Re: [PATCH v3 3/3] mm/madvise: free hwpoison and swapin error entry in madvise_free_pte_range

[HORIGUCHI NAOYA(堀口 直也)]

On Sun, Apr 24, 2022 at 05:11:05PM +0800, Miaohe Lin wrote:
> Once the MADV_FREE operation has succeeded, callers can expect they might
> get zero-fill pages if accessing the memory again. Therefore it should be
> safe to delete the hwpoison entry and swapin error entry. There is no
> reason to kill the process if it has called MADV_FREE on the range.
> 
> Suggested-by: Alistair Popple <apopple@xxxxxxxxxx>
> Signed-off-by: Miaohe Lin <linmiaohe@xxxxxxxxxx>
> Acked-by: David Hildenbrand <david@xxxxxxxxxx>

I confirmed that hwpoison entry is properly removed with madvise(MADV_FREE)
with this patch. This provides applications with the ability to recover from
memory errors in simpler way (applications don't have to munmap then mmap again
the error address). That's a good small improvement. Thank you.

Reviewed-by: Naoya Horiguchi <naoya.horiguchi@xxxxxxx>

> ---
>  mm/madvise.c | 13 ++++++++-----
>  1 file changed, 8 insertions(+), 5 deletions(-)
> 
> diff --git a/mm/madvise.c b/mm/madvise.c
> index 4d6592488b51..5f4537511532 100644
> --- a/mm/madvise.c
> +++ b/mm/madvise.c
> @@ -624,11 +624,14 @@ static int madvise_free_pte_range(pmd_t *pmd, unsigned long addr,
>  			swp_entry_t entry;
>  
>  			entry = pte_to_swp_entry(ptent);
> -			if (non_swap_entry(entry))
> -				continue;
> -			nr_swap--;
> -			free_swap_and_cache(entry);
> -			pte_clear_not_present_full(mm, addr, pte, tlb->fullmm);
> +			if (!non_swap_entry(entry)) {
> +				nr_swap--;
> +				free_swap_and_cache(entry);
> +				pte_clear_not_present_full(mm, addr, pte, tlb->fullmm);
> +			} else if (is_hwpoison_entry(entry) ||
> +				   is_swapin_error_entry(entry)) {
> +				pte_clear_not_present_full(mm, addr, pte, tlb->fullmm);
> +			}
>  			continue;
>  		}
>  
> -- 
> 2.23.0