> Am 28.11.2019 um 11:20 schrieb Michal Hocko <mhocko@xxxxxxxxxx>:
>
> On Wed 27-11-19 18:41:26, David Hildenbrand wrote:
>> Since commit d84f2f5a7552 ("drivers/base/node.c: simplify
>> unregister_memory_block_under_nodes()") we only have a single user of
>> get_nid_for_pfn(). Let's just inline that code and get rid of
>> get_nid_for_pfn().
>>
>> Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
>> Cc: "Rafael J. Wysocki" <rafael@xxxxxxxxxx>
>> Cc: Michal Hocko <mhocko@xxxxxxxxxx>
>> Cc: Oscar Salvador <osalvador@xxxxxxx>
>> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
>> Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
>
> I am not really sure this is an improvement. The code is ugly as hell
> and open coding it just makes register_mem_sect_under_node harder to
> read.
The issue I see is that this is a dangerous wrapper for pfn_to_nid() that is absolutely not obvious. The old second user on the memory removal path was completely buggy. IMHO nobody should be reusing that function. But it looks like a general „safe wrapper to get a nid“ - it‘s not.
How can we make that more obvious instead?
>
> If anything get_nid_for_pfn deserves a comment why
> CONFIG_DEFERRED_STRUCT_PAGE_INIT calls for special case as
> early_pfn_to_nid is not bound to that config (it is defined when
> CONFIG_HAVE_ARCH_EARLY_PFN_TO_NID || CONFIG_HAVE_MEMBLOCK_NODE_MAP
>
>> ---
>> drivers/base/node.c | 23 +++++++----------------
>> 1 file changed, 7 insertions(+), 16 deletions(-)
>>
>> diff --git a/drivers/base/node.c b/drivers/base/node.c
>> index 98a31bafc8a2..735073fd2926 100644
>> --- a/drivers/base/node.c
>> +++ b/drivers/base/node.c
>> @@ -744,17 +744,6 @@ int unregister_cpu_under_node(unsigned int cpu, unsigned int nid)
>> }
>>
>> #ifdef CONFIG_MEMORY_HOTPLUG_SPARSE
>> -static int __ref get_nid_for_pfn(unsigned long pfn)
>> -{
>> - if (!pfn_valid_within(pfn))
>> - return -1;
>> -#ifdef CONFIG_DEFERRED_STRUCT_PAGE_INIT
>> - if (system_state < SYSTEM_RUNNING)
>> - return early_pfn_to_nid(pfn);
>> -#endif
>> - return pfn_to_nid(pfn);
>> -}
>> -
>> /* register memory section under specified node if it spans that node */
>> static int register_mem_sect_under_node(struct memory_block *mem_blk,
>> void *arg)
>> @@ -766,8 +755,6 @@ static int register_mem_sect_under_node(struct memory_block *mem_blk,
>> unsigned long pfn;
>>
>> for (pfn = start_pfn; pfn <= end_pfn; pfn++) {
>> - int page_nid;
>> -
>> /*
>> * memory block could have several absent sections from start.
>> * skip pfn range from absent section
>> @@ -784,11 +771,15 @@ static int register_mem_sect_under_node(struct memory_block *mem_blk,
>> * block belong to the same node.
>> */
>> if (system_state == SYSTEM_BOOTING) {
>> - page_nid = get_nid_for_pfn(pfn);
>> - if (page_nid < 0)
>> + if (!pfn_valid_within(pfn))
>> continue;
>> - if (page_nid != nid)
>> +#ifdef CONFIG_DEFERRED_STRUCT_PAGE_INIT
>> + if (early_pfn_to_nid(pfn) != nid)
>> continue;
>> +#else
>> + if (pfn_to_nid(pfn) != nid)
>> + continue;
>> +#endif
>> }
>>
>> /*
>> --
>> 2.21.0
>
> --
> Michal Hocko
> SUSE Labs
>
