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I'm running PHP-FPM on my Debian servers. My question is about the memory usage. I can only set the memory_limit inside PHP, and that shouldn't be too low for some requests. I also can only set the number of processes in PHP-FPM and that, also, should not be too low since I'm running a lot of php requests.

In most cases, processes will only use around 2-20mb. The process limit is 512, so that's roughly 5-10GB of RAM. But since some php scripts can use a lot more memory, the maximum allowed memory is around 1TB (512 processes * 2048mb). And if something goes wrong, the Debian OOM Killer will just randomly kill processes.

Is there any way to limit the total memory usage for php-fpm? Like a hard limit where php-fpm won't spawn more processes because it's out of total RAM.

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  • Do you know which urls will lead to larger memory usage ? Commented Feb 27, 2015 at 7:18
  • I know sites where it's more likely to happen, yes. Commented Feb 27, 2015 at 7:19
  • Use different php-fpm pools for the larger memory sites. Commented Feb 27, 2015 at 7:20
  • I'll try if that works for me Commented Feb 27, 2015 at 7:22
  • Don't give it 512 processes, then. If you want to have a 2048 limit per process, then only have as much as the machine can handle. aka. 4 processes if the machine has 10gb ram. Using alternate pools sounds appropriate. Using ulimit over the parent process will not be graceful. Commented Feb 27, 2015 at 7:22

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Few days ago I had similar problem, when couple of php5-fpm masters spawned too much processes. OOM Killer helped a lot by killing nginx.

As solution I found cgroup mechanism with memory subsystem. It allows to put all FPM processes in 1 group which is limited to e.g. 60% of system RAM.

Great documentation: https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/6/html/Resource_Management_Guide/ch-Using_Control_Groups.html

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  • this looks like something :) Commented Feb 27, 2015 at 13:38

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