Re: [PATCH V2 2/2]: powerpc/hotplug/mm: Fix hot-add memory node assoc
From: Balbir Singh <bsingharora@gmail.com>
Date: 2017-05-26 03:23:26
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On Thu, 25 May 2017 12:37:40 -0500 Michael Bringmann [off-list ref] wrote:
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Removing or adding memory via the PowerPC hotplug interface shows anomalies in the association between memory and nodes. The code was updated to ensure that all nodes found at boot are still available to subsequent DLPAR hotplug-memory operations, even if they are not needed at boot time. Signed-off-by: Michael Bringmann <redacted> --- Changes in V2: -- Simplify patches to ensure more nodes in possible map, removing code from PowerPC numa.c that constrained possible map to size of online map. --- arch/powerpc/mm/numa.c | 7 ------- 1 file changed, 7 deletions(-)diff --git a/arch/powerpc/mm/numa.c b/arch/powerpc/mm/numa.c index 15c2dd5..18f3038 100644 --- a/arch/powerpc/mm/numa.c +++ b/arch/powerpc/mm/numa.c@@ -907,13 +907,6 @@ void __init initmem_init(void) memblock_dump_all(); - /* - * Reduce the possible NUMA nodes to the online NUMA nodes, - * since we do not support node hotplug. This ensures that we - * lower the maximum NUMA node ID to what is actually present. - */ - nodes_and(node_possible_map, node_possible_map, node_online_map); -
There is an overhead with turning this off if you have too many cgroups with the memory controller. I think this fix was added for a pathological test case. On my system I see 84 cgroups with 1 node, so the probable overhead is 84*255*sizeof(struct mem_cgroup_tree_per_node). I tried some patches to reduce the overhead, but those need more overhauling and rework. Balbir Singh.