NFS: Reduce the number of unnecessary COMMIT calls

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>

diff --git a/fs/nfs/write.c b/fs/nfs/write.c
index dc08a6f..fc05e35 100644 (file)
--- a/fs/nfs/write.c
+++ b/fs/nfs/write.c
@@ -1415,12 +1415,30 @@ 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;
+       struct nfs_inode *nfsi = NFS_I(inode);
+       int flags = FLUSH_SYNC;
+       int ret = 0;
 
-       ret = nfs_commit_inode(inode,
-                       wbc->sync_mode == WB_SYNC_ALL ? FLUSH_SYNC : 0);
-       if (ret >= 0)
+       /* Don't commit yet if this is a non-blocking flush and there are
+        * lots of outstanding writes for this mapping.
+        */
+       if (wbc->sync_mode == WB_SYNC_NONE &&
+           nfsi->ncommit <= (nfsi->npages >> 1))
+               goto out_mark_dirty;
+
+       if (wbc->nonblocking)
+               flags = 0;
+       ret = nfs_commit_inode(inode, flags);
+       if (ret >= 0) {
+               if (wbc->sync_mode == WB_SYNC_NONE) {
+                       if (ret < wbc->nr_to_write)
+                               wbc->nr_to_write -= ret;
+                       else
+                               wbc->nr_to_write = 0;
+               }
                return 0;
+       }
+out_mark_dirty:
        __mark_inode_dirty(inode, I_DIRTY_DATASYNC);
        return ret;
 }