Re: [PATCH v3 2/3] mm: rmap: Fix CONT-PTE/PMD size hugetlb issue when migration

[Baolin Wang]

On 5/11/2022 7:28 AM, Andrew Morton wrote:
> On Tue, 10 May 2022 16:17:39 -0700 Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote:
>
> > > +
> > > +static inline pte_t huge_ptep_clear_flush(struct vm_area_struct *vma,
> > > +					  unsigned long addr, pte_t *ptep)
> > > +{
> > > +	return ptep_get(ptep);
> > > +}
> > > +
> > > +static inline void set_huge_pte_at(struct mm_struct *mm, unsigned long addr,
> > > +				   pte_t *ptep, pte_t pte)
> > > +{
> > > +}
> > >   #endif	/* CONFIG_HUGETLB_PAGE */
> > >   
> >
> > This blows up nommu (arm allnoconfig):
> >
> > In file included from fs/io_uring.c:71:
> > ./include/linux/hugetlb.h: In function 'huge_ptep_clear_flush':
> > ./include/linux/hugetlb.h:1100:16: error: implicit declaration of function 'ptep_get' [-Werror=implicit-function-declaration]
> >   1100 |         return ptep_get(ptep);
> >        |                ^~~~~~~~
> >
> >
> > huge_ptep_clear_flush() is only used in CONFIG_NOMMU=n files, so I simply
> > zapped this change.
>
> Well that wasn't a great success.  Doing this instead.  It's pretty
> nasty - something nicer would be nicer please.

Thanks for fixing the building issue. I'll look at this to simplify the 
dummy function. Myabe just remove the ptep_get().

diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -1097,7 +1097,7 @@ static inline void set_huge_swap_pte_at(struct 
mm_struct *mm, unsigned long addr
 static inline pte_t huge_ptep_clear_flush(struct vm_area_struct *vma,
                                          unsigned long addr, pte_t *ptep)
 {
-       return ptep_get(ptep);
+       return *ptep;
 }

> --- a/include/linux/hugetlb.h~mm-rmap-fix-cont-pte-pmd-size-hugetlb-issue-when-migration-fix
> +++ a/include/linux/hugetlb.h
> @@ -1094,6 +1094,7 @@ static inline void set_huge_swap_pte_at(
>   {
>   }
>   
> +#ifdef CONFIG_MMU
>   static inline pte_t huge_ptep_clear_flush(struct vm_area_struct *vma,
>   					  unsigned long addr, pte_t *ptep)
>   {
> @@ -1104,6 +1105,7 @@ static inline void set_huge_pte_at(struc
>   				   pte_t *ptep, pte_t pte)
>   {
>   }
> +#endif
>   #endif	/* CONFIG_HUGETLB_PAGE */
>   
>   static inline spinlock_t *huge_pte_lock(struct hstate *h,
> _