How to solve Process 'ForkPoolWorker-1' pid:2133000 exited with 'signal 9 (SIGKILL)'?

I am using django, celery and xhtml2pdf to generate pdfs. Small size pdf are created but when pdf size gets larger and few images is added. I get following error. Process 'ForkPoolWorker-1' pid:2133000 exited with 'signal 9 (SIGKILL)' Can somebody help to solve this?