Sunday, June 22, 2014

Does CloudLinux (CentOS) CL6.5 use more memory than CL5.9?

The majority of our Sydney web hosting accounts recently moved to CloudLinux CL6.5 (from a CL5.9 server). As you may be aware, CloudLinux has revolutionised the hosting industry with a pseudo 'virtualisation' at the user-account level. As part of CloudLinux CageFS, alt-php has improved the security of servers worldwide, allowing various php versions to coexist in peace, with security. 

From the moment the accounts began to operate on CL6.5 many began firing alerts (PT_USERMEM notification by CSF) because of high memory usage. This only affected accounts on alt-php versions, but the peak (and frequent) memory usage was almost double CL5.9.

N.B. I'm quick to add here that performance isn't inhibited - we ensure all accounts have plenty of resources available; but from a hosts perspective, double memory consumption is significant and so surely it's been observed by other admins.

cPanel & CloudLinux Support
cPanel support created two servers to test the difference between CL5.9 and CL6.5 and did not a similar difference in virtual memory consumption, however the test was not conclusive. Similarly, CloudLinux support haven't been able to point to anything out of place, and while they confirm CL6.5 is so different it could like use memory very differently, they don't appear to have any evidence to support it. Could we be the only host that has noticed?

Notably, the difference has occasionally even been observed on accounts not making MySQL database queries, which are also not resource-intensive accounts, nor particularly busy.

So I'd like to throw the question open: 
Have you noticed greater (nearly double) virtual memory consumption on alt-php accounts on CloudLinux 6 versions?

How about CentOS 6 as opposed to 5, without the CloudLinux installation? While we have narrowed down alt-php sites, have you seen greater memory consumption on CentOS 6.x servers?

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