Re: [PATCH] more mapcount page as kpage could reduce total replacement times than fewer mapcount one in probability.

[Andrew Morton]

On Tue, 14 Jun 2016 17:17:37 +0800 <zhouxianrong@xxxxxxxxxx> wrote:

> From: z00281421 <z00281421@xxxxxxxxxxxxxxxxxxxx>
> 
> more mapcount page as kpage could reduce total replacement 
> times than fewer mapcount one when ksmd scan and replace 
> among forked pages later.
> 

Hopefully Hugh will be able to have a think about this.

> --- a/mm/ksm.c
> +++ b/mm/ksm.c
> @@ -1094,6 +1094,21 @@ static struct page *try_to_merge_two_pages(struct rmap_item *rmap_item,
>  {
>  	int err;
>  
> +	/*
> +	 * select more mapcount page as kpage
> +	 */
> +	if (page_mapcount(page) < page_mapcount(tree_page)) {
> +		struct page *tmp_page;
> +		struct rmap_item *tmp_rmap_item;
> +
> +		tmp_page = page;
> +		page = tree_page;
> +		tree_page = tmp_page;
> +		tmp_rmap_item = rmap_item;
> +		rmap_item = tree_rmap_item;
> +		tree_rmap_item = tmp_rmap_item;
> +	}

kernel.h provides a swap() macro.

>  	err = try_to_merge_with_ksm_page(rmap_item, page, NULL);
>  	if (!err) {
>  		err = try_to_merge_with_ksm_page(tree_rmap_item,