src/Services/QueuedJobService.php
protected function getMemoryLimit()
    {
        // Limit to smaller of explicit limit or php memory limit
        $limit = $this->parseMemory(static::config()->get('memory_limit'));
        if ($limit) {
            return $limit;
        }

        // Fallback to php memory limit
        $phpLimit = $this->getPHPMemoryLimit();
        if ($phpLimit) {
            return $phpLimit;
        }
    }
protected function getMemoryLimit()
    {
        // Limit to smaller of explicit limit or php memory limit
        $limit = $this->parseMemory(static::config()->get('memory_limit'));
        if ($limit) {
            return $limit;
        }

        // Fallback to php memory limit
        $phpLimit = $this->getPHPMemoryLimit();
        if ($phpLimit) {
            return $phpLimit;
        }
    }
Determines the memory limit (in bytes) for this application
Limits to the smaller of memory_limit configured via php.ini or silverstripe config

@return float Memory limit in bytes