Re: [PATCH v4] KSM: numa awareness sysfs knob
From: Rik van Riel
Date: Thu Sep 27 2012 - 11:45:29 EST
On 09/23/2012 08:56 PM, Petr Holasek wrote:
Introduces new sysfs boolean knob /sys/kernel/mm/ksm/merge_across_nodes
which control merging pages across different numa nodes.
When it is set to zero only pages from the same node are merged,
otherwise pages from all nodes can be merged together (default behavior).
Typical use-case could be a lot of KVM guests on NUMA machine
and cpus from more distant nodes would have significant increase
of access latency to the merged ksm page. Sysfs knob was choosen
for higher variability when some users still prefers higher amount
of saved physical memory regardless of access latency.
Every numa node has its own stable & unstable trees because of faster
searching and inserting. Changing of merge_nodes value is possible only
when there are not any ksm shared pages in system.
I've tested this patch on numa machines with 2, 4 and 8 nodes and
measured speed of memory access inside of KVM guests with memory pinned
to one of nodes with this benchmark:
Acked-by: Rik van Riel <riel@xxxxxxxxxx>
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