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Message-ID: <5004F570.80508@cn.fujitsu.com>
Date: Tue, 17 Jul 2012 13:17:36 +0800
From: Wen Congyang <wency@...fujitsu.com>
To: Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>
CC: linux-mm@...ck.org, linux-kernel@...r.kernel.org,
linuxppc-dev@...ts.ozlabs.org, linux-acpi@...r.kernel.org,
rientjes@...gle.com, liuj97@...il.com, len.brown@...el.com,
benh@...nel.crashing.org, paulus@...ba.org, cl@...ux.com,
minchan.kim@...il.com, akpm@...ux-foundation.org,
kosaki.motohiro@...fujitsu.com
Subject: Re: [RFC PATCH v3 2/13] memory-hotplug : add physical memory hotplug
code to acpi_memory_device_remove
At 07/17/2012 12:51 PM, Yasuaki Ishimatsu Wrote:
> Hi Wen,
>
> 2012/07/17 12:32, Wen Congyang wrote:
>> 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 <rientjes@...gle.com>
>>>>>>>> CC: Jiang Liu <liuj97@...il.com>
>>>>>>>> CC: Len Brown <len.brown@...el.com>
>>>>>>>> CC: Benjamin Herrenschmidt <benh@...nel.crashing.org>
>>>>>>>> CC: Paul Mackerras <paulus@...ba.org>
>>>>>>>> CC: Christoph Lameter <cl@...ux.com>
>>>>>>>> Cc: Minchan Kim <minchan.kim@...il.com>
>>>>>>>> CC: Andrew Morton <akpm@...ux-foundation.org>
>>>>>>>> CC: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
>>>>>>>> CC: Wen Congyang <wency@...fujitsu.com>
>>>>>>>> Signed-off-by: Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>
>>>>>>>>
>>>>>>>> ---
>>>>>>>> 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?
>
> It seems you do not understand my concern.
> When memory_remove() and offline_pages() run to same memory simultaneously,
> offline_pages runs to removed memory.
>
> memory_remove() | offline_pages()
> -----------------------------------------------------------
> lock_memory_hotplug() |
> | wait at lock_memory_hotplug()
> remove memory |
> unlock_memory_hotplug() |
> | wake up and start offline_pages()
> | offline page
> | => but the memory has already removed
> | by memory_remove()
>
> In this case, offline_page() may access removed memory.
Yes, in this case, the kernel may panic.
I think we can call pfn_present() in online_pages()/offline_pages()
to check whether the memory is removed.
Thanks
Wen Congyang
>
> Thanks,
> Yasuaki Ishimatsu
>
>>
>> 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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>>>>>
>>>>>
>>>>>
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