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SubjectRe: [RFC][PATCH] page reclaim throttle take2
David Rientjes wrote:
> On Wed, 27 Feb 2008, KOSAKI Motohiro wrote:
>>> I disagree, the config option is indeed static but so is the NUMA topology
>>> of the machine. It represents the maximum number of page reclaim threads
>>> that should be allowed for that specific topology; a maximum should not
>>> need to be redefined with yet another sysctl and should remain independent
>>> of various workloads.
>> ok.
>>> However, I would recommend adding the word "MAX" to the config option.
> I'd use _THREAD instead of _TASK, but I'd also wait for Balbir's input
> because perhaps I missed something in my original analysis that this
> config option represents only the maximum number of concurrent reclaim
> threads and other heuristics are used in addition to this that determine
> the exact number of threads depending on VM strain.

Things are changing, with memory hot-add remove, CPU hotplug , the topology can
change and is no longer static. One can create fake NUMA nodes on the fly using
a boot option as well.

Since we're talking of parallel reclaims, I think it's a function of CPUs and
Nodes. I'd rather keep it as a sysctl with a good default value based on the
topology. If we end up getting it wrong, the system administrator has a choice.
That is better than expecting him/her to recompile the kernel and boot that. A
sysctl does not create problems either w.r.t changing the number of threads, no
hard to solve race-conditions - it is fairly straight forward

Warm Regards,
Balbir Singh
Linux Technology Center

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