linux-kernel - Re: [RFC PATCH 10/12] mm: add the buddy system interface

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Date:	Fri, 26 Jun 2015 17:34:35 +0900
From:	Kamezawa Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Xishi Qiu <qiuxishi@...wei.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>, nao.horiguchi@...il.com,
	Yinghai Lu <yinghai@...nel.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>, mingo@...e.hu,
	Xiexiuqi <xiexiuqi@...wei.com>,
	Hanjun Guo <guohanjun@...wei.com>,
	"Luck, Tony" <tony.luck@...el.com>, Linux MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH 10/12] mm: add the buddy system interface

On 2015/06/26 10:43, Xishi Qiu wrote:
> On 2015/6/26 7:54, Kamezawa Hiroyuki wrote:
>
>> On 2015/06/25 18:44, Xishi Qiu wrote:
>>> On 2015/6/10 11:06, Kamezawa Hiroyuki wrote:
>>>
>>>> On 2015/06/09 19:04, Xishi Qiu wrote:
>>>>> On 2015/6/9 15:12, Kamezawa Hiroyuki wrote:
>>>>>
>>>>>> On 2015/06/04 22:04, Xishi Qiu wrote:
>>>>>>> Add the buddy system interface for address range mirroring feature.
>>>>>>> Allocate mirrored pages in MIGRATE_MIRROR list. If there is no mirrored pages
>>>>>>> left, use other types pages.
>>>>>>>
>>>>>>> Signed-off-by: Xishi Qiu <qiuxishi@...wei.com>
>>>>>>> ---
>>>>>>>      mm/page_alloc.c | 40 +++++++++++++++++++++++++++++++++++++++-
>>>>>>>      1 file changed, 39 insertions(+), 1 deletion(-)
>>>>>>>
>>>>>>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>>>>>>> index d4d2066..0fb55288 100644
>>>>>>> --- a/mm/page_alloc.c
>>>>>>> +++ b/mm/page_alloc.c
>>>>>>> @@ -599,6 +599,26 @@ static inline bool is_mirror_pfn(unsigned long pfn)
>>>>>>>
>>>>>>>          return false;
>>>>>>>      }
>>>>>>> +
>>>>>>> +static inline bool change_to_mirror(gfp_t gfp_flags, int high_zoneidx)
>>>>>>> +{
>>>>>>> +    /*
>>>>>>> +     * Do not alloc mirrored memory below 4G, because 0-4G is
>>>>>>> +     * all mirrored by default, and the list is always empty.
>>>>>>> +     */
>>>>>>> +    if (high_zoneidx < ZONE_NORMAL)
>>>>>>> +        return false;
>>>>>>> +
>>>>>>> +    /* Alloc mirrored memory for only kernel */
>>>>>>> +    if (gfp_flags & __GFP_MIRROR)
>>>>>>> +        return true;
>>>>>>
>>>>>> GFP_KERNEL itself should imply mirror, I think.
>>>>>>
>>>>>
>>>>> Hi Kame,
>>>>>
>>>>> How about like this: #define GFP_KERNEL (__GFP_WAIT | __GFP_IO | __GFP_FS | __GFP_MIRROR) ?
>>>>>
>>>>
>>>> Hm.... it cannot cover GFP_ATOMIC at el.
>>>>
>>>> I guess, mirrored memory should be allocated if !__GFP_HIGHMEM or !__GFP_MOVABLE
>>>
>>>
>>> Hi Kame,
>>>
>>> Can we distinguish allocations form user or kernel only by GFP flags?
>>>
>>
>> Allocation from user and file caches are now *always* done with __GFP_MOVABLE.
>>
>> By this, pages will be allocated from MIGRATE_MOVABLE migration type.
>> MOVABLE migration type means it's can
>> be the target for page compaction or memory-hot-remove.
>>
>> Thanks,
>> -Kame
>>
>
> So if we want all kernel memory allocated from mirror, how about change like this?
> __alloc_pages_nodemask()
>    gfpflags_to_migratetype()
>      if (!(gfp_mask & __GFP_MOVABLE))
> 	return MIGRATE_MIRROR

Maybe used with jump label can reduce performance impact.
==
static inline bool memory_mirror_enabled(void)
{
         return static_key_false(&memory_mirror_enabled);
}



gfpflags_to_migratetype()
   if (memory_mirror_enabled()) { /* We want to mirror all unmovable pages */
       if (!(gfp_mask & __GFP_MOVABLE))
            return MIGRATE_MIRROR
   }
==

BTW, I think current memory compaction code scans ranges of MOVABLE migrate type.
So, if you use other migration type than MOVABLE for user pages, you may see
page fragmentation. If you want to expand this MIRROR to user pages, please check
mm/compaction.c


Thanks,
-Kame




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