On Fri, Jul 14, 2017 at 02:39:41PM +0200, Michal Hocko wrote:
> On Fri 14-07-17 13:32:42, Mel Gorman wrote:
> > On Fri, Jul 14, 2017 at 12:50:04PM +0200, Michal Hocko wrote:
> > > On Fri 14-07-17 10:48:10, Mel Gorman wrote:
> > > > 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.
> > >
> > > I am not sure I understand. I am using for_each_online_cpu...
> >
> > Yes, but within a loop that looks like
> >
> > for_each_online_node(nid)
> > ...
> > for_each_online_cpu(cpu)
> >
> > Or maybe you aren't because we are looking at different baselines. I had
> > minor fuzz and conflicts applying the series.
>
> The current mmotm after this patch looks like this
> if (self && !node_online(self->node_id)) {
> build_zonelists(self);
> } else {
> for_each_online_node(nid) {
> pg_data_t *pgdat = NODE_DATA(nid);
>
> build_zonelists(pgdat);
> }
>
> #ifdef CONFIG_HAVE_MEMORYLESS_NODES
> /*
> * 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.
> */
> for_each_online_cpu(cpu)
> set_cpu_numa_mem(cpu, local_memory_node(cpu_to_node(cpu)));
> #endif
> }
>
Ok, that makes more sense.
Acked-by: Mel Gorman <mgorman@xxxxxxx>
--
Mel Gorman
SUSE Labs
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