Subject: [PATCH v2 1/5] mm: Enable CONFIG_NODES_SPAN_OTHER_NODES by default for NUMA

From: Hoan Tran OS <[email-masked]>
Date: Thu, 11 Jul 2019 23:25:46 +0000

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. This patch enables
CONFIG_NODES_SPAN_OTHER_NODES by default for NUMA to fix this issue.

Signed-off-by: Hoan Tran <[email-masked]>
---
 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 d66bc8a..6335505 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1413,7 +1413,7 @@ 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)
 {
-- 
2.7.4

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