linux-kernel - Re: [PATCH v3 3/3] mm/madvise: free hwpoison and swapin error entry in madvise_free_pte

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Date:   Mon, 25 Apr 2022 09:59:36 +0800
From:   Miaohe Lin <linmiaohe@...wei.com>
To:     HORIGUCHI NAOYA(堀口 直也) 
        <naoya.horiguchi@....com>
CC:     "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "willy@...radead.org" <willy@...radead.org>,
        "vbabka@...e.cz" <vbabka@...e.cz>,
        "dhowells@...hat.com" <dhowells@...hat.com>,
        "neilb@...e.de" <neilb@...e.de>,
        "david@...hat.com" <david@...hat.com>,
        "apopple@...dia.com" <apopple@...dia.com>,
        "surenb@...gle.com" <surenb@...gle.com>,
        "minchan@...nel.org" <minchan@...nel.org>,
        "peterx@...hat.com" <peterx@...hat.com>,
        "sfr@...b.auug.org.au" <sfr@...b.auug.org.au>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 3/3] mm/madvise: free hwpoison and swapin error entry
 in madvise_free_pte_range

On 2022/4/25 7:41, HORIGUCHI NAOYA(堀口 直也) wrote:
> 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@...dia.com>
>> Signed-off-by: Miaohe Lin <linmiaohe@...wei.com>
>> Acked-by: David Hildenbrand <david@...hat.com>
> 
> 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@....com>

Many thanks for your testing and review! :)

> 
>> ---
>>  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