[PATCH v4 20/21] NFS: Reduce number of RPC calls when doing uncached readdir

[trondmy@kernel.org]

From: Trond Myklebust <trond.myklebust@hammerspace.com>

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>
---
 fs/nfs/dir.c | 79 ++++++++++++++++++++++++++++++----------------------
 1 file changed, 46 insertions(+), 33 deletions(-)

diff --git a/fs/nfs/dir.c b/fs/nfs/dir.c
index b6c3501e8f61..238872d116f7 100644
--- a/fs/nfs/dir.c
+++ b/fs/nfs/dir.c
@@ -694,12 +694,14 @@ 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 +727,22 @@ 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 (narrays > 1) {
+			narrays--;
+			arrays++;
+			page = *arrays;
+		} else {
+			if (page->mapping != mapping)
+				break;
+			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 +759,7 @@ 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 +799,11 @@ 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 +845,8 @@ 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 +895,8 @@ 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) {
@@ -976,35 +987,37 @@ 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 = 16;
 	__be32		verf[NFS_DIR_VERIFIER_SIZE];
 	int		status;
 
 	dfprintk(DIRCACHE, "NFS: uncached_readdir() searching for cookie %Lu\n",
 			(unsigned long long)desc->dir_cookie);
 
-	page = alloc_page(GFP_HIGHUSER);
-	if (!page) {
-		status = -ENOMEM;
-		goto out;
-	}
+	arrays = nfs_readdir_alloc_pages(sz);
+	if (!arrays)
+		return -ENOMEM;
+	for (i = 0; i < sz; i++)
+		nfs_readdir_page_init_array(arrays[i], desc->dir_cookie);
 
 	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; i++) {
+		desc->page = arrays[i];
+		nfs_do_filldir(desc);
+	}
+	desc->page = NULL;
+
+
+	for (i = 0; i < sz; i++)
+		nfs_readdir_clear_array(arrays[i]);
+	nfs_readdir_free_pages(arrays, sz);
 
- out_release:
-	nfs_readdir_clear_array(desc->page);
-	nfs_readdir_page_put(desc);
- out:
 	dfprintk(DIRCACHE, "NFS: %s: returns %d\n",
 			__func__, status);
 	return status;
-- 
2.28.0