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

[Muchun Song]

On Sun, May 08, 2022 at 09:09:55PM +0800, Baolin Wang wrote:
> 
> 
> 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.
>

Got it. I see hugetlb.c per this rule, while others do not.
 
> [1]
> https://lore.kernel.org/all/495c4ebe-a5b4-afb6-4cb0-956c1b18d0cc@oracle.com/
>