Re: [PATCH 4/8] hugetlb: create remove_hugetlb_page() to separate functionality

[Miaohe Lin <linmiaohe@huawei.com>]

On 2021/3/27 3:57, Mike Kravetz wrote:
> On 3/25/21 7:10 PM, Miaohe Lin wrote:
>> On 2021/3/25 8:28, Mike Kravetz wrote:
>>> The new remove_hugetlb_page() routine is designed to remove a hugetlb
>>> page from hugetlbfs processing.  It will remove the page from the active
>>> or free list, update global counters and set the compound page
>>> destructor to NULL so that PageHuge() will return false for the 'page'.
>>> After this call, the 'page' can be treated as a normal compound page or
>>> a collection of base size pages.
>>>
>>> remove_hugetlb_page is to be called with the hugetlb_lock held.
>>>
>>> Creating this routine and separating functionality is in preparation for
>>> restructuring code to reduce lock hold times.
>>>
>>> Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>
>>> ---
>>>  mm/hugetlb.c | 70 +++++++++++++++++++++++++++++++++-------------------
>>>  1 file changed, 45 insertions(+), 25 deletions(-)
>>>
>>> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
>>> index 404b0b1c5258..3938ec086b5c 100644
>>> --- a/mm/hugetlb.c
>>> +++ b/mm/hugetlb.c
>>> @@ -1327,6 +1327,46 @@ static inline void destroy_compound_gigantic_page(struct page *page,
>>>  						unsigned int order) { }
>>>  #endif
>>>  
>>> +/*
>>> + * Remove hugetlb page from lists, and update dtor so that page appears
>>> + * as just a compound page.  A reference is held on the page.
>>> + * NOTE: hugetlb specific page flags stored in page->private are not
>>> + *	 automatically cleared.  These flags may be used in routines
>>> + *	 which operate on the resulting compound page.
>>
>> It seems HPageFreed and HPageTemporary is cleared. Which hugetlb specific page flags
>> is reserverd here and why? Could you please give a simple example to clarify
>> this in the comment to help understand this NOTE?
>>
> 
> I will remove that NOTE: in the comment to avoid any confusion.
> 
> The NOTE was add in the RFC that contained a separate patch to add a flag
> that tracked huge pages allocated from CMA.  That flag needed to remain
> for subsequent freeing of such pages.  This is no longer needed.
> 

Many thanks for explaination. I was confused about that NOTE. :)

>> The code looks good to me. Many thanks!
>> Reviewed-by: Miaohe Lin <linmiaohe@huawei.com>
> 
> Thanks,
>