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Rafal Wojtczuk 2010-09-23 16:14:58 +00:00
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Qmemman.md
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@ -21,10 +21,10 @@ Therefore, in Qubes another solution is used. There is the *qmemman* dom0 daemon
Similarly, when there is need for Xen free memory (for instance, in order to create a new VM), traditionally the memory is obtained from dom0 only. When *qmemman* is running, it offers interface to obtain memory from all domains.
To sum up, pros and cons. Pros:
To sum up, *qmemman* pros and cons. Pros:
- provides automatic balancing of memory across participating PV and HVM domains, based on their memory demand
- works well in practise, particularly with less than 1% CPU consumption in the idle case
- works well in practice, with less than 1% CPU consumption in the idle case
- simple, concise implementation
Cons:
@ -38,7 +38,7 @@ Interface
*qmemman* listens for the following events:
- writes to `/local/domain/domid/memory/meminfo` xenstore keys by *meminfo-writer* process in VM. The content of this key is taken from the VM's `/proc/meminfo` pseudofile ; *meminfo-writer* just strips some unused lines from it. Note that *meminfo-writer* writes its xenstore key only if the VM memory usage has changed significantly enough since the last update (by default 30MB)
- writes to `/local/domain/domid/memory/meminfo` xenstore keys by *meminfo-writer* process in VM. The content of this key is taken from the VM's `/proc/meminfo` pseudofile ; *meminfo-writer* just strips some unused lines from it. Note that *meminfo-writer* writes its xenstore key only if the VM memory usage has changed significantly enough since the last update (by default 30MB), to prevent flooding with almost identical data
- commands issued over Unix socket `/var/run/qubes/qmemman.sock`. Currently, the only command recognized is to free the specified amount of memory. The QMemmanClient class implements the protocol.
- if the `/var/run/qubes/do-not-membalance` file exists, *qmemman* suspends memory balancing. It is primarily used when allocating memory for a to-be-created domain, to prevent using up the free Xen memory by the balancing algorithm before the domain creation is completed.
@ -56,9 +56,9 @@ Whenever *meminfo-writer* running in domain A provides new data on memory usage
1. for all domains whose `prefmem` is less than actual memory, shrink them to their `prefmem`
2. redistribute memory reclaimed in the previous step between the rest of domains, proportionally to their `prefmem`
The memory redistribution is actually executed only if one of the below conditions hold:
In order to avoid too frequent memory redistribution, it is actually executed only if one of the below conditions hold:
- the sum of memory changes for all domains is more than MIN\_TOTAL\_MEMORY\_TRANSFER (150MB)
- the sum of memory size changes for all domains is more than MIN\_TOTAL\_MEMORY\_TRANSFER (150MB)
- one of the domains is below its `prefmem`, and more than MIN\_MEM\_CHANGE\_WHEN\_UNDER\_PREF (15MB) would be added to it
Additionally, the balance algorithm is tuned so that XEN\_FREE\_MEM\_LEFT (50MB) is always left as Xen free memory, to make coherent memory allocations in driver domains work.