Subject: Re: [RFC PATCH v3 2/13] memory-hotplug : add physical memory hotplug code to acpi_memory_device_remove

From: Yasuaki Ishimatsu <[email-masked]>
Date: Tue, 17 Jul 2012 10:44:59 +0900

Hi Wen,

2012/07/13 12:35, Wen Congyang wrote:
> At 07/09/2012 06:24 PM, Yasuaki Ishimatsu Wrote:
>> acpi_memory_device_remove() has been prepared to remove physical memory.
>> But, the function only frees acpi_memory_device currentlry.
>>
>> The patch adds following functions into acpi_memory_device_remove():
>>    - offline memory
>>    - remove physical memory (only return -EBUSY)
>>    - free acpi_memory_device
>>
>> CC: David Rientjes <[email-masked]>
>> CC: Jiang Liu <[email-masked]>
>> CC: Len Brown <[email-masked]>
>> CC: Benjamin Herrenschmidt <[email-masked]>
>> CC: Paul Mackerras <[email-masked]>
>> CC: Christoph Lameter <[email-masked]>
>> Cc: Minchan Kim <[email-masked]>
>> CC: Andrew Morton <[email-masked]>
>> CC: KOSAKI Motohiro <[email-masked]>
>> CC: Wen Congyang <[email-masked]>
>> Signed-off-by: Yasuaki Ishimatsu <[email-masked]>
>>
>> ---
>>   drivers/acpi/acpi_memhotplug.c |   26 +++++++++++++++++++++++++-
>>   drivers/base/memory.c          |   39 +++++++++++++++++++++++++++++++++++++++
>>   include/linux/memory.h         |    5 +++++
>>   include/linux/memory_hotplug.h |    1 +
>>   mm/memory_hotplug.c            |    8 ++++++++
>>   5 files changed, 78 insertions(+), 1 deletion(-)
>>
>> Index: linux-3.5-rc6/drivers/acpi/acpi_memhotplug.c
>> ===================================================================
>> --- linux-3.5-rc6.orig/drivers/acpi/acpi_memhotplug.c	2012-07-09 18:08:29.946888653 +0900
>> +++ linux-3.5-rc6/drivers/acpi/acpi_memhotplug.c	2012-07-09 18:08:43.470719531 +0900
>> @@ -29,6 +29,7 @@
>>   #include <linux/module.h>
>>   #include <linux/init.h>
>>   #include <linux/types.h>
>> +#include <linux/memory.h>
>>   #include <linux/memory_hotplug.h>
>>   #include <linux/slab.h>
>>   #include <acpi/acpi_drivers.h>
>> @@ -452,12 +453,35 @@ static int acpi_memory_device_add(struct
>>   static int acpi_memory_device_remove(struct acpi_device *device, int type)
>>   {
>>   	struct acpi_memory_device *mem_device = NULL;
>> -
>> +	struct acpi_memory_info *info, *tmp;
>> +	int result;
>> +	int node;
>>
>>   	if (!device || !acpi_driver_data(device))
>>   		return -EINVAL;
>>
>>   	mem_device = acpi_driver_data(device);
>> +
>> +	node = acpi_get_node(mem_device->device->handle);
>> +
>> +	list_for_each_entry_safe(info, tmp, &mem_device->res_list, list) {
>> +		if (!info->enabled)
>> +			continue;
>> +
>> +		if (!is_memblk_offline(info->start_addr, info->length)) {
>> +			result = offline_memory(info->start_addr, info->length);
>> +			if (result)
>> +				return result;
>> +		}
>> +
>> +		result = remove_memory(node, info->start_addr, info->length);
> 
> The user may online the memory between offline_memory() and remove_memory().
> So I think we should lock memory hotplug before check the memory's status
> and release it after remove_memory().

How about get "mem_block->state_mutex" of removed memory? When offlining
memory, we need to change "memory_block->state" into "MEM_OFFLINE".
In this case, we get mem_block->state_mutex. So I think the mutex lock
is beneficial.

Thanks,
Yasuaki Ishimatsu

> 
> Thanks
> Wen Congyang
> 
>> +		if (result)
>> +			return result;
>> +
>> +		list_del(&info->list);
>> +		kfree(info);
>> +	}
>> +
>>   	kfree(mem_device);
>>
>>   	return 0;
>> Index: linux-3.5-rc6/include/linux/memory_hotplug.h
>> ===================================================================
>> --- linux-3.5-rc6.orig/include/linux/memory_hotplug.h	2012-07-09 18:08:29.955888542 +0900
>> +++ linux-3.5-rc6/include/linux/memory_hotplug.h	2012-07-09 18:08:43.471719518 +0900
>> @@ -233,6 +233,7 @@ static inline int is_mem_section_removab
>>   extern int mem_online_node(int nid);
>>   extern int add_memory(int nid, u64 start, u64 size);
>>   extern int arch_add_memory(int nid, u64 start, u64 size);
>> +extern int remove_memory(int nid, u64 start, u64 size);
>>   extern int offline_memory(u64 start, u64 size);
>>   extern int sparse_add_one_section(struct zone *zone, unsigned long start_pfn,
>>   								int nr_pages);
>> Index: linux-3.5-rc6/mm/memory_hotplug.c
>> ===================================================================
>> --- linux-3.5-rc6.orig/mm/memory_hotplug.c	2012-07-09 18:08:29.953888567 +0900
>> +++ linux-3.5-rc6/mm/memory_hotplug.c	2012-07-09 18:08:43.476719455 +0900
>> @@ -659,6 +659,14 @@ out:
>>   }
>>   EXPORT_SYMBOL_GPL(add_memory);
>>
>> +int remove_memory(int nid, u64 start, u64 size)
>> +{
>> +	return -EBUSY;
>> +
>> +}
>> +EXPORT_SYMBOL_GPL(remove_memory);
>> +
>> +
>>   #ifdef CONFIG_MEMORY_HOTREMOVE
>>   /*
>>    * A free page on the buddy free lists (not the per-cpu lists) has PageBuddy
>> Index: linux-3.5-rc6/drivers/base/memory.c
>> ===================================================================
>> --- linux-3.5-rc6.orig/drivers/base/memory.c	2012-07-09 18:08:29.947888640 +0900
>> +++ linux-3.5-rc6/drivers/base/memory.c	2012-07-09 18:10:54.880076739 +0900
>> @@ -70,6 +70,45 @@ void unregister_memory_isolate_notifier(
>>   }
>>   EXPORT_SYMBOL(unregister_memory_isolate_notifier);
>>
>> +bool is_memblk_offline(unsigned long start, unsigned long size)
>> +{
>> +	struct memory_block *mem = NULL;
>> +	struct mem_section *section;
>> +	unsigned long start_pfn, end_pfn;
>> +	unsigned long pfn, section_nr;
>> +
>> +	start_pfn = PFN_DOWN(start);
>> +	end_pfn = start_pfn + PFN_DOWN(start);
>> +
>> +	for (pfn = start_pfn; pfn < end_pfn; pfn += PAGES_PER_SECTION) {
>> +		section_nr = pfn_to_section_nr(pfn);
>> +		if (!present_section_nr(section_nr));
>> +			continue;
>> +
>> +		section = __nr_to_section(section_nr);
>> +		/* same memblock? */
>> +		if (mem)
>> +			if((section_nr >= mem->start_section_nr) &&
>> +			   (section_nr <= mem->end_section_nr))
>> +				continue;
>> +
>> +		mem = find_memory_block_hinted(section, mem);
>> +		if (!mem)
>> +			continue;
>> +		if (mem->state == MEM_OFFLINE)
>> +			continue;
>> +
>> +		kobject_put(&mem->dev.kobj);
>> +		return false;
>> +	}
>> +
>> +	if (mem)
>> +		kobject_put(&mem->dev.kobj);
>> +
>> +	return true;
>> +}
>> +EXPORT_SYMBOL(is_memblk_offline);
>> +
>>   /*
>>    * register_memory - Setup a sysfs device for a memory block
>>    */
>> Index: linux-3.5-rc6/include/linux/memory.h
>> ===================================================================
>> --- linux-3.5-rc6.orig/include/linux/memory.h	2012-07-08 09:23:56.000000000 +0900
>> +++ linux-3.5-rc6/include/linux/memory.h	2012-07-09 18:08:43.484719355 +0900
>> @@ -106,6 +106,10 @@ static inline int memory_isolate_notify(
>>   {
>>   	return 0;
>>   }
>> +static inline bool is_memblk_offline(unsigned long start, unsigned long size)
>> +{
>> +	return false;
>> +}
>>   #else
>>   extern int register_memory_notifier(struct notifier_block *nb);
>>   extern void unregister_memory_notifier(struct notifier_block *nb);
>> @@ -120,6 +124,7 @@ extern int memory_isolate_notify(unsigne
>>   extern struct memory_block *find_memory_block_hinted(struct mem_section *,
>>   							struct memory_block *);
>>   extern struct memory_block *find_memory_block(struct mem_section *);
>> +extern bool is_memblk_offline(unsigned long start, unsigned long size);
>>   #define CONFIG_MEM_BLOCK_SIZE	(PAGES_PER_SECTION<<PAGE_SHIFT)
>>   enum mem_add_context { BOOT, HOTPLUG };
>>   #endif /* CONFIG_MEMORY_HOTPLUG_SPARSE */
>>
>>
> 
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