[PATCH v3] NFS: Fix writeback performance issue on cache invalidation

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

If a cache invalidation is triggered, and we happen to have a lot of
writebacks cached at the time, then the call to invalidate_inode_pages2()
will end up calling ->launder_page() on each and every dirty page in order
to sync its contents to disk, thus defeating write coalescing.
The following patch ensures that we try to sync the inode to disk before
calling invalidate_inode_pages2() so that we do the writeback as efficiently
as possible.

Reported-by: William Dauchy <william@gandi.net>
Reported-by: Pascal Bouchareine <pascal@gandi.net>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
Tested-by: William Dauchy <william@gandi.net>
Reviewed-by: Jeff Layton <jlayton@redhat.com>
---
v2: Add check for regular file as per Jeff Layton's suggestion.
v3: Minor cleanup and add Jeff as a reviewer

 fs/nfs/inode.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/fs/nfs/inode.c b/fs/nfs/inode.c
index af6e806..3ea4f64 100644
--- a/fs/nfs/inode.c
+++ b/fs/nfs/inode.c
@@ -963,9 +963,15 @@ EXPORT_SYMBOL_GPL(nfs_revalidate_inode);
 static int nfs_invalidate_mapping(struct inode *inode, struct address_space *mapping)
 {
 	struct nfs_inode *nfsi = NFS_I(inode);
-	
+	int ret;
+
 	if (mapping->nrpages != 0) {
-		int ret = invalidate_inode_pages2(mapping);
+		if (S_ISREG(inode->i_mode)) {
+			ret = nfs_sync_mapping(mapping);
+			if (ret < 0)
+				return ret;
+		}
+		ret = invalidate_inode_pages2(mapping);
 		if (ret < 0)
 			return ret;
 	}
-- 
1.8.3.1