On 2012年08月31日 22:46, Daniel P. Berrange wrote:
On Fri, Aug 31, 2012 at 04:56:01PM +0800, Osier Yang wrote:
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;
See my next comment about this...
/* * 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"
The other constants here are all tunable parameters. This one however is an action. IMHO we should not use a {Get,Set}Parameters style APIs for actions. We should have an explicit API for invoking them.
Understand, and I tend to agree, how about a separate API like "virNodeManageSharedMemory"?
/* * 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.
As a general point, we should not use the term 'KSM' in the API names, since that is an implementation specific name. We want some more generic name. eg
Completely agreed. :-)
virNodeSetMemorySharingParameters
But I recall we once used term "sharedMemory" before. So to be consistent, "SharedMemory" should be better. Regards, Osier