Re: [PATCH v2 5/5] mm/rmap: add anon folio unmap dispatcher

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

On 10/07/26 5:57 pm, David Hildenbrand (Arm) wrote:
> On 7/10/26 07:59, 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.
>>
>> Keep restoration of cleared PTEs in the caller, where the PTEs were
>> removed.
>>
>> No functional change intended.
>>
>> Signed-off-by: Dev Jain <dev.jain@arm.com>
>> ---
>>  mm/rmap.c | 47 +++++++++++++++++++++++++----------------------
>>  1 file changed, 25 insertions(+), 22 deletions(-)
>>
>> diff --git a/mm/rmap.c b/mm/rmap.c
>> index 68459f23f5c0a..55aa3ff8bf216 100644
>> --- a/mm/rmap.c
>> +++ b/mm/rmap.c
>> @@ -2172,6 +2172,28 @@ static bool ttu_anon_swapbacked_folio(struct vm_area_struct *vma,
>>  	return true;
>>  }
>>  
>> +static bool ttu_anon_folio(struct vm_area_struct *vma, struct folio *folio,
>> +		struct page *page, unsigned long address, pte_t *ptep,
>> +		pte_t pteval, unsigned long nr_pages)
>> +{
>> +	/*
>> +	 * 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);
> 
> Can't you directly do
> 
> if (WARN_ON_ONCE(...))
> 	return false;

Right. I didn't do it perhaps because I was playing with if (VM_WARN_ON_ONCE) somewhere
and that didn't build. But this is without the VM_ , this will work.

Andrew, could you you squash this diff:

diff --git a/mm/rmap.c b/mm/rmap.c
index 55aa3ff8bf216..41a049e7dd231 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -2180,11 +2180,9 @@ static bool ttu_anon_folio(struct vm_area_struct *vma, struct folio *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 (WARN_ON_ONCE(folio_test_swapbacked(folio) !=
+                        folio_test_swapcache(folio)))
                return false;
-       }

        if (!folio_test_swapbacked(folio))
                return ttu_anon_lazyfree_folio(vma, folio, nr_pages);


> 
> That even implies the unlikely() :)
> 
>> +		return false;
>> +	}
>> +
>> +	if (!folio_test_swapbacked(folio))
>> +		return ttu_anon_lazyfree_folio(vma, folio, nr_pages);
>> +
>> +	/* nr_pages > 1 not supported yet */
>> +	return ttu_anon_swapbacked_folio(vma, folio, page, address, ptep,
> 
> LGTM
> 
> Acked-by: David Hildenbrand (Arm) <david@kernel.org>
>