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 12:08:53 +0900

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.

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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>>
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