Subject: Re: [PATCH v3 11/12] memory-hotplug: remove sysfs file of node

From: Wen Congyang <[email-masked]>
Date: Tue, 27 Nov 2012 10:24:49 +0800

At 11/26/2012 10:27 PM, Jianguo Wu Wrote:
> On 2012/11/1 17:44, Wen Congyang wrote:
>> This patch introduces a new function try_offline_node() to
>> remove sysfs file of node when all memory sections of this
>> node are removed. If some memory sections of this node are
>> not removed, this function does nothing.
>>
>> CC: David Rientjes <[email-masked]>
>> CC: Jiang Liu <[email-masked]>
>> CC: Len Brown <[email-masked]>
>> CC: Christoph Lameter <[email-masked]>
>> Cc: Minchan Kim <[email-masked]>
>> CC: Andrew Morton <[email-masked]>
>> CC: KOSAKI Motohiro <[email-masked]>
>> CC: Yasuaki Ishimatsu <[email-masked]>
>> Signed-off-by: Wen Congyang <[email-masked]>
>> ---
>>  drivers/acpi/acpi_memhotplug.c |  8 +++++-
>>  include/linux/memory_hotplug.h |  2 +-
>>  mm/memory_hotplug.c            | 58 ++++++++++++++++++++++++++++++++++++++++--
>>  3 files changed, 64 insertions(+), 4 deletions(-)
>>
>> diff --git a/drivers/acpi/acpi_memhotplug.c b/drivers/acpi/acpi_memhotplug.c
>> index 24c807f..0780f99 100644
>> --- a/drivers/acpi/acpi_memhotplug.c
>> +++ b/drivers/acpi/acpi_memhotplug.c
>> @@ -310,7 +310,9 @@ static int acpi_memory_disable_device(struct acpi_memory_device *mem_device)
>>  {
>>  	int result;
>>  	struct acpi_memory_info *info, *n;
>> +	int node;
>>  
>> +	node = acpi_get_node(mem_device->device->handle);
>>  
>>  	/*
>>  	 * Ask the VM to offline this memory range.
>> @@ -318,7 +320,11 @@ static int acpi_memory_disable_device(struct acpi_memory_device *mem_device)
>>  	 */
>>  	list_for_each_entry_safe(info, n, &mem_device->res_list, list) {
>>  		if (info->enabled) {
>> -			result = remove_memory(info->start_addr, info->length);
>> +			if (node < 0)
>> +				node = memory_add_physaddr_to_nid(
>> +					info->start_addr);
>> +			result = remove_memory(node, info->start_addr,
>> +				info->length);
>>  			if (result)
>>  				return result;
>>  		}
>> diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h
>> index d4c4402..7b4cfe6 100644
>> --- a/include/linux/memory_hotplug.h
>> +++ b/include/linux/memory_hotplug.h
>> @@ -231,7 +231,7 @@ extern int arch_add_memory(int nid, u64 start, u64 size);
>>  extern int offline_pages(unsigned long start_pfn, unsigned long nr_pages);
>>  extern int offline_memory_block(struct memory_block *mem);
>>  extern bool is_memblock_offlined(struct memory_block *mem);
>> -extern int remove_memory(u64 start, u64 size);
>> +extern int remove_memory(int node, u64 start, u64 size);
>>  extern int sparse_add_one_section(struct zone *zone, unsigned long start_pfn,
>>  								int nr_pages);
>>  extern void sparse_remove_one_section(struct zone *zone, struct mem_section *ms);
>> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
>> index 7bcced0..d965da3 100644
>> --- a/mm/memory_hotplug.c
>> +++ b/mm/memory_hotplug.c
>> @@ -29,6 +29,7 @@
>>  #include <linux/suspend.h>
>>  #include <linux/mm_inline.h>
>>  #include <linux/firmware-map.h>
>> +#include <linux/stop_machine.h>
>>  
>>  #include <asm/tlbflush.h>
>>  
>> @@ -1299,7 +1300,58 @@ static int is_memblock_offlined_cb(struct memory_block *mem, void *arg)
>>  	return ret;
>>  }
>>  
>> -int __ref remove_memory(u64 start, u64 size)
>> +static int check_cpu_on_node(void *data)
>> +{
>> +	struct pglist_data *pgdat = data;
>> +	int cpu;
>> +
>> +	for_each_present_cpu(cpu) {
>> +		if (cpu_to_node(cpu) == pgdat->node_id)
>> +			/*
>> +			 * the cpu on this node isn't removed, and we can't
>> +			 * offline this node.
>> +			 */
>> +			return -EBUSY;
>> +	}
>> +
>> +	return 0;
>> +}
>> +
>> +/* offline the node if all memory sections of this node are removed */
>> +static void try_offline_node(int nid)
>> +{
>> +	unsigned long start_pfn = NODE_DATA(nid)->node_start_pfn;
>> +	unsigned long end_pfn = start_pfn + NODE_DATA(nid)->node_spanned_pages;
>> +	unsigned long pfn;
>> +
>> +	for (pfn = start_pfn; pfn < end_pfn; pfn += PAGES_PER_SECTION) {
>> +		unsigned long section_nr = pfn_to_section_nr(pfn);
>> +
>> +		if (!present_section_nr(section_nr))
>> +			continue;
>> +
>> +		if (pfn_to_nid(pfn) != nid)
>> +			continue;
>> +
>> +		/*
>> +		 * some memory sections of this node are not removed, and we
>> +		 * can't offline node now.
>> +		 */
>> +		return;
>> +	}
>> +
>> +	if (stop_machine(check_cpu_on_node, NODE_DATA(nid), NULL))
>> +		return;
> 
> how about:
> 	if (nr_cpus_node(nid))

If all cpus on the node is offlined, but not removed, nr_cpus_node(nid) will
return 0. In this case, we still can't offline the node.

Another purpose to use stop_machine() is to prevent cpu hotplug. We can't lock
cpuhotplug here.

Thanks
Wen Congyang

> 		return;
>> +
>> +	/*
>> +	 * all memory/cpu of this node are removed, we can offline this
>> +	 * node now.
>> +	 */
>> +	node_set_offline(nid);
>> +	unregister_one_node(nid);
>> +}
>> +
>> +int __ref remove_memory(int nid, u64 start, u64 size)
>>  {
>>  	unsigned long start_pfn, end_pfn;
>>  	int ret = 0;
>> @@ -1346,6 +1398,8 @@ repeat:
>>  
>>  	arch_remove_memory(start, size);
>>  
>> +	try_offline_node(nid);
>> +
>>  	unlock_memory_hotplug();
>>  
>>  	return 0;
>> @@ -1355,7 +1409,7 @@ int offline_pages(unsigned long start_pfn, unsigned long nr_pages)
>>  {
>>  	return -EINVAL;
>>  }
>> -int remove_memory(u64 start, u64 size)
>> +int remove_memory(int nid, u64 start, u64 size)
>>  {
>>  	return -EINVAL;
>>  }
>>
> 
>