Re: [PATCH 5/5] mm/rmap: add anon folio unmap dispatcher function

[Dev Jain <dev.jain@arm.com>]

On 07/07/26 7:58 pm, David Hildenbrand (Arm) wrote:
> On 7/7/26 14:11, Dev Jain wrote:
>> Add ttu_anon_folio() as the common entry point for anonymous folio
>> unmapping. It dispatches to the lazyfree or swapbacked helper as
>> appropriate, and centralizes restoration of cleared PTEs on failure.
>>
>> No functional change intended.
>>
>> Signed-off-by: Dev Jain <dev.jain@arm.com>
>> ---
>>  mm/rmap.c | 59 +++++++++++++++++++++++++++++++++----------------------
>>  1 file changed, 36 insertions(+), 23 deletions(-)
>>
>> diff --git a/mm/rmap.c b/mm/rmap.c
>> index ade78df5be2bd..f021ecd51a4a2 100644
>> --- a/mm/rmap.c
>> +++ b/mm/rmap.c
>> @@ -2171,6 +2171,40 @@ static inline bool ttu_anon_swapbacked_folio(struct vm_area_struct *vma, struct
>>  	return true;
>>  }
>>  
>> +static inline bool ttu_anon_folio(struct vm_area_struct *vma, struct folio *folio,
>> +		struct page *subpage, unsigned long address, pte_t *ptep,
>> +		pte_t pteval, unsigned long nr_pages)
>> +{
>> +	struct mm_struct *mm = vma->vm_mm;
>> +	bool ret;
>> +
>> +	/*
>> +	 * Store the swap location in the pte.
>> +	 * See handle_pte_fault() ...
>> +	 */
>> +	if (unlikely(folio_test_swapbacked(folio) !=
>> +			folio_test_swapcache(folio))) {
>> +		WARN_ON_ONCE(1);
>> +		return false;
>> +	}
>> +
>> +	/* MADV_FREE page check */
>> +	if (!folio_test_swapbacked(folio)) {
>> +		ret = ttu_anon_lazyfree_folio(vma, folio);
>> +		if (ret)
>> +			add_mm_counter(mm, MM_ANONPAGES, -nr_pages);
> 
> Can't the be handled in there as well?

Okay.

> 
>> +	} else {
>> +		/* nr_pages > 1 not supported yet */
>> +		ret = ttu_anon_swapbacked_folio(vma, folio, subpage, address,
>> +						ptep, pteval);
>> +	}
>> +
>> +	if (!ret)
>> +		set_ptes(mm, address, ptep, pteval, nr_pages);
> 
> It might be cleaner to do that in the caller, where we actually removed the ptes
> in the first place?

Yes.

> 
>> +
>> +	return ret;
>> +}
>> +
>>  /*
>>   * @arg: enum ttu_flags will be passed to this argument
>>   */
>> @@ -2351,31 +2385,10 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma,
>>  			 */
>>  			dec_mm_counter(mm, mm_counter(folio));
>>  		} else if (folio_test_anon(folio)) {
>> -			/*
>> -			 * Store the swap location in the pte.
>> -			 * See handle_pte_fault() ...
>> -			 */
>> -			if (unlikely(folio_test_swapbacked(folio) !=
>> -					folio_test_swapcache(folio))) {
>> -				WARN_ON_ONCE(1);
>> +			if (!ttu_anon_folio(vma, folio, subpage, address,
>> +					    pvmw.pte, pteval, nr_pages))
>>  				goto walk_abort;
>> -			}
>>  
>> -			/* MADV_FREE page check */
>> -			if (!folio_test_swapbacked(folio)) {
>> -				if (!ttu_anon_lazyfree_folio(vma, folio)) {
>> -					set_ptes(mm, address, pvmw.pte, pteval, nr_pages);
>> -					goto walk_abort;
>> -				}
>> -				add_mm_counter(mm, MM_ANONPAGES, -nr_pages);
>> -				goto finish_unmap;
>> -			}
>> -
>> -			if (!ttu_anon_swapbacked_folio(vma, folio, subpage, address,
>> -						pvmw.pte, pteval)) {
>> -				set_pte_at(mm, address, pvmw.pte, pteval);
>> -				goto walk_abort;
>> -			}
>>  			goto finish_unmap;
>>  		} else {
>>  			/*
> 
> Very nice.
>