Re: [PATCH v7 12/14] arm64/numa: remove the limitation that cpu0 must bind to node0

Leizhen (ThunderTown)
2016-08-29T06:57:22Z

On 2016/8/26 23:49, Will Deacon wrote:
> On Wed, Aug 24, 2016 at 03:44:51PM +0800, Zhen Lei wrote:
>> 1. Currently only cpu0 set on cpu_possible_mask and percpu areas have not
>> been initialized.
This description refer to below:
- for_each_possible_cpu(cpu)
- set_cpu_numa_node(cpu, NUMA_NO_NODE);

1. When the above code is executed, only the bit of cpu0 was set on cpu_possible_mask.
So that, only set_cpu_numa_node(0, NUMA_NO_NODE); will be executed.
2. set_cpu_numa_node will access percpu variable numa_node, but setup_per_cpu_areas is
called after current time. Without the first problem, it will lead kernel crash.

I changed the title of this patch in v7, the original is "remove some useless code".
I think I should separate this into a new patch.

>> 2. No reason to limit cpu0 must belongs to node0.
>
> Whilst I suspect you're using enumerated lists in order to try to make
> things clearer, I'm having a really hard time understanding the commit
> messages you have in this series. It's actually much better if you
> structure them as concise paragraphs explaining:
>
> - What is the problem that you're fixing?
>
> - How does that problem manifest?
>
> - How does the patch fix it?
>
> As far as I can see, this patch just removes a bunch of code with no
> explanation as to why it's not required or any problems caused by
> keeping it around.
>
> Will
>
>> Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
>> ---
>> arch/arm64/mm/numa.c | 12 ++----------
>> 1 file changed, 2 insertions(+), 10 deletions(-)
>>
>> diff --git a/arch/arm64/mm/numa.c b/arch/arm64/mm/numa.c
>> index 114180f..07a1978 100644
>> --- a/arch/arm64/mm/numa.c
>> +++ b/arch/arm64/mm/numa.c
>> @@ -94,7 +94,6 @@ void numa_clear_node(unsigned int cpu)
>> */
>> static void __init setup_node_to_cpumask_map(void)
>> {
>> - unsigned int cpu;
>> int node;
>>
>> /* setup nr_node_ids if not done yet */
>> @@ -107,9 +106,6 @@ static void __init setup_node_to_cpumask_map(void)
>> cpumask_clear(node_to_cpumask_map[node]);
>> }
>>
>> - for_each_possible_cpu(cpu)
>> - set_cpu_numa_node(cpu, NUMA_NO_NODE);
>> -
>> /* cpumask_of_node() will now work */
>> pr_debug("Node to cpumask map for %d nodes\n", nr_node_ids);
>> }
>> @@ -119,13 +115,13 @@ static void __init setup_node_to_cpumask_map(void)
>> */
>> void numa_store_cpu_info(unsigned int cpu)
>> {
>> - map_cpu_to_node(cpu, numa_off ? 0 : cpu_to_node_map[cpu]);
>> + map_cpu_to_node(cpu, cpu_to_node_map[cpu]);
>> }
>>
>> void __init early_map_cpu_to_node(unsigned int cpu, int nid)
>> {
>> /* fallback to node 0 */
>> - if (nid < 0 || nid >= MAX_NUMNODES)
>> + if (nid < 0 || nid >= MAX_NUMNODES || numa_off)
>> nid = 0;
After the below code have been removed, we should make the corresponding adjustment.
otherwise, kernel will be crashed if "numa=off" was set in bootargs.

>>
>> cpu_to_node_map[cpu] = nid;
>> @@ -375,10 +371,6 @@ static int __init numa_init(int (*init_func)(void))
>>
>> setup_node_to_cpumask_map();
>>
>> - /* init boot processor */
>> - cpu_to_node_map[0] = 0;
>> - map_cpu_to_node(0, 0);
These code limit cpu0 must belong to node0, but our current implementation deesn't
have this limitation.

>> -
>> return 0;
>> }
>>
>> --
>> 2.5.0
>>
>>
>
> .
>