linux-kernel - Re: [PATCH v2 3/3] mm/madvise: free hwpoison and swapin error entry in madvise_free_pte

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Date:   Thu, 21 Apr 2022 10:28:44 -0400
From:   Peter Xu <peterx@...hat.com>
To:     Miaohe Lin <linmiaohe@...wei.com>
Cc:     akpm@...ux-foundation.org, willy@...radead.org, vbabka@...e.cz,
        dhowells@...hat.com, neilb@...e.de, david@...hat.com,
        apopple@...dia.com, surenb@...gle.com, minchan@...nel.org,
        sfr@...b.auug.org.au, naoya.horiguchi@....com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 3/3] mm/madvise: free hwpoison and swapin error entry
 in madvise_free_pte_range

On Thu, Apr 21, 2022 at 08:53:48PM +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@...dia.com>
> Signed-off-by: Miaohe Lin <linmiaohe@...wei.com>
> ---
>  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);

Nitpick: IMHO you don't need to invert non_swap_entry() then it'll generate
a smaller diff, just add the new code above "continue".

> +			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);

Since it's been discussed and you're reposting a new version anyway, why
not start with either reusing hwpoison or pte markers?  Or do you think it
should be for future to drop the new swap entry again?

Thanks,

-- 
Peter Xu