Date:	Tue, 7 Jun 2016 20:57:42 +0800
From:	"Leizhen (ThunderTown)" <thunder.leizhen@...wei.com>
To:	Ganapatrao Kulkarni <gpkulkarni@...il.com>
CC:	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>,
	linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
	Ganapatrao Kulkarni <gkulkarni@...iumnetworks.com>,
	Robert Richter <rrichter@...ium.com>,
	"David Daney" <david.daney@...ium.com>,
	Rob Herring <robh+dt@...nel.org>,
	"Frank Rowand" <frowand.list@...il.com>,
	Grant Likely <grant.likely@...aro.org>,
	devicetree <devicetree@...r.kernel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Xinwei Hu <huxinwei@...wei.com>, Zefan Li <lizefan@...wei.com>,
	Hanjun Guo <guohanjun@...wei.com>,
	Tianhong Ding <dingtianhong@...wei.com>
Subject: Re: [PATCH v4 11/14] arm64/numa: support HAVE_MEMORYLESS_NODES



On 2016/6/7 16:31, Ganapatrao Kulkarni wrote:
> On Tue, Jun 7, 2016 at 1:38 PM, Zhen Lei <thunder.leizhen@...wei.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)

>>
>> 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@...wei.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;
>> +}
>> +
>>  /**
>>   * 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);
>> +       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@...ts.infradead.org
>> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
> 
> .
> 

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