Triggered by the requirement to control the new sys knob
/sys/kernel/mm/ksm/merge_nodes for a NUMA aware host by
patch:
http://permalink.gmane.org/gmane.linux.kernel.mm/81497
It shows there is no methods to manage the KSM in
libvirt. This proposes the new APIs like following, thanks
for suggestions/idea in advance.
== The macros and enums for the params' fields
/* virNodeKSMRunMode:
*
* Represents the modes of /sys/kernel/mm/ksm/run.
*/
typedef enum {
/* Stop ksmd from running but keep merged pages */
VIR_NODE_STOP_KSM_KEEP_MERGED_PAGES = 0,
/* Start ksmd */
VIR_NODE_START_KSM = 1,
/* Stop ksmd and and unmerge all pages currently merged */
VIR_NODE_STOP_KSM_UNMERGE_PAGES = 2,
} virNodeKSMRunMode;
/*
* VIR_NODE_KSM_PAGES_TO_SCAN:
*
* Macro for typed parameter that represents how many present pages
* to scan before ksmd goes to sleep.
*/
# define VIR_NODE_KSM_PAGES_TO_SCAN "pages_to_scan"
/*
* VIR_NODE_KSM_SLEEP_MILLISECS:
*
* Macro for typed parameter that represents how many milliseconds
* ksmd should sleep before next scan.
*/
# define VIR_NODE_KSM_SLEEP_MILLISECS "sleep_millisecs"
/*
* VIR_NODE_KSM_RUN:
*
* Macro for typed parameter that is used to control ksmd's state, as
* an int containing a virNodeKSMRunMode value.
*/
# define VIR_NODE_KSM_RUN "run"
/*
* VIR_NODE_KSM_PAGES_SHARED:
*
* Macro for typed parameter that represents how many ksm shared pages
* are being used.
*/
# define VIR_NODE_KSM_PAGES_SHARED "pages_shared"
/*
* VIR_NODE_KSM_PAGES_SHARING:
*
* Macro for typed parameter that represents how many sites are
* sharing the pages i.e. how much saved.
*/
# define VIR_NODE_KSM_PAGES_SHARING "pages_sharing"
/* VIR_NODE_KSM_PAGES_UNSHARED:
*
* Macro for typed parameter that represents how many pages unique
* but repeatedly checked for merging.
*/
# define VIR_NODE_KSM_PAGES_UNSHARED "pages_unshared"
/* VIR_NODE_KSM_PAGES_VOLATILE:
*
* Macro for typed parameter that represents how many pages changing
* too fast to be placed in a tree.
*/
# define VIR_NODE_KSM_PAGES_VOLATILE "pages_volatile"
/* VIR_NODE_KSM_FULL_SCAN:
*
* Macro for typed parameter that represents how many times all
* mergeable areas have been scanned.
*/
# define VIR_NODE_KSM_FULL_SCAN "full_scan"
== API to Get KSM parameters.
/*
* virNodeGetKSMParameters:
* @conn: pointer to the hypervisor connection
* @params: pointer to memory parameter object
* (return value, allocated by the caller)
* @nparams: pointer to number of memory parameters; input and output
* @flags: extra flags; not used yet, so callers should always pass 0
*
* ... Detailed comments ommitted ...
*
* Returns 0 in case of success, and -1 in case of failure.
*/
int
virNodeGetKSMParameters(virConnectPtr conn,
virTypedParameterPtr params,
int *nparams,
unsigned int flags);
== API to set KSM parameters.
Currently only "run", "pages_to_scan", and "sleep_millisecs"
are writable. The new boolearn sys knob "merge_nodes" could
be added once it's acceptted by kernel upstream.
/*
* virNodeSetKSMParameters:
* @conn: pointer to the hypervisor connection
* @params: pointer to scheduler parameter objects
* @naprams: number of scheduler parameter objects
* (this value can be the same or less than the returned
* value nparams of virDomainGetSchedulerType)
* @flags: extra flags; not used yet, so callers should always pass 0
*
* ... Detailed comments ommitted ...
*
* Returns 0 in case of success, -1 in case of failure.
*/
int
virNodeSetKSMParameters(virConnectPtr conn,
virTypedParameterPtr params,
int nparams,
unsigned int flags);
BTW, the other thing libvirt misses is to tell ksmtuned to retune
when a domain is started or destroyed. Which is outlined in
the Red Hat Virtualization Administration Guide doc, but it's
not true. So either we have a hole in libvirt, or lacks a fix
for the document.
<...>
The KSM tuning service
The ksmtuned service does not have any options. The ksmtuned service
loops and adjusts ksm. The ksmtuned service is notified by libvirt when
a guest is created or destroyed.
</...>
https://access.redhat.com/knowledge/docs/en-US/Red_Hat_Enterprise_Linux/6/html/Virtualization_Administration_Guide/chap-KSM.html
Regards,
Osier
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