Cloudlinux - Understanding LVE limits

Lightweight Virtual Environments (LVE) is a transparent kernel level technology developed by CloudLinux.

The main goal of LVE is to make sure that no website brings down the web server by limiting each account to utilize configurable resource limits.

DCPU Usage

Specifies how much of the allocated CPU resources you are currently using. The amount of CPU resources is a percentage of one CPU core.
Therefore, if a limit is set to 100% and it's a quad core server. It translates to 25% of the server total or 100% of one core.
If an LVE CPU limit reaches 100% it means that the account is using all of the CPU resources allocated, and any new processes will be put to sleep until the existing processes complete. This can cause a website to slow down dramatically and in extreme cases even time out.

Virtual Memory Usage (vMEM/vM)

Corresponds to the amount of memory, processes can allocate within LVE. When the process tries to allocate memory, CloudLinux checks if the new total virtual memory used by all processes in LVE is within the limit set. If it is not, CloudLinux will prevent memory from being allocated and in most cases this causes the process to fail.

Physical Memory Usage (pMEM/pM)

Is the actual memory allocated for your account. Virtual memory is usually a file on a disk drive that the operating system uses to store information when the real memory becomes full, for instance the swap file on a Linux system. 
If an account hits this limit the webpage will see a CloudLinux 508 "resource limit reached" page. These errors are typically only brief and once the usage has reduced to below the limit, will automatically clear.

Entry Processes (EP)

The number of processes that can be run at once for an account. For example, every PHP page that is accessed will usually generate a single entry process. Many people misinterpret this value as number of visitors on a website at once. Whilst it is true that each visitor accessing a PHP page will spawn an entry process, these processes usually end so quickly that it is extremely unlikely that 10 will be spawned concurrently and at a single moment unless you had a significantly large number of simultaneous visitors on the website at once. SSH sessions and cron jobs also count as entry processes.

Number of Processes (nPROC/nP)

This limit is similar to the above but includes all processes generated by the account rather than the specific PHP, SSH or cron jobs. This number is typically very low, even under high activity, as non-PHP tasks execute and complete even more quickly.

I/O Usage

Represents how much I/O or disk activity the account is using. Any task which makes use of the server's drives (such as reading or writing to the server) will consume I/O. A limit can be set as a maximum for each account to ensure that no single account can saturate the speed of the disk drives which would result in poor performance for all the accounts.