RE: [PATCH v2 1/3] arm64/numa: export memory_add_physaddr_to_nid as EXPORT_SYMBOL_GPL

From: Justin He <Justin.He@arm.com>
To: Michal Hocko <mhocko@kernel.org>, David Hildenbrand <david@redhat.com>
Cc: Catalin Marinas <Catalin.Marinas@arm.com>,
	Will Deacon <will@kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Mike Rapoport <rppt@linux.ibm.com>, Baoquan He <bhe@redhat.com>,
	Chuhong Yuan <hslester96@gmail.com>,
	"linux-arm-kernel@lists.infradead.org"
	<linux-arm-kernel@lists.infradead.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"linux-mm@kvack.org" <linux-mm@kvack.org>,
	"linux-nvdimm@lists.01.org" <linux-nvdimm@lists.01.org>,
	Kaly Xin <Kaly.Xin@arm.com>
Subject: RE: [PATCH v2 1/3] arm64/numa: export memory_add_physaddr_to_nid as EXPORT_SYMBOL_GPL
Date: Wed, 8 Jul 2020 02:20:17 +0000	[thread overview]
Message-ID: <AM6PR08MB406907F9F2B13DA6DC893AD9F7670@AM6PR08MB4069.eurprd08.prod.outlook.com> (raw)
In-Reply-To: <20200707115454.GN5913@dhcp22.suse.cz>

Hi Michal and David

> -----Original Message-----
> From: Michal Hocko <mhocko@kernel.org>
> Sent: Tuesday, July 7, 2020 7:55 PM
> To: Justin He <Justin.He@arm.com>
> Cc: Catalin Marinas <Catalin.Marinas@arm.com>; Will Deacon
> <will@kernel.org>; Dan Williams <dan.j.williams@intel.com>; Vishal Verma
> <vishal.l.verma@intel.com>; Dave Jiang <dave.jiang@intel.com>; Andrew
> Morton <akpm@linux-foundation.org>; Mike Rapoport <rppt@linux.ibm.com>;
> Baoquan He <bhe@redhat.com>; Chuhong Yuan <hslester96@gmail.com>; linux-
> arm-kernel@lists.infradead.org; linux-kernel@vger.kernel.org; linux-
> mm@kvack.org; linux-nvdimm@lists.01.org; Kaly Xin <Kaly.Xin@arm.com>
> 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 <david@redhat.com>
> > Signed-off-by: Jia He <justin.he@arm.com>
> > ---
> >  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?

--
Cheers,
Justin (Jia He)

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