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

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

quoted

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

quoted

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.

quoted

quoted

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

quoted

quoted

 /**
  * 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.

quoted

quoted

+       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

quoted

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