Re: [PATCH 1/3] mm: fix set pageblock migratetype in deferred struct page init

[Xishi Qiu]

On 2016/8/16 18:12, Vlastimil Babka wrote:

> On 08/16/2016 11:23 AM, Michal Hocko wrote:
>> On Tue 16-08-16 16:56:54, Xishi Qiu wrote:
>>> On 2016/8/16 16:41, Michal Hocko wrote:
>>>
>>>> On Thu 04-08-16 19:25:03, Xishi Qiu wrote:
>>>>> MAX_ORDER_NR_PAGES is usually 4M, and a pageblock is usually 2M, so we only
>>>>> set one pageblock's migratetype in deferred_free_range() if pfn is aligned
>>>>> to MAX_ORDER_NR_PAGES.
>>>>
>>>> Do I read the changelog correctly and the bug causes leaking unmovable
>>>> allocations into movable zones?
>>>
>>> Hi Michal,
>>>
>>> This bug will cause uninitialized migratetype, you can see from
>>> "cat /proc/pagetypeinfo", almost half blocks are Unmovable.
>>
>> Please add that information to the changelog. Leaking unmovable
>> allocations to the movable zones defeats the whole purpose of the
>> movable zone so I guess we really want to mark this for stable.
> 
> Note that it's not as severe. Pageblock migratetype is just heuristic against fragmentation. It should not allow unmovable allocations from movable zones (although I can't find what really does govern it).
> 

Yes, leaking unmovable migratetype to movable zone is fine for mem-offline,
we will check every page in offline_pages().
But as I pointed that we missed to free the last block in deferred_init_memmap(),
this will lead to mem-offline fail.

Thanks,
Xishi Qiu

>> AFAICS it should also note:
>> Fixes: ac5d2539b238 ("mm: meminit: reduce number of times pageblocks are set during struct page init")
>> and stable 4.2+
> 
> 
> 
> 
> .
>