RE: [PATCH v2 1/3] arm64/numa: export memory_add_physaddr_to_nid as EXPORT_SYMBOL_GPL | linux-arm-kernel

quoted

Hi Dan

-----Original Message-----
From: Dan Williams <redacted>
Sent: Wednesday, July 8, 2020 1:48 PM
To: Mike Rapoport <redacted>
Cc: Justin He <redacted>; Michal Hocko <mhocko@kernel.org>; David
Hildenbrand [off-list ref]; Catalin Marinas [off-list ref];
Will Deacon [off-list ref]; Vishal Verma [off-list ref];
Dave Jiang [off-list ref]; Andrew Morton <akpm@linux-
foundation.org>; 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, Jul 7, 2020 at 10:33 PM Mike Rapoport [off-list ref] wrote:
On Tue, Jul 07, 2020 at 08:56:36PM -0700, Dan Williams wrote:
On Tue, Jul 7, 2020 at 7:20 PM Justin He [off-list ref] wrote:
Hi Michal and David

-----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:
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,
- * 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
+ * id may be probed as NUMA_NO_NODE by acpi, Here provide a
fallback
option.
  */
 int memory_add_physaddr_to_nid(u64 addr)
 {
-   pr_warn("Unknown node for memory at 0x%llx, assuming node
0\n",
addr);
    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?
Especially for architectures that use memblock info for numa info
(which seems to be everyone except x86) why not implement a generic
memory_add_physaddr_to_nid() that does:
That would be only arm64.
Darn, I saw ARCH_KEEP_MEMBLOCK and had delusions of grandeur that it
could solve my numa api woes. At least for x86 the problem is already
solved with reserved numa_meminfo, but now I'm trying to write generic
drivers that use those apis and finding these gaps on other archs.
Even on arm64, there is a dependency issue in dax_pmem kmem case.
If dax pmem uses memory_add_physaddr_to_nid() to decide which node that
memblock should add into, get_pfn_range_for_nid() might not have
the correct memblock info at that time. That is, get_pfn_range_for_nid()
can't get the correct memblock info before add_memory()

So IMO, memory_add_physaddr_to_nid() still have to implement as noop on
arm64 (return 0) together with sh,s390x? Powerpc, x86,ia64 can use their
own implementation. And phys_to_target_node() can use your suggested(
for_each_online_node() ...)

What do you think of it? Thanks

--
Cheers,
Justin (Jia He)


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