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 21:44:39 +0800
From:   Miaohe Lin <linmiaohe@...wei.com>
To:     David Hildenbrand <david@...hat.com>, <akpm@...ux-foundation.org>
CC:     <willy@...radead.org>, <vbabka@...e.cz>, <dhowells@...hat.com>,
        <neilb@...e.de>, <apopple@...dia.com>, <surenb@...gle.com>,
        <minchan@...nel.org>, <peterx@...hat.com>, <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 2022/4/21 21:25, David Hildenbrand wrote:
> On 21.04.22 14:53, 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);
>> +			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;
>>  		}
>>  
> 
> Reading the man page that should be fine, but might not be required.
> 
> "[...] the kernel can free the pages at any time. Once pages in the
> range have been freed, the caller will see zero-fill-on-demand pages
> upon subsequent page references."

Yes, this part is not mentioned in the man page.

> 
> 
> LGTM
> 
> Acked-by: David Hildenbrand <david@...hat.com>
> 

Many thanks for your quick respond and review!