On Sun, Jan 26, 2020 at 02:44:31PM -0800, David Rientjes wrote:
>On Sun, 26 Jan 2020, Wei Yang wrote:
>
>> When onlining a cpu, kswapd_cpu_online() is called to adjust kswapd cpu
>> affinity.
>>
>> Current routine does like this:
>>
>> * Iterate all the numa node
>> * Adjust cpu affinity when node has an online cpu
>>
>> Actually we could improve this by:
>>
>> * Just adjust the numa node to which current online cpu belongs
>>
>> Because we know which numa node the cpu belongs to and this cpu would
>> not affect other node.
>>
>
>Is there ever a situation where the cpu to be onlined would have appeared
>in the cpumask of another node and so a different kswapd's cpumask would
>now include an off-node cpu?
No, I don't think so.
Per my understanding, kswapd_cpu_online() will be invoked when a cpu is
onlined. And the particular cpu belongs to a particular numa node. So it is
not necessary to iterate on every nodes.
And current code use cpumask_and_any() to do the check. If my understanding is
correct, the check would return true if this node has any online cpu. This is
likely to be true.
This is why I want to make the logic clear.
>
>> Signed-off-by: Wei Yang <richardw.yang@xxxxxxxxxxxxxxx>
>> ---
>> mm/vmscan.c | 19 ++++++++++---------
>> 1 file changed, 10 insertions(+), 9 deletions(-)
>>
>> diff --git a/mm/vmscan.c b/mm/vmscan.c
>> index 572fb17c6273..19c92d35045c 100644
>> --- a/mm/vmscan.c
>> +++ b/mm/vmscan.c
>> @@ -4049,18 +4049,19 @@ unsigned long shrink_all_memory(unsigned long nr_to_reclaim)
>> restore their cpu bindings. */
>> static int kswapd_cpu_online(unsigned int cpu)
>> {
>> - int nid;
>> + int nid = cpu_to_node(cpu);
>> + pg_data_t *pgdat;
>> + const struct cpumask *mask;
>>
>> - for_each_node_state(nid, N_MEMORY) {
>> - pg_data_t *pgdat = NODE_DATA(nid);
>> - const struct cpumask *mask;
>> + if (!node_state(nid, N_MEMORY))
>> + return 0;
>>
>> - mask = cpumask_of_node(pgdat->node_id);
>> + pgdat = NODE_DATA(nid);
>> + mask = cpumask_of_node(nid);
>> +
>> + /* One of our CPUs online: restore mask */
>> + set_cpus_allowed_ptr(pgdat->kswapd, mask);
>>
>> - if (cpumask_any_and(cpu_online_mask, mask) < nr_cpu_ids)
>> - /* One of our CPUs online: restore mask */
>> - set_cpus_allowed_ptr(pgdat->kswapd, mask);
>> - }
>> return 0;
>> }
>>
>> --
>> 2.17.1
>>
>>
>>
--
Wei Yang
Help you, Help me
