ext4: use pagevec_lookup_range_tag()

We want only pages from given range in ext4_writepages().  Use
pagevec_lookup_range_tag() instead of pagevec_lookup_tag() and remove
unnecessary code.

Link: http://lkml.kernel.org/r/20171009151359.31984-5-jack@suse.cz
Signed-off-by: Jan Kara <jack@suse.cz>
Reviewed-by: Daniel Jordan <daniel.m.jordan@oracle.com>
Cc: "Theodore Ts'o" <tytso@mit.edu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/ext4/inode.c

@@ -2620,24 +2620,14 @@ static int mpage_prepare_extent_to_map(struct mpage_da_data *mpd)
 	mpd->map.m_len = 0;
 	mpd->next_page = index;
 	while (index <= end) {
-		nr_pages = pagevec_lookup_tag(&pvec, mapping, &index, tag,
-			      min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1);
+		nr_pages = pagevec_lookup_range_tag(&pvec, mapping, &index, end,
+				tag, PAGEVEC_SIZE);
 		if (nr_pages == 0)
 			goto out;
 
 		for (i = 0; i < nr_pages; i++) {
 			struct page *page = pvec.pages[i];
 
-			/*
-			 * At this point, the page may be truncated or
-			 * invalidated (changing page->mapping to NULL), or
-			 * even swizzled back from swapper_space to tmpfs file
-			 * mapping. However, page->index will not change
-			 * because we have a reference on the page.
-			 */
-			if (page->index > end)
-				goto out;
-
 			/*
 			 * Accumulated enough dirty pages? This doesn't apply
 			 * to WB_SYNC_ALL mode. For integrity sync we have to