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

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Message-Id: <20160614151426.0e893a1f7b4e549a7c6e7fdf@linux-foundation.org>
Date:	Tue, 14 Jun 2016 15:14:26 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	<zhouxianrong@...wei.com>
Cc:	<linux-mm@...ck.org>, <hughd@...gle.com>, <aarcange@...hat.com>,
	<kirill.shutemov@...ux.intel.com>, <dave.hansen@...ux.intel.com>,
	<zhouchengming1@...wei.com>, <geliangtang@....com>,
	<linux-kernel@...r.kernel.org>, <zhouxiyu@...wei.com>,
	<wanghaijun5@...wei.com>, Hugh Dickins <hughd@...gle.com>
Subject: Re: [PATCH] more mapcount page as kpage could reduce total
 replacement times than fewer mapcount one in probability.

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

> From: z00281421 <z00281421@...esmail.huawei.com>
> 
> 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,