pnfs: align layoutget requests on page boundaries

Signed-off-by: Benny Halevy <bhalevy@panasas.com>

fs/nfs/pnfs.c

@@ -850,6 +850,7 @@ pnfs_update_layout(struct inode *ino,
 		.offset = pos,
 		.length = count,
 	};
+	unsigned pg_offset;
 	struct nfs_inode *nfsi = NFS_I(ino);
 	struct nfs_client *clp = NFS_SERVER(ino)->nfs_client;
 	struct pnfs_layout_hdr *lo;
@@ -899,6 +900,13 @@ pnfs_update_layout(struct inode *ino,
 		spin_unlock(&clp->cl_lock);
 	}
 
+	pg_offset = arg.offset & ~PAGE_CACHE_MASK;
+	if (pg_offset) {
+		arg.offset -= pg_offset;
+		arg.length += pg_offset;
+	}
+	arg.length = PAGE_CACHE_ALIGN(arg.length);
+
 	lseg = send_layoutget(lo, ctx, &arg, gfp_flags);
 	if (!lseg && first) {
 		spin_lock(&clp->cl_lock);