[PATCH v4 11/14] arm64/numa: support HAVE_MEMORYLESS_NODES

[Ganapatrao Kulkarni]

On Tue, Jun 7, 2016 at 6:27 PM, Leizhen (ThunderTown)
<thunder.leizhen at huawei.com> wrote:
>
>
> On 2016/6/7 16:31, Ganapatrao Kulkarni wrote:
>> On Tue, Jun 7, 2016 at 1:38 PM, Zhen Lei <thunder.leizhen at huawei.com> wrote:
>>> Some numa nodes may have no memory. For example:
>>> 1. cpu0 on node0
>>> 2. cpu1 on node1
>>> 3. device0 access the momory from node0 and node1 take the same time.
>>
>> i am wondering, if access to both nodes is same, then why you need numa.
>> the example you are quoting is against the basic principle of "numa"
>> what is device0 here? cpu?
> The device0 can also be a cpu. I drew a simple diagram:
>
>   cpu0     cpu1        cpu2/device0
>     |        |              |
>     |        |              |
>    DDR0     DDR1    No DIMM slots or no DIMM plugged
>  (node0)  (node1)         (node2)
>

thanks for the clarification. your example is for 3 node system, where
third node is memory less node.
do you see any issue in supporting this topology with existing code?
I think, this use case should be supported with present code.

>>>
>>> So, we can not simply classify device0 to node0 or node1, but we can
>>> define a node2 which distances to node0 and node1 are the same.
>>>
>>> Signed-off-by: Zhen Lei <thunder.leizhen at huawei.com>
>>> ---
>>>  arch/arm64/Kconfig      |  4 ++++
>>>  arch/arm64/kernel/smp.c |  1 +
>>>  arch/arm64/mm/numa.c    | 43 +++++++++++++++++++++++++++++++++++++++++--
>>>  3 files changed, 46 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
>>> index 05c1bf1..5904a62 100644
>>> --- a/arch/arm64/Kconfig
>>> +++ b/arch/arm64/Kconfig
>>> @@ -581,6 +581,10 @@ config NEED_PER_CPU_EMBED_FIRST_CHUNK
>>>         def_bool y
>>>         depends on NUMA
>>>
>>> +config HAVE_MEMORYLESS_NODES
>>> +       def_bool y
>>> +       depends on NUMA
>>> +
>>>  source kernel/Kconfig.preempt
>>>  source kernel/Kconfig.hz
>>>
>>> diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
>>> index d099306..9e15297 100644
>>> --- a/arch/arm64/kernel/smp.c
>>> +++ b/arch/arm64/kernel/smp.c
>>> @@ -620,6 +620,7 @@ static void __init of_parse_and_init_cpus(void)
>>>                         }
>>>
>>>                         bootcpu_valid = true;
>>> +                       early_map_cpu_to_node(0, of_node_to_nid(dn));
>>>
>>>                         /*
>>>                          * cpu_logical_map has already been
>>> diff --git a/arch/arm64/mm/numa.c b/arch/arm64/mm/numa.c
>>> index df5c842..d73b0a0 100644
>>> --- a/arch/arm64/mm/numa.c
>>> +++ b/arch/arm64/mm/numa.c
>>> @@ -128,6 +128,14 @@ void __init early_map_cpu_to_node(unsigned int cpu, int nid)
>>>                 nid = 0;
>>>
>>>         cpu_to_node_map[cpu] = nid;
>>> +
>>> +       /*
>>> +        * We should set the numa node of cpu0 as soon as possible, because it
>>> +        * has already been set up online before. cpu_to_node(0) will soon be
>>> +        * called.
>>> +        */
>>> +       if (!cpu)
>>> +               set_cpu_numa_node(cpu, nid);
>>>  }
>>>
>>>  #ifdef CONFIG_HAVE_SETUP_PER_CPU_AREA
>>> @@ -215,6 +223,35 @@ int __init numa_add_memblk(int nid, u64 start, u64 end)
>>>         return ret;
>>>  }
>>>
>>> +static u64 __init alloc_node_data_from_nearest_node(int nid, const size_t size)
>>> +{
>>> +       int i, best_nid, distance;
>>> +       u64 pa;
>>> +       DECLARE_BITMAP(nodes_map, MAX_NUMNODES);
>>> +
>>> +       bitmap_zero(nodes_map, MAX_NUMNODES);
>>> +       bitmap_set(nodes_map, nid, 1);
>>> +
>>> +find_nearest_node:
>>> +       best_nid = NUMA_NO_NODE;
>>> +       distance = INT_MAX;
>>> +
>>> +       for_each_clear_bit(i, nodes_map, MAX_NUMNODES)
>>> +               if (numa_distance[nid][i] < distance) {
>>> +                       best_nid = i;
>>> +                       distance = numa_distance[nid][i];
>>> +               }
>>> +
>>> +       pa = memblock_alloc_nid(size, SMP_CACHE_BYTES, best_nid);
>>> +       if (!pa) {
>>> +               BUG_ON(best_nid == NUMA_NO_NODE);
>>> +               bitmap_set(nodes_map, best_nid, 1);
>>> +               goto find_nearest_node;
>>> +       }
>>> +
>>> +       return pa;
>>> +}
>>> +

why do we need this function in arch specific code.
dont you think common code will take care of this? when you define
HAVE_MEMORYLESS_NODES

>>>  /**
>>>   * Initialize NODE_DATA for a node on the local memory
>>>   */
>>> @@ -228,7 +265,9 @@ static void __init setup_node_data(int nid, u64 start_pfn, u64 end_pfn)
>>>         pr_info("Initmem setup node %d [mem %#010Lx-%#010Lx]\n",
>>>                 nid, start_pfn << PAGE_SHIFT, (end_pfn << PAGE_SHIFT) - 1);
>>>
>>> -       nd_pa = memblock_alloc_try_nid(nd_size, SMP_CACHE_BYTES, nid);

this function try to allocate from a nid, if fails, it allocates from
node 0(local node).
this is ok for memory less node i guess.

>>> +       nd_pa = memblock_alloc_nid(nd_size, SMP_CACHE_BYTES, nid);
>>> +       if (!nd_pa)
>>> +               nd_pa = alloc_node_data_from_nearest_node(nid, nd_size);
>>>         nd = __va(nd_pa);
>>>
>>>         /* report and initialize */
>>> @@ -238,7 +277,7 @@ static void __init setup_node_data(int nid, u64 start_pfn, u64 end_pfn)
>>>         if (tnid != nid)
>>>                 pr_info("    NODE_DATA(%d) on node %d\n", nid, tnid);
>>>
>>> -       node_data[nid] = nd;
>>> +       NODE_DATA(nid) = nd;
>>>         memset(NODE_DATA(nid), 0, sizeof(pg_data_t));
>>>         NODE_DATA(nid)->node_id = nid;
>>>         NODE_DATA(nid)->node_start_pfn = start_pfn;
>>> --
>>> 2.5.0
>>>
>>>
>> Ganapat
>>>
>>> _______________________________________________
>>> linux-arm-kernel mailing list
>>> linux-arm-kernel at lists.infradead.org
>>> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
>>
>> .
>>
>