# UBC consistency check

User Beancounters
Definition
/proc/user_beancounters
/proc/bc/
General information
Units of measurement
VSwap
Parameters description
Primary parameters
numproc, numtcpsock, numothersock, vmguarpages
Secondary parameters
kmemsize, tcpsndbuf, tcprcvbuf, othersockbuf, dgramrcvbuf, oomguarpages, privvmpages
Auxiliary parameters
lockedpages, shmpages, physpages, numfile, numflock, numpty, numsiginfo, dcachesize, numiptent, swappages
Internals
User pages accounting
On-demand accounting
UBC consistency
Consistency formulae
System-wide configuration
vzubc(8)
Configuration examples
Basic
Derived
Intermediate configurations
Tables
List of parameters
Parameter properties
Consistency
Config examples

System resource control parameters have certain interdependencies. Constraints on the parameter settings are listed below. Indexes bar and lim in the formulae below mean the barrier and the limit of the parameters, respectively.

Configuration of resource control parameters for a Virtual Environment is invalid if these constraints are not satisfied. The best way to ensure the validity of the configuration is to use vzcfgvalidate(8) utility.

All the interdependencies discussed below and their importance are summarized in UBC interdependencies table.

The configured limits can be checked through

• /proc/user beancounters interface;
• Virtual Environment configuration files in /etc/vz/conf/ directory.

## kmemsize should be enough for the expected number of processes

${\displaystyle kmemsize_{bar}\geq 40KB\cdot avnumproc+dcachesize_{lim}}$

(avnumproc here stands for the expected average number of processes).

This constraint is important for reliable work of applications in the Virtual Environment. If it is not satisfied, applications will start to fail at the middle of operations instead of failing at the moment of spawning more processes, and the application abilities to handle resource shortage will be very limited.

## Memory allocation limits should not be less than the guarantee

${\displaystyle privvmpages_{bar}\geq vmguarpages_{bar}}$

If this constraint is not satisfied, vmguarpages will not work.

## Send buffers should have enough space for all sockets

${\displaystyle tcpsndbuf_{lim}-tcpsndbuf_{bar}\geq 2.5KB\cdot numtcpsock}$

${\displaystyle othersockbuf_{lim}-othersockbuf_{bar}\geq 2.5KB\cdot numothersock}$

These constraints are also important. If they are not satisfied, transmission of data over the sockets may hang in some circumstances.

## Other TCP socket buffers should be big enough

${\displaystyle tcprcvbuf_{lim}-tcprcvbuf_{bar}\geq 2.5KB\cdot numtcpsock}$

${\displaystyle tcprcvbuf_{bar}\geq 64KB}$

${\displaystyle tcpsndbuf_{bar}\geq 64KB}$

Selecting the left side equal to the right side in the inequalities above ensures minimal performance of network communications. Increasing the left side will increase performance to certain extent.

## UDP socket buffers should be big enough if the system is not tight on memory

${\displaystyle dgramrcvbuf_{bar}\geq 129KB}$

${\displaystyle othersockbuf_{bar}\geq 129KB}$

These constraints are desired, but not essential. Big enough buffers for UDP sockets improve reliability of datagram delivery. However, note that if the UDP traffic is so bursty that it needs larger buffers, the datagrams will likely be lost not because of resource control limits, but because of other memory and performance limitations.

## Number of file limit should be adequate for the expected number of processes

${\displaystyle numfile\geq avnumproc\cdot 32}$

Note that each process after execve(2) system call requires a file for each loaded shared library. Too low numfile limit will increase the chances of failures during execve(2) call with diagnostics not clear for the users.

## The limit on the total size of dentry and inode structures locked in memory should be adequate for allowed number of files

${\displaystyle dcachesize_{bar}\geq numfile\cdot 384\ {\rm {(bytes)}}}$

Too low dcachesize limit will increase the chances of file operation refusals not expected by applications.

## Barrier should be less or equal than limit

In addition to the conditions listed above,

${\displaystyle barrier\leq limit}$

should be maintained for each parameter.