Override pagination in search results [closed]

Question

I have pagination set low in reading settings, which is a problem for search results. For the search.php template I'm looking for all returned results to be shown.

What do I need to change with this? This is showing all posts in the DB

<?php get_header(); query_posts( 'posts_per_page=-1&cat=' . $cat ) ?>

would be better to use something like this? how could this be applied to show all search results on one page regardless of reading settings?

<?php
function custom_posts_per_page( $query ) {
    if ( $query->is_tax('mytaxonomy') || $query->is_category('mycategory') ) {
        set_query_var('posts_per_page', 9);
    }
}
add_action( 'pre_get_posts', 'custom_posts_per_page' ); ?>