Re: [PATCH v2 14/14] arm64/mm: Add ptep_get_and_clear_full() to optimize process teardown

Barry Song
2023-11-28T07:33:37Z

> +#define __HAVE_ARCH_PTEP_GET_AND_CLEAR_FULL
> +static inline pte_t ptep_get_and_clear_full(struct mm_struct *mm,
> + unsigned long addr, pte_t *ptep, int full)
> +{
> + pte_t orig_pte = __ptep_get(ptep);
> +
> + if (!pte_valid_cont(orig_pte) || !full) {
> + contpte_try_unfold(mm, addr, ptep, orig_pte);
> + return __ptep_get_and_clear(mm, addr, ptep);
> + } else
> + return contpte_ptep_get_and_clear_full(mm, addr, ptep);
> +}
> +

Hi Ryan,

I feel quite hard to understand the code. when !pte_valid_cont(orig_pte),
we will call contpte_try_unfold(mm, addr, ptep, orig_pte);

but in contpte_try_unfold(), we call unfold only if pte_valid_cont()
is true:
static inline void contpte_try_unfold(struct mm_struct *mm, unsigned long addr,
pte_t *ptep, pte_t pte)
{
if (contpte_is_enabled(mm) && pte_valid_cont(pte))
__contpte_try_unfold(mm, addr, ptep, pte);
}

so do you mean the below?

if (!pte_valid_cont(orig_pte))
return __ptep_get_and_clear(mm, addr, ptep);

if (!full) {
contpte_try_unfold(mm, addr, ptep, orig_pte);
return __ptep_get_and_clear(mm, addr, ptep);
} else {
return contpte_ptep_get_and_clear_full(mm, addr, ptep);
}

Thanks
Barry