nfs: use GFP_NOFS preloads for radix-tree insertion

NFS should use GFP_NOFS mode radix tree preloads rather than GFP_ATOMIC
allocations at radix-tree insertion-time.  This is important to reduce the
atomic memory requirement.
Signed-off-by: Nick Piggin <npiggin@suse.de>
Cc: Trond Myklebust <trond.myklebust@fys.uio.no>
Cc: "J. Bruce Fields" <bfields@fieldses.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

fs/nfs/write.c

@@ -360,15 +360,13 @@ int nfs_writepages(struct address_space *mapping, struct writeback_control *wbc)
 /*
  * Insert a write request into an inode
  */
-static int nfs_inode_add_request(struct inode *inode, struct nfs_page *req)
+static void nfs_inode_add_request(struct inode *inode, struct nfs_page *req)
 {
 	struct nfs_inode *nfsi = NFS_I(inode);
 	int error;
 
 	error = radix_tree_insert(&nfsi->nfs_page_tree, req->wb_index, req);
-	BUG_ON(error == -EEXIST);
-	if (error)
-		return error;
+	BUG_ON(error);
 	if (!nfsi->npages) {
 		igrab(inode);
 		if (nfs_have_delegation(inode, FMODE_WRITE))
@@ -378,8 +376,8 @@ static int nfs_inode_add_request(struct inode *inode, struct nfs_page *req)
 	set_page_private(req->wb_page, (unsigned long)req);
 	nfsi->npages++;
 	kref_get(&req->wb_kref);
-	radix_tree_tag_set(&nfsi->nfs_page_tree, req->wb_index, NFS_PAGE_TAG_LOCKED);
-	return 0;
+	radix_tree_tag_set(&nfsi->nfs_page_tree, req->wb_index,
+				NFS_PAGE_TAG_LOCKED);
 }
 
 /*
@@ -591,6 +589,13 @@ static struct nfs_page * nfs_update_request(struct nfs_open_context* ctx,
 		/* Loop over all inode entries and see if we find
 		 * A request for the page we wish to update
 		 */
+		if (new) {
+			if (radix_tree_preload(GFP_NOFS)) {
+				nfs_release_request(new);
+				return ERR_PTR(-ENOMEM);
+			}
+		}
+
 		spin_lock(&inode->i_lock);
 		req = nfs_page_find_request_locked(page);
 		if (req) {
@@ -601,28 +606,27 @@ static struct nfs_page * nfs_update_request(struct nfs_open_context* ctx,
 				error = nfs_wait_on_request(req);
 				nfs_release_request(req);
 				if (error < 0) {
-					if (new)
+					if (new) {
+						radix_tree_preload_end();
 						nfs_release_request(new);
+					}
 					return ERR_PTR(error);
 				}
 				continue;
 			}
 			spin_unlock(&inode->i_lock);
-			if (new)
+			if (new) {
+				radix_tree_preload_end();
 				nfs_release_request(new);
+			}
 			break;
 		}
 
 		if (new) {
-			int error;
 			nfs_lock_request_dontget(new);
-			error = nfs_inode_add_request(inode, new);
-			if (error) {
-				spin_unlock(&inode->i_lock);
-				nfs_unlock_request(new);
-				return ERR_PTR(error);
-			}
+			nfs_inode_add_request(inode, new);
 			spin_unlock(&inode->i_lock);
+			radix_tree_preload_end();
 			req = new;
 			goto zero_page;
 		}