Hi Michal and David

quoted

-----Original Message-----
From: Michal Hocko <mhocko@kernel.org>
Sent: Tuesday, July 7, 2020 7:55 PM
To: Justin He <redacted>
Cc: Catalin Marinas <Catalin.Marinas@arm.com>; Will Deacon
[off-list ref]; Dan Williams [off-list ref]; Vishal Verma
[off-list ref]; Dave Jiang [off-list ref]; Andrew
Morton [off-list ref]; Mike Rapoport [off-list ref];
Baoquan He [off-list ref]; Chuhong Yuan [off-list ref]; linux-
arm-kernel@lists.infradead.org; linux-kernel@vger.kernel.org; linux-
mm@kvack.org; linux-nvdimm@lists.01.org; Kaly Xin [off-list ref]
Subject: Re: [PATCH v2 1/3] arm64/numa: export memory_add_physaddr_to_nid
as EXPORT_SYMBOL_GPL

On Tue 07-07-20 13:59:15, Jia He wrote:

quoted

This exports memory_add_physaddr_to_nid() for module driver to use.

memory_add_physaddr_to_nid() is a fallback option to get the nid in case
NUMA_NO_NID is detected.

Suggested-by: David Hildenbrand <redacted>
Signed-off-by: Jia He <redacted>
---
 arch/arm64/mm/numa.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/mm/numa.c b/arch/arm64/mm/numa.c
index aafcee3e3f7e..7eeb31740248 100644
--- a/arch/arm64/mm/numa.c
+++ b/arch/arm64/mm/numa.c

@@ -464,10 +464,11 @@ void __init arm64_numa_init(void)

 /*
  * We hope that we will be hotplugging memory on nodes we already know

about,

quoted

- * such that acpi_get_node() succeeds and we never fall back to this...
+ * such that acpi_get_node() succeeds. But when SRAT is not present,

the node

quoted

+ * id may be probed as NUMA_NO_NODE by acpi, Here provide a fallback

option.

quoted

  */
 int memory_add_physaddr_to_nid(u64 addr)
 {
-   pr_warn("Unknown node for memory at 0x%llx, assuming node 0\n",

addr);

quoted

    return 0;
 }
+EXPORT_SYMBOL_GPL(memory_add_physaddr_to_nid);

Does it make sense to export a noop function? Wouldn't make more sense
to simply make it static inline somewhere in a header? I haven't checked
whether there is an easy way to do that sanely bu this just hit my eyes.

Okay, I can make a change in memory_hotplug.h, sth like:

--- a/include/linux/memory_hotplug.h
+++ b/include/linux/memory_hotplug.h

@@ -149,13 +149,13 @@ int add_pages(int nid, unsigned long start_pfn, unsigned long nr_pages,
              struct mhp_params *params);
 #endif /* ARCH_HAS_ADD_PAGES */

-#ifdef CONFIG_NUMA
-extern int memory_add_physaddr_to_nid(u64 start);
-#else
+#if !defined(CONFIG_NUMA) || !defined(memory_add_physaddr_to_nid)
 static inline int memory_add_physaddr_to_nid(u64 start)
 {
        return 0;
 }
+#else
+extern int memory_add_physaddr_to_nid(u64 start);
 #endif

And then check the memory_add_physaddr_to_nid() helper on all arches,
if it is noop(return 0), I can simply remove it.
if it is not noop, after the helper,
#define memory_add_physaddr_to_nid

What do you think of this proposal?