[PATCH 04/12] NFS: Reduce the number of unnecessary COMMIT calls

[Trond Myklebust <Trond.Myklebust@netapp.com>]

If the caller is doing a non-blocking flush, and there are still writebacks
pending on the wire, we can usually defer the COMMIT call until those
writes are done.

Also ensure that we honour the wbc->nonblocking flag.

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
---

 fs/nfs/write.c |   17 ++++++++++++++---
 1 files changed, 14 insertions(+), 3 deletions(-)

diff --git a/fs/nfs/write.c b/fs/nfs/write.c
index e2e7464..0bc1d5b 100644
--- a/fs/nfs/write.c
+++ b/fs/nfs/write.c
@@ -1409,12 +1409,23 @@ static int nfs_commit_inode(struct inode *inode, int how)
 
 static int nfs_commit_unstable_pages(struct inode *inode, struct writeback_control *wbc)
 {
-	int ret;
+	int flags = FLUSH_SYNC;
+	int ret = 0;
 
-	ret = nfs_commit_inode(inode,
-			wbc->sync_mode == WB_SYNC_ALL ? FLUSH_SYNC : 0);
+	/* Don't commit yet if this is a non-blocking flush and there are
+	 * outstanding writes for this mapping.
+	 */
+	if (wbc->sync_mode != WB_SYNC_ALL &&
+	    radix_tree_tagged(&NFS_I(inode)->nfs_page_tree,
+		    NFS_PAGE_TAG_LOCKED))
+		goto out_mark_dirty;
+
+	if (wbc->nonblocking)
+		flags = 0;
+	ret = nfs_commit_inode(inode, flags);
 	if (ret >= 0)
 		return 0;
+out_mark_dirty:
 	__mark_inode_dirty(inode, I_DIRTY_DATASYNC);
 	return ret;
 }