[PATCH v3 1/5] mm: Enable CONFIG_NODES_SPAN_OTHER_NODES by default for NUMA

Hoan Tran
2020-03-28T18:31:52Z

In NUMA layout which nodes have memory ranges that span across other nodes,
the mm driver can detect the memory node id incorrectly.

For example, with layout below
Node 0 address: 0000 xxxx 0000 xxxx
Node 1 address: xxxx 1111 xxxx 1111

Note:
- Memory from low to high
- 0/1: Node id
- x: Invalid memory of a node

When mm probes the memory map, without CONFIG_NODES_SPAN_OTHER_NODES
config, mm only checks the memory validity but not the node id.
Because of that, Node 1 also detects the memory from node 0 as below
when it scans from the start address to the end address of node 1.

Node 0 address: 0000 xxxx xxxx xxxx
Node 1 address: xxxx 1111 1111 1111

This layout could occur on any architecture. Most of them enables
this config by default with CONFIG_NUMA. This patch, by default, enables
CONFIG_NODES_SPAN_OTHER_NODES or uses early_pfn_in_nid() for NUMA.

Signed-off-by: Hoan Tran <Hoan@os.amperecomputing.com>
---
mm/page_alloc.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index d047bf7..948c1c9 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1467,7 +1467,7 @@ int __meminit early_pfn_to_nid(unsigned long pfn)
}
#endif

-#ifdef CONFIG_NODES_SPAN_OTHER_NODES
+#ifdef CONFIG_NUMA
/* Only safe to use early in boot when initialisation is single-threaded */
static inline bool __meminit early_pfn_in_nid(unsigned long pfn, int node)
{
--
1.8.3.1