Re: [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@xxxxxxxxxxxxxxxxx>
> > Acked-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
>
> Reviewed-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>

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@xxxxxxxxxx/