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VSwap

4,307 bytes added, 15:57, 17 July 2020
vswap in vz7 details added
'''New [[Download/kernel/rhel6|RHEL6-based OpenVZ]] kernel ''' has a new memory management model, which supersedes [[UBC|User beancounters]]. It is called '''VSwap'''.
Now you can set == Primary parameters == With VSwap, there are two primary required parameters: <code>ram</code> and <code>swap</code> (a.k.a. <code>physpages</code> and <code>swappages</code>, while all ). All the other beancounters become secondaryoptional.
* '''physpages'''
: This parameter limits sets the amount of fast physical memory (RAM) available to processes inside a container, in memory pages. Currently (as of 042stab042 kernel) the user memory, the kernel memory and the page cache are accounted into <code>physpages</code>. : The <code>barrier</code> is ignoredand should be set to 0, and the <code>limit</code> sets the limit. * '''ram''': Currently the user memory and the page cache are accounted into <code>is an easy shortcut for physpages</code>.limit, and is measured in bytes
* '''swappages'''
: This parameter limits sets the amount of swap space which can be used for "slower memory" (vswap) available to processes inside a container, in memory pages. : The <code>barrier</code> is ignoredand should be set to 0, and the <code>limit</code> sets the limit. * '''swap''': is an easy shortcut for swappages.limit, and is measured in bytes
The sum of <code>physpages.limit</code> and <code>swappages.limit</code> limits the maximum amount
of allocated memory which can be used by a container. When physpages limit
is reached, memory pages belonging to the container are pushed out to
so called virtual swap (''vswap''). The difference between normal swap
on the system.
{{Note|swap used by a container can exceed <code>swappages.limit</code>, but is always within sum of <code>physpages.limit</code> and <code>swappages.limit</code>.}} === Secondary Implicit UBC parameters === Since vzctl 4.6, if some optional beancounters are not set, vzctl sets them implicitly,based on '''ram''' and '''swap'''Even though these settings . The following formulae are classed as secondaryused: <math>lockedpages_{bar} = oomguarpages_{bar} = ram</math> <math>lockedpages_{lim} = oomguarpages_{lim} = \infty</math> <math>vmguarpages_{bar} = vmguarpages_{lim} = ram + swap</math> ==== VM overcommit and privvmpages ==== vzctl 4.6 adds a new parameter, <code>--vm_overcommit</code>.Its only purpose is to be used in privvmpages calculation,in case VSwap is used and there is no explicit settingfor privvmpages. If <math>vm\_overcommit</math> is set: : <math>privvmpages_{bar} = privvmpages_{lim} = (ram + swap) \times vm\_overcommit</math> If it is not set: : <math>privvmpages_{bar} = privvmpages_{lim} = \infty</math> == Setting == {{Note|for VSwap, you need vswap-enabled kernel, ie [[Download/kernel/rhel6|RHEL6-based OpenVZ]] kernel.}} Since vzctl 3.0.30, you can use <code>--ram</code> and <code>--swap</code> parameters, like this: vzctl set 777 --ram 512M --swap 1G --save == Convert non-VSwap CT to VSwap == If you have an existing container with usual UBC parameters set, and you want to convert this one into VSwap enabled config, here's what you need to do. # Decide on how much RAM and swap you want this CT to have. Generally, sum of your new RAM+swap should be more or less equal to sum of old PRIVVMPAGES and KMEMSIZE.# Manually remove all UBC parameters from config. '''This is optional''', they are you can still important settings!have UBC limits applied if you want.# Add PHYSPAGES and SWAPPAGES parameters to config. Easiest way is to use <code>vzctl set $CTID --ram N --swap M --save</code> Now your config is vswap enabled, and when you (re)start it (or use <code>--reset_ub</code>), vswap mechanism will be used by the kernel for this CT. Here is an example of the above steps:  CTID=123 RAM=1G SWAP=2G CFG=/etc/vz/conf/${CTID}.conf cp $CFG $CFG.pre-vswap grep -Ev '^(KMEMSIZE|LOCKEDPAGES|PRIVVMPAGES|SHMPAGES|NUMPROC|PHYSPAGES|VMGUARPAGES|OOMGUARPAGES|NUMTCPSOCK|NUMFLOCK|NUMPTY|NUMSIGINFO|TCPSNDBUF|TCPRCVBUF|OTHERSOCKBUF|DGRAMRCVBUF|NUMOTHERSOCK|DCACHESIZE|NUMFILE|AVNUMPROC|NUMIPTENT|ORIGIN_SAMPLE|SWAPPAGES)=' > $CFG < $CFG.pre-vswap vzctl set $CTID --ram $RAM --swap $SWAP --save vzctl set $CTID --reset_ub == How to distinguish between vswap and non-vswap configs? == Both <code>vzctl</code> and the kernel treats a configuration file as vswap one if PHYSPAGES limit is '''not'''set to <code>unlimited</code> (a.k.a. [[LONG_MAX]]). You can also use the following command:   # vzlist -o vswap $CTID
In addition , vzctl checks if kernel support vswap, and refuses to start a vswap-enabled container on a non vswap capable kernel. The check is presence of <code>physpages</code> and <code>swappagesproc/vz/vswap</code> being set, it is ''currently'' recommended to:file.
* Set <code>kmemsize</code> to no more than 1/2 of <code>physpages</code>* Set <code>dcachesize</code> to no more than 1/2 of <code>kmemsize</code>* Set <code>lockedpages</code> to no more than 1/2 of <code>physpages</code>== Details about vSwap implementation in Virtuozzo 7 ==
VSwap CT config samples (like [http://gitThe Container swapping process is similar to that on a standalone computer.openvz<br>This means in particular that some pages may get into the swap even if there is some free memory reported in the Container.org/?p=vzctl;<br>This may validly happen in case kernel memory management system detects some anonymous memory which is not touched for a=blob;f=etc/conf/velong time by Container processes and decides that it's moreefficient to put these anonymous pages into the swap and use more caches in a Container instead. The Container swap space resides in physical node swap file.<br>When the swap-vswapout for a Container starts, appropriate number of pages are allocated in physical swap on the host. Next# if there is no free memory on the host, the real swap-256mout of Container's memory to physical swap happens# if there is free memory on the host, the Container's memory is saved in a special swap cache in host's RAM and no real write to host's physical swap occurs {{Note|The physical swap space is allocated in both cases anyway, this guarantees all amount of host's swap cache for Containers memory can be written into physical swap on host in case the host gets short of RAM.conf-sample ve-vswap-256m}} * '''Consequence 1''': without any configured node swap file the Container's `SWAPPAGES` parameter will be ignored.conf * '''Consequence 2''': if node's swap size is less than sum of all Containers' swap sizes on the node, Containers won't be able to use 100% of their swap simultaneously -sample] that come with vzctl are currently implementing these recommendationssimilar to RAM settings.
{{Note|VSwap feature is still being worked on, so these recommendation might change == See also ==* [http://openvz.livejournal.com/39644.html On vSwap and 042stab04x kernel improvements]* [http://openvz.livejournal.com/39765.html Recent improvements in the future.}}vzctl]
[[Category: UBC]]