memory usage increasing when using opcache.enable_cli and opcache.file_cache_only

[rbro]

Description

The below script using opcache.enable_cli=1 and opcache.file_cache_only=1 causes the PHP memory usage to continue to increase. If I disable file_cache_only, then the memory usage remains constant. I was able to reproduce in PHP 8.1, 8.2, and 7.4.

To reproduce, set-up scripts test.php and test2.php as listed below, create an empty directory /tmp/opcache, and then run:

php \
  -n \
  -d "zend_extension=opcache" \
  -d "opcache.enable_cli=1" \
  -d "opcache.file_cache=/tmp/opcache" \
  -d "opcache.file_cache_only=1" \
  test.php

When I run the above, the value of memory_get_usage() continues to increase. If I remove the line for "opcache.file_cache_only=1", then memory_get_usage() remains constant.

If it doesn't happen the 1st time, then try running it a 2nd time.

Can you please check why the memory usage continues to grow in this scenario?

Thanks for your help.

test.php:

<?php
for ($i = 0; $i < 10000; $i++)
{
	echo number_format(memory_get_usage())."\n";

	require('test2.php');
}

test2.php:

<?php
return;

PHP Version

PHP 8.1.11

Operating System

AlmaLinux 8

[arnaud-lb]

Related: https://bugs.php.net/bug.php?id=76982

[mvorisek]

related PR #7563 asserting the non-leaking behavour with configurations where possible, I would be happy if someone can merge it

and fix for every configuration of course highly welcomed

[nikic]

Pretty sure there was a bug report and analysis for this issue on the old bug tracker, but I can't find it.

This issue should be unrelated to the dynamic defs issue linked above. The problem (I believe) is that file cache loads the cached file into an arena allocation, and usually that arena allocation gets discarded after moving the contents to SHM. Of course, this does not happen if file_cache_only is used. In that case we end up performing the arena allocation on every include, without ever freeing it.

[cmb69]

Pretty sure there was a bug report and analysis for this issue on the old bug tracker, but I can't find it.

I think this is about https://bugs.php.net/78076.