GFS2: introduce AIL lock

The log lock is currently used to protect the AIL lists and
the movements of buffers into and out of them. The lists
are self contained and no log specific items outside the
lists are accessed when starting or emptying the AIL lists.

Hence the operation of the AIL does not require the protection
of the log lock so split them out into a new AIL specific lock
to reduce the amount of traffic on the log lock. This will
also reduce the amount of serialisation that occurs when
the gfs2_logd pushes on the AIL to move it forward.

This reduces the impact of log pushing on sequential write
throughput.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>

1 files changed, 1 insertions, 0 deletions

diff --git a/fs/gfs2/incore.h b/fs/gfs2/incore.h
index 59aaaa051136..870a89d6d4dc 100644
--- a/fs/gfs2/incore.h
+++ b/fs/gfs2/incore.h
@@ -651,6 +651,7 @@ struct gfs2_sbd {
 	unsigned int sd_log_flush_head;
 	u64 sd_log_flush_wrapped;
 
+	spinlock_t sd_ail_lock;
 	struct list_head sd_ail1_list;
 	struct list_head sd_ail2_list;
 	u64 sd_ail_sync_gen;