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

From: Wen Congyang <[email-masked]>
Date: Tue, 17 Jul 2012 11:32:18 +0800

At 07/17/2012 11:08 AM, Yasuaki Ishimatsu Wrote:
> Hi Wen,
> 
> 2012/07/17 11:32, Wen Congyang wrote:
>> At 07/17/2012 09:54 AM, Yasuaki Ishimatsu Wrote:
>>> Hi Wen,
>>>
>>> 2012/07/17 10:44, Yasuaki Ishimatsu wrote:
>>>> 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.
>>>
>>> It is not good idea since remove_memory frees mem_block structure...
>>> Do you have any ideas?
>>
>> Hmm, split offline_memory() to 2 functions: offline_pages() and __offline_pages()
>>
>> offline_pages()
>> 	lock_memory_hotplug();
>> 	__offline_pages();
>> 	unlock_memory_hotplug();
>>
>> and implement remove_memory() like this:
>> remove_memory()
>> 	lock_memory_hotplug()
>> 	if (!is_memblk_offline()) {
>> 		__offline_pages();
>> 	}
>> 	// cleanup
>> 	unlock_memory_hotplug();
>>
>> What about this?
> 
> I also thought about it once. But a problem remains. Current offilne_pages()
> cannot realize the memory has been removed by remove_memory(). So even if
> protecting the race by lock_memory_hotplug(), offline_pages() can offline
> the removed memory. offline_pages() should have the means to know the memory
> was removed. But I don't have good idea.

We can not online/offline part of memory block, so what about this?

remove_memory()
	lock_memory_hotplug()
	for each memory block:
		if (!is_memblk_offline()) {
			__offline_pages();
		}
	// cleanup
	unlock_memory_hotplug();

Thanks
Wen Congyang
> 
> Thanks,
> Yasuaki Ishimatsu
> 
>>
>> Thanks
>> Wen Congyang
>>>
>>> Thanks,
>>> Yasuaki Ishimatsu
>>>
>>>> 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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>>>>>
>>>>
>>>>
>>>>
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> 
> 
> 
>