Re: [PATCH v2 3/3] mm/madvise: free hwpoison and swapin error entry in madvise_free_pte_range

[Miaohe Lin]

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@xxxxxxxxxx>
>> Signed-off-by: Miaohe Lin <linmiaohe@xxxxxxxxxx>
>> ---
>>  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@xxxxxxxxxx>
> 

Many thanks for your quick respond and review!