9 +1203,7 @@ xlog_grant_push_ail(xfs_mount_t	*mp,
     ASSERT(BTOBB(need_bytes) < log->l_logBBsize);
 
     spin_lock(&log->l_grant_lock);
-    free_bytes = xlog_space_left(log,
-                                 log->l_grant_reserve_cycle,
-                                 log->l_grant_reserve_bytes);
+    free_bytes = xlog_space_left(log, &log->l_grant_reserve_head);
     tail_lsn = log->l_tail_lsn;
     free_blocks = BTOBBT(free_bytes);
 
@@ -1325,10 +1336,8 @@ xlog_sync(xlog_t		*log,
 
         /* move grant heads by roundoff in sync */
         spin_lock(&log->l_grant_lock);
-        xlog_grant_add_space(log, &log->l_grant_reserve_cycle,
-                                &log->l_grant_reserve_bytes, roundoff);
-        xlog_grant_add_space(log, &log->l_grant_write_cycle,
-                                &log->l_grant_write_bytes, roundoff);
+        xlog_grant_add_space(log, &log->l_grant_reserve_head, roundoff);
+        xlog_grant_add_space(log, &log->l_grant_write_head, roundoff);
         spin_unlock(&log->l_grant_lock);
 
         /* put cycle number in every block */
@@ -2531,8 +2540,7 @@ redo:
         if (XLOG_FORCED_SHUTDOWN(log))
                 goto error_return;
 
-        free_bytes = xlog_space_left(log, log->l_grant_reserve_cycle,
-                                     log->l_grant_reserve_bytes);
+        free_bytes = xlog_space_left(log, &log->l_grant_reserve_head);
         if (free_bytes < need_bytes) {
                 if (list_empty(&tic->t_queue))
                         list_add_tail(&tic->t_queue, &log->l_reserveq);
@@ -2558,10 +2566,8 @@ redo:
         list_del_init(&tic->t_queue);
 
         /* we've got enough space */
-        xlog_grant_add_space(log, &log->l_grant_reserve_cycle,
-                                &log->l_grant_reserve_bytes, need_bytes);
-        xlog_grant_add_space(log, &log->l_grant_write_cycle,
-                                &log->l_grant_write_bytes, need_bytes);
+        xlog_grant_add_space(log, &log->l_grant_reserve_head, need_bytes);
+        xlog_grant_add_space(log, &log->l_grant_write_head, need_bytes);
         trace_xfs_log_grant_exit(log, tic);
         xlog_verify_grant_head(log, 1);
         xlog_verify_grant_tail(log);
@@ -2622,8 +2628,7 @@ xlog_regrant_write_log_space(xlog_t	   *log,
         need_bytes = tic->t_unit_res;
         if (!list_empty(&log->l_writeq)) {
                 struct xlog_ticket *ntic;
-                free_bytes = xlog_space_left(log, log->l_grant_write_cycle,
-                                             log->l_grant_write_bytes);
+                free_bytes = xlog_space_left(log, &log->l_grant_write_head);
                 list_for_each_entry(ntic, &log->l_writeq, t_queue) {
                         ASSERT(ntic->t_flags & XLOG_TIC_PERM_RESERV);
 
@@ -2662,8 +2667,7 @@ redo:
         if (XLOG_FORCED_SHUTDOWN(log))
                 goto error_return;
 
-        free_bytes = xlog_space_left(log, log->l_grant_write_cycle,
-                                     log->l_grant_write_bytes);
+        free_bytes = xlog_space_left(log, &log->l_grant_write_head);
         if (free_bytes < need_bytes) {
                 if (list_empty(&tic->t_queue))
                         list_add_tail(&tic->t_queue, &log->l_writeq);
@@ -2688,8 +2692,7 @@ redo:
         list_del_init(&tic->t_queue);
 
         /* we've got enough space */
-        xlog_grant_add_space(log, &log->l_grant_write_cycle,
-                                &log->l_grant_write_bytes, need_bytes);
+        xlog_grant_add_space(log, &log->l_grant_write_head, need_bytes);
         trace_xfs_log_regrant_write_exit(log, tic);
         xlog_verify_grant_head(log, 1);
         xlog_verify_grant_tail(log);
@@ -2730,12 +2733,10 @@ xlog_regrant_reserve_log_space(xlog_t	     *log,
                 ticket->t_cnt--;
 
         spin_lock(&log->l_grant_lock);
-        xlog_grant_sub_space(log, &log->l_grant_reserve_cycle,
-                                &log->l_grant_reserve_bytes,
-                                ticket->t_curr_res);
-        xlog_grant_sub_space(log, &log->l_grant_write_cycle,
-                                &log->l_grant_write_bytes,
-                                ticket->t_curr_res);
+        xlog_grant_sub_space(log, &log->l_grant_reserve_head,
+                                        ticket->t_curr_res);
+        xlog_grant_sub_space(log, &log->l_grant_write_head,
+                                        ticket->t_curr_res);
         ticket->t_curr_res = ticket->t_unit_res;
         xlog_tic_reset_res(ticket);
 
@@ -2749,9 +2750,8 @@ xlog_regrant_reserve_log_space(xlog_t	     *log,
                 return;
         }
 
-        xlog_grant_add_space(log, &log->l_grant_reserve_cycle,
-                                &log->l_grant_reserve_bytes,
-                                ticket->t_unit_res);
+        xlog_grant_add_space(log, &log->l_grant_reserve_head,
+                                        ticket->t_unit_res);
 
         trace_xfs_log_regrant_reserve_exit(log, ticket);
 
@@ -2799,10 +2799,8 @@ xlog_ungrant_log_space(xlog_t	     *log,
                 bytes += ticket->t_unit_res*ticket->t_cnt;
         }
 
-        xlog_grant_sub_space(log, &log->l_grant_reserve_cycle,
-                                &log->l_grant_reserve_bytes, bytes);
-        xlog_grant_sub_space(log, &log->l_grant_write_cycle,
-                                &log->l_grant_write_bytes, bytes);
+        xlog_grant_sub_space(log, &log->l_grant_reserve_head, bytes);
+        xlog_grant_sub_space(log, &log->l_grant_write_head, bytes);
 
         trace_xfs_log_ungrant_exit(log, ticket);
 
@@ -3430,22 +3428,31 @@ xlog_verify_dest_ptr(
 STATIC void
 xlog_verify_grant_head(xlog_t *log, int equals)
 {
-    if (log->l_grant_reserve_cycle == log->l_grant_write_cycle) {
-        if (equals)
-            ASSERT(log->l_grant_reserve_bytes >= log->l_grant_write_bytes);
-        else
-            ASSERT(log->l_grant_reserve_bytes > log->l_grant_write_bytes);
-    } else {
-        ASSERT(log->l_grant_reserve_cycle-1 == log->l_grant_write_cycle);
-        ASSERT(log->l_grant_write_bytes >= log->l_grant_reserve_bytes);
-    }
-}       /* xlog_verify_grant_head */
+        int     reserve_cycle, reserve_space;
+        int     write_cycle, write_space;
+
+        xlog_crack_grant_head(&log->l_grant_reserve_head,
+                                        &reserve_cycle, &reserve_space);
+        xlog_crack_grant_head(&log->l_grant_write_head,
+                                        &write_cycle, &write_space);
+
+        if (reserve_cycle == write_cycle) {
+                if (equals)
+                        ASSERT(reserve_space >= write_space);
+                else
+                        ASSERT(reserve_space > write_space);
+        } else {
+                ASSERT(reserve_cycle - 1 == write_cycle);
+                ASSERT(write_space >= reserve_space);
+        }
+}
 
 STATIC void
 xlog_verify_grant_tail(
         struct log      *log)
 {
         xfs_lsn_t       tail_lsn = log->l_tail_lsn;
+        int             cycle, space;
 
         /*
          * Check to make sure the grant write head didn't just over lap the
@@ -3453,9 +3460,10 @@ xlog_verify_grant_tail(
          * Otherwise, make sure that the cycles differ by exactly one and
          * check the byte count.
          */
-        if (CYCLE_LSN(tail_lsn) != log->l_grant_write_cycle) {
-                ASSERT(log->l_grant_write_cycle - 1 == CYCLE_LSN(tail_lsn));
-                ASSERT(log->l_grant_write_bytes <= BBTOB(BLOCK_LSN(tail_lsn)));
+        xlog_crack_grant_head(&log->l_grant_write_head, &cycle, &space);
+        if (CYCLE_LSN(tail_lsn) != cycle) {
+                ASSERT(cycle - 1 == CYCLE_LSN(tail_lsn));
+                ASSERT(space <= BBTOB(BLOCK_LSN(tail_lsn)));
         }
 }
 
diff --git a/fs/xfs/xfs_log_priv.h b/fs/xfs/xfs_log_priv.h
index a5b3c021a40..2f74c80a7a4 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);
diff --git a/fs/xfs/xfs_log_recover.c b/fs/xfs/xfs_log_recover.c
index 4abe7a9b380..1550404a8ae 100644
--- a/fs/xfs/xfs_log_recover.c
+++ b/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