[PATCH v2 1/3] mm: change huge_ptep_clear_flush() to return the original pte

[Baolin Wang]

On 5/8/2022 7:09 PM, Muchun Song wrote:
> On Sun, May 08, 2022 at 05:36:39PM +0800, Baolin Wang wrote:
>> It is incorrect to use ptep_clear_flush() to nuke a hugetlb page
>> table when unmapping or migrating a hugetlb page, and will change
>> to use huge_ptep_clear_flush() instead in the following patches.
>>
>> So this is a preparation patch, which changes the huge_ptep_clear_flush()
>> to return the original pte to help to nuke a hugetlb page table.
>>
>> Signed-off-by: Baolin Wang <baolin.wang at linux.alibaba.com>
>> Acked-by: Mike Kravetz <mike.kravetz at oracle.com>
> 
> Reviewed-by: Muchun Song <songmuchun at bytedance.com>

Thanks for reviewing.

> 
> But one nit below:
> 
> [...]
>> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
>> index 8605d7e..61a21af 100644
>> --- a/mm/hugetlb.c
>> +++ b/mm/hugetlb.c
>> @@ -5342,7 +5342,7 @@ static vm_fault_t hugetlb_wp(struct mm_struct *mm, struct vm_area_struct *vma,
>>   		ClearHPageRestoreReserve(new_page);
>>   
>>   		/* Break COW or unshare */
>> -		huge_ptep_clear_flush(vma, haddr, ptep);
>> +		(void)huge_ptep_clear_flush(vma, haddr, ptep);
> 
> Why add a "(void)" here? Is there any warning if no "(void)"?
> IIUC, I think we can remove this, right?

I did not meet any warning without the casting, but this is per Mike's 
comment[1] to make the code consistent with other functions casting to 
void type explicitly in hugetlb.c file.

[1] 
https://lore.kernel.org/all/495c4ebe-a5b4-afb6-4cb0-956c1b18d0cc@oracle.com/