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

Baolin Wang
2022-05-11T03:59:36Z

On 5/11/2022 7:28 AM, Andrew Morton wrote:
> On Tue, 10 May 2022 16:17:39 -0700 Andrew Morton <akpm@linux-foundation.org> 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,
> _