Re: [PATCH V6] mm: memory hot-add: memory can not be added to movable zone defaultly

[Tang Chen <tangchen@cn.fujitsu.com>]

Hi Ishimatsu,

On 10/10/2015 02:13 AM, Yasuaki Ishimatsu wrote:
> Hi Tang,
>
> On Fri, 9 Oct 2015 15:59:38 +0800
> Tang Chen <tangchen@cn.fujitsu.com> wrote:
>
>> Hi,
>>
>> I don't mean to offend, but I really think it is not necessary to do this.
>>
>> hot-added memory will be added to ZONE_NORMAL by default. You can
>> modify it when you online memory. I think it is enough for users.
> But we cannot automatically create movable memory even if we use udev rules.
> Thus user must create original scrip to online memory as movable.
>
> Do you think every user understand the rule that ZONE_NORMAL must be on the
> left side of ZONE_MOVABLE?

I think memory hotplug users should understand this.

>
> If we can change the behavir of kernel by sysctl, user can create
> movable memory by only the following udev rule.
>
> SUBSYSTEM=="memory", ACTION=="add", ATTR{state}=="offline", ATTR{state}="online"

OK, that is fine. And I think it is better to add this to the commit 
message.

Thanks.

>
> Thanks,
> Yasuaki Ishimatsu
>
>> And a sysctl interface is also unnecessary. I think one default behaviour
>> is enough for kernel. We'd better keep it in the current way, or change it
>> and document it. It just makes no sense to enable users to modify it.
>> Can you please share any use case of this sysctl interface ?
>>
>> I suggest just keep the current implement. But I'm OK with that if other
>> reviewers or users could clarify it is useful. :)
>>
>> And BTW, please don't cc the following reviewers. Their email addresses
>> have changed.
>>
>> Cc: Zhang Yanfei<zhangyanfei@cn.fujitsu.com>
>> Cc: Hu Tao<hutao@cn.fujitsu.com>
>> Cc: Lai Jiangshan<laijs@cn.fujitsu.com>
>> Cc: Gu Zheng<guz.fnst@cn.fujitsu.com>
>>
>>
>> Thanks. :)
>>
>> On 10/09/2015 03:12 PM, Changsheng Liu wrote:
>>> From: Changsheng Liu <liuchangcheng@inspur.com>
>>>
>>> After the user config CONFIG_MOVABLE_NODE,
>>> When the memory is hot added, should_add_memory_movable() return 0
>>> because all zones including movable zone are empty,
>>> so the memory that was hot added will be added  to the normal zone
>>> and the normal zone will be created firstly.
>>> But we want the whole node to be added to movable zone defaultly.
>>>
>>> So we change should_add_memory_movable(): if the user config
>>> CONFIG_MOVABLE_NODE and sysctl parameter hotadd_memory_as_movable and
>>> the ZONE_NORMAL is empty or the pfn of the hot-added memory
>>> is after the end of the ZONE_NORMAL it will always return 1
>>> and all zones is empty at the same time,
>>> so that the movable zone will be created firstly
>>> and then the whole node will be added to movable zone defaultly.
>>> If we want the node to be added to normal zone,
>>> we can do it as follows:
>>> "echo online_kernel > /sys/devices/system/memory/memoryXXX/state"
>>>
>>> Signed-off-by: Changsheng Liu <liuchangsheng@inspur.com>
>>> Signed-off-by: Xiaofeng Yan <yanxiaofeng@inspur.com>
>>> Tested-by: Dongdong Fan <fandd@inspur.com>
>>> Cc: Wang Nan <wangnan0@huawei.com>
>>> Cc: Zhang Yanfei <zhangyanfei@cn.fujitsu.com>
>>> Cc: Dave Hansen <dave.hansen@intel.com>
>>> Cc: Yinghai Lu <yinghai@kernel.org>
>>> Cc: Tang Chen <tangchen@cn.fujitsu.com>
>>> Cc: Hu Tao <hutao@cn.fujitsu.com>
>>> Cc: Lai Jiangshan <laijs@cn.fujitsu.com>
>>> Cc: Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>
>>> Cc: Gu Zheng <guz.fnst@cn.fujitsu.com>
>>> Cc: Toshi Kani <toshi.kani@hp.com>
>>> Cc: Xishi Qiu <qiuxishi@huawei.com>
>>> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
>>> ---
>>>    Documentation/memory-hotplug.txt |    5 ++++-
>>>    kernel/sysctl.c                  |   15 +++++++++++++++
>>>    mm/memory_hotplug.c              |   23 +++++++++++++++++++++++
>>>    3 files changed, 42 insertions(+), 1 deletions(-)
>>>
>>> diff --git a/Documentation/memory-hotplug.txt b/Documentation/memory-hotplug.txt
>>> index ce2cfcf..7e6b4f4 100644
>>> --- a/Documentation/memory-hotplug.txt
>>> +++ b/Documentation/memory-hotplug.txt
>>> @@ -277,7 +277,7 @@ And if the memory block is in ZONE_MOVABLE, you can change it to ZONE_NORMAL:
>>>    After this, memory block XXX's state will be 'online' and the amount of
>>>    available memory will be increased.
>>>    
>>> -Currently, newly added memory is added as ZONE_NORMAL (for powerpc, ZONE_DMA).
>>> +Currently, newly added memory is added as ZONE_NORMAL or ZONE_MOVABLE (for powerpc, ZONE_DMA).
>>>    This may be changed in future.
>>>    
>>>    
>>> @@ -319,6 +319,9 @@ creates ZONE_MOVABLE as following.
>>>      Size of memory not for movable pages (not for offline) is TOTAL - ZZZZ.
>>>      Size of memory for movable pages (for offline) is ZZZZ.
>>>    
>>> +And a sysctl parameter for assigning the hot added memory to ZONE_MOVABLE is
>>> +supported. If the value of "kernel/hotadd_memory_as_movable" is 1,the hot added
>>> +memory will be assigned to ZONE_MOVABLE defautly.
>>>    
>>>    Note: Unfortunately, there is no information to show which memory block belongs
>>>    to ZONE_MOVABLE. This is TBD.
>>> diff --git a/kernel/sysctl.c b/kernel/sysctl.c
>>> index 19b62b5..855c48e 100644
>>> --- a/kernel/sysctl.c
>>> +++ b/kernel/sysctl.c
>>> @@ -166,6 +166,10 @@ extern int unaligned_dump_stack;
>>>    extern int no_unaligned_warning;
>>>    #endif
>>>    
>>> +#ifdef CONFIG_MOVABLE_NODE
>>> +extern int hotadd_memory_as_movable;
>>> +#endif
>>> +
>>>    #ifdef CONFIG_PROC_SYSCTL
>>>    
>>>    #define SYSCTL_WRITES_LEGACY	-1
>>> @@ -1139,6 +1143,17 @@ static struct ctl_table kern_table[] = {
>>>    		.proc_handler	= timer_migration_handler,
>>>    	},
>>>    #endif
>>> +/*If the value of "kernel/hotadd_memory_as_movable" is 1,the hot added
>>> + * memory will be assigned to ZONE_MOVABLE defautly.*/
>>> +#ifdef CONFIG_MOVABLE_NODE
>>> +	{
>>> +		.procname	= "hotadd_memory_as_movable",
>>> +		.data		= &hotadd_memory_as_movable,
>>> +		.maxlen		= sizeof(int),
>>> +		.mode		= 0644,
>>> +		.proc_handler	= proc_dointvec,
>>> +	},
>>> +#endif
>>>    	{ }
>>>    };
>>>    
>>> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
>>> index 26fbba7..5bcaf74 100644
>>> --- a/mm/memory_hotplug.c
>>> +++ b/mm/memory_hotplug.c
>>> @@ -37,6 +37,10 @@
>>>    
>>>    #include "internal.h"
>>>    
>>> +/*If the global variable value is 1,
>>> + * the hot added memory will be assigned to ZONE_MOVABLE defautly*/
>>> +int hotadd_memory_as_movable;
>>> +
>>>    /*
>>>     * online_page_callback contains pointer to current page onlining function.
>>>     * Initially it is generic_online_page(). If it is required it could be
>>> @@ -1190,6 +1194,9 @@ static int check_hotplug_memory_range(u64 start, u64 size)
>>>    /*
>>>     * If movable zone has already been setup, newly added memory should be check.
>>>     * If its address is higher than movable zone, it should be added as movable.
>>> + * And if system config CONFIG_MOVABLE_NODE and set the sysctl parameter
>>> + * "hotadd_memory_as_movable" and added memory does not overlap the zone
>>> + * before MOVABLE_ZONE,the memory is added as movable.
>>>     * Without this check, movable zone may overlap with other zone.
>>>     */
>>>    static int should_add_memory_movable(int nid, u64 start, u64 size)
>>> @@ -1197,6 +1204,22 @@ static int should_add_memory_movable(int nid, u64 start, u64 size)
>>>    	unsigned long start_pfn = start >> PAGE_SHIFT;
>>>    	pg_data_t *pgdat = NODE_DATA(nid);
>>>    	struct zone *movable_zone = pgdat->node_zones + ZONE_MOVABLE;
>>> +	struct zone *pre_zone = pgdat->node_zones + (ZONE_MOVABLE - 1);
>>> +	/*
>>> +	 * The system configs CONFIG_MOVABLE_NODE to assign a node
>>> +	 * which has only movable memory,so the hot-added memory should
>>> +	 * be assigned to ZONE_MOVABLE defaultly,
>>> +	 * but the function zone_for_memory() assign the hot-added memory
>>> +	 * to ZONE_NORMAL(x86_64) defaultly.Kernel does not allow to
>>> +	 * create ZONE_MOVABLE before ZONE_NORMAL,so If the value of
>>> +	 * sysctl parameter "hotadd_memory_as_movable" is 1
>>> +	 * and the ZONE_NORMAL is empty or the pfn of the hot-added memory
>>> +	 * is after the end of the ZONE_NORMAL
>>> +	 * the hot-added memory will be assigned to ZONE_MOVABLE.
>>> +	 */
>>> +	if (hotadd_memory_as_movable
>>> +	&& (zone_is_empty(pre_zone) || zone_end_pfn(pre_zone) <= start_pfn))
>>> +		return 1;
>>>    
>>>    	if (zone_is_empty(movable_zone))
>>>    		return 0;
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