[PATCH 7/8] vfs: Remove unnecessary flushing of block devices

[Jan Kara <jack@suse.cz>]

It is not necessary to write block devices twice. The reason why we first did
flush and then proper sync is that
  for_each_bdev() {
    write_bdev()
    wait_for_completion()
  }
is much slower than
  for_each_bdev()
    write_bdev()
  for_each_bdev()
    wait_for_completion()
when there is bigger amount of data. But as is seen in the above, there's no real
need to scan pages and submit them twice. We just need to separate the submission
and waiting part. This patch does that.

Signed-off-by: Jan Kara <jack@suse.cz>
---
 fs/sync.c |   12 ++++++------
 1 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/fs/sync.c b/fs/sync.c
index ccaaa1b..d8b9dd1 100644
--- a/fs/sync.c
+++ b/fs/sync.c
@@ -126,14 +126,14 @@ static void sync_all_bdevs(int wait)
 	iput(old_inode);
 }
 
-static void flush_one_bdev(struct block_device *bdev, void *arg)
+static void fdatawrite_one_bdev(struct block_device *bdev, void *arg)
 {
-	__sync_blockdev(bdev, 0);
+	filemap_fdatawrite(bdev->bd_inode->i_mapping);
 }
 
-static void sync_one_bdev(struct block_device *bdev, void *arg)
+static void fdatawait_one_bdev(struct block_device *bdev, void *arg)
 {
-	sync_blockdev(bdev);
+	filemap_fdatawait(bdev->bd_inode->i_mapping);
 }
 
 /*
@@ -147,10 +147,10 @@ SYSCALL_DEFINE0(sync)
 	wakeup_flusher_threads(0, WB_REASON_SYNC);
 	iterate_supers(writeback_inodes_one_sb, NULL);
 	iterate_supers(sync_fs_one_sb, &nowait);
-	iterate_bdevs(flush_one_bdev, NULL);
 	iterate_supers(sync_inodes_one_sb, NULL);
 	iterate_supers(sync_fs_one_sb, &wait);
-	iterate_bdevs(sync_one_bdev, NULL);
+	iterate_bdevs(fdatawrite_one_bdev, NULL);
+	iterate_bdevs(fdatawait_one_bdev, NULL);
 	if (unlikely(laptop_mode))
 		laptop_sync_completion();
 	return 0;
-- 
1.7.1