Status: New
Owner: ----
New issue 1122 by [email protected]: Feature Request: memory_ratio
ipolicy parameter for overcommitting memory
https://code.google.com/p/ganeti/issues/detail?id=1122
Ganeti’s current memory resource model assumes that each instance reserves
a fixed amount of memory. KVM instances, however, from the point of view of
the host operating system, do not initially use all of their memory.
Instead, a KVM process’s memory usage will gradually approach its cap. Once
the instances stabilize at their maximum ram usage, Ganeti is able to
properly track memory usage. However, because Ganeti tracks memory free on
a node instead of memory allocated, Ganeti’s current memory accounting
cannot take into account memory overcommitting.
For KVM memory overcommitting, the steady state of the node’s memory usage
is (assuming no cpu or disk constraints) completely full memory and swap,
with most of the swapped-out memory being free memory in the instances. In
this state, Ganeti will consider the node to have no free memory and will
refuse to place more instances on the node, even if the desired overcommit
ratio has not been reached.
To resolve this, Ganeti’s memory model should be modified to match its cpu
model: a mem_ratio ipolicy parameter (similar to vcpu_ratio) should be
added and Ganeti should track instance max memory (as it does with instance
vcpus) instead of free memory on the node.The semantics of these parameters
should match those of their cpu counterparts.
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