On Fri, Jul 14, 2017 at 10:00:00AM +0200, Michal Hocko wrote:
> From: Michal Hocko <mhocko@xxxxxxxx>
>
> __build_all_zonelists reinitializes each online cpu local node for
> CONFIG_HAVE_MEMORYLESS_NODES. This makes sense because previously memory
> less nodes could gain some memory during memory hotplug and so the local
> node should be changed for CPUs close to such a node. It makes less
> sense to do that unconditionally for a newly creaded NUMA node which is
> still offline and without any memory.
>
> Let's also simplify the cpu loop and use for_each_online_cpu instead of
> an explicit cpu_online check for all possible cpus.
>
> Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>
> ---
> mm/page_alloc.c | 6 ++----
> 1 file changed, 2 insertions(+), 4 deletions(-)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 7746824a425d..ebc3311555b1 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -5096,10 +5096,8 @@ static int __build_all_zonelists(void *data)
>
> build_zonelists(pgdat);
> }
> - }
>
> #ifdef CONFIG_HAVE_MEMORYLESS_NODES
> - for_each_possible_cpu(cpu) {
> /*
> * We now know the "local memory node" for each node--
> * i.e., the node of the first zone in the generic zonelist.
> @@ -5108,10 +5106,10 @@ static int __build_all_zonelists(void *data)
> * secondary cpus' numa_mem as they come on-line. During
> * node/memory hotplug, we'll fixup all on-line cpus.
> */
> - if (cpu_online(cpu))
> + for_each_online_cpu(cpu)
> set_cpu_numa_mem(cpu, local_memory_node(cpu_to_node(cpu)));
> - }
> #endif
> + }
>
This is not as clear a benefit. For each online node, we now go through
all online CPUs once per node. There would be some rationale for using
for_each_online_cpu.
--
Mel Gorman
SUSE Labs
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