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[PATCH 26/34] xfs: combine grant heads into a single 64 bit integer

To: xfs@xxxxxxxxxxx
Subject: [PATCH 26/34] xfs: combine grant heads into a single 64 bit integer
From: Dave Chinner <david@xxxxxxxxxxxxx>
Date: Tue, 21 Dec 2010 18:29:22 +1100
In-reply-to: <1292916570-25015-1-git-send-email-david@xxxxxxxxxxxxx>
References: <1292916570-25015-1-git-send-email-david@xxxxxxxxxxxxx>
From: Dave Chinner <dchinner@xxxxxxxxxx>

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@xxxxxxxxxx>
Reviewed-by: Christoph Hellwig <hch@xxxxxx>
---
 fs/xfs/linux-2.6/xfs_trace.h |   10 ++-
 fs/xfs/xfs_log.c             |  166 ++++++++++++++++++++++--------------------
 fs/xfs/xfs_log_priv.h        |   26 ++++++-
 fs/xfs/xfs_log_recover.c     |    8 +-
 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 69b9e1f..3ff6b35 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 9a4b9ed..6bba8b4 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 a5b3c02..2f74c80 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 4abe7a9..1550404 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
-- 
1.7.2.3

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