btrfs: remove unnecessary parameter delalloc_start for writepage_delalloc()

In function __extent_writepage() we always pass page start to
@delalloc_start for writepage_delalloc().

Thus we don't really need @delalloc_start parameter as we can extract it
from @page.

Remove @delalloc_start parameter and make __extent_writepage() to
declare @page_start and @page_end as const.
Signed-off-by: NQu Wenruo <wqu@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

fs/btrfs/extent_io.c

@@ -3768,10 +3768,11 @@ static void update_nr_written(struct writeback_control *wbc,
  */
 static noinline_for_stack int writepage_delalloc(struct btrfs_inode *inode,
 		struct page *page, struct writeback_control *wbc,
-		u64 delalloc_start, unsigned long *nr_written)
+		unsigned long *nr_written)
 {
-	u64 page_end = delalloc_start + PAGE_SIZE - 1;
+	u64 page_end = page_offset(page) + PAGE_SIZE - 1;
 	bool found;
+	u64 delalloc_start = page_offset(page);
 	u64 delalloc_to_write = 0;
 	u64 delalloc_end = 0;
 	int ret;
@@ -4049,8 +4050,8 @@ static int __extent_writepage(struct page *page, struct writeback_control *wbc,
 			      struct extent_page_data *epd)
 {
 	struct inode *inode = page->mapping->host;
-	u64 start = page_offset(page);
-	u64 page_end = start + PAGE_SIZE - 1;
+	const u64 page_start = page_offset(page);
+	const u64 page_end = page_start + PAGE_SIZE - 1;
 	int ret;
 	int nr = 0;
 	size_t pg_offset;
@@ -4085,8 +4086,7 @@ static int __extent_writepage(struct page *page, struct writeback_control *wbc,
 	}
 
 	if (!epd->extent_locked) {
-		ret = writepage_delalloc(BTRFS_I(inode), page, wbc, start,
-					 &nr_written);
+		ret = writepage_delalloc(BTRFS_I(inode), page, wbc, &nr_written);
 		if (ret == 1)
 			return 0;
 		if (ret)
@@ -4136,7 +4136,7 @@ static int __extent_writepage(struct page *page, struct writeback_control *wbc,
 	 * capable of that.
 	 */
 	if (PageError(page))
-		end_extent_writepage(page, ret, start, page_end);
+		end_extent_writepage(page, ret, page_start, page_end);
 	unlock_page(page);
 	ASSERT(ret <= 0);
 	return ret;