Re: [PATCHv2, RFC 00/30] Transparent huge page cache

[Ric Mason <ric.masonn@gmail.com>]

On 03/18/2013 07:42 PM, Kirill A. Shutemov wrote:
> Simon Jeons wrote:
>> Hi Kirill,
>> On 03/18/2013 07:19 PM, Kirill A. Shutemov wrote:
>>> Simon Jeons wrote:
>>>> On 03/18/2013 12:03 PM, Simon Jeons wrote:
>>>>> Hi Kirill,
>>>>> On 03/15/2013 01:50 AM, Kirill A. Shutemov wrote:
>>>>>> From: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
>>>>>>
>>>>>> Here's the second version of the patchset.
>>>>>>
>>>>>> The intend of the work is get code ready to enable transparent huge page
>>>>>> cache for the most simple fs -- ramfs.
>>>>>>
>>>>>> We have read()/write()/mmap() functionality now. Still plenty work
>>>>>> ahead.
>>>>> One offline question.
>>>>>
>>>>> Why set PG_mlocked to page_tail which be splited in function
>>>>> __split_huge_page_refcount?
>>> Not set, but copied from head page. Head page represents up-to-date sate
>>> of compound page, we need to copy it to all tail pages on split.
>> I always see up-to-date state, could you conclude to me which state can
>> be treated as up-to-date? :-)
> While we work with huge page we only alter flags (like mlocked or
> uptodate) of head page, but not tail, so we have to copy flags to all tail
> pages on split. We also need to distribute _count and _mapcount properly.
> Just read the code.

Sorry, you can treat this question as an offline one and irrelevant thp. 
Which state of page can be treated as up-to-date?

>
>>>    
>>>> Also why can't find where _PAGE_SPLITTING and _PAGE_PSE flags are
>>>> cleared in split_huge_page path?
>>>    
>>> The pmd is invalidated and replaced with reference to page table at the end
>>> of __split_huge_page_map.
>> Since pmd is populated by page table and new flag why need
>> invalidated(clear present flag) before it?
> Comment just before pmdp_invalidate() in __split_huge_page_map() is fairly
> informative.
>