xfs: introduce new locks for the log grant ticket wait queues

The log grant ticket wait queues are currently protected by the log
grant lock.  However, the queues are functionally independent from
each other, and operations on them only require serialisation
against other queue operations now that all of the other log
variables they use are atomic values.

Hence, we can make them independent of the grant lock by introducing
new locks just to protect the lists operations. because the lists
are independent, we can use a lock per list and ensure that reserve
and write head queuing do not contend.

To ensure forced shutdowns work correctly in conjunction with the
new fast paths, ensure that we check whether the log has been shut
down in the grant functions once we hold the relevant spin locks but
before we go to sleep. This is needed to co-ordinate correctly with
the wakeups that are issued on the ticket queues so we don't leave
any processes sleeping on the queues during a shutdown.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>

1 files changed, 12 insertions, 4 deletions

diff --git a/fs/xfs/xfs_log_priv.h b/fs/xfs/xfs_log_priv.h
index 7619d6a02388..befb2fc5b027 100644
--- a/fs/xfs/xfs_log_priv.h
+++ b/fs/xfs/xfs_log_priv.h
@@ -512,10 +512,6 @@ typedef struct log {
 
         /* The following block of fields are changed while holding grant_lock */
         spinlock_t              l_grant_lock ____cacheline_aligned_in_smp;
-        struct list_head        l_reserveq;
-        struct list_head        l_writeq;
-        atomic64_t                      l_grant_reserve_head;
-        atomic64_t                      l_grant_write_head;
 
         /*
          * l_last_sync_lsn and l_tail_lsn are atomics so they can be set and
@@ -528,6 +524,18 @@ typedef struct log {
         /* lsn of 1st LR with unflushed * buffers */
         atomic64_t              l_tail_lsn ____cacheline_aligned_in_smp;
 
+        /*
+         * ticket grant locks, queues and accounting have their own cachlines
+         * as these are quite hot and can be operated on concurrently.
+         */
+        spinlock_t              l_grant_reserve_lock ____cacheline_aligned_in_smp;
+        struct list_head        l_reserveq;
+        atomic64_t              l_grant_reserve_head;
+
+        spinlock_t              l_grant_write_lock ____cacheline_aligned_in_smp;
+        struct list_head        l_writeq;
+        atomic64_t              l_grant_write_head;
+
         /* The following field are used for debugging; need to hold icloglock */
 #ifdef DEBUG
         char                    *l_iclog_bak[XLOG_MAX_ICLOGS];