max_memory_limit¶
max_memory_limit is not a PHP core directive: it designates the pattern, used by several frameworks and CMS, of defining an upper bound that a script is allowed to raise memory_limit to at runtime, on top of the regular, lower, day-to-day memory_limit.
The best known example is WordPress’ WP_MAX_MEMORY_LIMIT constant, which caps the value that wp_raise_memory_limit() may apply with ini_set('memory_limit', ...) when running memory-hungry admin tasks, such as image processing or plugin updates, while WP_MEMORY_LIMIT keeps the front-end footprint low.
This two-tier approach avoids granting every request the same generous ceiling: routine requests keep a conservative memory_limit, while a small set of known heavy operations may temporarily request more, up to max_memory_limit, without risking unbounded memory consumption on the rest of the application.
<?php
// WordPress-style pattern
define('WP_MEMORY_LIMIT', '64M');
define('WP_MAX_MEMORY_LIMIT', '256M');
function raise_memory_limit(string $context = 'admin'): void {
$current = ini_get('memory_limit');
$limit = $context === 'admin' ? WP_MAX_MEMORY_LIMIT : WP_MEMORY_LIMIT;
if ($current !== '-1' && wp_convert_hr_to_bytes($limit) > wp_convert_hr_to_bytes($current)) {
ini_set('memory_limit', $limit);
}
}
?>
See also WordPress increase_memory_limit.
Related : memory_limit, php://memory, Vertical Scaling, ini_set()