vfs: Remove unnecessary flushing of block devices

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>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

diff --git a/fs/sync.c b/fs/sync.c
index 0b166f26362d216c8f8c8bfefe175401c812d926..131ddae87a1d74a625fb1393ab862a14b05c29fa 100644 (file)
--- a/fs/sync.c
+++ b/fs/sync.c
@@ -85,14 +85,14 @@ static void sync_fs_one_sb(struct super_block *sb, void *arg)
                sb->s_op->sync_fs(sb, *(int *)arg);
 }
 
-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);
 }
 
 /*
@@ -106,10 +106,10 @@ 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;
@@ -125,10 +125,10 @@ static void do_sync_work(struct work_struct *work)
         */
        iterate_supers(sync_inodes_one_sb, &nowait);
        iterate_supers(sync_fs_one_sb, &nowait);
-       iterate_bdevs(flush_one_bdev, NULL);
+       iterate_bdevs(fdatawrite_one_bdev, NULL);
        iterate_supers(sync_inodes_one_sb, &nowait);
        iterate_supers(sync_fs_one_sb, &nowait);
-       iterate_bdevs(flush_one_bdev, NULL);
+       iterate_bdevs(fdatawrite_one_bdev, NULL);
        printk("Emergency Sync complete\n");
        kfree(work);
 }