On Wed, Jun 8, 2016 at 7:46 AM, Leizhen (ThunderTown)
[off-list ref] wrote:

On 2016/6/7 22:01, Ganapatrao Kulkarni wrote:

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On Tue, Jun 7, 2016 at 6:27 PM, Leizhen (ThunderTown)
[off-list ref] wrote:

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On 2016/6/7 16:31, Ganapatrao Kulkarni wrote:

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On Tue, Jun 7, 2016 at 1:38 PM, Zhen Lei [off-list ref] wrote:

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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?

If opened HAVE_MEMORYLESS_NODES, it will pick the nearest node for the cpus on
memoryless node.

i see couple of arch enabled HAVE_MEMORYLESS_NODES, but i don't see
any code in arch specific numa code for this.
is that means the core code will take care of this?

For example, in include/linux/topology.h
#ifdef CONFIG_HAVE_MEMORYLESS_NODES
...
static inline int cpu_to_mem(int cpu)
{
        return per_cpu(_numa_mem_, cpu);
}
...
#else
...
static inline int cpu_to_mem(int cpu)
{
        return cpu_to_node(cpu);
}
...
#endif

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I think, this use case should be supported with present code.

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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 <redacted>
---
 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.

I also considered put these code(include HAVE_SETUP_PER_CPU_AREA) into drivers/of/of_numa.c,
but if I do that, it will make acpi numa dependent on of numa.

numa core/common code is mainly in directory mm/
drivers/of/of_numa.c implements only device tree numa binding.

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dont you think common code will take care of this? when you define
HAVE_MEMORYLESS_NODES

I have searched CONFIG_HAVE_MEMORYLESS_NODES in *.c, but did not find the relevant content.
So maybe other ARCHs also missed this.

as mentioned above, arch code may not need any changes for this.

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 /**
  * 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.

Yes, the function is OK, but the performance is not.

Suppose there are 3 nodes:
1. cpu0 on node0, cpu1 on node1, cpu2 on node2.
2. cpu2 access the memory on node1 take 1us, but access the memory on node1 take 5us.
   That is, distance[2,1] is shorter than distance[2,0].
3. And node2 is a memoryless node.

So if NODE_DATA(2) allocated from node0, it will take more time than allocted from node1 at run time.
Because NODE_DATA will be accessed at run time.

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+       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

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.

.

thanks
Ganapat