Re: + mm-hugetlb-fix-race-when-migrate-pages.patch added to -mm tree

[zhong jiang <zhongjiang@huawei.com>]

On 2016/7/21 22:01, Michal Hocko wrote:
> On Thu 21-07-16 21:58:23, zhong jiang wrote:
>> On 2016/7/21 21:40, Michal Hocko wrote:
>>> On Thu 21-07-16 21:25:38, zhong jiang wrote:
>>>> On 2016/7/21 20:55, Michal Hocko wrote:
>>> [...]
>>>>> OK, now I understand what you mean. So you mean that a different process
>>>>> initiates the migration while this path copies to pte. That is certainly
>>>>> possible but I still fail to see what is the problem about that.
>>>>> huge_pte_alloc will return the identical pte whether it is regular or
>>>>> migration one. So what exactly is the problem?
>>>>>
>>>> copy_hugetlb_page_range obtain the shared dst_pte, it may be not equal
>>>> to the src_pte.  The dst_pte can come from other process sharing the
>>>> mapping.
>>> So you mean that the parent doesn't have the shared pte while the child
>>> would get one?
>>>  
>>  no, parent must have the shared pte because the the child copy the
>> parent. but parent is not the only source pte we can get. when we
>> scan the maping->i_mmap, firstly ,it can obtain a shared pte from
>> other process. but I am not sure.
> But then all the shared ptes should be identical, no? Or am I missing
> something?
 all the shared ptes should be identical, but  there is  a possibility that new process
 want to share the pte from other process ,  other than the parent,  For the first time
 the process is about to share pte with it.   is it possiblity?

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