linux-kernel - Re: [PATCH 1/4] mm/ksm: fix ksm_pages

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Message-ID: <36168dfd-bdfa-42cd-965a-f7a0e108108e@linux.dev>
Date: Wed, 8 May 2024 18:35:06 +0800
From: Chengming Zhou <chengming.zhou@...ux.dev>
To: Andrew Morton <akpm@...ux-foundation.org>,
 David Hildenbrand <david@...hat.com>, Stefan Roesch <shr@...kernel.io>,
 xu xin <xu.xin16@....com.cn>
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org,
 zhouchengming@...edance.com
Subject: Re: [PATCH 1/4] mm/ksm: fix ksm_pages_scanned accounting

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@...ux.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)
>