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UBC secondary parameters

3,071 bytes added, 01:17, 23 August 2006
filled in oomguarpages
== oomguarpages ==
FIXMEThe guaranteed amount of memory for the case the memory is “over-booked”(out-of-memory kill guarantee). <code>Oomguarpages</code> parameter is related to <code>[[vmguarpages]]</code>.If applications start to consume more memory than the computer has,the system faces an out-of-memory condition.In this case the operating system will start to kill Virtual Environment'sprocesses to free some memory and prevent the total deathof the system. Although it happens very rarely in typical system loads,killing processes in out-of-memory situations is a normal reaction of thesystem, and it is built into every Linux kernel<ref>The possible reasonsof out-of-memory situations are the excess of total<code>[[vmguarpages]]</code> guarantees the available physical resources or high memoryconsumption by system processes. Also, the kernel might allow someVirtual Environments to allocate memory above their <code>[[vmguarpages]]</code>guarantees when the system had a lot of free memory, and later, when otherVirtual Environments claim their guarantees, the system will experience thememory shortage.</ref>. <code>[[Oomguarpages]]</code> parameter accounts the total amount ofmemory and swap space used by the processes of a particularVirtual Environment.The <code>barrier</code> of the <code>oomguarpages</code> parameter is the out-of-memoryguarantee. If the current usage of memory and swap space(the value of <code>oomguarpages</code>) plus the amount of used kernel memory(<code>[[kmemsize]]</code>) and socket buffers is below the <code>barrier</code>,processes in this Virtual Environment are guaranteed not to be killed inout-of-memory situations.If the system is in out-of-memory situation and there are severalVirtual Environments with <code>oomguarpages</code> excess, applications in theVirtual Environment with the biggest excess will be killed first.The <code>failcnt</code> counter of <code>oomguarpages</code> parameterincreases when a process in this Virtual Environment is killed becauseof out-of-memory situation. If the administrator needs to make sure that some application won't beforcedly killed regardless of the application's behavior,setting the <code>[[privvmpages]]</code> limit to a value not greater than the<code>oomguarpages</code> guarantee significantly reduce the likelihood ofthe application being killed,and setting it to a half of the <code>oomguarpages</code> guarantee completelyprevents it.Such configurations are not popular because they significantly reducethe utilization of the hardware. The meaning of the <code></code>limit for the <code>oomguarpages</code> parameter isunspecified in the current version. The total out-of-memory guarantees given to the Virtual Environments shouldnot exceed the physical capacity of the computer, as discussed in [[UBC systemwide configuration#Memory and swap space]].If guarantees are given for more than the system has, in out-of-memorysituations applications in Virtual Environments with guaranteed level ofservice and system daemons may be killed.
== privvmpages ==
FIXME