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SubjectRe: [RFC Patch V1 28/30] mm: Update _mem_id_[] for every possible CPU when memory configuration changes
On 11.07.2014 [15:37:45 +0800], Jiang Liu wrote:
> Current kernel only updates _mem_id_[cpu] for onlined CPUs when memory
> configuration changes. So kernel may allocate memory from remote node
> for a CPU if the CPU is still in absent or offline state even if the
> node associated with the CPU has already been onlined.

This just sounds like the topology information is being updated at the
wrong place/time? That is, the memory is online, the CPU is being
brought online, but isn't associated with any node?

> This patch tries to improve performance by updating _mem_id_[cpu] for
> each possible CPU when memory configuration changes, thus kernel could
> always allocate from local node once the node is onlined.

Ok, what is the impact? Do you actually see better performance?

> We check node_online(cpu_to_node(cpu)) because:
> 1) local_memory_node(nid) needs to access NODE_DATA(nid)
> 2) try_offline_node(nid) just zeroes out NODE_DATA(nid) instead of free it
>
> Signed-off-by: Jiang Liu <jiang.liu@linux.intel.com>
> ---
> mm/page_alloc.c | 10 +++++-----
> 1 file changed, 5 insertions(+), 5 deletions(-)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 0ea758b898fd..de86e941ed57 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -3844,13 +3844,13 @@ static int __build_all_zonelists(void *data)
> /*
> * We now know the "local memory node" for each node--
> * i.e., the node of the first zone in the generic zonelist.
> - * Set up numa_mem percpu variable for on-line cpus. During
> - * boot, only the boot cpu should be on-line; we'll init the
> - * secondary cpus' numa_mem as they come on-line. During
> - * node/memory hotplug, we'll fixup all on-line cpus.
> + * Set up numa_mem percpu variable for all possible cpus
> + * if associated node has been onlined.
> */
> - if (cpu_online(cpu))
> + if (node_online(cpu_to_node(cpu)))
> set_cpu_numa_mem(cpu, local_memory_node(cpu_to_node(cpu)));
> + else
> + set_cpu_numa_mem(cpu, NUMA_NO_NODE);
> #endif




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