Use the number of pages in the folio to check the reference count as
preparation for supporting shmem mTHP collapse.

Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
---
 mm/khugepaged.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index f11b4f172e61..60d95f08610c 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -1994,7 +1994,7 @@ static int collapse_file(struct mm_struct *mm, unsigned long addr,
 		/*
 		 * We control three references to the folio:
 		 *  - we hold a pin on it;
-		 *  - one reference from page cache;
+		 *  - nr_pages reference from page cache;
 		 *  - one from lru_isolate_folio;
 		 * If those are the only references, then any new usage
 		 * of the folio will have to fetch it from the page
@@ -2002,7 +2002,7 @@ static int collapse_file(struct mm_struct *mm, unsigned long addr,
 		 * truncate, so any new usage will be blocked until we
 		 * unlock folio after collapse/during rollback.
 		 */
-		if (folio_ref_count(folio) != 3) {
+		if (folio_ref_count(folio) != 2 + folio_nr_pages(folio)) {
 			result = SCAN_PAGE_COUNT;
 			xas_unlock_irq(&xas);
 			folio_putback_lru(folio);
@@ -2185,7 +2185,7 @@ static int collapse_file(struct mm_struct *mm, unsigned long addr,
 		folio_clear_active(folio);
 		folio_clear_unevictable(folio);
 		folio_unlock(folio);
-		folio_put_refs(folio, 3);
+		folio_put_refs(folio, 2 + folio_nr_pages(folio));
 	}
 
 	goto out;
-- 
2.39.3

On 19.08.24 10:14, Baolin Wang wrote:
> Use the number of pages in the folio to check the reference count as
> preparation for supporting shmem mTHP collapse.
> 
> Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
> ---
>   mm/khugepaged.c | 6 +++---
>   1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> index f11b4f172e61..60d95f08610c 100644
> --- a/mm/khugepaged.c
> +++ b/mm/khugepaged.c
> @@ -1994,7 +1994,7 @@ static int collapse_file(struct mm_struct *mm, unsigned long addr,
>   		/*
>   		 * We control three references to the folio:

^ "three" is wrong now.

>   		 *  - we hold a pin on it;
> -		 *  - one reference from page cache;
> +		 *  - nr_pages reference from page cache;
>   		 *  - one from lru_isolate_folio;
>   		 * If those are the only references, then any new usage
>   		 * of the folio will have to fetch it from the page
> @@ -2002,7 +2002,7 @@ static int collapse_file(struct mm_struct *mm, unsigned long addr,
>   		 * truncate, so any new usage will be blocked until we
>   		 * unlock folio after collapse/during rollback.
>   		 */
> -		if (folio_ref_count(folio) != 3) {
> +		if (folio_ref_count(folio) != 2 + folio_nr_pages(folio)) {
>   			result = SCAN_PAGE_COUNT;
>   			xas_unlock_irq(&xas);
>   			folio_putback_lru(folio);
> @@ -2185,7 +2185,7 @@ static int collapse_file(struct mm_struct *mm, unsigned long addr,
>   		folio_clear_active(folio);
>   		folio_clear_unevictable(folio);
>   		folio_unlock(folio);
> -		folio_put_refs(folio, 3);
> +		folio_put_refs(folio, 2 + folio_nr_pages(folio));
>   	}
>   
>   	goto out;

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

-- 
Cheers,

David / dhildenb

On 2024/8/19 17:40, David Hildenbrand wrote:
> On 19.08.24 10:14, Baolin Wang wrote:
>> Use the number of pages in the folio to check the reference count as
>> preparation for supporting shmem mTHP collapse.
>>
>> Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
>> ---
>>   mm/khugepaged.c | 6 +++---
>>   1 file changed, 3 insertions(+), 3 deletions(-)
>>
>> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
>> index f11b4f172e61..60d95f08610c 100644
>> --- a/mm/khugepaged.c
>> +++ b/mm/khugepaged.c
>> @@ -1994,7 +1994,7 @@ static int collapse_file(struct mm_struct *mm, 
>> unsigned long addr,
>>           /*
>>            * We control three references to the folio:
> 
> ^ "three" is wrong now.

Ah, good catch. Will change to '2 + nr_pages'.

> 
>>            *  - we hold a pin on it;
>> -         *  - one reference from page cache;
>> +         *  - nr_pages reference from page cache;
>>            *  - one from lru_isolate_folio;
>>            * If those are the only references, then any new usage
>>            * of the folio will have to fetch it from the page
>> @@ -2002,7 +2002,7 @@ static int collapse_file(struct mm_struct *mm, 
>> unsigned long addr,
>>            * truncate, so any new usage will be blocked until we
>>            * unlock folio after collapse/during rollback.
>>            */
>> -        if (folio_ref_count(folio) != 3) {
>> +        if (folio_ref_count(folio) != 2 + folio_nr_pages(folio)) {
>>               result = SCAN_PAGE_COUNT;
>>               xas_unlock_irq(&xas);
>>               folio_putback_lru(folio);
>> @@ -2185,7 +2185,7 @@ static int collapse_file(struct mm_struct *mm, 
>> unsigned long addr,
>>           folio_clear_active(folio);
>>           folio_clear_unevictable(folio);
>>           folio_unlock(folio);
>> -        folio_put_refs(folio, 3);
>> +        folio_put_refs(folio, 2 + folio_nr_pages(folio));
>>       }
>>       goto out;
> 
> Acked-by: David Hildenbrand <david@redhat.com>

Thanks for reviewing.