linux-ext4 - [PATCH] ext4: remove filemap_fdatawrite() when synchronizing a data journaled file

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Date:	Tue, 28 Jul 2015 02:17:27 +0000 (GMT)
From:	Daeho Jeong <daeho.jeong@...sung.com>
To:	"tytso@....edu" <tytso@....edu>, linux-ext4@...r.kernel.org,
	daehojng@...il.com
Subject: [PATCH] ext4: remove filemap_fdatawrite() when synchronizing a data
 journaled file

When fsync() system call is executed, all data of the file should be written on the storage.
But, in a case of that the file is operated in data journal mode, the data doesn't need to be
flushed out and waited for its I/O completion. Moreover, by invoking filemap_fdatawrite()
function on the data journaled file, ext4_sync_file() suffers from an unnecessary delay
which is caused by flushing out and waiting for the I/O completion of a ton of newly-dirtied
pages which were dirtied by the previous commit.

Signed-off-by: Daeho Jeong <daeho.jeong@...sung.com>
---
 fs/ext4/fsync.c |   11 +++++------
 1 file changed, 5 insertions(+), 6 deletions(-)
diff --git a/fs/ext4/fsync.c b/fs/ext4/fsync.c
index 8850254..e0fabf7 100644
--- a/fs/ext4/fsync.c
+++ b/fs/ext4/fsync.c
@@ -112,9 +112,6 @@ int ext4_sync_file(struct file *file, loff_t start, loff_t end, int datasync)
   goto out;
  }
 
- ret = filemap_write_and_wait_range(inode->i_mapping, start, end);
- if (ret)
-  return ret;
  /*
   * data=writeback,ordered:
   *  The caller's filemap_fdatawrite()/wait will sync the data.
@@ -125,13 +122,15 @@ int ext4_sync_file(struct file *file, loff_t start, loff_t end, int datasync)
   *  filemap_fdatawrite won't do anything (the buffers are clean).
   *  ext4_force_commit will write the file data into the journal and
   *  will wait on that.
-  *  filemap_fdatawait() will encounter a ton of newly-dirtied pages
-  *  (they were dirtied by commit).  But that's OK - the blocks are
-  *  safe in-journal, which is all fsync() needs to ensure.
   */
  if (ext4_should_journal_data(inode)) {
   ret = ext4_force_commit(inode->i_sb);
   goto out;
+ } else {
+  ret = filemap_write_and_wait_range(inode->i_mapping,
+         start, end);
+  if (ret)
+   return ret;
  }
 
  commit_tid = datasync ? ei->i_datasync_tid : ei->i_sync_tid;
-- 
1.7.9.5