nilfs2: do not update log cursor for small change

Super blocks of nilfs are periodically overwritten in order to record
the recent log position.  This shortens recovery time after unclean
unmount, but the current implementation performs the update even for a
few blocks of change.  If the filesystem gets small changes slowly and
continually, super blocks may be updated excessively.

This moderates the issue by skipping update of log cursor if it does
not cross a segment boundary.

Signed-off-by: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>

1 files changed, 11 insertions, 0 deletions

diff --git a/fs/nilfs2/the_nilfs.c b/fs/nilfs2/the_nilfs.c
index 88c8976..f2efc8c 100644
--- a/fs/nilfs2/the_nilfs.c
+++ b/fs/nilfs2/the_nilfs.c
@@ -47,6 +47,16 @@ void nilfs_set_last_segment(struct the_nilfs *nilfs,
 	nilfs->ns_last_pseg = start_blocknr;
 	nilfs->ns_last_seq = seq;
 	nilfs->ns_last_cno = cno;
+
+	if (!nilfs_sb_dirty(nilfs)) {
+		if (nilfs->ns_prev_seq == nilfs->ns_last_seq)
+			goto stay_cursor;
+
+		set_nilfs_sb_dirty(nilfs);
+	}
+	nilfs->ns_prev_seq = nilfs->ns_last_seq;
+
+ stay_cursor:
 	spin_unlock(&nilfs->ns_last_segment_lock);
 }
 
@@ -267,6 +277,7 @@ static int nilfs_store_log_cursor(struct the_nilfs *nilfs,
 	nilfs->ns_last_cno = le64_to_cpu(sbp->s_last_cno);
 	nilfs->ns_last_seq = le64_to_cpu(sbp->s_last_seq);
 
+	nilfs->ns_prev_seq = nilfs->ns_last_seq;
 	nilfs->ns_seg_seq = nilfs->ns_last_seq;
 	nilfs->ns_segnum =
 		nilfs_get_segnum_of_block(nilfs, nilfs->ns_last_pseg);