ceph: kill ceph alloc_page_vec()

There is a helper function alloc_page_vec() that, despite its
generic sounding name depends heavily on an osd request structure
being populated with certain information.

There is only one place this function is used, and it ends up
being a bit simpler to just open code what it does, so get
rid of the helper.

The real motivation for this is deferring building the of the osd
request message, and this is a step in that direction.
Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>

fs/ceph/addr.c

@@ -631,29 +631,6 @@ static void writepages_finish(struct ceph_osd_request *req,
 	ceph_osdc_put_request(req);
 }
 
-/*
- * allocate a page vec, either directly, or if necessary, via a the
- * mempool.  we avoid the mempool if we can because req->r_data_out.length
- * may be less than the maximum write size.
- */
-static void alloc_page_vec(struct ceph_fs_client *fsc,
-			   struct ceph_osd_request *req)
-{
-	size_t size;
-	int num_pages;
-
-	num_pages = calc_pages_for((u64)req->r_data_out.alignment,
-					(u64)req->r_data_out.length);
-	size = sizeof (struct page *) * num_pages;
-	req->r_data_out.pages = kmalloc(size, GFP_NOFS);
-	if (!req->r_data_out.pages) {
-		req->r_data_out.pages = mempool_alloc(fsc->wb_pagevec_pool,
-							GFP_NOFS);
-		req->r_data_out.pages_from_pool = 1;
-		WARN_ON(!req->r_data_out.pages);
-	}
-}
-
 static struct ceph_osd_request *
 ceph_writepages_osd_request(struct inode *inode, u64 offset, u64 *len,
 				struct ceph_snap_context *snapc,
@@ -851,6 +828,9 @@ static int ceph_writepages_start(struct address_space *mapping,
 			if (locked_pages == 0) {
 				struct ceph_vino vino;
 				int num_ops = do_sync ? 2 : 1;
+				size_t size;
+				struct page **pages;
+				mempool_t *pool = NULL;
 
 				/* prepare async write request */
 				offset = (u64) page_offset(page);
@@ -870,13 +850,24 @@ static int ceph_writepages_start(struct address_space *mapping,
 					num_ops, ops, snapc, vino.snap,
 					&inode->i_mtime);
 
+				req->r_callback = writepages_finish;
+				req->r_inode = inode;
+
+				max_pages = calc_pages_for(0, (u64)len);
+				size = max_pages * sizeof (*pages);
+				pages = kmalloc(size, GFP_NOFS);
+				if (!pages) {
+					pool = fsc->wb_pagevec_pool;
+
+					pages = mempool_alloc(pool, GFP_NOFS);
+					WARN_ON(!pages);
+				}
+
+				req->r_data_out.pages = pages;
+				req->r_data_out.pages_from_pool = !!pool;
 				req->r_data_out.type = CEPH_OSD_DATA_TYPE_PAGES;
 				req->r_data_out.length = len;
 				req->r_data_out.alignment = 0;
-				max_pages = calc_pages_for(0, (u64)len);
-				alloc_page_vec(fsc, req);
-				req->r_callback = writepages_finish;
-				req->r_inode = inode;
 			}
 
 			/* note position of first page in pvec */