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 10:32:23 +0800

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?

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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