NFS: Reduce number of RPC calls when doing uncached readdir

If we're doing uncached readdir, allocate multiple pages in order to
try to avoid duplicate RPC calls for the same getdents() call.
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
Reviewed-by: Benjamin Coddington <bcodding@redhat.com>
Tested-by: Benjamin Coddington <bcodding@redhat.com>
Tested-by: Dave Wysochanski <dwysocha@redhat.com>

fs/nfs/dir.c

@@ -199,6 +199,23 @@ void nfs_readdir_clear_array(struct page *page)
 	kunmap_atomic(array);
 }
 
+static struct page *
+nfs_readdir_page_array_alloc(u64 last_cookie, gfp_t gfp_flags)
+{
+	struct page *page = alloc_page(gfp_flags);
+	if (page)
+		nfs_readdir_page_init_array(page, last_cookie);
+	return page;
+}
+
+static void nfs_readdir_page_array_free(struct page *page)
+{
+	if (page) {
+		nfs_readdir_clear_array(page);
+		put_page(page);
+	}
+}
+
 static void nfs_readdir_array_set_eof(struct nfs_cache_array *array)
 {
 	array->page_is_eof = 1;
@@ -694,12 +711,14 @@ void nfs_prime_dcache(struct dentry *parent, struct nfs_entry *entry,
 static int nfs_readdir_page_filler(struct nfs_readdir_descriptor *desc,
 				   struct nfs_entry *entry,
 				   struct page **xdr_pages,
-				   struct page *fillme, unsigned int buflen)
+				   unsigned int buflen,
+				   struct page **arrays,
+				   size_t narrays)
 {
 	struct address_space *mapping = desc->file->f_mapping;
 	struct xdr_stream stream;
 	struct xdr_buf buf;
-	struct page *scratch, *new, *page = fillme;
+	struct page *scratch, *new, *page = *arrays;
 	int status;
 
 	scratch = alloc_page(GFP_KERNEL);
@@ -725,15 +744,25 @@ static int nfs_readdir_page_filler(struct nfs_readdir_descriptor *desc,
 		if (status != -ENOSPC)
 			continue;
 
-		if (page->mapping != mapping)
-			break;
-		new = nfs_readdir_page_get_next(mapping, page->index + 1,
-						entry->prev_cookie);
-		if (!new)
-			break;
-		if (page != fillme)
-			nfs_readdir_page_unlock_and_put(page);
-		page = new;
+		if (page->mapping != mapping) {
+			if (!--narrays)
+				break;
+			new = nfs_readdir_page_array_alloc(entry->prev_cookie,
+							   GFP_KERNEL);
+			if (!new)
+				break;
+			arrays++;
+			*arrays = page = new;
+		} else {
+			new = nfs_readdir_page_get_next(mapping,
+							page->index + 1,
+							entry->prev_cookie);
+			if (!new)
+				break;
+			if (page != *arrays)
+				nfs_readdir_page_unlock_and_put(page);
+			page = new;
+		}
 		status = nfs_readdir_add_to_array(entry, page);
 	} while (!status && !entry->eof);
 
@@ -750,7 +779,7 @@ static int nfs_readdir_page_filler(struct nfs_readdir_descriptor *desc,
 		break;
 	}
 
-	if (page != fillme)
+	if (page != *arrays)
 		nfs_readdir_page_unlock_and_put(page);
 
 	put_page(scratch);
@@ -790,10 +819,11 @@ static struct page **nfs_readdir_alloc_pages(size_t npages)
 }
 
 static int nfs_readdir_xdr_to_array(struct nfs_readdir_descriptor *desc,
-				    struct page *page, __be32 *verf_arg,
-				    __be32 *verf_res)
+				    __be32 *verf_arg, __be32 *verf_res,
+				    struct page **arrays, size_t narrays)
 {
 	struct page **pages;
+	struct page *page = *arrays;
 	struct nfs_entry *entry;
 	size_t array_size;
 	struct inode *inode = file_inode(desc->file);
@@ -835,7 +865,8 @@ static int nfs_readdir_xdr_to_array(struct nfs_readdir_descriptor *desc,
 			break;
 		}
 
-		status = nfs_readdir_page_filler(desc, entry, pages, page, pglen);
+		status = nfs_readdir_page_filler(desc, entry, pages, pglen,
+						 arrays, narrays);
 	} while (!status && nfs_readdir_page_needs_filling(page));
 
 	nfs_readdir_free_pages(pages, array_size);
@@ -884,8 +915,8 @@ static int find_and_lock_cache_page(struct nfs_readdir_descriptor *desc)
 	if (!desc->page)
 		return -ENOMEM;
 	if (nfs_readdir_page_needs_filling(desc->page)) {
-		res = nfs_readdir_xdr_to_array(desc, desc->page,
-					       nfsi->cookieverf, verf);
+		res = nfs_readdir_xdr_to_array(desc, nfsi->cookieverf, verf,
+					       &desc->page, 1);
 		if (res < 0) {
 			nfs_readdir_page_unlock_and_put_cached(desc);
 			if (res == -EBADCOOKIE || res == -ENOTSYNC) {
@@ -976,37 +1007,39 @@ static void nfs_do_filldir(struct nfs_readdir_descriptor *desc)
  */
 static int uncached_readdir(struct nfs_readdir_descriptor *desc)
 {
-	struct page	*page = NULL;
+	struct page	**arrays;
+	size_t		i, sz = 512;
 	__be32		verf[NFS_DIR_VERIFIER_SIZE];
-	int		status;
+	int		status = -ENOMEM;
 
-	dfprintk(DIRCACHE, "NFS: uncached_readdir() searching for cookie %Lu\n",
+	dfprintk(DIRCACHE, "NFS: uncached_readdir() searching for cookie %llu\n",
 			(unsigned long long)desc->dir_cookie);
 
-	page = alloc_page(GFP_HIGHUSER);
-	if (!page) {
-		status = -ENOMEM;
+	arrays = kcalloc(sz, sizeof(*arrays), GFP_KERNEL);
+	if (!arrays)
+		goto out;
+	arrays[0] = nfs_readdir_page_array_alloc(desc->dir_cookie, GFP_KERNEL);
+	if (!arrays[0])
 		goto out;
-	}
 
 	desc->page_index = 0;
 	desc->last_cookie = desc->dir_cookie;
-	desc->page = page;
 	desc->duped = 0;
 
-	nfs_readdir_page_init_array(page, desc->dir_cookie);
-	status = nfs_readdir_xdr_to_array(desc, page, desc->verf, verf);
-	if (status < 0)
-		goto out_release;
+	status = nfs_readdir_xdr_to_array(desc, desc->verf, verf, arrays, sz);
 
-	nfs_do_filldir(desc);
+	for (i = 0; !desc->eof && i < sz && arrays[i]; i++) {
+		desc->page = arrays[i];
+		nfs_do_filldir(desc);
+	}
+	desc->page = NULL;
 
- out_release:
-	nfs_readdir_clear_array(desc->page);
-	nfs_readdir_page_put(desc);
- out:
-	dfprintk(DIRCACHE, "NFS: %s: returns %d\n",
-			__func__, status);
+
+	for (i = 0; i < sz && arrays[i]; i++)
+		nfs_readdir_page_array_free(arrays[i]);
+out:
+	kfree(arrays);
+	dfprintk(DIRCACHE, "NFS: %s: returns %d\n", __func__, status);
 	return status;
 }