mm: use pagevec_lookup_range_tag() in __filemap_fdatawait_range()

Use pagevec_lookup_range_tag() in __filemap_fdatawait_range() as it is
interested only in pages from given range.  Remove unnecessary code
resulting from this.

Link: http://lkml.kernel.org/r/20171009151359.31984-11-jack@suse.cz
Signed-off-by: Jan Kara <jack@suse.cz>
Reviewed-by: Daniel Jordan <daniel.m.jordan@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/filemap.c

@@ -420,19 +420,17 @@ static void __filemap_fdatawait_range(struct address_space *mapping,
 		return;
 
 	pagevec_init(&pvec, 0);
-	while ((index <= end) &&
-			(nr_pages = pagevec_lookup_tag(&pvec, mapping, &index,
-			PAGECACHE_TAG_WRITEBACK,
-			min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1)) != 0) {
+	while (index <= end) {
 		unsigned i;
 
+		nr_pages = pagevec_lookup_range_tag(&pvec, mapping, &index,
+				end, PAGECACHE_TAG_WRITEBACK, PAGEVEC_SIZE);
+		if (!nr_pages)
+			break;
+
 		for (i = 0; i < nr_pages; i++) {
 			struct page *page = pvec.pages[i];
 
-			/* until radix tree lookup accepts end_index */
-			if (page->index > end)
-				continue;
-
 			wait_on_page_writeback(page);
 			ClearPageError(page);
 		}