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Re: [Cluster-devel] Re: [GFS2] Don't flush everything on fdatasync [70/70]



Steven Whitehouse wrote:
Hi,

On Fri, 2006-12-01 at 11:09 -0800, Andrew Morton wrote:
I was taking my cue here from ext3 which does something similar. The
filemap_fdatawrite() is done by the VFS before this is called with a
filemap_fdatawait() afterwards. This was intended to flush the metadata
via (eventually) ->write_inode() although I guess I should be calling
write_inode_now() instead?
oh I see, you're jsut trying to write the inode itself, not the pages.

write_inode_now() will write the pages, which you seem to not want to do.
Whatever.  The APIs here are a bit awkward.

I've added a comment to explain whats going on here, and also the
following patch. I know it could be better, but its still an improvement
on what was there before,


Steve,

I'm in the middle of something else and don't have upstream kernel source handy at this moment. But I read akpm's comment as "write_inode_now" would do writepage and that is *not* what you want (?) (since vfs has done that before this call is invoked). I vaguely recalled I did try write_inode_now() on GFS1 once but had to replace it with "sync_inode" on RHEL4 (for the reason that I can't remember at this moment). I suggest you keep "sync_inode" (at least for a while until we can prove other call can do better). This "sync_inode" has been well tested out (with GFS1's fsync call).

There is another issue. It is a gray area. Note that you don't grab any glock here ... so if someone *has* written something in other nodes, this sync could miss it (?). This depends on how people expects a fsync/fdatasync should behave in a cluster filesystem. GFS1 asks for a shared lock here so it will force other node to flush the data (I personally think this is a more correct behavior). Your call though.

-- Wendy

--------------------------------------------------------------------------------------------

>From 34126f9f41901ca9d7d0031c2b11fc0d6c07b72d Mon Sep 17 00:00:00 2001
From: Steven Whitehouse <swhiteho redhat com>
Date: Thu, 7 Dec 2006 09:13:14 -0500
Subject: [PATCH] [GFS2] Change gfs2_fsync() to use write_inode_now()

This is a bit better than the previous version of gfs2_fsync()
although it would be better still if we were able to call a
function which only wrote the inode & metadata. Its no big deal
though that this will potentially write the data as well since
the VFS has already done that before calling gfs2_fsync(). I've
also added a comment to explain whats going on here.

Signed-off-by: Steven Whitehouse <swhiteho redhat com>
Cc: Andrew Morton <akpm osdl org>
---
 fs/gfs2/ops_file.c |   11 ++++++-----
 1 files changed, 6 insertions(+), 5 deletions(-)

diff --git a/fs/gfs2/ops_file.c b/fs/gfs2/ops_file.c
index 7bd971b..b3f1e03 100644
--- a/fs/gfs2/ops_file.c
+++ b/fs/gfs2/ops_file.c
@@ -510,6 +510,11 @@ static int gfs2_close(struct inode *inod
  * is set. For stuffed inodes we must flush the log in order to
  * ensure that all data is on disk.
  *
+ * The call to write_inode_now() is there to write back metadata and
+ * the inode itself. It does also try and write the data, but thats
+ * (hopefully) a no-op due to the VFS having already called filemap_fdatawrite()
+ * for us.
+ *
  * Returns: errno
  */
@@ -518,10 +523,6 @@ static int gfs2_fsync(struct file *file,
 	struct inode *inode = dentry->d_inode;
 	int sync_state = inode->i_state & (I_DIRTY_SYNC|I_DIRTY_DATASYNC);
 	int ret = 0;
-	struct writeback_control wbc = {
-		.sync_mode = WB_SYNC_ALL,
-		.nr_to_write = 0,
-	};
if (gfs2_is_jdata(GFS2_I(inode))) {
 		gfs2_log_flush(GFS2_SB(inode), GFS2_I(inode)->i_gl);
@@ -530,7 +531,7 @@ static int gfs2_fsync(struct file *file,
if (sync_state != 0) {
 		if (!datasync)
-			ret = sync_inode(inode, &wbc);
+			ret = write_inode_now(inode, 0);
if (gfs2_is_stuffed(GFS2_I(inode)))
 			gfs2_log_flush(GFS2_SB(inode), GFS2_I(inode)->i_gl);


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