NFS: Optimize allocation of nfs_read/write_data structures

Clean up use of page_array, and fix an off-by-one error noticed by Tom
Talpey which causes kmalloc calls in cases where using the page_array
is sufficient.

Test plan:
Normal client functional testing with r/wsize=32768.
Signed-off-by: Chuck Lever <cel@netapp.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

fs/nfs/read.c

@@ -51,14 +51,11 @@ struct nfs_read_data *nfs_readdata_alloc(unsigned int pagecount)
 	if (p) {
 		memset(p, 0, sizeof(*p));
 		INIT_LIST_HEAD(&p->pages);
-		if (pagecount < NFS_PAGEVEC_SIZE)
-			p->pagevec = &p->page_array[0];
+		if (pagecount <= ARRAY_SIZE(p->page_array))
+			p->pagevec = p->page_array;
 		else {
-			size_t size = ++pagecount * sizeof(struct page *);
-			p->pagevec = kmalloc(size, GFP_NOFS);
-			if (p->pagevec) {
-				memset(p->pagevec, 0, size);
-			} else {
+			p->pagevec = kcalloc(pagecount, sizeof(struct page *), GFP_NOFS);
+			if (!p->pagevec) {
 				mempool_free(p, nfs_rdata_mempool);
 				p = NULL;
 			}

fs/nfs/write.c

@@ -98,11 +98,10 @@ struct nfs_write_data *nfs_commit_alloc(unsigned int pagecount)
 	if (p) {
 		memset(p, 0, sizeof(*p));
 		INIT_LIST_HEAD(&p->pages);
-		if (pagecount < NFS_PAGEVEC_SIZE)
-			p->pagevec = &p->page_array[0];
+		if (pagecount <= ARRAY_SIZE(p->page_array))
+			p->pagevec = p->page_array;
 		else {
-			size_t size = ++pagecount * sizeof(struct page *);
-			p->pagevec = kzalloc(size, GFP_NOFS);
+			p->pagevec = kcalloc(pagecount, sizeof(struct page *), GFP_NOFS);
 			if (!p->pagevec) {
 				mempool_free(p, nfs_commit_mempool);
 				p = NULL;
@@ -126,14 +125,11 @@ struct nfs_write_data *nfs_writedata_alloc(unsigned int pagecount)
 	if (p) {
 		memset(p, 0, sizeof(*p));
 		INIT_LIST_HEAD(&p->pages);
-		if (pagecount < NFS_PAGEVEC_SIZE)
-			p->pagevec = &p->page_array[0];
+		if (pagecount <= ARRAY_SIZE(p->page_array))
+			p->pagevec = p->page_array;
 		else {
-			size_t size = ++pagecount * sizeof(struct page *);
-			p->pagevec = kmalloc(size, GFP_NOFS);
-			if (p->pagevec) {
-				memset(p->pagevec, 0, size);
-			} else {
+			p->pagevec = kcalloc(pagecount, sizeof(struct page *), GFP_NOFS);
+			if (!p->pagevec) {
 				mempool_free(p, nfs_wdata_mempool);
 				p = NULL;
 			}

include/linux/nfs_xdr.h

@@ -694,7 +694,7 @@ struct nfs_read_data {
 #ifdef CONFIG_NFS_V4
 	unsigned long		timestamp;	/* For lease renewal */
 #endif
-	struct page		*page_array[NFS_PAGEVEC_SIZE + 1];
+	struct page		*page_array[NFS_PAGEVEC_SIZE];
 };
 
 struct nfs_write_data {
@@ -712,7 +712,7 @@ struct nfs_write_data {
 #ifdef CONFIG_NFS_V4
 	unsigned long		timestamp;	/* For lease renewal */
 #endif
-	struct page		*page_array[NFS_PAGEVEC_SIZE + 1];
+	struct page		*page_array[NFS_PAGEVEC_SIZE];
 };
 
 struct nfs_access_entry;