xfs: convert l_last_sync_lsn to an atomic variable

log->l_last_sync_lsn is updated in only one critical spot - log
buffer Io completion - and is protected by the grant lock here. This
requires the grant lock to be taken for every log buffer IO
completion. Converting the l_last_sync_lsn variable to an atomic64_t
means that we do not need to take the grant lock in log buffer IO
completion to update it.

This also removes the need for explicitly holding a spinlock to read
the l_last_sync_lsn on 32 bit platforms.

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

1 files changed, 3 insertions, 3 deletions

diff --git a/fs/xfs/xfs_log_recover.c b/fs/xfs/xfs_log_recover.c
index 1550404a8aeb..18e1e18d7147 100644
--- a/fs/xfs/xfs_log_recover.c
+++ b/fs/xfs/xfs_log_recover.c
@@ -937,7 +937,7 @@ xlog_find_tail(
         if (found == 2)
                 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);
+        atomic64_set(&log->l_last_sync_lsn, be64_to_cpu(rhead->h_lsn));
         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,
@@ -989,9 +989,9 @@ xlog_find_tail(
                         log->l_tail_lsn =
                                 xlog_assign_lsn(log->l_curr_cycle,
                                                 after_umount_blk);
-                        log->l_last_sync_lsn =
+                        atomic64_set(&log->l_last_sync_lsn,
                                 xlog_assign_lsn(log->l_curr_cycle,
-                                                after_umount_blk);
+                                                after_umount_blk));
                         *tail_blk = after_umount_blk;
 
                         /*