During testing, I found ksm_pages_scanned is unchanged although the
scan_get_next_rmap_item() did return valid rmap_item that is not NULL.

The reason is the scan_get_next_rmap_item() will return NULL after
a full scan, so ksm_do_scan() just return without accounting of the
ksm_pages_scanned.

Fix it by just putting ksm_pages_scanned accounting in that loop,
and it will be accounted more timely if that loop would last for
a long time.

Signed-off-by: Chengming Zhou <chengming.zhou@linux.dev>
---
 mm/ksm.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/mm/ksm.c b/mm/ksm.c
index e1034bf1c937..0f9c491552ff 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -2753,18 +2753,16 @@ static void ksm_do_scan(unsigned int scan_npages)
 {
 	struct ksm_rmap_item *rmap_item;
 	struct page *page;
-	unsigned int npages = scan_npages;
 
-	while (npages-- && likely(!freezing(current))) {
+	while (scan_npages-- && likely(!freezing(current))) {
 		cond_resched();
 		rmap_item = scan_get_next_rmap_item(&page);
 		if (!rmap_item)
 			return;
 		cmp_and_merge_page(page, rmap_item);
 		put_page(page);
+		ksm_pages_scanned++;
 	}
-
-	ksm_pages_scanned += scan_npages - npages;
 }
 
 static int ksmd_should_run(void)

-- 
2.45.0

On 2024/5/8 17:55, Chengming Zhou wrote:
> During testing, I found ksm_pages_scanned is unchanged although the
> scan_get_next_rmap_item() did return valid rmap_item that is not NULL.
> 
> The reason is the scan_get_next_rmap_item() will return NULL after
> a full scan, so ksm_do_scan() just return without accounting of the
> ksm_pages_scanned.
> 
> Fix it by just putting ksm_pages_scanned accounting in that loop,
> and it will be accounted more timely if that loop would last for
> a long time.
> 

Fixes: b348b5fe2b5f ("mm/ksm: add pages scanned metric")

> Signed-off-by: Chengming Zhou <chengming.zhou@linux.dev>
> ---
>  mm/ksm.c | 6 ++----
>  1 file changed, 2 insertions(+), 4 deletions(-)
> 
> diff --git a/mm/ksm.c b/mm/ksm.c
> index e1034bf1c937..0f9c491552ff 100644
> --- a/mm/ksm.c
> +++ b/mm/ksm.c
> @@ -2753,18 +2753,16 @@ static void ksm_do_scan(unsigned int scan_npages)
>  {
>  	struct ksm_rmap_item *rmap_item;
>  	struct page *page;
> -	unsigned int npages = scan_npages;
>  
> -	while (npages-- && likely(!freezing(current))) {
> +	while (scan_npages-- && likely(!freezing(current))) {
>  		cond_resched();
>  		rmap_item = scan_get_next_rmap_item(&page);
>  		if (!rmap_item)
>  			return;
>  		cmp_and_merge_page(page, rmap_item);
>  		put_page(page);
> +		ksm_pages_scanned++;
>  	}
> -
> -	ksm_pages_scanned += scan_npages - npages;
>  }
>  
>  static int ksmd_should_run(void)
>

On 08.05.24 12:35, Chengming Zhou wrote:
> On 2024/5/8 17:55, Chengming Zhou wrote:
>> During testing, I found ksm_pages_scanned is unchanged although the
>> scan_get_next_rmap_item() did return valid rmap_item that is not NULL.
>>
>> The reason is the scan_get_next_rmap_item() will return NULL after
>> a full scan, so ksm_do_scan() just return without accounting of the
>> ksm_pages_scanned.
>>
>> Fix it by just putting ksm_pages_scanned accounting in that loop,
>> and it will be accounted more timely if that loop would last for
>> a long time.
>>
> 
> Fixes: b348b5fe2b5f ("mm/ksm: add pages scanned metric")

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

-- 
Cheers,

David / dhildenb