f2fs: use find_get_pages_tag() for looking up single page

__get_first_dirty_index() wants to lookup only the first dirty page
after given index.  There's no point in using pagevec_lookup_tag() for
that.  Just use find_get_pages_tag() directly.

Link: http://lkml.kernel.org/r/20171009151359.31984-8-jack@suse.cz
Signed-off-by: Jan Kara <jack@suse.cz>
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Reviewed-by: Daniel Jordan <daniel.m.jordan@oracle.com>
Cc: Jaegeuk Kim <jaegeuk@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/f2fs/file.c

@@ -313,18 +313,19 @@ int f2fs_sync_file(struct file *file, loff_t start, loff_t end, int datasync)
 static pgoff_t __get_first_dirty_index(struct address_space *mapping,
 						pgoff_t pgofs, int whence)
 {
-	struct pagevec pvec;
+	struct page *page;
 	int nr_pages;
 
 	if (whence != SEEK_DATA)
 		return 0;
 
 	/* find first dirty page index */
-	pagevec_init(&pvec, 0);
-	nr_pages = pagevec_lookup_tag(&pvec, mapping, &pgofs,
-					PAGECACHE_TAG_DIRTY, 1);
-	pgofs = nr_pages ? pvec.pages[0]->index : ULONG_MAX;
-	pagevec_release(&pvec);
+	nr_pages = find_get_pages_tag(mapping, &pgofs, PAGECACHE_TAG_DIRTY,
+				      1, &page);
+	if (!nr_pages)
+		return ULONG_MAX;
+	pgofs = page->index;
+	put_page(page);
 	return pgofs;
 }