Re: [PATCH 2/3] mm: don't rely on system state to detect hot-plug operations

David Hildenbrand
2020-09-14T09:19:04Z

On 14.09.20 11:16, Laurent Dufour wrote:
> Le 14/09/2020 à 10:31, David Hildenbrand a écrit :
>>>> static int register_mem_sect_under_node_hotplug(struct memory_block *mem_blk,
>>>> void *arg)
>>>> {
>>>> const int nid = *(int *)arg;
>>>> int ret;
>>>>
>>>> /* Hotplugged memory has no holes and belongs to a single node. */
>>>> mem_blk->nid = nid;
>>>> ret = sysfs_create_link_nowarn(&node_devices[nid]->dev.kobj,
>>>> &mem_blk->dev.kobj,
>>>> kobject_name(&mem_blk->dev.kobj));
>>>> if (ret)
>>>> returnr et;
>>>> return sysfs_create_link_nowarn(&mem_blk->dev.kobj,
>>>> &node_devices[nid]->dev.kobj,
>>>> kobject_name(&node_devices[nid]->dev.kobj));
>>>>
>>>> }
>>>>
>>>> Cleaner, right? :) No unnecessary checks.
>>>
>>> I tend to agree here, I like more a simplistic version for hotplug.
>>>
>>
>> ... and while we're at it, we should rename register_mem_sect_under_node
>> to something like "register_memory_block_under_node" - "section" is a
>> legacy leftover here.
>>
>> We could factor out both sysfs_create_link_nowarn() calls into something
>> like "do_register_memory_block_under_node" or similar, to minimize code
>> duplication.
>>
>>>> One could argue if link_mem_section_hotplug() would be better than passing around the context.
>>>
>>> I am not sure if I would duplicate the code there.
>>> We could just pass the pointer of the function we want to call to
>>> link_mem_sections? either register_mem_sect_under_node_hotplug or
>>> register_mem_sect_under_node_early?
>>> Would not that be clean and clear enough?
>>
>> I don't particularly like passing around function pointers where it can
>> be avoided (e.g., here exporting 3 functions now instead 1). Makes the
>> interface harder to get IMHO. But I don't really care about that
>> interface, easy to change later on.
>>
>
> This would lead to the following.
>
> Do everyone agree?
>
> diff --git a/drivers/base/node.c b/drivers/base/node.c
> index 508b80f6329b..444808a7c9b6 100644
> --- a/drivers/base/node.c
> +++ b/drivers/base/node.c
> @@ -761,9 +761,32 @@ static int __ref get_nid_for_pfn(unsigned long pfn)
> return pfn_to_nid(pfn);
> }
>
> +static int do_register_memory_block_under_node(int nid,
> + struct memory_block *mem_blk)
> +{
> + int ret;
> +
> + /*
> + * If this memory block spans multiple nodes, we only indicate
> + * the last processed node.
> + */
> + mem_blk->nid = nid;
> +
> + ret = sysfs_create_link_nowarn(&node_devices[nid]->dev.kobj,
> + &mem_blk->dev.kobj,
> + kobject_name(&mem_blk->dev.kobj));
> + if (ret)
> + return ret;
> +
> + return sysfs_create_link_nowarn(&mem_blk->dev.kobj,
> + &node_devices[nid]->dev.kobj,
> + kobject_name(&node_devices[nid]->dev.kobj));
> +
> +}
> +
> /* 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)
> +static int register_mem_block_under_node_early(struct memory_block *mem_blk,
> + void *arg)
> {
> unsigned long memory_block_pfns = memory_block_size_bytes() / PAGE_SIZE;
> unsigned long start_pfn = section_nr_to_pfn(mem_blk->start_section_nr);
> @@ -785,38 +808,35 @@ static int register_mem_sect_under_node(struct
> memory_block *mem_blk,
> }
>
> /*
> - * We need to check if page belongs to nid only for the boot
> - * case, during hotplug we know that all pages in the memory
> - * block belong to the same node.
> + * We need to check if page belongs to nid only at the boot
> + * case because node's ranges can be interleaved.
> */
> - if (system_state = SYSTEM_BOOTING) {
> - page_nid = get_nid_for_pfn(pfn);
> - if (page_nid < 0)
> - continue;
> - if (page_nid != nid)
> - continue;
> - }
> -
> - /*
> - * If this memory block spans multiple nodes, we only indicate
> - * the last processed node.
> - */
> - mem_blk->nid = nid;
> + page_nid = get_nid_for_pfn(pfn);
> + if (page_nid < 0)
> + continue;
> + if (page_nid != nid)
> + continue;
>
> - ret = sysfs_create_link_nowarn(&node_devices[nid]->dev.kobj,
> - &mem_blk->dev.kobj,
> - kobject_name(&mem_blk->dev.kobj));
> + ret = do_register_memory_block_under_node(nid, mem_blk);
> if (ret)
> return ret;

You have to do an unconditional

return ret;

here AFAIKS. For me this looks much better.

Reviewed-by: David Hildenbrand <david@redhat.com>

--
Thanks,

David / dhildenb